Can we move device drivers into user-space?

Can we move device drivers into user-space?

[Jidong Xiao]

Hi,

I am just curious. Since the concept user-space device drivers has
been proposed for several years, and some related projects and
research papers have demonstrated the feasibility of of moving device
drivers into use space. In particular, this paper:

Tolerating Malicious Device Drivers in Linux.
http://pdos.csail.mit.edu/papers/sud:usenix10.pdf

In this paper, existing device driver code need not to be changed,
which should help the idea to be applied in practice.

The advantage and disadvantage of move device drivers into use space
of both obvious:

Advantage: Since most of kernel bugs are caused by device drivers
issues, moving device drivers into user space can reduce the impact of
device driver bugs. From security perspective, the system can be more
secure and robust if most device drivers are working in user space.
Disadvantage: At least, existing techniques as well as the above paper
showed a relatively high overhead.

So is it mainly because the high overhead that prevents the user-space
device drivers ideas being accepted in Linux?

Regards
-Jidong

Re: Can we move device drivers into user-space?

[Cong Wang]

On 02/23/2012 12:56 PM, Jidong Xiao wrote:
> Hi,

Hi,

> So is it mainly because the high overhead that prevents the user-space
> device drivers ideas being accepted in Linux?
>

At least UIO drivers are already in Linux kernel, see drivers/uio/.

Re: Can we move device drivers into user-space?

[Jidong Xiao]

On Thu, Feb 23, 2012 at 10:57 AM, Cong Wang <xiyou.wangcong@gmail.com> wrote:
> On 02/23/2012 12:56 PM, Jidong Xiao wrote:
>>
>> Hi,
>
>
> Hi,
>
>
>> So is it mainly because the high overhead that prevents the user-space
>> device drivers ideas being accepted in Linux?
>>
>
> At least UIO drivers are already in Linux kernel, see drivers/uio/.
>

Oh, so does it make sense to move existing device drivers into user
space? For example, move most of the stuff located under drivers/usb
into user-space?

-Jidong

Re: Can we move device drivers into user-space?

[david]

On Thu, 23 Feb 2012, Jidong Xiao wrote:

>>
>> At least UIO drivers are already in Linux kernel, see drivers/uio/.
>>
>
> Oh, so does it make sense to move existing device drivers into user
> space? For example, move most of the stuff located under drivers/usb
> into user-space?

Why would you want to? What advantage are you looking to gain from all the 
effort?

David Lang

Re: Can we move device drivers into user-space?

[Jidong Xiao]

On Thu, Feb 23, 2012 at 3:48 PM,  <david@lang.hm> wrote:
> On Thu, 23 Feb 2012, Jidong Xiao wrote:
>
>>>
>>> At least UIO drivers are already in Linux kernel, see drivers/uio/.
>>>
>>
>> Oh, so does it make sense to move existing device drivers into user
>> space? For example, move most of the stuff located under drivers/usb
>> into user-space?
>
>
> Why would you want to? What advantage are you looking to gain from all the
> effort?
>
Since device drivers are a significant source of bugs in OS. Moving
them to user space can reduce the impact of these bugs. Otherwise, why
UIO, or drivers/uio, is accepted by mainstream Linux kernel.

-Jidong

Re: Can we move device drivers into user-space?

[Mauro Carvalho Chehab]

Em Thu, 23 Feb 2012 16:01:56 -0500
Jidong Xiao <jidong.xiao@gmail.com> escreveu:

> On Thu, Feb 23, 2012 at 3:48 PM,  <david@lang.hm> wrote:
> > On Thu, 23 Feb 2012, Jidong Xiao wrote:
> >
> >>>
> >>> At least UIO drivers are already in Linux kernel, see drivers/uio/.
> >>>
> >>
> >> Oh, so does it make sense to move existing device drivers into user
> >> space? For example, move most of the stuff located under drivers/usb
> >> into user-space?
> >
> >
> > Why would you want to? What advantage are you looking to gain from all the
> > effort?
> >
> Since device drivers are a significant source of bugs in OS. Moving
> them to user space can reduce the impact of these bugs. Otherwise, why
> UIO, or drivers/uio, is accepted by mainstream Linux kernel.

Moving a buggy driver to userspace won't fix the bug. You're just moving
it from one place to another place. Also, the code will likely require changes
to work on userspace, so, the chances are that you're actually introducing more
bugs.

The impact of the bug won't also reduce, on most cases, as the userspace driver
will very likely require root capabilities.

Also, as driver talks directly with the hardware, an userspace block driver
would have access to the raw disk data. So, even if you find a way for it to
run unprivileged, it can still mangle the data written on the disk, and
even have a malicious code there that adds or allows to add a malware at the
disk partitions.

That's said, there are much more eyes inspecting the kernel sources than on any 
other userspace project. So, the risk of a bad code to be inserted unnoticed at
the Linux kernel is degrees of magnitude lower than on an userspace driver.

So, I can't see any advantage on doing something like that.

> 
> -Jidong
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-- 
Cheers,
Mauro

---

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Red Hat ranks #1 in value among software vendors.
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Re: Can we move device drivers into user-space?

[Eduard - Gabriel Munteanu]

On Fri, Feb 24, 2012 at 04:21:09PM -0200, Mauro Carvalho Chehab wrote:
> Moving a buggy driver to userspace won't fix the bug. You're just moving
> it from one place to another place. Also, the code will likely require changes
> to work on userspace, so, the chances are that you're actually introducing more
> bugs.

Hi,


It does provide isolation, see below.

> The impact of the bug won't also reduce, on most cases, as the userspace driver
> will very likely require root capabilities.

Not as proposed, that's the point. For IOMMU-enabled systems, you can
safely delegate an entire device to a userspace device and minimize
privileged code. If I understand correctly, the performance impact is
also minimal with respect to driver <-> device interaction. I'm not sure
if driver <-> client might be problematic, but you can probably have the
device DMA directly from/into client memory given the right mechanisms.

This is currently employed by virtualization software to do PCI
passthrough. The guest OS can directly control the hardware.

Sure, you can't do it without proper hardware support. The question is
how we can reuse existing code.

> Also, as driver talks directly with the hardware, an userspace block driver
> would have access to the raw disk data. So, even if you find a way for it to
> run unprivileged, it can still mangle the data written on the disk, and
> even have a malicious code there that adds or allows to add a malware at the
> disk partitions.

That's true, but it still makes sense for other drivers, say NIC
drivers. Why should corrupting a network driver possibly result in total
privilege escalation?

> That's said, there are much more eyes inspecting the kernel sources than on any 
> other userspace project. So, the risk of a bad code to be inserted unnoticed at
> the Linux kernel is degrees of magnitude lower than on an userspace driver.

Those much more eyes have already missed important bugs in the past. No
disrespect here, I'm just saying in many cases (like the one mentioned
above) this approach almost eliminates the issue altogether. It's one
reason we keep certain userspace out of the kernel.

> So, I can't see any advantage on doing something like that.
> 

Another advantage is you can debug and/or profile the driver more
easily. Consider a failed takeover attempt that results in a core dump
(which also wouldn't result in a complete DoS of the machine).

Anyway, I'm not arguing "this is the way it should be done". After all,
not all machines are able to handle such a setup. But don't throw the
baby out with the water, it's worth considering ways to make things
safer. Also, let's not label things like this one as "microkernel" or
"academia" and totally reject them; instead consider whether it's
practical given recent advancements.


	Regards,
	Eduard

Re: Can we move device drivers into user-space?

[Mauro Carvalho Chehab]

Em 25-02-2012 13:10, Eduard - Gabriel Munteanu escreveu:
> On Fri, Feb 24, 2012 at 04:21:09PM -0200, Mauro Carvalho Chehab wrote:
>> Moving a buggy driver to userspace won't fix the bug. You're just moving
>> it from one place to another place. Also, the code will likely require changes
>> to work on userspace, so, the chances are that you're actually introducing more
>> bugs.
> 
> Hi,
> 
> 
> It does provide isolation, see below.

It depends on what you call isolation. Moving drivers to userspace
will protect ring 0, this but won't prevent OS attacks. See below.
> 
>> The impact of the bug won't also reduce, on most cases, as the userspace driver
>> will very likely require root capabilities.
> 
> Not as proposed, that's the point. For IOMMU-enabled systems, you can
> safely delegate an entire device to a userspace device and minimize
> privileged code. If I understand correctly, the performance impact is
> also minimal with respect to driver <-> device interaction. I'm not sure
> if driver <-> client might be problematic, but you can probably have the
> device DMA directly from/into client memory given the right mechanisms.
> 
> This is currently employed by virtualization software to do PCI
> passthrough. The guest OS can directly control the hardware.
> 
> Sure, you can't do it without proper hardware support. The question is
> how we can reuse existing code.
> 
>> Also, as driver talks directly with the hardware, an userspace block driver
>> would have access to the raw disk data. So, even if you find a way for it to
>> run unprivileged, it can still mangle the data written on the disk, and
>> even have a malicious code there that adds or allows to add a malware at the
>> disk partitions.
> 
> That's true, but it still makes sense for other drivers, say NIC
> drivers. Why should corrupting a network driver possibly result in total
> privilege escalation?

Bad NIC drivers could allow overriding firewall settings, making an external
packet to look as if it were a local one.

>> That's said, there are much more eyes inspecting the kernel sources than on any 
>> other userspace project. So, the risk of a bad code to be inserted unnoticed at
>> the Linux kernel is degrees of magnitude lower than on an userspace driver.
> 
> Those much more eyes have already missed important bugs in the past.

Yes, nobody is perfect. But the probability that something passes on a 4000+ people
review is lower than the probability of a bug on a piece of code where just one 
or two people are looking on it.

> No disrespect here, I'm just saying in many cases (like the one mentioned
> above) this approach almost eliminates the issue altogether.

It doesn't. Security is based on 3 pilars: confidentiality, integrity, availability (CIA).

Moving a driver from kernelspace to userspace will likely weak all 3:

- it is easier to inspect the data, reducing confidentiality;
- it is easier to forge data or to mangle, reducing integrity;
- the driver availability will likely weak, as less people will likely be looking
  into it, and the driver doesn't need to have the generally stronger criteria
  adopted by the Kernel maintainers to accept it[1].


[1] Ok, if an userspace driver stops, the kernel can still run (this is not different
than the great majority of kernel driver OOPSes: only the driver stops). Yet, if 
the driver is needed for normal operation of that system, having it stopped drops
the system availability.

Also, it is easier to replace an userspace driver than a kernel one, especially
if the distro has some mechanism to taint non-signed drivers, or if module
support is disabled.

> It's one reason we keep certain userspace out of the kernel.
> 
>> So, I can't see any advantage on doing something like that.
>>
> 
> Another advantage is you can debug and/or profile the driver more
> easily.

This is only partially true. The current debug tools available on the
Kernel are not hard to deal with, and are not behind what's available
on userspace.

> Consider a failed takeover attempt that results in a core dump
> (which also wouldn't result in a complete DoS of the machine).
>
> Anyway, I'm not arguing "this is the way it should be done". After all,
> not all machines are able to handle such a setup. But don't throw the
> baby out with the water, it's worth considering ways to make things
> safer. Also, let's not label things like this one as "microkernel" or
> "academia" and totally reject them; instead consider whether it's
> practical given recent advancements.
> 
> 
> 	Regards,
> 	Eduard
> 

Re: Can we move device drivers into user-space?

[Richard Yao]

On Sat, Feb 25, 2012 at 7:06 PM, Mauro Carvalho Chehab
<mchehab@redhat.com> wrote:
> This is only partially true. The current debug tools available on the
> Kernel are not hard to deal with, and are not behind what's available
> on userspace.

Is there documentation available for these tools? I would find that useful.

Re: Can we move device drivers into user-space?

[Mauro Carvalho Chehab]

Em 25-02-2012 22:29, Richard Yao escreveu:
> On Sat, Feb 25, 2012 at 7:06 PM, Mauro Carvalho Chehab
> <mchehab@redhat.com> wrote:
>> This is only partially true. The current debug tools available on the
>> Kernel are not hard to deal with, and are not behind what's available
>> on userspace.
> 
> Is there documentation available for these tools? I would find that useful.

See Documentation/. You'll see there lots of interesting things that could
be used to debug a driver, including fixing performance issues on it: kdbg,
remote console, perf, dynamic printk's, etc.

Mauro.

Re: Can we move device drivers into user-space?

[Dr. David Alan Gilbert]

* Mauro Carvalho Chehab (mchehab@redhat.com) wrote:
> Em 25-02-2012 13:10, Eduard - Gabriel Munteanu escreveu:
> > On Fri, Feb 24, 2012 at 04:21:09PM -0200, Mauro Carvalho Chehab wrote:
> >> Moving a buggy driver to userspace won't fix the bug. You're just moving
> >> it from one place to another place. Also, the code will likely require changes
> >> to work on userspace, so, the chances are that you're actually introducing more
> >> bugs.
> > 

<snip>

> >> That's said, there are much more eyes inspecting the kernel sources than on any 
> >> other userspace project. So, the risk of a bad code to be inserted unnoticed at
> >> the Linux kernel is degrees of magnitude lower than on an userspace driver.
> > 
> > Those much more eyes have already missed important bugs in the past.
> 
> Yes, nobody is perfect. But the probability that something passes on a 4000+ people
> review is lower than the probability of a bug on a piece of code where just one 
> or two people are looking on it.

That there are 4000+ people reading a driver is a big assumption; for common
drivers I'd agree - one problem though is there are a lot of drivers for obscure
hardware or old/dead hardware/protocols that frankly near to nobody cares about.

Very few people read those drivers; yet sometimes they get built and distributed
and someone then finds that since no one has looked at them they're full of holes,
and given a malicious USB device for example, you can suddenly create one of these
devices that only 3 people have bothered to read the source to - 5 years ago.
(The Econet security bug recently would be an example of that).

There is a line which says that things that really aren't used
just shouldn't be built; but then there are things that are only used
by a few people, and then ones only used by a few organisations - and
it gets very difficult to say at what point you say just turn it off.

Dave
-- 
 -----Open up your eyes, open up your mind, open up your code -------   
/ Dr. David Alan Gilbert    |       Running GNU/Linux       | Happy  \ 
\ gro.gilbert @ treblig.org |                               | In Hex /
 \ _________________________|_____ http://www.treblig.org   |_______/

Re: Can we move device drivers into user-space?

[arts zhao]

Basically, I agree with your idea that taking most of device drivers
away the kernel scope to user space.
Then we can easily debug them and maintain them.
However, some device drivers or some layer should  be also still
existing in kernel scope.
such as pci/pcie low-lever driver....
To keep the overhead as lower as possible...

thanks
-wenke

2012/2/26 Dr. David Alan Gilbert <linux@treblig.org>:
> * Mauro Carvalho Chehab (mchehab@redhat.com) wrote:
>> Em 25-02-2012 13:10, Eduard - Gabriel Munteanu escreveu:
>> > On Fri, Feb 24, 2012 at 04:21:09PM -0200, Mauro Carvalho Chehab wrote:
>> >> Moving a buggy driver to userspace won't fix the bug. You're just moving
>> >> it from one place to another place. Also, the code will likely require changes
>> >> to work on userspace, so, the chances are that you're actually introducing more
>> >> bugs.
>> >
>
> <snip>
>
>> >> That's said, there are much more eyes inspecting the kernel sources than on any
>> >> other userspace project. So, the risk of a bad code to be inserted unnoticed at
>> >> the Linux kernel is degrees of magnitude lower than on an userspace driver.
>> >
>> > Those much more eyes have already missed important bugs in the past.
>>
>> Yes, nobody is perfect. But the probability that something passes on a 4000+ people
>> review is lower than the probability of a bug on a piece of code where just one
>> or two people are looking on it.
>
> That there are 4000+ people reading a driver is a big assumption; for common
> drivers I'd agree - one problem though is there are a lot of drivers for obscure
> hardware or old/dead hardware/protocols that frankly near to nobody cares about.
>
> Very few people read those drivers; yet sometimes they get built and distributed
> and someone then finds that since no one has looked at them they're full of holes,
> and given a malicious USB device for example, you can suddenly create one of these
> devices that only 3 people have bothered to read the source to - 5 years ago.
> (The Econet security bug recently would be an example of that).
>
> There is a line which says that things that really aren't used
> just shouldn't be built; but then there are things that are only used
> by a few people, and then ones only used by a few organisations - and
> it gets very difficult to say at what point you say just turn it off.
>
> Dave
> --
>  -----Open up your eyes, open up your mind, open up your code -------
> / Dr. David Alan Gilbert    |       Running GNU/Linux       | Happy  \
> \ gro.gilbert @ treblig.org |                               | In Hex /
>  \ _________________________|_____ http://www.treblig.org   |_______/
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

Re: Can we move device drivers into user-space?

[Mauro Carvalho Chehab]

Em 25-02-2012 23:58, Dr. David Alan Gilbert escreveu:
> * Mauro Carvalho Chehab (mchehab@redhat.com) wrote:
>> Em 25-02-2012 13:10, Eduard - Gabriel Munteanu escreveu:
>>> On Fri, Feb 24, 2012 at 04:21:09PM -0200, Mauro Carvalho Chehab wrote:
>>>> Moving a buggy driver to userspace won't fix the bug. You're just moving
>>>> it from one place to another place. Also, the code will likely require changes
>>>> to work on userspace, so, the chances are that you're actually introducing more
>>>> bugs.
>>>
> 
> <snip>
> 
>>>> That's said, there are much more eyes inspecting the kernel sources than on any 
>>>> other userspace project. So, the risk of a bad code to be inserted unnoticed at
>>>> the Linux kernel is degrees of magnitude lower than on an userspace driver.
>>>
>>> Those much more eyes have already missed important bugs in the past.
>>
>> Yes, nobody is perfect. But the probability that something passes on a 4000+ people
>> review is lower than the probability of a bug on a piece of code where just one 
>> or two people are looking on it.
> 
> That there are 4000+ people reading a driver is a big assumption; for common
> drivers I'd agree - one problem though is there are a lot of drivers for obscure
> hardware or old/dead hardware/protocols that frankly near to nobody cares about.

Drivers for dead hardware won't offer security risks: those drivers will not load,
as such hardware won't be found at the machine. The same applies to old hardware drivers:
they won't run on modern machines.

Yet, even those old/dead drivers have people looking into it. I receive lots of patches
from the janitors team touching those old stuff, fixing potential issues on them.

If the userspace drivers become fragmented into hundreds of independent projects,
I doubt that most of those projects would have a janitors or a security team. Yet,
they can offer security risks.

> Very few people read those drivers; yet sometimes they get built and distributed
> and someone then finds that since no one has looked at them they're full of holes,
> and given a malicious USB device for example, you can suddenly create one of these
> devices that only 3 people have bothered to read the source to - 5 years ago.
> (The Econet security bug recently would be an example of that).

If a malicious person has physical access to the hardware, he can certainly compromise
the machine even without an USB device: if he powers off the machine, a DoS is caused;
if he stoles the hard disks, confidentiality is compromised; if he boots a live CD,
he can insert malicious code there, etc.

> There is a line which says that things that really aren't used
> just shouldn't be built; but then there are things that are only used
> by a few people, and then ones only used by a few organisations - and
> it gets very difficult to say at what point you say just turn it off.

True. If such organizations have high security requirements, they should be hardening 
the OS, disabling anything that allows to load a driver at runtime. The consulting
services for it I've worked with in the past generally disables not only all unused
drivers, but also any other drivers that would allow the usage of external media
(USB, CD rom, memory stick drivers) and userspace ones.

Regards,
Mauro

Re: Can we move device drivers into user-space?

[Richard Yao]

> The impact of the bug won't also reduce, on most cases, as the userspace driver
> will very likely require root capabilities.

This is incorrect. root capabilities can be isolated via security
frameworks like SELinux. Ring 0 code cannot.

Re: Can we move device drivers into user-space?

[Roland Dreier]

On Thu, Feb 23, 2012 at 12:48 PM,  <david@lang.hm> wrote:
> Why would you want to? What advantage are you looking to gain from all the
> effort?

If someone has a paragraph that starts "Advantage:" in their email, that
is usually a good place to look for what they think the advantage of their
idea is.

Re: Can we move device drivers into user-space?

[Jidong Xiao]

On Wed, Feb 22, 2012 at 11:56 PM, Jidong Xiao <jidong.xiao@gmail.com> wrote:
> Hi,
>
> I am just curious. Since the concept user-space device drivers has
> been proposed for several years, and some related projects and
> research papers have demonstrated the feasibility of of moving device
> drivers into use space. In particular, this paper:
>
> Tolerating Malicious Device Drivers in Linux.
> http://pdos.csail.mit.edu/papers/sud:usenix10.pdf
>
> In this paper, existing device driver code need not to be changed,
> which should help the idea to be applied in practice.
>
> The advantage and disadvantage of move device drivers into use space
> of both obvious:
>
> Advantage: Since most of kernel bugs are caused by device drivers
> issues, moving device drivers into user space can reduce the impact of
> device driver bugs. From security perspective, the system can be more
> secure and robust if most device drivers are working in user space.
> Disadvantage: At least, existing techniques as well as the above paper
> showed a relatively high overhead.
>
> So is it mainly because the high overhead that prevents the user-space
> device drivers ideas being accepted in Linux?
>

Actually, my major concern is, since UIO has been accepted, then why
don't we move all the rest device drivers into user space as well. As
I understand, currently, some of device drivers are running on user
space, while the other (or say the majority of) device drivers are
running on kernel space, so why don't we maintain a consistent device
drivers infrastructure, say, either all in user space, or all in
kernel space. (Sure some critical device drivers still need to be kept
in kernel space.)

-Jidong

Re: Can we move device drivers into user-space?

[Greg KH]

On Fri, Feb 24, 2012 at 10:19:36AM -0500, Jidong Xiao wrote:
> On Wed, Feb 22, 2012 at 11:56 PM, Jidong Xiao <jidong.xiao@gmail.com> wrote:
> > Hi,
> >
> > I am just curious. Since the concept user-space device drivers has
> > been proposed for several years, and some related projects and
> > research papers have demonstrated the feasibility of of moving device
> > drivers into use space. In particular, this paper:
> >
> > Tolerating Malicious Device Drivers in Linux.
> > http://pdos.csail.mit.edu/papers/sud:usenix10.pdf
> >
> > In this paper, existing device driver code need not to be changed,
> > which should help the idea to be applied in practice.
> >
> > The advantage and disadvantage of move device drivers into use space
> > of both obvious:
> >
> > Advantage: Since most of kernel bugs are caused by device drivers
> > issues, moving device drivers into user space can reduce the impact of
> > device driver bugs. From security perspective, the system can be more
> > secure and robust if most device drivers are working in user space.
> > Disadvantage: At least, existing techniques as well as the above paper
> > showed a relatively high overhead.
> >
> > So is it mainly because the high overhead that prevents the user-space
> > device drivers ideas being accepted in Linux?
> >
> 
> Actually, my major concern is, since UIO has been accepted, then why
> don't we move all the rest device drivers into user space as well. As
> I understand, currently, some of device drivers are running on user
> space, while the other (or say the majority of) device drivers are
> running on kernel space, so why don't we maintain a consistent device
> drivers infrastructure, say, either all in user space, or all in
> kernel space. (Sure some critical device drivers still need to be kept
> in kernel space.)

Feel free to create patches to do so, and handle all of the userspace
changes needed in order to implement this.

I think you haven't thought through the true reason we have device
drivers, and why Linux isn't a microkernel...

And I'd take exception to your "advantage:" line above, I don't believe
that is true at all.

Best of luck with your work,

greg k-h

Re: Can we move device drivers into user-space?

[Jidong Xiao]

On Fri, Feb 24, 2012 at 10:38 AM, Greg KH <greg@kroah.com> wrote:
> On Fri, Feb 24, 2012 at 10:19:36AM -0500, Jidong Xiao wrote:
>> On Wed, Feb 22, 2012 at 11:56 PM, Jidong Xiao <jidong.xiao@gmail.com> wrote:
>> > Hi,
>> >
>> > I am just curious. Since the concept user-space device drivers has
>> > been proposed for several years, and some related projects and
>> > research papers have demonstrated the feasibility of of moving device
>> > drivers into use space. In particular, this paper:
>> >
>> > Tolerating Malicious Device Drivers in Linux.
>> > http://pdos.csail.mit.edu/papers/sud:usenix10.pdf
>> >
>> > In this paper, existing device driver code need not to be changed,
>> > which should help the idea to be applied in practice.
>> >
>> > The advantage and disadvantage of move device drivers into use space
>> > of both obvious:
>> >
>> > Advantage: Since most of kernel bugs are caused by device drivers
>> > issues, moving device drivers into user space can reduce the impact of
>> > device driver bugs. From security perspective, the system can be more
>> > secure and robust if most device drivers are working in user space.
>> > Disadvantage: At least, existing techniques as well as the above paper
>> > showed a relatively high overhead.
>> >
>> > So is it mainly because the high overhead that prevents the user-space
>> > device drivers ideas being accepted in Linux?
>> >
>>
>> Actually, my major concern is, since UIO has been accepted, then why
>> don't we move all the rest device drivers into user space as well. As
>> I understand, currently, some of device drivers are running on user
>> space, while the other (or say the majority of) device drivers are
>> running on kernel space, so why don't we maintain a consistent device
>> drivers infrastructure, say, either all in user space, or all in
>> kernel space. (Sure some critical device drivers still need to be kept
>> in kernel space.)
>
> Feel free to create patches to do so, and handle all of the userspace
> changes needed in order to implement this.
>
> I think you haven't thought through the true reason we have device
> drivers, and why Linux isn't a microkernel...
>
> And I'd take exception to your "advantage:" line above, I don't believe
> that is true at all.
>
> Best of luck with your work,
>
Although I was asking "can we" do something, I am not actually
strongly in favor of either move or not move, as indeed it costs too
much to do the moving job.

But when you say "handle all of the userspace changes needed in order
to implement this", if the device driver can be moved without
modification (like the paper above shows), there should not be much
changes required for user space applications.

Also, if user space device drivers is a bad idea, why drivers/uio has
been created and merged into mainline kernel?

Regarding "And I'd take exception to your "advantage:" line above, I
don't believe that is true at all", do you agree that a significant
portion of kernel crash incidents are due to bugs in drivers?

As to "Linux isn't a microkernel", even though the debate between
Linux and microkernel have never stopped, it's hard to deny the fact
that Linux is slowly slowly moving towards a microkernel structure:
LKM, fuse, uio, etc.

Regards
Jidong

Re: Can we move device drivers into user-space?

[Greg KH]

On Fri, Feb 24, 2012 at 11:38:54AM -0500, Jidong Xiao wrote:
> On Fri, Feb 24, 2012 at 10:38 AM, Greg KH <greg@kroah.com> wrote:
> > On Fri, Feb 24, 2012 at 10:19:36AM -0500, Jidong Xiao wrote:
> >> On Wed, Feb 22, 2012 at 11:56 PM, Jidong Xiao <jidong.xiao@gmail.com> wrote:
> >> > Hi,
> >> >
> >> > I am just curious. Since the concept user-space device drivers has
> >> > been proposed for several years, and some related projects and
> >> > research papers have demonstrated the feasibility of of moving device
> >> > drivers into use space. In particular, this paper:
> >> >
> >> > Tolerating Malicious Device Drivers in Linux.
> >> > http://pdos.csail.mit.edu/papers/sud:usenix10.pdf
> >> >
> >> > In this paper, existing device driver code need not to be changed,
> >> > which should help the idea to be applied in practice.

Please note, that one of the strengths of Linux is that we CAN change
driver code, and we do, which makes implementations like this nice from
an academic point of view, but unrealistic from a real-world point of
view.

> >> Actually, my major concern is, since UIO has been accepted, then why
> >> don't we move all the rest device drivers into user space as well. As
> >> I understand, currently, some of device drivers are running on user
> >> space, while the other (or say the majority of) device drivers are
> >> running on kernel space, so why don't we maintain a consistent device
> >> drivers infrastructure, say, either all in user space, or all in
> >> kernel space. (Sure some critical device drivers still need to be kept
> >> in kernel space.)
> >
> > Feel free to create patches to do so, and handle all of the userspace
> > changes needed in order to implement this.
> >
> > I think you haven't thought through the true reason we have device
> > drivers, and why Linux isn't a microkernel...
> >
> > And I'd take exception to your "advantage:" line above, I don't believe
> > that is true at all.
> >
> > Best of luck with your work,
> >
> Although I was asking "can we" do something, I am not actually
> strongly in favor of either move or not move, as indeed it costs too
> much to do the moving job.

Then why even discuss this at all?  What is your goal here?  If it is to
have others do work based on an idea you pointed out, you are in the
wrong place.

> But when you say "handle all of the userspace changes needed in order
> to implement this", if the device driver can be moved without
> modification (like the paper above shows), there should not be much
> changes required for user space applications.

The paper shows one such implementation that purports to not need
userspace changes.  As we have yet to see any code, I remain
unconvinced.

> Also, if user space device drivers is a bad idea, why drivers/uio has
> been created and merged into mainline kernel?

UIO fits a real need for some types of devices, why wouldn't it be
merged?  You are trying to say it is to be used for all drivers, which
is totally missing the point.

> Regarding "And I'd take exception to your "advantage:" line above, I
> don't believe that is true at all", do you agree that a significant
> portion of kernel crash incidents are due to bugs in drivers?

No I do not.  If you refer to the references from the paper where they
make that claim, they are talking about a different operating system
than Linux.  But, by virtue of the fact that the majority of the code
running in your kernel is drivers, yes, odds are drivers will have a
small majority of the bugs overall, given the percentages involved.
However, the bugs-per-line-of-code for Linux drivers is _much_ less than
other operating systems, especially given the fact that Linux drivers
require much less lines of code overall than other operating systems
(30% at the most for the majority of device types.)  So I would like to
see real numbers backing up your claim before I agree with it.

> As to "Linux isn't a microkernel", even though the debate between
> Linux and microkernel have never stopped,

Um, who is having such a debate?  We aren't, so I don't think the debate
has ever started.

> it's hard to deny the fact that Linux is slowly slowly moving towards
> a microkernel structure: LKM, fuse, uio, etc.

"LKM", what do you mean by that?

FUSE and UIO fit the needs of some specific devices / filesystems, that
is why Linux supports them.  To claim that their presence indicates that
Linux is becoming a microkernel is to show a lack of understanding what
a real microkernel is.

thanks,

greg k-h

Re: Can we move device drivers into user-space?

[Jidong Xiao]

On Fri, Feb 24, 2012 at 11:54 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
> On Fri, Feb 24, 2012 at 11:38:54AM -0500, Jidong Xiao wrote:
>> On Fri, Feb 24, 2012 at 10:38 AM, Greg KH <greg@kroah.com> wrote:
>> > On Fri, Feb 24, 2012 at 10:19:36AM -0500, Jidong Xiao wrote:
>> >> On Wed, Feb 22, 2012 at 11:56 PM, Jidong Xiao <jidong.xiao@gmail.com> wrote:
>> >> > Hi,
>> >> >
>> >> > I am just curious. Since the concept user-space device drivers has
>> >> > been proposed for several years, and some related projects and
>> >> > research papers have demonstrated the feasibility of of moving device
>> >> > drivers into use space. In particular, this paper:
>> >> >
>> >> > Tolerating Malicious Device Drivers in Linux.
>> >> > http://pdos.csail.mit.edu/papers/sud:usenix10.pdf
>> >> >
>> >> > In this paper, existing device driver code need not to be changed,
>> >> > which should help the idea to be applied in practice.
>
> Please note, that one of the strengths of Linux is that we CAN change
> driver code, and we do, which makes implementations like this nice from
> an academic point of view, but unrealistic from a real-world point of
> view.
>
>> >> Actually, my major concern is, since UIO has been accepted, then why
>> >> don't we move all the rest device drivers into user space as well. As
>> >> I understand, currently, some of device drivers are running on user
>> >> space, while the other (or say the majority of) device drivers are
>> >> running on kernel space, so why don't we maintain a consistent device
>> >> drivers infrastructure, say, either all in user space, or all in
>> >> kernel space. (Sure some critical device drivers still need to be kept
>> >> in kernel space.)
>> >
>> > Feel free to create patches to do so, and handle all of the userspace
>> > changes needed in order to implement this.
>> >
>> > I think you haven't thought through the true reason we have device
>> > drivers, and why Linux isn't a microkernel...
>> >
>> > And I'd take exception to your "advantage:" line above, I don't believe
>> > that is true at all.
>> >
>> > Best of luck with your work,
>> >
>> Although I was asking "can we" do something, I am not actually
>> strongly in favor of either move or not move, as indeed it costs too
>> much to do the moving job.
>
> Then why even discuss this at all?  What is your goal here?  If it is to
> have others do work based on an idea you pointed out, you are in the
> wrong place.
>
>> But when you say "handle all of the userspace changes needed in order
>> to implement this", if the device driver can be moved without
>> modification (like the paper above shows), there should not be much
>> changes required for user space applications.
>
> The paper shows one such implementation that purports to not need
> userspace changes.  As we have yet to see any code, I remain
> unconvinced.
>
>> Also, if user space device drivers is a bad idea, why drivers/uio has
>> been created and merged into mainline kernel?
>
> UIO fits a real need for some types of devices, why wouldn't it be
> merged?  You are trying to say it is to be used for all drivers, which
> is totally missing the point.
>
>> Regarding "And I'd take exception to your "advantage:" line above, I
>> don't believe that is true at all", do you agree that a significant
>> portion of kernel crash incidents are due to bugs in drivers?
>
> No I do not.  If you refer to the references from the paper where they
> make that claim, they are talking about a different operating system
> than Linux.  But, by virtue of the fact that the majority of the code
> running in your kernel is drivers, yes, odds are drivers will have a
> small majority of the bugs overall, given the percentages involved.
> However, the bugs-per-line-of-code for Linux drivers is _much_ less than
> other operating systems, especially given the fact that Linux drivers
> require much less lines of code overall than other operating systems
> (30% at the most for the majority of device types.)  So I would like to
> see real numbers backing up your claim before I agree with it.
>
>> As to "Linux isn't a microkernel", even though the debate between
>> Linux and microkernel have never stopped,
>
> Um, who is having such a debate?  We aren't, so I don't think the debate
> has ever started.
>

Here is the classic debate between Andrew S. Tanenbaum and Linus Torvalds:
http://en.wikipedia.org/wiki/Tanenbaum%E2%80%93Torvalds_debate

Regards
Jidong

Re: Can we move device drivers into user-space?

[Greg KH]

On Fri, Feb 24, 2012 at 12:06:54PM -0500, Jidong Xiao wrote:
> On Fri, Feb 24, 2012 at 11:54 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
> >> As to "Linux isn't a microkernel", even though the debate between
> >> Linux and microkernel have never stopped,
> >
> > Um, who is having such a debate?  We aren't, so I don't think the debate
> > has ever started.
> >
> 
> Here is the classic debate between Andrew S. Tanenbaum and Linus Torvalds:
> http://en.wikipedia.org/wiki/Tanenbaum%E2%80%93Torvalds_debate

That was 20 years ago, to assume that anyone rational was still having
that debate today is insane.

Re: Can we move device drivers into user-space?

[Jidong Xiao]

On Fri, Feb 24, 2012 at 12:13 PM, Greg KH <gregkh@linuxfoundation.org> wrote:
> On Fri, Feb 24, 2012 at 12:06:54PM -0500, Jidong Xiao wrote:
>> On Fri, Feb 24, 2012 at 11:54 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
>> >> As to "Linux isn't a microkernel", even though the debate between
>> >> Linux and microkernel have never stopped,
>> >
>> > Um, who is having such a debate?  We aren't, so I don't think the debate
>> > has ever started.
>> >
>>
>> Here is the classic debate between Andrew S. Tanenbaum and Linus Torvalds:
>> http://en.wikipedia.org/wiki/Tanenbaum%E2%80%93Torvalds_debate
>
> That was 20 years ago, to assume that anyone rational was still having
> that debate today is insane.
>

You probably missed the second paragraph.

"This subject was revisited in 2006 after Tanenbaum wrote a cover
story for Computer magazine titled "Can We Make Operating Systems
Reliable and Secure?".[3] While Tanenbaum himself has mentioned that
he did not write the article to renew the debate on kernel design,[4]
the juxtaposition of the article and an archived copy of the 1992
debate on the technology site Slashdot caused the subject to be
rekindled.[5] Torvalds posted a rebuttal of Tanenbaum's arguments via
an online discussion forum,[6] and several technology news sites began
reporting the issue.[7] This prompted Jonathan Shapiro to respond that
most of the field-proven reliable and secure computer systems use a
more microkernel-like approach.[8]"

Re: Can we move device drivers into user-space?

[Greg KH]

On Fri, Feb 24, 2012 at 12:21:27PM -0500, Jidong Xiao wrote:
> On Fri, Feb 24, 2012 at 12:13 PM, Greg KH <gregkh@linuxfoundation.org> wrote:
> > On Fri, Feb 24, 2012 at 12:06:54PM -0500, Jidong Xiao wrote:
> >> On Fri, Feb 24, 2012 at 11:54 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
> >> >> As to "Linux isn't a microkernel", even though the debate between
> >> >> Linux and microkernel have never stopped,
> >> >
> >> > Um, who is having such a debate?  We aren't, so I don't think the debate
> >> > has ever started.
> >> >
> >>
> >> Here is the classic debate between Andrew S. Tanenbaum and Linus Torvalds:
> >> http://en.wikipedia.org/wiki/Tanenbaum%E2%80%93Torvalds_debate
> >
> > That was 20 years ago, to assume that anyone rational was still having
> > that debate today is insane.
> >
> 
> You probably missed the second paragraph.

You assume incorrectly.

Re: Can we move device drivers into user-space?

[Richard Yao]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 02/24/12 12:13, Greg KH wrote:
> On Fri, Feb 24, 2012 at 12:06:54PM -0500, Jidong Xiao wrote:
>> On Fri, Feb 24, 2012 at 11:54 AM, Greg KH <gregkh@linuxfoundation.org>
wrote:
>>>> As to "Linux isn't a microkernel", even though the debate between
>>>> Linux and microkernel have never stopped,
>>>
>>> Um, who is having such a debate? We aren't, so I don't think the debate
>>> has ever started.
>>>
>>
>> Here is the classic debate between Andrew S. Tanenbaum and Linus Torvalds:
>> http://en.wikipedia.org/wiki/Tanenbaum%E2%80%93Torvalds_debate
>
> That was 20 years ago, to assume that anyone rational was still having
> that debate today is insane.
Jidong Xiao was correct in saying that there was a debate. It continues
much like the Korean war does today.

With that said, I suggest that Jidong Xiao switch to MINIX, GNU or his
own OS based on one of the L4 kernels (SEL4 maybe?).

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Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/

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Re: Can we move device drivers into user-space?

[Jidong Xiao]

Thank you everyone! I opened this thread mainly because I was
wondering whether it makes sense to move device drivers into user
space. I had no clear idea, but I learnt a lot from the whole
discussion between everyone, and I think I am not the only one who
benefits from this discussion.

Regards
Jidong

On Fri, Feb 24, 2012 at 9:33 PM, Richard Yao <ryao@cs.stonybrook.edu> wrote:
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 02/24/12 12:13, Greg KH wrote:
>> On Fri, Feb 24, 2012 at 12:06:54PM -0500, Jidong Xiao wrote:
>>> On Fri, Feb 24, 2012 at 11:54 AM, Greg KH <gregkh@linuxfoundation.org>
> wrote:
>>>>> As to "Linux isn't a microkernel", even though the debate between
>>>>> Linux and microkernel have never stopped,
>>>>
>>>> Um, who is having such a debate? We aren't, so I don't think the debate
>>>> has ever started.
>>>>
>>>
>>> Here is the classic debate between Andrew S. Tanenbaum and Linus Torvalds:
>>> http://en.wikipedia.org/wiki/Tanenbaum%E2%80%93Torvalds_debate
>>
>> That was 20 years ago, to assume that anyone rational was still having
>> that debate today is insane.
> Jidong Xiao was correct in saying that there was a debate. It continues
> much like the Korean war does today.
>
> With that said, I suggest that Jidong Xiao switch to MINIX, GNU or his
> own OS based on one of the L4 kernels (SEL4 maybe?).
>
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>

Re: Can we move device drivers into user-space?

[Al Viro]

On Fri, Feb 24, 2012 at 08:54:48AM -0800, Greg KH wrote:

> > As to "Linux isn't a microkernel", even though the debate between
> > Linux and microkernel have never stopped,
> 
> Um, who is having such a debate?  We aren't, so I don't think the debate
> has ever started.
> 
> > it's hard to deny the fact that Linux is slowly slowly moving towards
> > a microkernel structure: LKM, fuse, uio, etc.
> 
> "LKM", what do you mean by that?

At a guess, modules.  As to WTF would those possibly have to do with
microkernels, your guess is as good as mine...

Re: Can we move device drivers into user-space?

[Jidong Xiao]

On Fri, Feb 24, 2012 at 11:54 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
> On Fri, Feb 24, 2012 at 11:38:54AM -0500, Jidong Xiao wrote:
>> On Fri, Feb 24, 2012 at 10:38 AM, Greg KH <greg@kroah.com> wrote:
>> > On Fri, Feb 24, 2012 at 10:19:36AM -0500, Jidong Xiao wrote:
>> >> On Wed, Feb 22, 2012 at 11:56 PM, Jidong Xiao <jidong.xiao@gmail.com> wrote:
>> >> > Hi,
>> >> >
>> >> > I am just curious. Since the concept user-space device drivers has
>> >> > been proposed for several years, and some related projects and
>> >> > research papers have demonstrated the feasibility of of moving device
>> >> > drivers into use space. In particular, this paper:
>> >> >
>> >> > Tolerating Malicious Device Drivers in Linux.
>> >> > http://pdos.csail.mit.edu/papers/sud:usenix10.pdf
>> >> >
>> >> > In this paper, existing device driver code need not to be changed,
>> >> > which should help the idea to be applied in practice.
>
> Please note, that one of the strengths of Linux is that we CAN change
> driver code, and we do, which makes implementations like this nice from
> an academic point of view, but unrealistic from a real-world point of
> view.
>
>> >> Actually, my major concern is, since UIO has been accepted, then why
>> >> don't we move all the rest device drivers into user space as well. As
>> >> I understand, currently, some of device drivers are running on user
>> >> space, while the other (or say the majority of) device drivers are
>> >> running on kernel space, so why don't we maintain a consistent device
>> >> drivers infrastructure, say, either all in user space, or all in
>> >> kernel space. (Sure some critical device drivers still need to be kept
>> >> in kernel space.)
>> >
>> > Feel free to create patches to do so, and handle all of the userspace
>> > changes needed in order to implement this.
>> >
>> > I think you haven't thought through the true reason we have device
>> > drivers, and why Linux isn't a microkernel...
>> >
>> > And I'd take exception to your "advantage:" line above, I don't believe
>> > that is true at all.
>> >
>> > Best of luck with your work,
>> >
>> Although I was asking "can we" do something, I am not actually
>> strongly in favor of either move or not move, as indeed it costs too
>> much to do the moving job.
>
> Then why even discuss this at all?  What is your goal here?  If it is to
> have others do work based on an idea you pointed out, you are in the
> wrong place.
>
>> But when you say "handle all of the userspace changes needed in order
>> to implement this", if the device driver can be moved without
>> modification (like the paper above shows), there should not be much
>> changes required for user space applications.
>
> The paper shows one such implementation that purports to not need
> userspace changes.  As we have yet to see any code, I remain
> unconvinced.
>
>> Also, if user space device drivers is a bad idea, why drivers/uio has
>> been created and merged into mainline kernel?
>
> UIO fits a real need for some types of devices, why wouldn't it be
> merged?  You are trying to say it is to be used for all drivers, which
> is totally missing the point.
>
>> Regarding "And I'd take exception to your "advantage:" line above, I
>> don't believe that is true at all", do you agree that a significant
>> portion of kernel crash incidents are due to bugs in drivers?
>
> No I do not.  If you refer to the references from the paper where they
> make that claim, they are talking about a different operating system
> than Linux.  But, by virtue of the fact that the majority of the code
> running in your kernel is drivers, yes, odds are drivers will have a
> small majority of the bugs overall, given the percentages involved.
> However, the bugs-per-line-of-code for Linux drivers is _much_ less than
> other operating systems, especially given the fact that Linux drivers
> require much less lines of code overall than other operating systems
> (30% at the most for the majority of device types.)  So I would like to
> see real numbers backing up your claim before I agree with it.
>
Hi, Greg,

These two studies support my point. If the first one is too old, then
the second one should be more convincing. To save your time, you can
take a look at their conclusion first.

An Empirical Study of Operating Systems Errors
http://www.stanford.edu/~engler/metrics-sosp-01.pdf

Faults in Linux: Ten Years Later
http://pagesperso-systeme.lip6.fr/Suman.Saha/src/asplos11.pdf

Regards
Jidong

Re: Can we move device drivers into user-space?

[Greg KH]

On Sat, Feb 25, 2012 at 02:23:07PM -0500, Jidong Xiao wrote:
> Hi, Greg,
> 
> These two studies support my point. If the first one is too old, then
> the second one should be more convincing. To save your time, you can
> take a look at their conclusion first.
> 
> An Empirical Study of Operating Systems Errors
> http://www.stanford.edu/~engler/metrics-sosp-01.pdf
> 
> Faults in Linux: Ten Years Later
> http://pagesperso-systeme.lip6.fr/Suman.Saha/src/asplos11.pdf

This second paper proves my point, it's funny that you tried to use it
to prove yours, you obviously must not have read the conclusion...

Anyway, any paper that goes "look at all of these problems in the code!"
and isn't instantly followed by patches fixing ALL of those problems by
the authors of the paper, should be ignored as a troll masquerading as a
"study".

greg k-h

Re: Can we move device drivers into user-space?

[Jidong Xiao]

On Sat, Feb 25, 2012 at 3:55 PM, Greg KH <gregkh@linuxfoundation.org> wrote:
> On Sat, Feb 25, 2012 at 02:23:07PM -0500, Jidong Xiao wrote:
>> Hi, Greg,
>>
>> These two studies support my point. If the first one is too old, then
>> the second one should be more convincing. To save your time, you can
>> take a look at their conclusion first.
>>
>> An Empirical Study of Operating Systems Errors
>> http://www.stanford.edu/~engler/metrics-sosp-01.pdf
>>
>> Faults in Linux: Ten Years Later
>> http://pagesperso-systeme.lip6.fr/Suman.Saha/src/asplos11.pdf
>
> This second paper proves my point, it's funny that you tried to use it
> to prove yours, you obviously must not have read the conclusion...
>
> Anyway, any paper that goes "look at all of these problems in the code!"
> and isn't instantly followed by patches fixing ALL of those problems by
> the authors of the paper, should be ignored as a troll masquerading as a
> "study".
>
My point was "a significant portion of kernel crash incidents are due
to bugs in drivers". You said no. I did *not* say bugs in device
drivers are the dominant factor of kernel crashes/faults. So at least
my point matches with the conclusion of the second paper. You can
certainly say these academic studies are meaningless because they are
not telling the whole story, but you can not deny the fact that
because of the large code base, it is the almost impossible to
eliminate all the bugs/problems from device drivers. That's why people
are doing research to mitigate this problem, even though moving device
drivers to user space may not be a good idea, or it is unrealistic in
Linux, those researchers as well as their results deserve more
respect. Everyone in the whole community, including kernel developers
and researchers, shares the same goal, namely, improving the kernel
code quality.

Regards
Jidong

Re: Can we move device drivers into user-space?

[Greg KH]

On Sat, Feb 25, 2012 at 06:43:58PM -0500, Jidong Xiao wrote:
> On Sat, Feb 25, 2012 at 3:55 PM, Greg KH <gregkh@linuxfoundation.org> wrote:
> > On Sat, Feb 25, 2012 at 02:23:07PM -0500, Jidong Xiao wrote:
> >> Hi, Greg,
> >>
> >> These two studies support my point. If the first one is too old, then
> >> the second one should be more convincing. To save your time, you can
> >> take a look at their conclusion first.
> >>
> >> An Empirical Study of Operating Systems Errors
> >> http://www.stanford.edu/~engler/metrics-sosp-01.pdf
> >>
> >> Faults in Linux: Ten Years Later
> >> http://pagesperso-systeme.lip6.fr/Suman.Saha/src/asplos11.pdf
> >
> > This second paper proves my point, it's funny that you tried to use it
> > to prove yours, you obviously must not have read the conclusion...
> >
> > Anyway, any paper that goes "look at all of these problems in the code!"
> > and isn't instantly followed by patches fixing ALL of those problems by
> > the authors of the paper, should be ignored as a troll masquerading as a
> > "study".
> >
> My point was "a significant portion of kernel crash incidents are due
> to bugs in drivers". You said no. I did *not* say bugs in device
> drivers are the dominant factor of kernel crashes/faults. So at least
> my point matches with the conclusion of the second paper. You can
> certainly say these academic studies are meaningless because they are
> not telling the whole story, but you can not deny the fact that
> because of the large code base, it is the almost impossible to
> eliminate all the bugs/problems from device drivers. That's why people
> are doing research to mitigate this problem, even though moving device
> drivers to user space may not be a good idea, or it is unrealistic in
> Linux, those researchers as well as their results deserve more
> respect. Everyone in the whole community, including kernel developers
> and researchers, shares the same goal, namely, improving the kernel
> code quality.

I don't see much help from the majority of researchers toward actually
helping change Linux for the better, their goals usually are just
publishing a paper and then moving on.

Yes, some stick around, and some people are working on making the
intersection between researchers and real-life more condusive toward
helping us out, but that is a hard task given that the goals of the two
groups are usually totally different in the end.

I suggest, if you have the time, to try to work with the researchers to
resolve the problems that they find.  They said that they found hundreds
of problems.  Why aren't those problems all now fixed?  What kept them
from getting fixed after they found them?  Was it something that the
community ignored, or did they not even try?  Find out the root cause of
that, and then, for their next paper, they might have something totally
different to report...

good luck,

greg k-h

Re: Can we move device drivers into user-space?

[Greg KH]

On Sat, Feb 25, 2012 at 12:55:40PM -0800, Greg KH wrote:
> On Sat, Feb 25, 2012 at 02:23:07PM -0500, Jidong Xiao wrote:
> > Hi, Greg,
> > 
> > These two studies support my point. If the first one is too old, then
> > the second one should be more convincing. To save your time, you can
> > take a look at their conclusion first.
> > 
> > An Empirical Study of Operating Systems Errors
> > http://www.stanford.edu/~engler/metrics-sosp-01.pdf
> > 
> > Faults in Linux: Ten Years Later
> > http://pagesperso-systeme.lip6.fr/Suman.Saha/src/asplos11.pdf
> 
> This second paper proves my point, it's funny that you tried to use it
> to prove yours, you obviously must not have read the conclusion...
> 
> Anyway, any paper that goes "look at all of these problems in the code!"
> and isn't instantly followed by patches fixing ALL of those problems by
> the authors of the paper, should be ignored as a troll masquerading as a
> "study".

Oops, it was pointed out to me that one of the authors of that paper
really is contributing patches, my appologies to them.  Julia has
probably fixed more bugs than almost anyone else in the kernel
community.  I did not mean to make light of her contributions at all,
again my mistake.

greg k-h

Re: Can we move device drivers into user-space?

[Bernd Petrovitsch]

On Fre, 2012-02-24 at 11:38 -0500, Jidong Xiao wrote:
[...]
> Although I was asking "can we" do something, I am not actually
> strongly in favor of either move or not move, as indeed it costs too
> much to do the moving job.

You obviously missed a crucial point in the little corner "LKML" of the
universe: You are (automatically, implicitly) expected to start the work
and produce patches and keep on working on it and actually *do* the job.
If only to show that you are serious, that the "ideas" are actually
useful and you are not just trolling around. Possibly people will help
you though.

Quoting some studies is nice for reference (implying that they are
relevant and applicable which should be checked before blindly believing
in it) but most here have read too many "studies" to be impressed any
number of them.

That's usually worded in (and meant with) "show patches" or "try it out"
or "talk is cheap, show me the code".

	Bernd
-- 
Bernd Petrovitsch                  Email : bernd@petrovitsch.priv.at
                     LUGA : http://www.luga.at

Re: Can we move device drivers into user-space?

[Guenter Roeck]

On Fri, 2012-02-24 at 10:38 -0500, Greg KH wrote:
> On Fri, Feb 24, 2012 at 10:19:36AM -0500, Jidong Xiao wrote:
> > On Wed, Feb 22, 2012 at 11:56 PM, Jidong Xiao <jidong.xiao@gmail.com> wrote:
> > > Hi,
> > >
> > > I am just curious. Since the concept user-space device drivers has
> > > been proposed for several years, and some related projects and
> > > research papers have demonstrated the feasibility of of moving device
> > > drivers into use space. In particular, this paper:
> > >
> > > Tolerating Malicious Device Drivers in Linux.
> > > http://pdos.csail.mit.edu/papers/sud:usenix10.pdf
> > >
> > > In this paper, existing device driver code need not to be changed,
> > > which should help the idea to be applied in practice.
> > >
> > > The advantage and disadvantage of move device drivers into use space
> > > of both obvious:
> > >
> > > Advantage: Since most of kernel bugs are caused by device drivers
> > > issues, moving device drivers into user space can reduce the impact of
> > > device driver bugs. From security perspective, the system can be more
> > > secure and robust if most device drivers are working in user space.
> > > Disadvantage: At least, existing techniques as well as the above paper
> > > showed a relatively high overhead.
> > >
> > > So is it mainly because the high overhead that prevents the user-space
> > > device drivers ideas being accepted in Linux?
> > >
> > 
> > Actually, my major concern is, since UIO has been accepted, then why
> > don't we move all the rest device drivers into user space as well. As
> > I understand, currently, some of device drivers are running on user
> > space, while the other (or say the majority of) device drivers are
> > running on kernel space, so why don't we maintain a consistent device
> > drivers infrastructure, say, either all in user space, or all in
> > kernel space. (Sure some critical device drivers still need to be kept
> > in kernel space.)
> 
> Feel free to create patches to do so, and handle all of the userspace
> changes needed in order to implement this.
> 
> I think you haven't thought through the true reason we have device
> drivers, and why Linux isn't a microkernel...
> 
> And I'd take exception to your "advantage:" line above, I don't believe
> that is true at all.

I second that. Worse, the real disadvantages are ignored. Crappy
user-space code, code is kept proprietary, code is no longer submitted
upstream, people don't care about implementing interrupts and instead
implement polling loops, porting to later kernel versions is a pain. The
list goes on and on. This is all more than annoying.

I would prefer another approach: Fix the problematic drivers, and spend
time researching how to improve forced module unload to a point where
modules can be re-loaded after an OOPS.

How about dropping UIO support from the kernel ? That would make more
sense to me.

Guenter

Re: Can we move device drivers into user-space?

[Greg KH]

On Fri, Feb 24, 2012 at 09:07:09AM -0800, Guenter Roeck wrote:
> How about dropping UIO support from the kernel ? That would make more
> sense to me.

Again, UIO solves a real need, are you to tell the users of that code
that somehow we are now not going to support them anymore?

UIO was created when Thomas and I sat in the back of a conference
presentation and saw, for the umpteenth time, a presentation by someone
who was trying to write userspace drivers, and obviously didn't know
what they were doing.

UIO provides a framework that actually works (unlike all of the previous
research papers were trying to do), and is used in real systems (laser
welding robots!) every day, manufacturing things that you use and rely
on.

You remove UIO at the risk of pissing off those robots, the choice is
yours, I know I'm not going to do it...

greg k-h

Re: Can we move device drivers into user-space?

[Guenter Roeck]

On Fri, 2012-02-24 at 12:17 -0500, Greg KH wrote:
> On Fri, Feb 24, 2012 at 09:07:09AM -0800, Guenter Roeck wrote:
> > How about dropping UIO support from the kernel ? That would make more
> > sense to me.
> 
> Again, UIO solves a real need, are you to tell the users of that code
> that somehow we are now not going to support them anymore?
> 
> UIO was created when Thomas and I sat in the back of a conference
> presentation and saw, for the umpteenth time, a presentation by someone
> who was trying to write userspace drivers, and obviously didn't know
> what they were doing.
> 
> UIO provides a framework that actually works (unlike all of the previous
> research papers were trying to do), and is used in real systems (laser
> welding robots!) every day, manufacturing things that you use and rely
> on.
> 
> You remove UIO at the risk of pissing off those robots, the choice is
> yours, I know I'm not going to do it...

I understand the background and reasoning, but ...

I have seen UIO used for networking drivers, hwmon drivers, I2C bus
master drivers (with matching I2C client drivers in user-space), mfd
devices, and so on. I have seen existing kernel drivers re-implemented
as UIO drivers. I have seen UIO drivers where the kernel part of the
driver is larger than the entire driver written as kernel driver. I have
seen UIO drivers using polling instead of interrupts "because it is
faster than interrupts".

Often, those drivers are then re-written for the next board (to support
the same chip) because they were not written with HW-independence in
mind and don't support HW abstraction.

Yes, there may be real need for UIO in some cases, but all I have seen
it used for so far is what I would call abuse, resulting in maintenance
nightmares.

Given the choice, I would be quite happy to piss off some robots. Call
it a prejudice if you like ;).

Guenter

Re: Can we move device drivers into user-space?

[Greg KH]

On Fri, Feb 24, 2012 at 09:47:48AM -0800, Guenter Roeck wrote:
> > You remove UIO at the risk of pissing off those robots, the choice is
> > yours, I know I'm not going to do it...
> 
> I understand the background and reasoning, but ...
> 
> I have seen UIO used for networking drivers, hwmon drivers, I2C bus
> master drivers (with matching I2C client drivers in user-space), mfd
> devices, and so on.

And all of those uses are wrong.  Go kick those developers and companies
today.  Hard.

> I have seen existing kernel drivers re-implemented as UIO drivers. 

Where?  By whom?

> I have seen UIO drivers where the kernel part of the
> driver is larger than the entire driver written as kernel driver. I have
> seen UIO drivers using polling instead of interrupts "because it is
> faster than interrupts".

We can't prevent people from being stupid, can we?

> Often, those drivers are then re-written for the next board (to support
> the same chip) because they were not written with HW-independence in
> mind and don't support HW abstraction.
> 
> Yes, there may be real need for UIO in some cases, but all I have seen
> it used for so far is what I would call abuse, resulting in maintenance
> nightmares.

Again, that's using the interface wrong, and foolishly.  Don't do that.

> Given the choice, I would be quite happy to piss off some robots. Call
> it a prejudice if you like ;).

You can't control how people use an interface.  You will note that there
are no stupid users of the UIO interface in the kernel today, we can't
control what people do in the privacy of their own companies/homes,
despite numerous governments trying to do so in the past.

So yes, people will always do stupid, foolish things.  And they were
doing them before UIO came along, now they just have the chance to at
least do those foolish things in a way that interfaces with the kernel
in a semi-sane manner, not messing anything else in the kernel up.

sorry,

greg k-h

Re: Can we move device drivers into user-space?

[Henrik Rydberg]

> > Given the choice, I would be quite happy to piss off some robots. Call
> > it a prejudice if you like ;).
> 
> You can't control how people use an interface.  You will note that there
> are no stupid users of the UIO interface in the kernel today, we can't
> control what people do in the privacy of their own companies/homes,
> despite numerous governments trying to do so in the past.
> 
> So yes, people will always do stupid, foolish things.  And they were
> doing them before UIO came along, now they just have the chance to at
> least do those foolish things in a way that interfaces with the kernel
> in a semi-sane manner, not messing anything else in the kernel up.

So the question is; can the uio example be repeated in other areas, to
bring more kernel power to userspace?

No doubt, the kernel has fostered an unprecedented code-quality view,
which, IMHO, is the bottom line. As long as that quality remains
unchallenged, having all drivers in-kernel will remain the best
choice. But, suppose some entity managed to keep that quality in
userspace, would there be any reason to think of it as a bad idea? I
think not.

Henrik

Re: Can we move device drivers into user-space?

[Greg KH]

On Fri, Feb 24, 2012 at 08:15:35PM +0100, Henrik Rydberg wrote:
> > > Given the choice, I would be quite happy to piss off some robots. Call
> > > it a prejudice if you like ;).
> > 
> > You can't control how people use an interface.  You will note that there
> > are no stupid users of the UIO interface in the kernel today, we can't
> > control what people do in the privacy of their own companies/homes,
> > despite numerous governments trying to do so in the past.
> > 
> > So yes, people will always do stupid, foolish things.  And they were
> > doing them before UIO came along, now they just have the chance to at
> > least do those foolish things in a way that interfaces with the kernel
> > in a semi-sane manner, not messing anything else in the kernel up.
> 
> So the question is; can the uio example be repeated in other areas, to
> bring more kernel power to userspace?

What exactly do you mean by "more kernel power"?  You can write
userspace char drivers, filesystems, usb drivers, usb gadget drivers,
and lots of other things today with the interfaces we provide from the
kernel.

And even better yet, please show what you mean with patches.

greg k-h

Re: Can we move device drivers into user-space?

[Henrik Rydberg]

> > > So yes, people will always do stupid, foolish things.  And they were
> > > doing them before UIO came along, now they just have the chance to at
> > > least do those foolish things in a way that interfaces with the kernel
> > > in a semi-sane manner, not messing anything else in the kernel up.
> > 
> > So the question is; can the uio example be repeated in other areas, to
> > bring more kernel power to userspace?
> 
> What exactly do you mean by "more kernel power"?  You can write
> userspace char drivers, filesystems, usb drivers, usb gadget drivers,
> and lots of other things today with the interfaces we provide from the
> kernel.

This is all good, but the thread was started for some generic reason
not covered by those examples. The uio interface was pointed out
because it brings pci(e) to userland, which was not (readily)
accessible before. However, every driver that cannot be implemented in
userspace is another example.

I am not complaining about the kernel and its driver structure - on
the contrary. I do, however, see a reason why constructing lower-level
interfaces to userspace may be of benefit. The kernel is growing
tremendously fast. Sooner or later, parts of the present driver
responsibility will have to be split into smaller chunks. Why not
place those chunks outside the kernel itself?

> And even better yet, please show what you mean with patches.

Sure. This particular thread seems to transcend patches, though. It
does not hurt to vent public opinion every now and then.

Henrik

Re: Can we move device drivers into user-space?

[Greg KH]

On Fri, Feb 24, 2012 at 09:10:27PM +0100, Henrik Rydberg wrote:
> I am not complaining about the kernel and its driver structure - on
> the contrary. I do, however, see a reason why constructing lower-level
> interfaces to userspace may be of benefit. The kernel is growing
> tremendously fast. Sooner or later, parts of the present driver
> responsibility will have to be split into smaller chunks. Why not
> place those chunks outside the kernel itself?

I fail to understand why you think the growth of the kernel will require
drivers to be split into chunks in the future.  Are we somehow growing
faster than is required / needed / wanted and outstripping the size of
what we are allowed to take up on machines?

greg k-h

Re: Can we move device drivers into user-space?

[Henrik Rydberg]

On Fri, Feb 24, 2012 at 12:16:55PM -0800, Greg KH wrote:
> On Fri, Feb 24, 2012 at 09:10:27PM +0100, Henrik Rydberg wrote:
> > I am not complaining about the kernel and its driver structure - on
> > the contrary. I do, however, see a reason why constructing lower-level
> > interfaces to userspace may be of benefit. The kernel is growing
> > tremendously fast. Sooner or later, parts of the present driver
> > responsibility will have to be split into smaller chunks. Why not
> > place those chunks outside the kernel itself?
> 
> I fail to understand why you think the growth of the kernel will require
> drivers to be split into chunks in the future.  Are we somehow growing
> faster than is required / needed / wanted and outstripping the size of
> what we are allowed to take up on machines?

How long can one grow and still claim to _be_ a kernel? The current
(arbitrary) split between kernel and userland was made a long time
ago. For a number of reasons, of course, but not least out of
convenience. Projecting the current kernel growth ten years into the
future, will there still not be another (arbitrary) convenient split?

Even so, the main point was not whether a secondary split may or may
not happen, but what will happen to the quality of the total system
when/if that happens. I doubt the fate of userland drivers would be so
heatedly discussed if everyone believed that work would be carried out
with the same quality currently found in the kernel.

Henrik

Re: Can we move device drivers into user-space?

[Greg KH]

On Fri, Feb 24, 2012 at 09:37:15PM +0100, Henrik Rydberg wrote:
> On Fri, Feb 24, 2012 at 12:16:55PM -0800, Greg KH wrote:
> > On Fri, Feb 24, 2012 at 09:10:27PM +0100, Henrik Rydberg wrote:
> > > I am not complaining about the kernel and its driver structure - on
> > > the contrary. I do, however, see a reason why constructing lower-level
> > > interfaces to userspace may be of benefit. The kernel is growing
> > > tremendously fast. Sooner or later, parts of the present driver
> > > responsibility will have to be split into smaller chunks. Why not
> > > place those chunks outside the kernel itself?
> > 
> > I fail to understand why you think the growth of the kernel will require
> > drivers to be split into chunks in the future.  Are we somehow growing
> > faster than is required / needed / wanted and outstripping the size of
> > what we are allowed to take up on machines?
> 
> How long can one grow and still claim to _be_ a kernel?

You tell me.  I know of lots of "kernels" that are far bigger than
Linux, and people still consider them a kernel.

> The current
> (arbitrary) split between kernel and userland was made a long time
> ago. For a number of reasons, of course, but not least out of
> convenience. Projecting the current kernel growth ten years into the
> future, will there still not be another (arbitrary) convenient split?

Why?  What problems are we having with our existing user/kernel split
that would drive such a change?

> Even so, the main point was not whether a secondary split may or may
> not happen, but what will happen to the quality of the total system
> when/if that happens. I doubt the fate of userland drivers would be so
> heatedly discussed if everyone believed that work would be carried out
> with the same quality currently found in the kernel.

Quality is not the only reason we don't want userspace drivers for some
types of devices.  Realize what drivers provide to userspace today and
you will understand that.

thanks,

greg k-h

Re: Can we move device drivers into user-space?

[Henrik Rydberg]

> > How long can one grow and still claim to _be_ a kernel?
> 
> You tell me.  I know of lots of "kernels" that are far bigger than
> Linux, and people still consider them a kernel.

I would love to be enligthened.

> > The current
> > (arbitrary) split between kernel and userland was made a long time
> > ago. For a number of reasons, of course, but not least out of
> > convenience. Projecting the current kernel growth ten years into the
> > future, will there still not be another (arbitrary) convenient split?
> 
> Why?  What problems are we having with our existing user/kernel split
> that would drive such a change?

Maintenance. Sure, as soon as an area grows too large for a single
person, the current structure will ensure it divides so that the patch
stream becomes manageable. We have already seen ample examples of
that. But the overall structure of the kernel will become less and
less manageable, and the likelihood of duplicates and maintenance
problems will increase. At some point, intra-system interfaces will be
introduced, such that several areas may coexist and expand
individually. At that point, the convenience split will already have
been made, and the subsystems may well reside in different places.


> > Even so, the main point was not whether a secondary split may or may
> > not happen, but what will happen to the quality of the total system
> > when/if that happens. I doubt the fate of userland drivers would be so
> > heatedly discussed if everyone believed that work would be carried out
> > with the same quality currently found in the kernel.
> 
> Quality is not the only reason we don't want userspace drivers for some
> types of devices.  Realize what drivers provide to userspace today and
> you will understand that.

I think I do understand how software interfaces and streamlining
works, so I fail to get the point here.

Thanks,
Henrik

Re: Can we move device drivers into user-space?

[Ted Ts'o]

On Fri, Feb 24, 2012 at 10:22:38PM +0100, Henrik Rydberg wrote:
> 
> Maintenance. Sure, as soon as an area grows too large for a single
> person, the current structure will ensure it divides so that the patch
> stream becomes manageable. We have already seen ample examples of
> that. But the overall structure of the kernel will become less and
> less manageable, and the likelihood of duplicates and maintenance
> problems will increase.

Not necessarily.  The primary area of growth has been hardware support
(i.e., drivers), and that scales quite well.

The main issue is the grown of intra-system interfaces, and you
haven't shown that this has happened in anything approaching the
levels where we need to worry.  If we add a new file system, like
btrfs, that doesn't add a whole new set of VFS interfaces, and it's
not like we need to worry about communication interfaces between btrfs
and ext4....

						- Ted

Re: Can we move device drivers into user-space?

[Henrik Rydberg]

On Fri, Feb 24, 2012 at 04:30:27PM -0500, Ted Ts'o wrote:
> On Fri, Feb 24, 2012 at 10:22:38PM +0100, Henrik Rydberg wrote:
> > 
> > Maintenance. Sure, as soon as an area grows too large for a single
> > person, the current structure will ensure it divides so that the patch
> > stream becomes manageable. We have already seen ample examples of
> > that. But the overall structure of the kernel will become less and
> > less manageable, and the likelihood of duplicates and maintenance
> > problems will increase.
> 
> Not necessarily.  The primary area of growth has been hardware support
> (i.e., drivers), and that scales quite well.
> 
> The main issue is the grown of intra-system interfaces, and you
> haven't shown that this has happened in anything approaching the
> levels where we need to worry.  If we add a new file system, like
> btrfs, that doesn't add a whole new set of VFS interfaces, and it's
> not like we need to worry about communication interfaces between btrfs
> and ext4....

True, and the emergent interface (vfs) is even accessible in
userspace, so all is good in that department for now. Conversely, you
have not shown that this can go on forever. ;-)

The main issue that set me off has been sufficiently diluted in the
(selective) discussion so as to no longer make sense as a reply: At
some point, in-tree or out-of-tree will no longer be distinguishable,
and the question is if/when/why something would/should happen as a
consequence. A matter of politics, if you will. It seemed like an
honest question starting this thread, and I think it is fair to keep
it in mind as such.

Thanks.
Henrik

Re: Can we move device drivers into user-space?

[Greg KH]

On Fri, Feb 24, 2012 at 11:14:59PM +0100, Henrik Rydberg wrote:
> The main issue that set me off has been sufficiently diluted in the
> (selective) discussion so as to no longer make sense as a reply: At
> some point, in-tree or out-of-tree will no longer be distinguishable,
> and the question is if/when/why something would/should happen as a
> consequence. A matter of politics, if you will. It seemed like an
> honest question starting this thread, and I think it is fair to keep
> it in mind as such.

If something happens to require such a change in the future, we will
deal with it, at that time.  Remember the rule, "Linux is evolution, not
intelligent design."

greg k-h

Re: Can we move device drivers into user-space?

[Henrik Rydberg]

On Fri, Feb 24, 2012 at 02:20:34PM -0800, Greg KH wrote:
> On Fri, Feb 24, 2012 at 11:14:59PM +0100, Henrik Rydberg wrote:
> > The main issue that set me off has been sufficiently diluted in the
> > (selective) discussion so as to no longer make sense as a reply: At
> > some point, in-tree or out-of-tree will no longer be distinguishable,
> > and the question is if/when/why something would/should happen as a
> > consequence. A matter of politics, if you will. It seemed like an
> > honest question starting this thread, and I think it is fair to keep
> > it in mind as such.
> 
> If something happens to require such a change in the future, we will
> deal with it, at that time.  Remember the rule, "Linux is evolution, not
> intelligent design."

Who "we" is is exactly the point.

For the not-so-important record, evolution does actually create
intelligent designs.

Thanks,
Henrik

Re: Can we move device drivers into user-space?

[Greg KH]

On Fri, Feb 24, 2012 at 11:49:30PM +0100, Henrik Rydberg wrote:
> On Fri, Feb 24, 2012 at 02:20:34PM -0800, Greg KH wrote:
> > On Fri, Feb 24, 2012 at 11:14:59PM +0100, Henrik Rydberg wrote:
> > > The main issue that set me off has been sufficiently diluted in the
> > > (selective) discussion so as to no longer make sense as a reply: At
> > > some point, in-tree or out-of-tree will no longer be distinguishable,
> > > and the question is if/when/why something would/should happen as a
> > > consequence. A matter of politics, if you will. It seemed like an
> > > honest question starting this thread, and I think it is fair to keep
> > > it in mind as such.
> > 
> > If something happens to require such a change in the future, we will
> > deal with it, at that time.  Remember the rule, "Linux is evolution, not
> > intelligent design."
> 
> Who "we" is is exactly the point.

The kernel development community will handle it.

> For the not-so-important record, evolution does actually create
> intelligent designs.

For some things yes, for others (like your tailbone), perhaps not :)

greg k-h

Re: Can we move device drivers into user-space?

[Henrik Rydberg]

On Fri, Feb 24, 2012 at 02:54:37PM -0800, Greg KH wrote:
> On Fri, Feb 24, 2012 at 11:49:30PM +0100, Henrik Rydberg wrote:
> > On Fri, Feb 24, 2012 at 02:20:34PM -0800, Greg KH wrote:
> > > On Fri, Feb 24, 2012 at 11:14:59PM +0100, Henrik Rydberg wrote:
> > > > The main issue that set me off has been sufficiently diluted in the
> > > > (selective) discussion so as to no longer make sense as a reply: At
> > > > some point, in-tree or out-of-tree will no longer be distinguishable,
> > > > and the question is if/when/why something would/should happen as a
> > > > consequence. A matter of politics, if you will. It seemed like an
> > > > honest question starting this thread, and I think it is fair to keep
> > > > it in mind as such.
> > > 
> > > If something happens to require such a change in the future, we will
> > > deal with it, at that time.  Remember the rule, "Linux is evolution, not
> > > intelligent design."
> > 
> > Who "we" is is exactly the point.
> 
> The kernel development community will handle it.

That's nice to hear, it seems like a fairly bright bunch.

> > For the not-so-important record, evolution does actually create
> > intelligent designs.
> 
> For some things yes, for others (like your tailbone), perhaps not :)

Oh no, that's where the matrix cord is plugged in. :-)

Cheers,
Henrik

Re: Can we move device drivers into user-space?

[Theodore Tso]

On Feb 24, 2012, at 5:14 PM, Henrik Rydberg wrote:

> True, and the emergent interface (vfs) is even accessible in
> userspace, so all is good in that department for now. Conversely, you
> have not shown that this can go on forever. ;-)

… and the performance is terrible --- as it must be.  If you don't understand why this must be, then we're wasting our time having this conversation.

And if you're the one wanting to make a change, then you are the one who has to provide the proof.   Otherwise we're just talking about hypotheticals, and that way lies over-design.  Why waste time engineering something that may never come to pass?

Of course, your time is something you are free to spend however you like.  So if you want to try implementing some of these grand plans of yours, show us the code….

-- Ted

Re: Can we move device drivers into user-space?

[Henrik Rydberg]

> … and the performance is terrible --- as it must be.  If you don't
> understand why this must be, then we're wasting our time having this
> conversation.

You are right, I don't understand the assumptions leading to that
conclusion. It does not seem to stop people from experimenting with
filesystems that do no even reside within the same computer (hdfs).

> And if you're the one wanting to make a change, then you are the one
> who has to provide the proof.

I know the drill, and I obviously already got hit on the head. ;-)

> Otherwise we're just talking about
> hypotheticals, and that way lies over-design.  Why waste time
> engineering something that may never come to pass?

This is a seriously defensive attitude, given that the thread was
hypothetical from the start.

> Of course, your time is something you are free to spend however you
> like.  So if you want to try implementing some of these grand plans
> of yours, show us the code….

If I put on rose-colored glasses and try really hard, I can almost
interpret this as an invitation to share code.

Thanks.
Henrik

Re: Can we move device drivers into user-space?

[Bobby Powers]

On Fri, Feb 24, 2012 at 5:14 PM, Henrik Rydberg <rydberg@euromail.se> wrote:
> On Fri, Feb 24, 2012 at 04:30:27PM -0500, Ted Ts'o wrote:
>> On Fri, Feb 24, 2012 at 10:22:38PM +0100, Henrik Rydberg wrote:
>> >
>> > Maintenance. Sure, as soon as an area grows too large for a single
>> > person, the current structure will ensure it divides so that the patch
>> > stream becomes manageable. We have already seen ample examples of
>> > that. But the overall structure of the kernel will become less and
>> > less manageable, and the likelihood of duplicates and maintenance
>> > problems will increase.
>>
>> Not necessarily.  The primary area of growth has been hardware support
>> (i.e., drivers), and that scales quite well.
>>
>> The main issue is the grown of intra-system interfaces, and you
>> haven't shown that this has happened in anything approaching the
>> levels where we need to worry.  If we add a new file system, like
>> btrfs, that doesn't add a whole new set of VFS interfaces, and it's
>> not like we need to worry about communication interfaces between btrfs
>> and ext4....
>
> True, and the emergent interface (vfs) is even accessible in
> userspace, so all is good in that department for now. Conversely, you
> have not shown that this can go on forever. ;-)
>
> The main issue that set me off has been sufficiently diluted in the
> (selective) discussion so as to no longer make sense as a reply: At
> some point, in-tree or out-of-tree will no longer be distinguishable,

Please explain how you would be unable to distinguish between a driver
that lives in the kernel source tree, and one that does not.

yours,
Bobby

> and the question is if/when/why something would/should happen as a
> consequence. A matter of politics, if you will. It seemed like an
> honest question starting this thread, and I think it is fair to keep
> it in mind as such.
>
> Thanks.
> Henrik
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/

Re: Can we move device drivers into user-space?

[Henrik Rydberg]

> > The main issue that set me off has been sufficiently diluted in the
> > (selective) discussion so as to no longer make sense as a reply: At
> > some point, in-tree or out-of-tree will no longer be distinguishable,
> 
> Please explain how you would be unable to distinguish between a driver
> that lives in the kernel source tree, and one that does not.

The SUD pointed to in the beginning of the thread is an example of
this, but I was not thinking of it in quite so literal terms. Rather,
I was imagining that as the kernel grows and the in-kernel interfaces
matures, the amount of actual communication between different portions
of the code diminishes. Code on opposite sides of a stable interface
is, for all practical purposes, separated. Whether that code lives
in-tree or out-of tree is then of little consequence.

To try to prevent another flame war, let's make it clear that I am not
saying that the most powerful in-kernel argument, that code can be
changed, is unimportant. Maybe code, like so many other things,
arranges itself in a scale-free critical fashion, which would forever
warrant a monolithic approach. Maybe it would even make sense to have
userspace join the same tree as well. There is however a frofoundly
political aspect here, which cannot be expressed in terms of
code. Also, in practise, breaking things down into manageable chunks
is usually a good idea in the end.

Thanks,
Henrik

Re: Can we move device drivers into user-space?

[Richard Yao]

On Sun, Feb 26, 2012 at 5:47 AM, Henrik Rydberg <rydberg@euromail.se> wrote:
>> > The main issue that set me off has been sufficiently diluted in the
>> > (selective) discussion so as to no longer make sense as a reply: At
>> > some point, in-tree or out-of-tree will no longer be distinguishable,
>>
>> Please explain how you would be unable to distinguish between a driver
>> that lives in the kernel source tree, and one that does not.
>
> The SUD pointed to in the beginning of the thread is an example of
> this, but I was not thinking of it in quite so literal terms. Rather,
> I was imagining that as the kernel grows and the in-kernel interfaces
> matures, the amount of actual communication between different portions
> of the code diminishes. Code on opposite sides of a stable interface
> is, for all practical purposes, separated. Whether that code lives
> in-tree or out-of tree is then of little consequence.
>
> To try to prevent another flame war, let's make it clear that I am not
> saying that the most powerful in-kernel argument, that code can be
> changed, is unimportant. Maybe code, like so many other things,
> arranges itself in a scale-free critical fashion, which would forever
> warrant a monolithic approach. Maybe it would even make sense to have
> userspace join the same tree as well. There is however a frofoundly
> political aspect here, which cannot be expressed in terms of
> code. Also, in practise, breaking things down into manageable chunks
> is usually a good idea in the end.

I do not see what prevents an in-kernel context switch into a ring 3
context with a different process address space. Is it necessary to
remove the code from the kernel tree before someone can do this?

Re: Can we move device drivers into user-space?

[Bernd Petrovitsch]

On Son, 2012-02-26 at 07:26 -0500, Richard Yao wrote:
> On Sun, Feb 26, 2012 at 5:47 AM, Henrik Rydberg <rydberg@euromail.se> wrote:
[...]
> > changed, is unimportant. Maybe code, like so many other things,
> > arranges itself in a scale-free critical fashion, which would forever

"Code arranges" not itself, but people arrange code the best they see
fit.

> > warrant a monolithic approach. Maybe it would even make sense to have

And the Linux kernel is BTW not really that monolitic in the spirit of
the definition of Tanenbaums book. It's just the category that sucks the
least there.

> > userspace join the same tree as well. There is however a frofoundly
> > political aspect here, which cannot be expressed in terms of
> > code. Also, in practise, breaking things down into manageable chunks
> > is usually a good idea in the end.

Yes, everybody learns that in the first lecture on programming. Please
sent patches to make actually things better and not just talk. Thank
you.

> I do not see what prevents an in-kernel context switch into a ring 3
> context with a different process address space. Is it necessary to
> remove the code from the kernel tree before someone can do this?

No, and that's the real problem here: Everybody who might think it's a
good idea may please implement - and thus propose - something concrete,
try it out and comeback with experience and performance numbers - and
not just try to come up with some theory and other misleading points
(what political aspect?!) and ideas what others should do and why it
might be better.

	Bernd
-- 
Bernd Petrovitsch                  Email : bernd@petrovitsch.priv.at
                     LUGA : http://www.luga.at

Re: Can we move device drivers into user-space?

[Henrik Rydberg]

> > > changed, is unimportant. Maybe code, like so many other things,
> > > arranges itself in a scale-free critical fashion, which would forever
> 
> "Code arranges" not itself, but people arrange code the best they see
> fit.

You seem to have missed the point of that sentence. Go pick on
somebody else.

> > > userspace join the same tree as well. There is however a frofoundly
> > > political aspect here, which cannot be expressed in terms of
> > > code. Also, in practise, breaking things down into manageable chunks
> > > is usually a good idea in the end.
> 
> Yes, everybody learns that in the first lecture on programming. Please
> sent patches to make actually things better and not just talk. Thank
> you.

I actually do on a regular basis. I wish everybody did.

Thanks.
Henrik

Re: Can we move device drivers into user-space?

[Richard Yao]

>> I do not see what prevents an in-kernel context switch into a ring 3
>> context with a different process address space. Is it necessary to
>> remove the code from the kernel tree before someone can do this?
>
> No, and that's the real problem here: Everybody who might think it's a
> good idea may please implement - and thus propose - something concrete,
> try it out and comeback with experience and performance numbers - and
> not just try to come up with some theory and other misleading points
> (what political aspect?!) and ideas what others should do and why it
> might be better.

It seems counterproductive to tell people to produce results without
doing the brainstorming that such results require.

If such discussion is not welcome here, then the FreeBSD project has a
similar kernel design. Perhaps it would be more productive for those
interested in this to brainstorm on their mailing list. If anything
materializes, it could be for their kernel instead. Nothing is forcing
anyone to do things with Linux.

Re: Can we move device drivers into user-space?

[Ted Ts'o]

On Sun, Feb 26, 2012 at 10:05:59AM -0500, Richard Yao wrote:
> >> I do not see what prevents an in-kernel context switch into a ring 3
> >> context with a different process address space. Is it necessary to
> >> remove the code from the kernel tree before someone can do this?
> >
> > No, and that's the real problem here: Everybody who might think it's a
> > good idea may please implement - and thus propose - something concrete,
> > try it out and comeback with experience and performance numbers - and
> > not just try to come up with some theory and other misleading points
> > (what political aspect?!) and ideas what others should do and why it
> > might be better.
> 
> It seems counterproductive to tell people to produce results without
> doing the brainstorming that such results require.

It's also counterproductive to tell kernel programmers how they should
do what they are being paid how to do.  If you just want to brainstorm
possibilities where **you** will do all of the work, as opposed to
asking the kernel development community to work on your pet theories,
it's helpful if you more carefully label your poposals as such.

> If such discussion is not welcome here, then the FreeBSD project has a
> similar kernel design. Perhaps it would be more productive for those
> interested in this to brainstorm on their mailing list. If anything
> materializes, it could be for their kernel instead. Nothing is forcing
> anyone to do things with Linux.

My experience is that most researchers produce code which is not of
production quality.  It's very easy to produce a proof of concept that
works well enough to publish a paper.  Making something which is
actually performant, is **hard**.  The problem is that you don't get
Ph.D.'s for counting cache line misses --- or for getting your
implementation to the point where cache line misses matter in the
first place.  So the threat that Linux will miss out on some great
breakthrough is something that is very hard for me to take seriously,
speaking quite frankly.

Usenix has awarded best paper awards to work that was done on obsolete
kernels, where if the goal of that work was to produce production
kernel code, was in fact horrible work.  But if the goal of that work
is to produce Ph.D. graduates, or to help the professor get tenure,
was perhaps more successful.

That being said, maybe you'd be happier engaging with the Minix 3
community.  They are folks who think (unproven, theoretical) safety is
more important than performance.  And they've created a kernel which
is a 140 times slower at process creation, ten times greater syscall
overhead, and file copies that were two to ten times slower.[1]

[1] http://lwn.net/Articles/220255/

And Prof. Tannenbaum is an academic, so his goals may be more closely
aligned to yours.

Best regards,

	      	   	       	    	   - Ted

Re: Can we move device drivers into user-space?

[Richard Yao]

Ted,

I think you have me confused with Jidong Xiao. He is the one who
suggested moving things to userspace. I happened to see the
conversation, noticed people had missed a few points and added them in
an attempt to be helpful. If you look at my emails to the mailing
list, you would see that I had said that this work should be done
elsewhere. The email to which you had replied was one that was meant
to say that if people were set on having those interested in doing
this to work with LInux, it should be okay for them to brainstorm on
the LKML.

With that said, please refrain from further outbursts. They hurt Linux.

Yours truly,
Richard Yao

On Sun, Feb 26, 2012 at 3:30 PM, Ted Ts'o <tytso@mit.edu> wrote:
> On Sun, Feb 26, 2012 at 10:05:59AM -0500, Richard Yao wrote:
>> >> I do not see what prevents an in-kernel context switch into a ring 3
>> >> context with a different process address space. Is it necessary to
>> >> remove the code from the kernel tree before someone can do this?
>> >
>> > No, and that's the real problem here: Everybody who might think it's a
>> > good idea may please implement - and thus propose - something concrete,
>> > try it out and comeback with experience and performance numbers - and
>> > not just try to come up with some theory and other misleading points
>> > (what political aspect?!) and ideas what others should do and why it
>> > might be better.
>>
>> It seems counterproductive to tell people to produce results without
>> doing the brainstorming that such results require.
>
> It's also counterproductive to tell kernel programmers how they should
> do what they are being paid how to do.  If you just want to brainstorm
> possibilities where **you** will do all of the work, as opposed to
> asking the kernel development community to work on your pet theories,
> it's helpful if you more carefully label your poposals as such.
>
>> If such discussion is not welcome here, then the FreeBSD project has a
>> similar kernel design. Perhaps it would be more productive for those
>> interested in this to brainstorm on their mailing list. If anything
>> materializes, it could be for their kernel instead. Nothing is forcing
>> anyone to do things with Linux.
>
> My experience is that most researchers produce code which is not of
> production quality.  It's very easy to produce a proof of concept that
> works well enough to publish a paper.  Making something which is
> actually performant, is **hard**.  The problem is that you don't get
> Ph.D.'s for counting cache line misses --- or for getting your
> implementation to the point where cache line misses matter in the
> first place.  So the threat that Linux will miss out on some great
> breakthrough is something that is very hard for me to take seriously,
> speaking quite frankly.
>
> Usenix has awarded best paper awards to work that was done on obsolete
> kernels, where if the goal of that work was to produce production
> kernel code, was in fact horrible work.  But if the goal of that work
> is to produce Ph.D. graduates, or to help the professor get tenure,
> was perhaps more successful.
>
> That being said, maybe you'd be happier engaging with the Minix 3
> community.  They are folks who think (unproven, theoretical) safety is
> more important than performance.  And they've created a kernel which
> is a 140 times slower at process creation, ten times greater syscall
> overhead, and file copies that were two to ten times slower.[1]
>
> [1] http://lwn.net/Articles/220255/
>
> And Prof. Tannenbaum is an academic, so his goals may be more closely
> aligned to yours.
>
> Best regards,
>
>                                           - Ted

Re: Can we move device drivers into user-space?

[Theodore Tso]

On Feb 26, 2012, at 4:25 PM, Richard Yao wrote:

> Ted,
> 
> I think you have me confused with Jidong Xiao. He is the one who
> suggested moving things to userspace. I happened to see the
> conversation, noticed people had missed a few points and added them in
> an attempt to be helpful. If you look at my emails to the mailing
> list, you would see that I had said that this work should be done
> elsewhere. The email to which you had replied was one that was meant
> to say that if people were set on having those interested in doing
> this to work with LInux, it should be okay for them to brainstorm on
> the LKML.

The problem is that there are a huge number of crackpots out there, and Linux is popular enough that many of them tend to gravitate to the LKML.    If they want to brainstorm, that's fine; but don't expect senior kernel developers to necessarily pay a lot of attention.

It would be like people insisting on being able to brainstorm about whether it's possible to square the circle, or solve the halting problem, on some abstract math theorist's mailing list.   It's possible they might be on the verge of a massive breakthrough, but when I was one of the postmaster of MIT, I got to field enough of these folks asking if we could make sure the chair of the math department would take a look at their proof, because they couldn't get anyone else to pay attention….

There is an old saying, "code talks, bullshit walks".    If someone is known to have produced real code, then people are much more likely to take the time to respond.    If someone hasn't yet produced real code, it's better if they try it, and show at least some kind of interesting result, before they try to waste a lot of people's time working on their pet theories.

And if they want to go do this "value add" on the FreeBSD list, I'd encourage them to do it, except I don't think I would be thanked by the FreeBSD folks….

-- Ted


> 
> With that said, please refrain from further outbursts. They hurt Linux.
> 
> Yours truly,
> Richard Yao
> 
> On Sun, Feb 26, 2012 at 3:30 PM, Ted Ts'o <tytso@mit.edu> wrote:
>> On Sun, Feb 26, 2012 at 10:05:59AM -0500, Richard Yao wrote:
>>>>> I do not see what prevents an in-kernel context switch into a ring 3
>>>>> context with a different process address space. Is it necessary to
>>>>> remove the code from the kernel tree before someone can do this?
>>>> 
>>>> No, and that's the real problem here: Everybody who might think it's a
>>>> good idea may please implement - and thus propose - something concrete,
>>>> try it out and comeback with experience and performance numbers - and
>>>> not just try to come up with some theory and other misleading points
>>>> (what political aspect?!) and ideas what others should do and why it
>>>> might be better.
>>> 
>>> It seems counterproductive to tell people to produce results without
>>> doing the brainstorming that such results require.
>> 
>> It's also counterproductive to tell kernel programmers how they should
>> do what they are being paid how to do.  If you just want to brainstorm
>> possibilities where **you** will do all of the work, as opposed to
>> asking the kernel development community to work on your pet theories,
>> it's helpful if you more carefully label your poposals as such.
>> 
>>> If such discussion is not welcome here, then the FreeBSD project has a
>>> similar kernel design. Perhaps it would be more productive for those
>>> interested in this to brainstorm on their mailing list. If anything
>>> materializes, it could be for their kernel instead. Nothing is forcing
>>> anyone to do things with Linux.
>> 
>> My experience is that most researchers produce code which is not of
>> production quality.  It's very easy to produce a proof of concept that
>> works well enough to publish a paper.  Making something which is
>> actually performant, is **hard**.  The problem is that you don't get
>> Ph.D.'s for counting cache line misses --- or for getting your
>> implementation to the point where cache line misses matter in the
>> first place.  So the threat that Linux will miss out on some great
>> breakthrough is something that is very hard for me to take seriously,
>> speaking quite frankly.
>> 
>> Usenix has awarded best paper awards to work that was done on obsolete
>> kernels, where if the goal of that work was to produce production
>> kernel code, was in fact horrible work.  But if the goal of that work
>> is to produce Ph.D. graduates, or to help the professor get tenure,
>> was perhaps more successful.
>> 
>> That being said, maybe you'd be happier engaging with the Minix 3
>> community.  They are folks who think (unproven, theoretical) safety is
>> more important than performance.  And they've created a kernel which
>> is a 140 times slower at process creation, ten times greater syscall
>> overhead, and file copies that were two to ten times slower.[1]
>> 
>> [1] http://lwn.net/Articles/220255/
>> 
>> And Prof. Tannenbaum is an academic, so his goals may be more closely
>> aligned to yours.
>> 
>> Best regards,
>> 
>>                                           - Ted

Re: Can we move device drivers into user-space?

[Richard Yao]

> The problem is that there are a huge number of crackpots out there, and Linux is popular enough that many of them tend to gravitate to the LKML.    If they want to brainstorm, that's fine; but don't expect senior kernel developers to necessarily pay a lot of attention.

I think it is nice for people to be interested in kernel design and
even if they have bad ideas, letting them discuss their ideas
generally gives them the opportunity to learn why they are bad, which
could generate good ideas in the process. microkernel designs are
nice, but Linux is not the right basis for one.

With that said, I suggest you refrain from being so quick to judge. It
is a slippery slope that can lead you to consider anyone absent from a
mental whitelist to be "a crackpot". It also causes problems when you
misidentify someone because he made an attempt to help less
knowledgeable people learn, rather than telling them with his vision
of how things work. This can happen whenever you meet new people who
would have been on your list had you known them better.

Yours truly,
Richard Yao

Re: Can we move device drivers into user-space?

[Bernd Petrovitsch]

On Son, 2012-02-26 at 17:03 -0500, Richard Yao wrote:
[...]
> I think it is nice for people to be interested in kernel design and
> even if they have bad ideas, letting them discuss their ideas
> generally gives them the opportunity to learn why they are bad, which
> could generate good ideas in the process.

Part of the learning experience is (or should be IMHO) to - at least -
try it out in someway at some point and not only "discuss" it or throw
ideas around.
And that is: look for one target like a char driver or a filesystem or
what ever one likes or seems fit and try to produce a somewhat working
prototype.
The performance point is probably valid but not every driver is a high
performance issue.
As for "filesystems", there is already FUSE around BTW. And IIRC there
were similar efforts for block and/or char drivers.

And of course, the "try it out" means primarily the OP - see the other
mail.

>                                           microkernel designs are
> nice, but Linux is not the right basis for one.

Yes, that's the reason that everyone uses a microkernel today. SCNR ....
And Mach got at times so fat so that people considered something else. 

	Bernd
-- 
Bernd Petrovitsch                  Email : bernd@petrovitsch.priv.at
                     LUGA : http://www.luga.at

Re: Can we move device drivers into user-space?

[david]

On Sun, 26 Feb 2012, Henrik Rydberg wrote:

>>> The main issue that set me off has been sufficiently diluted in the
>>> (selective) discussion so as to no longer make sense as a reply: At
>>> some point, in-tree or out-of-tree will no longer be distinguishable,
>>
>> Please explain how you would be unable to distinguish between a driver
>> that lives in the kernel source tree, and one that does not.
>
> The SUD pointed to in the beginning of the thread is an example of
> this, but I was not thinking of it in quite so literal terms. Rather,
> I was imagining that as the kernel grows and the in-kernel interfaces
> matures, the amount of actual communication between different portions
> of the code diminishes. Code on opposite sides of a stable interface
> is, for all practical purposes, separated. Whether that code lives
> in-tree or out-of tree is then of little consequence.

the point that you seem to be missing is that the interfaces between the 
different areas of the kernel are not stable, they change over time. When 
both sides of the interface are in the kernel, this is not a problem, both 
sides get changed, but if one side was out of the kernel, then you either 
can't make the change, or have a flag day change where both sides need to 
change in lock-step (and downgrading is hard as both sides need to change 
again)

This is completely ignoring the performance and security aspects of 
userspace components vs kernel components.

Ted is explaining the performance aspects well, but let's look at the 
security aspects as well.

It's not just a case of "if something in userspace crashes, it doesn't 
crash the kerenl", it's also a case that "if you have a userspace 
component, then the kernel must sanity check the userspace interface to 
defend against rogue userspace". Doing these checks is not cheap (adding 
to performance overhead), and may not even be possible (how do you know 
if the command being sent to the SCSI bus is safe or not?)

David Lang

Re: Can we move device drivers into user-space?

[Henrik Rydberg]

Hi David,

> the point that you seem to be missing is that the interfaces between
> the different areas of the kernel are not stable, they change over
> time.

The argument was based on the idea that they would stabilize over
time. However, I realize this may not be true, which was also touched
upon in a later reply. The heavy-tailed nature of large changes in
open-source projects seems to put some hard numbers behind that claim [1].

> When both sides of the interface are in the kernel, this is
> not a problem, both sides get changed, but if one side was out of
> the kernel, then you either can't make the change, or have a flag
> day change where both sides need to change in lock-step (and
> downgrading is hard as both sides need to change again)

Assuming the interfaces changes, this follows naturally, of course.

> This is completely ignoring the performance and security aspects of
> userspace components vs kernel components.

Indeed.

> Ted is explaining the performance aspects well, but let's look at
> the security aspects as well.
> 
> It's not just a case of "if something in userspace crashes, it
> doesn't crash the kerenl", it's also a case that "if you have a
> userspace component, then the kernel must sanity check the userspace
> interface to defend against rogue userspace". Doing these checks is
> not cheap (adding to performance overhead), and may not even be
> possible (how do you know if the command being sent to the SCSI bus
> is safe or not?)

No doubt, an open-ended system has its own set of problems. At any
given system size, the question is how this balances against a closed
system. The assumption I made was that as the system grows, the
balance would shift in favor of an open-ended system. This may not be
the case at all, as you are saying. It would be nice to be able to see
this in a quantitative manner if possible.

Thanks for taking the time to respond.

Henrik

[1] http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.91.7114

Re: Can we move device drivers into user-space?

[david]

On Mon, 27 Feb 2012, Henrik Rydberg wrote:

> Hi David,
>
>> the point that you seem to be missing is that the interfaces between
>> the different areas of the kernel are not stable, they change over
>> time.
>
> The argument was based on the idea that they would stabilize over
> time. However, I realize this may not be true, which was also touched
> upon in a later reply. The heavy-tailed nature of large changes in
> open-source projects seems to put some hard numbers behind that claim [1].

What you are hearing from the long-time kernel developers is that they 
expect the interfaces to change over time.

Remember, the linux kernel has been around for a long time, and as a 
result, the interfaces have gone through many iterations. There is no 
reason to believe that the current version is the final one, and the 
kernel developers now expect that the current interfaces are _not_ going 
to remain the same forever, they expect that new technology will drive 
changes in these interfaces. This is especially true for the types of 
things that device drivers need.

Take for example locking. That is an implicit part of the interface to the 
device drivers, and is are area with a fairly high rate of change today. 
Anyone who claims that the current locking is 'correct' and can be 
depended on by an out-of-tree driver for even a couple of kernel releases 
is going to be either laughed at or ignored as being too ignorant to 
matter.

Yes, you can look around and find interfaces in the kernel that have not 
changed for a long time, but I'll bet that for every example you find, 
someone else could find an example of an interface that had remained 
unchanged for just about as long, but has changed fairly recently.

David Lang

Re: Can we move device drivers into user-space?

[Henrik Rydberg]

> >The argument was based on the idea that they would stabilize over
> >time. However, I realize this may not be true, which was also touched
> >upon in a later reply. The heavy-tailed nature of large changes in
> >open-source projects seems to put some hard numbers behind that claim [1].
> 
> What you are hearing from the long-time kernel developers is that
> they expect the interfaces to change over time.

That is coming through clearly.  What I find interesting is that in
addition to the authorative voice of Linux experience, there is
physical evidence that the well-known phenomenon of self-organized
criticality governs open-source code development at large. The
collective stream of patches coming from individual decisions and
real-world adaption shows the same behavior as avalanches, solar
flares and earthquakes; there is always a bigger change around the
corner. This critical phenomenon manifests itself through heavy-tailed
distributions, as reported in reference [1].  To a physicist, this is
a big deal.

Coming back to interfaces, the conclusion is that a large code tree
which exhibits these qualities is susceptible to large changes, and
can therefore adapt better.  This puts extra weight behind the notion
that Linux is doing the Right Thing.

The measurement by Wu and Holt in 2006 [1] has probably been succeeded
many times over, perhaps someone else has pointers to more recent
studies.

> Remember, the linux kernel has been around for a long time, and as a
> result, the interfaces have gone through many iterations. There is
> no reason to believe that the current version is the final one, and
> the kernel developers now expect that the current interfaces are
> _not_ going to remain the same forever, they expect that new
> technology will drive changes in these interfaces. This is
> especially true for the types of things that device drivers need.

Theory, experiment and experience seems to say the same thing, so one
simply has to agree with this point.
 
> Take for example locking. That is an implicit part of the interface
> to the device drivers, and is are area with a fairly high rate of
> change today. Anyone who claims that the current locking is
> 'correct' and can be depended on by an out-of-tree driver for even a
> couple of kernel releases is going to be either laughed at or
> ignored as being too ignorant to matter.
> 
> Yes, you can look around and find interfaces in the kernel that have
> not changed for a long time, but I'll bet that for every example you
> find, someone else could find an example of an interface that had
> remained unchanged for just about as long, but has changed fairly
> recently.

Obviously there is no disagreement here anymore.  And I wouldn't bet
without first computing the probability of such a change. :-)

Thanks.
Henrik

Re: Can we move device drivers into user-space?

[Thomas Gleixner]

On Fri, 24 Feb 2012, Guenter Roeck wrote:
> On Fri, 2012-02-24 at 12:17 -0500, Greg KH wrote:
> > On Fri, Feb 24, 2012 at 09:07:09AM -0800, Guenter Roeck wrote:
> > > How about dropping UIO support from the kernel ? That would make more
> > > sense to me.
> > 
> > Again, UIO solves a real need, are you to tell the users of that code
> > that somehow we are now not going to support them anymore?
> > 
> > UIO was created when Thomas and I sat in the back of a conference
> > presentation and saw, for the umpteenth time, a presentation by someone
> > who was trying to write userspace drivers, and obviously didn't know
> > what they were doing.
> > 
> > UIO provides a framework that actually works (unlike all of the previous
> > research papers were trying to do), and is used in real systems (laser
> > welding robots!) every day, manufacturing things that you use and rely
> > on.
> > 
> > You remove UIO at the risk of pissing off those robots, the choice is
> > yours, I know I'm not going to do it...
> 
> I understand the background and reasoning, but ...
> 
> I have seen UIO used for networking drivers, hwmon drivers, I2C bus
> master drivers (with matching I2C client drivers in user-space), mfd
> devices, and so on. I have seen existing kernel drivers re-implemented
> as UIO drivers. I have seen UIO drivers where the kernel part of the
> driver is larger than the entire driver written as kernel driver. I have
> seen UIO drivers using polling instead of interrupts "because it is
> faster than interrupts".
> 
> Often, those drivers are then re-written for the next board (to support
> the same chip) because they were not written with HW-independence in
> mind and don't support HW abstraction.
> 
> Yes, there may be real need for UIO in some cases, but all I have seen
> it used for so far is what I would call abuse, resulting in maintenance
> nightmares.

UIO always had a clear target: devices which are application bound and
not related to any larger set of functonality (device class
frameworks, communication stacks, ...)

For that kind of devices in kernel drivers are overkill and
performance bottlenecks. The drivers which are in tree come with open
user space access libraries and are completely sane.

We can't punish the sane users for the asinnity of other people.

If people go there and abuse UIO for other purposes, we can't prevent
it. We can't prevent either that people write totally crappy kernel
drivers ...

> Given the choice, I would be quite happy to piss off some robots. Call
> it a prejudice if you like ;).

You might become less happy when the robot welds your ear onto a car
hood :)

Thanks,

	tglx

Re: Can we move device drivers into user-space?

[Valdis.Kletnieks]

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On Fri, 24 Feb 2012 10:19:36 EST, Jidong Xiao said:

> Actually, my major concern is, since UIO has been accepted, then why
> don't we move all the rest device drivers into user space as well. As
> I understand, currently, some of device drivers are running on user
> space, while the other (or say the majority of) device drivers are
> running on kernel space, so why don't we maintain a consistent device
> drivers infrastructure, say, either all in user space, or all in
> kernel space. (Sure some critical device drivers still need to be kept
> in kernel space.)

Sure we could do that, if you deal with all of the following issues:
1) All I/O would take a lot more CPU, due to the additional context switching
that would be required to start an I/O and handle the completion interrupt.
2) It makes it a lot harder to do zero-copy I/O.
3) Once we push the API to userspace, we're stuck with it.  See
Documentation/stable_api_nonsense.txt for the details.

And finally:

4) -ENOPATCH.  You think it's a good idea, do up a patch that works at
least as well as what we have now...

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