devfs

devfs

[Ian Molton]

On 11 Nov 2002 20:50:39 -0500
Robert Love <rml@tech9.net> wrote:

> On Mon, 2002-11-11 at 20:32, Ryan Anderson wrote:
> 
> > From an outsider point of view (and because nobody else responded),
> > I think the big question here would be: Would you use it after this
> > cleanup?
> > 
> > If you say yes, I'd say that's a good sign in its favor.
> 
> Good heuristic, except Al would not use devfs in either case :)

Personally I love devfs. I've not looked at its internals, but its never
failed me yet, and I like the way /dev only contains stuff that actually
exists.

And if Al doesnt like the code... hes free to reimplement it...

Re: devfs

[Xavier Bestel]

Le mar 12/11/2002 à 10:32, Ian Molton a écrit :
> On 11 Nov 2002 20:50:39 -0500
> Robert Love <rml@tech9.net> wrote:
> 
> > On Mon, 2002-11-11 at 20:32, Ryan Anderson wrote:
> > 
> > > From an outsider point of view (and because nobody else responded),
> > > I think the big question here would be: Would you use it after this
> > > cleanup?
> > > 
> > > If you say yes, I'd say that's a good sign in its favor.
> > 
> > Good heuristic, except Al would not use devfs in either case :)
> 
> Personally I love devfs. I've not looked at its internals, but its never
> failed me yet, and I like the way /dev only contains stuff that actually
> exists.

I'm wondering if a totally userspace solution could replace devs ?
Something using hotplug + sysfs and creating directories/nodes as they
appear on the system. This way, the policy (how do I name what) could be
moved out of the kernel.

	Xav

Re: devfs

[john slee]

On Tue, Nov 12, 2002 at 10:43:41AM +0100, Xavier Bestel wrote:
> I'm wondering if a totally userspace solution could replace devs ?
> Something using hotplug + sysfs and creating directories/nodes as they
> appear on the system. This way, the policy (how do I name what) could be
> moved out of the kernel.

curious!  you mean similar to (and a logical extension of) the 'disks'
command in solaris?  at least i think thats what its called...

j.

-- 
toyota power: http://indigoid.net/

Re: devfs

[Sean Neakums]

commence  john slee quotation:

> On Tue, Nov 12, 2002 at 10:43:41AM +0100, Xavier Bestel wrote:
>> I'm wondering if a totally userspace solution could replace devs ?
>> Something using hotplug + sysfs and creating directories/nodes as
>> they appear on the system. This way, the policy (how do I name
>> what) could be moved out of the kernel.
>
> curious!  you mean similar to (and a logical extension of) the
> 'disks' command in solaris?  at least i think thats what its
> called...

Except that a /sbin/hotplug er, "solution", would be dynamic.  I had
always assumed in the back of my mind that such a solution would make
devfs go away some day, although I don't think I actually read about
it anywhere.

Actually, here's a question: are /sbin/hotplug upcalls serialized in
some fashion?  I'd hate to online a thousand devices in my disk array
and have the machine forkbomb itself.

-- 
 /                          |
[|] Sean Neakums            |  Questions are a burden to others;
[|] <sneakums@zork.net>     |      answers a prison for oneself.
 \                          |

Re: devfs

[Oliver Neukum]

> Actually, here's a question: are /sbin/hotplug upcalls serialized in
> some fashion?  I'd hate to online a thousand devices in my disk array
> and have the machine forkbomb itself.

Nope, no serialisation. You don't have any guarantee even that
addition will be delivered before removal.

	Regards
		Oliver

Re: hotplug (was devfs)

[Nick Craig-Wood]

On Tue, Nov 12, 2002 at 01:51:08PM +0100, Oliver Neukum wrote:
> > Actually, here's a question: are /sbin/hotplug upcalls serialized in
> > some fashion?  I'd hate to online a thousand devices in my disk array
> > and have the machine forkbomb itself.
> 
> Nope, no serialisation. You don't have any guarantee even that
> addition will be delivered before removal.

And that is why (we finally discovered) we were getting
non-deterministic device numbering of USB nodes.

We have machines with 6 x 4 port USB <-> serial converters attached.
These would get randomly assigned usb device ids and hence random
/dev/ttyUSB nodes.  Not very useful when there is a load of different
things attached to the 24 serial ports!

Sometimes we also found that one of the devices wouldn't get
initialised properly.

We fixed these problems by removing hotplug and loading the relevant
kernel modules in the correct order and voila a perfectly
deterministic order for the /dev/ttyUSBs with all devices initialised.

Plugging in our USB bus with 24 devices on it does indeed produce a
mini-forkbomb effect ;-) (Especially since these Keyspan devices are
initialised twice - once without firmware and once with firmware.)

So - perhaps hotplug ought to be serialised?

-- 
Nick Craig-Wood
ncw1@axis.demon.co.uk

Re: hotplug (was devfs)

[Greg KH]

On Wed, Nov 13, 2002 at 10:48:09AM +0000, Nick Craig-Wood wrote:
> 
> We fixed these problems by removing hotplug and loading the relevant
> kernel modules in the correct order and voila a perfectly
> deterministic order for the /dev/ttyUSBs with all devices initialised.

deterministic for you :)

What hotplug will do is allow you to assign a /dev entry to a specific
device, so that you can go off of the topology, and not just the order
in which the devices are found.  That is how this problem will be
solved properly.

> Plugging in our USB bus with 24 devices on it does indeed produce a
> mini-forkbomb effect ;-) (Especially since these Keyspan devices are
> initialised twice - once without firmware and once with firmware.)
> 
> So - perhaps hotplug ought to be serialised?

No, it's not needed for this problem.  There has been talk of
serializing stuff in userspace, which is the proper way to handle some
of the remove before add was seen problems.

thanks,

greg k-h

Re: hotplug (was devfs)

[Nick Craig-Wood]

On Wed, Nov 13, 2002 at 09:02:04AM -0800, Greg KH wrote:
> On Wed, Nov 13, 2002 at 10:48:09AM +0000, Nick Craig-Wood wrote:
> > 
> > We fixed these problems by removing hotplug and loading the relevant
> > kernel modules in the correct order and voila a perfectly
> > deterministic order for the /dev/ttyUSBs with all devices initialised.
> 
> deterministic for you :)

Indeed!  It was deterministic in the sense of

1) I booted the machine 10 times and the devices came up in the same
order ;-)

2) the order of the devices was related to the usb topology, like this
(these are usb bus positions as noted by hub.c)

  1/1     <- hub1
  1/1/1   <- keyspan 1 /dev/ttyUSB0..3
  1/1/2   <- keyspan 2 /dev/ttyUSB4..7
  1/1/3   <- keyspan 3 /dev/ttyUSB8..11
  1/1/4   <- hub2
  1/1/4/1 <- keyspan 4 /dev/ttyUSB12..15
  1/1/4/2 <- keyspan 5 /dev/ttyUSB16..19
  1/1/4/3 <- keyspan 6 /dev/ttyUSB20..23

That seemed like a sensible order to me!

> What hotplug will do is allow you to assign a /dev entry to a specific
> device, so that you can go off of the topology, and not just the order
> in which the devices are found.  That is how this problem will be
> solved properly.

So I'll be able to say usb bus1/1/4/1 port 3 should be /dev/ttyUSB15
and it will always be that port?  That would be perfect.

> > Plugging in our USB bus with 24 devices on it does indeed produce a
> > mini-forkbomb effect ;-) (Especially since these Keyspan devices are
> > initialised twice - once without firmware and once with firmware.)
> > 
> > So - perhaps hotplug ought to be serialised?
> 
> No, it's not needed for this problem.  There has been talk of
> serializing stuff in userspace, which is the proper way to handle some
> of the remove before add was seen problems.

Userspace serialisation would have solved this problem for us too I
think without the extra mapping mechanism.

-- 
Nick Craig-Wood
ncw1@axis.demon.co.uk

Re: hotplug (was devfs)

[Greg KH]

On Wed, Nov 13, 2002 at 06:06:06PM +0000, Nick Craig-Wood wrote:
> 
> So I'll be able to say usb bus1/1/4/1 port 3 should be /dev/ttyUSB15
> and it will always be that port?  That would be perfect.

Yes, that is the goal.

thanks,

greg k-h

Re: hotplug (was devfs)

[Oliver Neukum]

> > So - perhaps hotplug ought to be serialised?
>
> No, it's not needed for this problem.  There has been talk of
> serializing stuff in userspace, which is the proper way to handle some
> of the remove before add was seen problems.

We may need some kind of load control.
The thought of firing up hundreds of hotplug scripts
simultaneously is not pretty.

	Regards
		Oliver

Re: devfs

[Xavier Bestel]

Le mar 12/11/2002 à 10:49, john slee a écrit :
> On Tue, Nov 12, 2002 at 10:43:41AM +0100, Xavier Bestel wrote:
> > I'm wondering if a totally userspace solution could replace devs ?
> > Something using hotplug + sysfs and creating directories/nodes as they
> > appear on the system. This way, the policy (how do I name what) could be
> > moved out of the kernel.
> 
> curious!  you mean similar to (and a logical extension of) the 'disks'
> command in solaris?  at least i think thats what its called...

I don't know solaris (from an admin POV), but I meant something like,
well, devfs. On top of which we could add feature like device naming
stability across system upgrades (I know solaris does that).

Xav

Re: devfs

[Alexander Viro]

On 12 Nov 2002, Xavier Bestel wrote:

> I'm wondering if a totally userspace solution could replace devs ?
> Something using hotplug + sysfs and creating directories/nodes as they
> appear on the system. This way, the policy (how do I name what) could be
> moved out of the kernel.

	Guys, may I remind you that Oct 31 had been more than a week ago?
Devfs *is* a race-ridden pile of crap, but we are in a goddamn feature
freeze, so let's get real.

	Interfaces can and should be cleaned up.  Ditto for semantics of
registering/unregistering - that allows to make glue in drivers more
straightforward.  Majestic flamewars about removing the thing completely/
moving it to userland/etc. are exercises in masturbation by that point.

	Again, WE ARE IN FEATURE FREEZE.

	Now, does somebody have technical comments on the proposed changes?

Re: devfs

[Ian Molton]

On Tue, 12 Nov 2002 05:04:41 -0500 (EST)
Alexander Viro <viro@math.psu.edu> wrote:

> 	Again, WE ARE IN FEATURE FREEZE.
> 
> 	Now, does somebody have technical comments on the proposed
> 	changes?

And since when did feature freeze affect, as the guy said, *purely*
userspace implementations?

(can it be done with current hotplug/sysfs?)

Re: devfs

[Dave Jones]

On Tue, Nov 12, 2002 at 10:25:35AM +0000, Ian Molton wrote:
 > > 	Again, WE ARE IN FEATURE FREEZE.
 > And since when did feature freeze affect, as the guy said, *purely*
 > userspace implementations?

 Since it would a *feature* to move it out of kernel space.
 To reiterate : _FEATURE_ _FREEZE_. Nothing[1] new[2]
 should be going into mainline at this point.

 We should now be in the stabilising period, where we don't require
 testers to have to upgrade their userspace every fortnight.

		Dave

[1] Rusty's modules rewrite and whatever else Linus queed up
    seems to have exemption from this rule. Hopefully there
    isn't too much of this stuff.
[2] Where 'new' can also mean 'bloody large reimplementation'
 
-- 
| Dave Jones.        http://www.codemonkey.org.uk
| SuSE Labs

Re: devfs

[Ian Molton]

On Tue, 12 Nov 2002 10:46:50 +0000
Dave Jones <davej@codemonkey.org.uk> wrote:

> > And since when did feature freeze affect, as the guy said, *purely*
>  > userspace implementations?
> 
>  Since it would a *feature* to move it out of kernel space.
>  To reiterate : _FEATURE_ _FREEZE_. Nothing[1] new[2]
>  should be going into mainline at this point.

nothing new WOULD be going in. nor would devfs need to move out - just
disable it. It *is* still an option, is it not?

>  We should now be in the stabilising period, where we don't require
>  testers to have to upgrade their userspace every fortnight.

its not a kernel issue anymore, if its totally in userspace, is it?

Re: devfs

[Rando Christensen]

Tue, 12 Nov 2002 10:46:50 +0000: Dave Jones (Dave Jones
<davej@codemonkey.org.uk>):

> On Tue, Nov 12, 2002 at 10:25:35AM +0000, Ian Molton wrote:
>  > > 	Again, WE ARE IN FEATURE FREEZE.
>  > And since when did feature freeze affect, as the guy said, *purely*
>  > userspace implementations?
>  Since it would a *feature* to move it out of kernel space.
>  To reiterate : _FEATURE_ _FREEZE_. Nothing[1] new[2]
>  should be going into mainline at this point.

Well, it does make sense to start planning out what might be done to
devfs in the /next/ devel kernel, then. If one were so inclined, they
could have a stable enough system for it ready for inclusion next time
around, depending on who they get to test it.

Clean up the devfs API for now, and start working on what might
eventually replace it- Whether that's devfs2 or a purely userspace
implementation or something new and wacky is up to whoever writes it.

Rather than saying "Devfs sucks, and we can't do anything about it other
than fix it's more minor problems because we're in feature freeze", we
should be saying "devfs sucks; we're a little late for feature freeze,
so let's clean up what we can and work on something much better for the
next time around."

Devfs as it is now is a nice idea, to me. It's an extremely organized
/dev which is also an accurate portrayal of what's available to use on a
particular machine. I'd hate to see it just ripped out entirely, and
while they've never affected me, I've heard of many issues with it. I'd
like to hear what ideas people may have /for/ a future replacement.

-- 
< There is a light that shines on the frontier >
<   And maybe someday, We're gonna be there.   >
<    Rando Christensen / rando@babblica.net    >

Re: devfs

[Alexander Viro]

On Tue, 12 Nov 2002, Rando Christensen wrote:

> Rather than saying "Devfs sucks, and we can't do anything about it other
> than fix it's more minor problems because we're in feature freeze", we
> should be saying "devfs sucks; we're a little late for feature freeze,
> so let's clean up what we can and work on something much better for the
> next time around."

Whatever is going to happen with devfs, believe me, the first thing
you'll need is stable glue in drivers - as simple and natural from the
driver POV as possible.  Complexity of doing development in 2.6 will
directly depend on the amount of code in drivers touched by patches.
BTDT - one can carry (and gradually merge) deep rewrites of core code
during -STABLE if it's done carefully.  But as soon as your patchset
hits the drivers - you are in for a world of pain just porting it to
next versions.

_That_ is critical - get interfaces right in -CURRENT, so that further
work would not cross these boundaries; then work in the resulting areas
becomes independent.  

And in situations like that of devfs, simple rules for callers are pretty
much the main criteria - if users of the interface have to jump through
some hoops, it's a sign that interface needs changes...

Re: devfs

[Alan Cox]

On Tue, 2002-11-12 at 10:46, Dave Jones wrote:
> On Tue, Nov 12, 2002 at 10:25:35AM +0000, Ian Molton wrote:
>  > > 	Again, WE ARE IN FEATURE FREEZE.
>  > And since when did feature freeze affect, as the guy said, *purely*
>  > userspace implementations?
> 
>  Since it would a *feature* to move it out of kernel space.
>  To reiterate : _FEATURE_ _FREEZE_. Nothing[1] new[2]
>  should be going into mainline at this point.

Who cares. You can do most of it already with hotplug and the remaining
bits are very much "oops should tell hotplug" bug fixes nothing more.

Alan

Re: devfs

[Ian Molton]

On 12 Nov 2002 14:53:38 +0000
Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:

> >  Since it would a *feature* to move it out of kernel space.
> >  To reiterate : _FEATURE_ _FREEZE_. Nothing[1] new[2]
> >  should be going into mainline at this point.
> 
> Who cares. You can do most of it already with hotplug and the
> remaining bits are very much "oops should tell hotplug" bug fixes
> nothing more.

The more I think about this userspace devfs, the more I like it. simple,
clean, AND doesnt affect the kernel.

Pure coding beauty.

Re: devfs

[Helge Hafting]

Alexander Viro wrote:
> 
> On 12 Nov 2002, Xavier Bestel wrote:
> 
> > I'm wondering if a totally userspace solution could replace devs ?
> > Something using hotplug + sysfs and creating directories/nodes as they
> > appear on the system. This way, the policy (how do I name what) could be
> > moved out of the kernel.
> 
>         Guys, may I remind you that Oct 31 had been more than a week ago?
> Devfs *is* a race-ridden pile of crap, but we are in a goddamn feature
> freeze, so let's get real.
> 
A kernel feature freeze don't apply to a pure userspace implemetation,
so let him try.  :-)  It won't affect the current devfs code, it'll
simply be configured out.
/dev on tmpfs, populated by hotplug. Could be interesting to see.

[...]
>         Now, does somebody have technical comments on the proposed changes?

Only the obvious - a cleanup is generally good and so is getting rid
of unused parameters.

Helge Hafting

Re: devfs

[Greg KH]

On Tue, Nov 12, 2002 at 10:43:41AM +0100, Xavier Bestel wrote:
> 
> I'm wondering if a totally userspace solution could replace devs ?
> Something using hotplug + sysfs and creating directories/nodes as they
> appear on the system. This way, the policy (how do I name what) could be
> moved out of the kernel.

Yes, that is _exactly_ what I am working on doing, and have stated as
such on this list a number of times in the past.

As for it being after the feature freeze comment, like Alan noted,
everything is already present to do this, it's just going to take some
more notifiers being added and some userspace code written.

And no, even if all of this gets done, I would not want to remove devfs
from the kernel, yet :)

thanks,

greg k-h

RE: hotplug (was devfs)

[Ed Vance]

On Wed, November 13, 2002 at 10:05 AM, Greg KH wrote: 
> 
> On Wed, Nov 13, 2002 at 06:06:06PM +0000, Nick Craig-Wood wrote:
> > 
> > So I'll be able to say usb bus1/1/4/1 port 3 should be /dev/ttyUSB15
> > and it will always be that port?  That would be perfect.
> 
> Yes, that is the goal.
> 

Do you expect that goal to eventually be applied to CompactPCI Hot-Swap
bus/slot port 3?

Thanks,
-Ed

---------------------------------------------------------------- 
Ed Vance              edv (at) macrolink (dot) com
Macrolink, Inc.       1500 N. Kellogg Dr  Anaheim, CA  92807
----------------------------------------------------------------

Re: hotplug (was devfs)

[Greg KH]

On Wed, Nov 13, 2002 at 10:45:43AM -0800, Ed Vance wrote:
> On Wed, November 13, 2002 at 10:05 AM, Greg KH wrote: 
> > 
> > On Wed, Nov 13, 2002 at 06:06:06PM +0000, Nick Craig-Wood wrote:
> > > 
> > > So I'll be able to say usb bus1/1/4/1 port 3 should be /dev/ttyUSB15
> > > and it will always be that port?  That would be perfect.
> > 
> > Yes, that is the goal.
> > 
> 
> Do you expect that goal to eventually be applied to CompactPCI Hot-Swap
> bus/slot port 3?

Yes, in a round-about way.  If the device that is in that specific slot
with that specific port, registers with, for example, the network
subsystem, and we have decided that anything in that slot should be
called "eth42", then we can do that based on the topology of the device.

It really depends on the device that is existing in a specific location
(network, scsi, etc.) and not so much as the specific location will
always be a network card called "ethX", as you have to look at the type
of device too.

Does that make sense?

I can tell it's getting to be the time to start writing all of this down
for people to hash out... :)

thanks,

greg k-h

RE: hotplug (was devfs)

[Ed Vance]

On Wed, November 13, 2002 at 10:45 AM, Greg KH wrote:
> On Wed, Nov 13, 2002 at 10:45:43AM -0800, Ed Vance wrote:
> > On Wed, November 13, 2002 at 10:05 AM, Greg KH wrote: 
> > > On Wed, Nov 13, 2002 at 06:06:06PM +0000, Nick Craig-Wood wrote:
> > > > 
> > > > So I'll be able to say usb bus1/1/4/1 port 3 should be 
> /dev/ttyUSB15
> > > > and it will always be that port?  That would be perfect.
> > > 
> > > Yes, that is the goal.
> > > 
> > 
> > Do you expect that goal to eventually be applied to 
> CompactPCI Hot-Swap
> > bus/slot port 3?
> 
> Yes, in a round-about way.  If the device that is in that 
> specific slot
> with that specific port, registers with, for example, the network
> subsystem, and we have decided that anything in that slot should be
> called "eth42", then we can do that based on the topology of 
> the device.
> 
> It really depends on the device that is existing in a 
> specific location
> (network, scsi, etc.) and not so much as the specific location will
> always be a network card called "ethX", as you have to look 
> at the type
> of device too.
> 
> Does that make sense?

Yes.
> 
> I can tell it's getting to be the time to start writing all 
> of this down
> for people to hash out... :)
> 

Very cool. 

Thanks,
Ed

---------------------------------------------------------------- 
Ed Vance              edv (at) macrolink (dot) com
Macrolink, Inc.       1500 N. Kellogg Dr  Anaheim, CA  92807
----------------------------------------------------------------