RFC: Device Namespaces

RFC: Device Namespaces

[Oren Laadan]

Hi everyone!

We [1] have been working on bringing lightweight virtualization to
Linux-based mobile devices like Android (or other Linux-based devices with
diverse I/O) and want to share our solution: device namespaces.

Imagine you could run several instances of your favorite mobile OS or other
distributions in isolated containers, each under the impression of having
exclusive access to device drivers; Interact and switch between them within
a blink, no flashing, no reboot.

Device namespaces are an extension to existing Linux kernel namespaces that
brings lightweight virtualization to Linux-based end-user devices,
primarily mobile devices.
Device namespaces introduce a private and virtual namespace for device
drivers to create the illusion for a process group that it interacts
exclusively with a set of drivers. Device namespaces also introduce the
concepts of an “active” namespace with which a user interacts, vs
“non-active” namespaces that run in the background, and the ability to
switch between them.[2]

We are planning to prepare individual patches to be submitted to the
relevant maintainers and mailing lists. In the meantime, we already want to
share a set of patches on top of the Android goldfish Kernel 3.4 as well as
a user-space demo, so you can see where we are heading and get an overview
of the approach and see how it works.

We are aware that the patches are not ready for submission in their current
state, and we'd highly appreciate any feedback or suggestions which may
come to your mind once you have a look [3]. Of particular interest is to
elaborate a proper userspace API with respect to existing and future
use-cases. To illustrate a simple use-case we also provide a simple
userspace demo for Android [4].

I will be presenting "The Case for Linux Device Namespace" [5] at LinuxCon
North America 2013 [6]. We will also be attending the Containers Track [7]
at LPC 2013 to present the current state of the patches and discuss the
best course to proceed.

We are looking forward to hear from you!

Thanks,

Oren.


1: http://www.cellrox.com/
2: https://github.com/Cellrox/devns-patches/wiki/DeviceNamespace
3: https://github.com/Cellrox/devns-patches
4: https://github.com/Cellrox/devns-demo
5: http://sched.co/1asN1v7
6: http://events.linuxfoundation.org/events/linuxcon-north-america
7: http://www.linuxplumbersconf.org/2013/ocw/events/LPC2013/tracks/153

-- 
 Oren Laadan
 Cellrox Ltd.

Re: RFC: Device Namespaces

[Serge Hallyn]

Quoting Oren Laadan (orenl@cellrox.com):
> Hi everyone!
> 
> We [1] have been working on bringing lightweight virtualization to
> Linux-based mobile devices like Android (or other Linux-based devices with
> diverse I/O) and want to share our solution: device namespaces.
> 
> Imagine you could run several instances of your favorite mobile OS or other
> distributions in isolated containers, each under the impression of having
> exclusive access to device drivers; Interact and switch between them within
> a blink, no flashing, no reboot.
> 
> Device namespaces are an extension to existing Linux kernel namespaces that
> brings lightweight virtualization to Linux-based end-user devices,
> primarily mobile devices.
> Device namespaces introduce a private and virtual namespace for device
> drivers to create the illusion for a process group that it interacts
> exclusively with a set of drivers. Device namespaces also introduce the
> concepts of an “active” namespace with which a user interacts, vs
> “non-active” namespaces that run in the background, and the ability to
> switch between them.[2]

Note that unless I'm misunderstanding what you're saying here, this is
also what net_ns does.  A netns can exist with no processes so long as
you've bound its /proc/$$/ns/net somewhere.  You can then re-enter that
ns using ns_attach.  I haven't looked closely enough yet to see whether
you should be (or are) using the same interface.

> We are planning to prepare individual patches to be submitted to the

Looking forward to it, and seeing you at the containers track  :)

> 2: https://github.com/Cellrox/devns-patches/wiki/DeviceNamespace
> 3: https://github.com/Cellrox/devns-patches
> 4: https://github.com/Cellrox/devns-demo

(Have looked over the wiki, will look over the patches as well)

-serge
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Re: RFC: Device Namespaces

[Oren Laadan]

Hi Serge,


On Thu, Aug 22, 2013 at 2:21 PM, Serge Hallyn <serge.hallyn-GeWIH/nMZzLQT0dZR+AlfA@public.gmane.org>wrote:

> Quoting Oren Laadan (orenl-3AfRa/s5aFdBDgjK7y7TUQ@public.gmane.org):
> > Hi everyone!
> >
> > We [1] have been working on bringing lightweight virtualization to
> > Linux-based mobile devices like Android (or other Linux-based devices
> with
> > diverse I/O) and want to share our solution: device namespaces.
> >
> > Imagine you could run several instances of your favorite mobile OS or
> other
> > distributions in isolated containers, each under the impression of having
> > exclusive access to device drivers; Interact and switch between them
> within
> > a blink, no flashing, no reboot.
> >
> > Device namespaces are an extension to existing Linux kernel namespaces
> that
> > brings lightweight virtualization to Linux-based end-user devices,
> > primarily mobile devices.
> > Device namespaces introduce a private and virtual namespace for device
> > drivers to create the illusion for a process group that it interacts
> > exclusively with a set of drivers. Device namespaces also introduce the
> > concepts of an “active” namespace with which a user interacts, vs
> > “non-active” namespaces that run in the background, and the ability to
> > switch between them.[2]
>
> Note that unless I'm misunderstanding what you're saying here, this is
> also what net_ns does.  A netns can exist with no processes so long as
> you've bound its /proc/$$/ns/net somewhere.  You can then re-enter that
> ns using ns_attach.  I haven't looked closely enough yet to see whether
> you should be (or are) using the same interface.
>
>
To illustrate the need for device namespaces, consider the use case of
running two containers of your favorite OS (say, Android), on a single
physical phone. As a user, you either work in one container, or in the
other, and you will want to be able to switch between them (just like with
apps on mobile devices: you interact with one application at a time, and
switch between them).

See here for a demo of how it works:  http://vimeo.com/60113683

To accomplish this, device namespaces solve two shortcomings of existing
namespaces:

1. A namespace for device drivers:  each (Android) container needs a
private view of all devices. This includes logical drivers, like binder (in
Android) but also loop device; and physical devices, like the framebuffer
and the touch-screen.

In other words, device namespaces virtualize the _major/minor_ and the
_state_ of device drivers. With the exception of VFS, network, and PTY
(note: all three offer/are virtual devices), device drivers are otherwise
not isolated between containers.

2. A namespace for interactive scenarios:  a namespace can be "active" - it
has access to the hardware, e.g. display and touch-screen. This will be the
container with which the user is interacting right now. Otherwise a
namespace is "non-active" - it still runs in the background, but can
neither alter the display nor receive input from the touch-screen.
Switching to another container means a context switch in the relevant
drivers, so that they restore the state and now "obey" the other namespace.

You can also think about the "active" namespace as foreground, and the
"non-active" as background, akin to foreground/background processes in a
terminal with job-control. Similar to how a terminal delivers input to the
foreground task only but not to the background tasks - this is enforced by
the new device namespace.

More details on this use-case are in the wiki:
https://github.com/Cellrox/devns-patches/wiki/Thinvisor).


> We are planning to prepare individual patches to be submitted to the
>
> Looking forward to it, and seeing you at the containers track  :)
>

Same here!


>
> > 2: https://github.com/Cellrox/devns-patches/wiki/DeviceNamespace
> > 3: https://github.com/Cellrox/devns-patches
> > 4: https://github.com/Cellrox/devns-demo
>
> (Have looked over the wiki, will look over the patches as well)
>
> -serge
>


Thanks,

Oren.

-- 
 Oren Laadan
 Cellrox Ltd.

Re: RFC: Device Namespaces

[Andy Lutomirski]

On 08/22/2013 10:43 AM, Oren Laadan wrote:
> Hi everyone!
> 
> We [1] have been working on bringing lightweight virtualization to
> Linux-based mobile devices like Android (or other Linux-based devices with
> diverse I/O) and want to share our solution: device namespaces.

Have you looked at systemd-logind?  It seems to do something similar.

Re: [lxc-devel] RFC: Device Namespaces

[Stéphane Graber]

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On Thu, Aug 29, 2013 at 12:06:38PM -0700, Andy Lutomirski wrote:
> On 08/22/2013 10:43 AM, Oren Laadan wrote:
> > Hi everyone!
> > 
> > We [1] have been working on bringing lightweight virtualization to
> > Linux-based mobile devices like Android (or other Linux-based devices with
> > diverse I/O) and want to share our solution: device namespaces.
> 
> Have you looked at systemd-logind?  It seems to do something similar.

logind can be used to know the list of existing user sessions and which
have console access, it also creates and to some extent manages cgroups
but it doesn't do anything that the device namespace would at the kernel
level.

The main benefit from having a device namespace in the kernel would be
to only get the uevents and device access for devices that are either
owned or shared with the container. Being able to have fake devices
replace some of the standard ones would also be nice to have.

-- 
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com

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Re: RFC: Device Namespaces

[Eric W. Biederman]

Oren Laadan <orenl@cellrox.com> writes:

> Hi Serge,
>
>
> On Thu, Aug 22, 2013 at 2:21 PM, Serge Hallyn <serge.hallyn@ubuntu.com>wrote:
>
>> Quoting Oren Laadan (orenl@cellrox.com):
>> > Hi everyone!
>> >
>> > We [1] have been working on bringing lightweight virtualization to
>> > Linux-based mobile devices like Android (or other Linux-based devices
>> with
>> > diverse I/O) and want to share our solution: device namespaces.
>> >
>> > Imagine you could run several instances of your favorite mobile OS or
>> other
>> > distributions in isolated containers, each under the impression of having
>> > exclusive access to device drivers; Interact and switch between them
>> within
>> > a blink, no flashing, no reboot.
>> >
>> > Device namespaces are an extension to existing Linux kernel namespaces
>> that
>> > brings lightweight virtualization to Linux-based end-user devices,
>> > primarily mobile devices.
>> > Device namespaces introduce a private and virtual namespace for device
>> > drivers to create the illusion for a process group that it interacts
>> > exclusively with a set of drivers. Device namespaces also introduce the
>> > concepts of an “active” namespace with which a user interacts, vs
>> > “non-active” namespaces that run in the background, and the ability to
>> > switch between them.[2]
>>
>> Note that unless I'm misunderstanding what you're saying here, this is
>> also what net_ns does.  A netns can exist with no processes so long as
>> you've bound its /proc/$$/ns/net somewhere.  You can then re-enter that
>> ns using ns_attach.  I haven't looked closely enough yet to see whether
>> you should be (or are) using the same interface.
>>
>>
> To illustrate the need for device namespaces, consider the use case of
> running two containers of your favorite OS (say, Android), on a single
> physical phone. As a user, you either work in one container, or in the
> other, and you will want to be able to switch between them (just like with
> apps on mobile devices: you interact with one application at a time, and
> switch between them).
>
> See here for a demo of how it works:  http://vimeo.com/60113683
>
> To accomplish this, device namespaces solve two shortcomings of existing
> namespaces:
>
> 1. A namespace for device drivers:  each (Android) container needs a
> private view of all devices. This includes logical drivers, like binder (in
> Android) but also loop device; and physical devices, like the framebuffer
> and the touch-screen.
>
> In other words, device namespaces virtualize the _major/minor_ and the
> _state_ of device drivers. With the exception of VFS, network, and PTY
> (note: all three offer/are virtual devices), device drivers are otherwise
> not isolated between containers.
>
> 2. A namespace for interactive scenarios:  a namespace can be "active" - it
> has access to the hardware, e.g. display and touch-screen. This will be the
> container with which the user is interacting right now. Otherwise a
> namespace is "non-active" - it still runs in the background, but can
> neither alter the display nor receive input from the touch-screen.
> Switching to another container means a context switch in the relevant
> drivers, so that they restore the state and now "obey" the other namespace.
>
> You can also think about the "active" namespace as foreground, and the
> "non-active" as background, akin to foreground/background processes in a
> terminal with job-control. Similar to how a terminal delivers input to the
> foreground task only but not to the background tasks - this is enforced by
> the new device namespace.
>
> More details on this use-case are in the wiki:
> https://github.com/Cellrox/devns-patches/wiki/Thinvisor).

I think this is going to take some talking, and looking at code.

I think you are talking about having wrappers around your devices so you
can share.  Which is not the quite same problem the rest of us have been
thinking of when talking about a device namespace.

My first impression is that this is better solved with more appropriate
abstractions in userspace or in the kernel.

But we can talk at LPC and see what we can hash out.

Eric
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Re: RFC: Device Namespaces

[Amir Goldstein]

On Fri, Sep 6, 2013 at 7:50 PM, Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>wrote:

> Oren Laadan <orenl-3AfRa/s5aFdBDgjK7y7TUQ@public.gmane.org> writes:
>
> > Hi Serge,
> >
> >
> > On Thu, Aug 22, 2013 at 2:21 PM, Serge Hallyn <serge.hallyn-GeWIH/nMZzLQT0dZR+AlfA@public.gmane.org
> >wrote:
> >
> >> Quoting Oren Laadan (orenl-3AfRa/s5aFdBDgjK7y7TUQ@public.gmane.org):
> >> > Hi everyone!
> >> >
> >> > We [1] have been working on bringing lightweight virtualization to
> >> > Linux-based mobile devices like Android (or other Linux-based devices
> >> with
> >> > diverse I/O) and want to share our solution: device namespaces.
> >> >
> >> > Imagine you could run several instances of your favorite mobile OS or
> >> other
> >> > distributions in isolated containers, each under the impression of
> having
> >> > exclusive access to device drivers; Interact and switch between them
> >> within
> >> > a blink, no flashing, no reboot.
> >> >
> >> > Device namespaces are an extension to existing Linux kernel namespaces
> >> that
> >> > brings lightweight virtualization to Linux-based end-user devices,
> >> > primarily mobile devices.
> >> > Device namespaces introduce a private and virtual namespace for device
> >> > drivers to create the illusion for a process group that it interacts
> >> > exclusively with a set of drivers. Device namespaces also introduce
> the
> >> > concepts of an “active” namespace with which a user interacts, vs
> >> > “non-active” namespaces that run in the background, and the ability to
> >> > switch between them.[2]
> >>
> >> Note that unless I'm misunderstanding what you're saying here, this is
> >> also what net_ns does.  A netns can exist with no processes so long as
> >> you've bound its /proc/$$/ns/net somewhere.  You can then re-enter that
> >> ns using ns_attach.  I haven't looked closely enough yet to see whether
> >> you should be (or are) using the same interface.
> >>
> >>
> > To illustrate the need for device namespaces, consider the use case of
> > running two containers of your favorite OS (say, Android), on a single
> > physical phone. As a user, you either work in one container, or in the
> > other, and you will want to be able to switch between them (just like
> with
> > apps on mobile devices: you interact with one application at a time, and
> > switch between them).
> >
> > See here for a demo of how it works:  http://vimeo.com/60113683
> >
> > To accomplish this, device namespaces solve two shortcomings of existing
> > namespaces:
> >
> > 1. A namespace for device drivers:  each (Android) container needs a
> > private view of all devices. This includes logical drivers, like binder
> (in
> > Android) but also loop device; and physical devices, like the framebuffer
> > and the touch-screen.
> >
> > In other words, device namespaces virtualize the _major/minor_ and the
> > _state_ of device drivers. With the exception of VFS, network, and PTY
> > (note: all three offer/are virtual devices), device drivers are otherwise
> > not isolated between containers.
> >
> > 2. A namespace for interactive scenarios:  a namespace can be "active" -
> it
> > has access to the hardware, e.g. display and touch-screen. This will be
> the
> > container with which the user is interacting right now. Otherwise a
> > namespace is "non-active" - it still runs in the background, but can
> > neither alter the display nor receive input from the touch-screen.
> > Switching to another container means a context switch in the relevant
> > drivers, so that they restore the state and now "obey" the other
> namespace.
> >
> > You can also think about the "active" namespace as foreground, and the
> > "non-active" as background, akin to foreground/background processes in a
> > terminal with job-control. Similar to how a terminal delivers input to
> the
> > foreground task only but not to the background tasks - this is enforced
> by
> > the new device namespace.
> >
> > More details on this use-case are in the wiki:
> > https://github.com/Cellrox/devns-patches/wiki/Thinvisor).
>
> I think this is going to take some talking, and looking at code.
>
>
Hi Eric,

If we can get people to take a quick look at the code before LPC
that could make the LPC discussions more effective.
Even looking at one of the subsystem patches can give a basic
idea of the work we have done:
https://github.com/Cellrox/linux/commits/devns-goldfish-3.4

I think you are talking about having wrappers around your devices so you
> can share.  Which is not the quite same problem the rest of us have been
> thinking of when talking about a device namespace.
>

We are interested in all problems related to virtualizated view of devices
inside a container, so let our work so far be a starting point to discuss
all of them.


>
> My first impression is that this is better solved with more appropriate
> abstractions in userspace or in the kernel.
>
> But we can talk at LPC and see what we can hash out.
>

Looking forward to that :-)

Amir.


>
> Eric
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>

Re: RFC: Device Namespaces

[Eric W. Biederman]

Amir Goldstein <amir@cellrox.com> writes:

> On Fri, Sep 6, 2013 at 7:50 PM, Eric W. Biederman
> <ebiederm@xmission.com> wrote:
>
> Hi Eric,
>
> If we can get people to take a quick look at the code before LPC
> that could make the LPC discussions more effective.
> Even looking at one of the subsystem patches can give a basic
> idea of the work we have done:
> https://github.com/Cellrox/linux/commits/devns-goldfish-3.4
>
>     I think you are talking about having wrappers around your devices
>     so you
>     can share.  Which is not the quite same problem the rest of us
>     have been
>     thinking of when talking about a device namespace.
>
> We are interested in all problems related to virtualizated view of
> devices
> inside a container, so let our work so far be a starting point to
> discuss all of them.
>
>     My first impression is that this is better solved with more
>     appropriate
>     abstractions in userspace or in the kernel.

As I read your code, you are solving the problem of one opener of a
device among a group of openers being able to access a device at a time.
Which leads to the question why can't the multiplexing happen in
userspace?

I think with your design it would not be possible to play a song in one
device namespace while doing work in the other.  As a security model
that isn't wrong but as someone trying to get work done that could be a
real pain.

The more common concern is to have devices we can use all of the time.

There may be a need for a device namespace and multiplexing access to
hardware devices makes that clearer.  So far nothing has risen to the
level of we actually need a device namespace to do X.  Especially in an
erra of hotplug and dynamic device numbers.

It is arguable that you could do your kind of device multiplexing with a
fuse device in userspace that implements your desired policy.

And policy is where cell situtation seems to fall down because it hard
codes one specific policy into the kernel, and a policy most situations
don't find useful.

Eric
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Re: RFC: Device Namespaces

[Amir Goldstein]

On Mon, Sep 9, 2013 at 2:51 AM, Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>wrote:

> Amir Goldstein <amir-3AfRa/s5aFdBDgjK7y7TUQ@public.gmane.org> writes:
>
> > On Fri, Sep 6, 2013 at 7:50 PM, Eric W. Biederman
> > <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org> wrote:
> >
> > Hi Eric,
> >
> > If we can get people to take a quick look at the code before LPC
> > that could make the LPC discussions more effective.
> > Even looking at one of the subsystem patches can give a basic
> > idea of the work we have done:
> > https://github.com/Cellrox/linux/commits/devns-goldfish-3.4
> >
> >     I think you are talking about having wrappers around your devices
> >     so you
> >     can share.  Which is not the quite same problem the rest of us
> >     have been
> >     thinking of when talking about a device namespace.
> >
> > We are interested in all problems related to virtualizated view of
> > devices
> > inside a container, so let our work so far be a starting point to
> > discuss all of them.
> >
> >     My first impression is that this is better solved with more
> >     appropriate
> >     abstractions in userspace or in the kernel.
>
> As I read your code, you are solving the problem of one opener of a
> device among a group of openers being able to access a device at a time.
> Which leads to the question why can't the multiplexing happen in
> userspace?
>
> I think with your design it would not be possible to play a song in one
> device namespace while doing work in the other.  As a security model
> that isn't wrong but as someone trying to get work done that could be a
> real pain.
>

As a matter of fact, in our multi persona phone, you *can* hear music played
from background persona, but you *cannot* see images drawn from background
persona.


> The more common concern is to have devices we can use all of the time.
>
> There may be a need for a device namespace and multiplexing access to
> hardware devices makes that clearer.  So far nothing has risen to the
> level of we actually need a device namespace to do X.  Especially in an
> erra of hotplug and dynamic device numbers.
>
> It is arguable that you could do your kind of device multiplexing with a
> fuse device in userspace that implements your desired policy.
>

I agree about it being arguable :-)
We shall present our arguments on LPC.


>
> And policy is where cell situtation seems to fall down because it hard
> codes one specific policy into the kernel, and a policy most situations
> don't find useful.
>
>
It's true that for our product, we have made hardcoded policy decisions in
our kernel
patches, but that was just as a proof of concept for the technique.

We do envision being able to dynamically assign a device to a specific devns
(e.g. block,loop) keep a device shared between multi devns (e.g. audio)
and in addition to that, being able to multiplex a device between multi
devns (e.g. framebuffer)



> Eric
>

Re: RFC: Device Namespaces

[Janne Karhunen]

On Tue, Sep 10, 2013 at 10:09 AM, Amir Goldstein <amir-3AfRa/s5aFdBDgjK7y7TUQ@public.gmane.org> wrote:
> On Mon, Sep 9, 2013 at 2:51 AM, Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>wrote:
>
>> Amir Goldstein <amir-3AfRa/s5aFdBDgjK7y7TUQ@public.gmane.org> writes:
>>
>> > On Fri, Sep 6, 2013 at 7:50 PM, Eric W. Biederman
>> > <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org> wrote:
>> >
>> > Hi Eric,
>> >
>> > If we can get people to take a quick look at the code before LPC
>> > that could make the LPC discussions more effective.

Hi,

I think we are curious enough to experiment with Erics idea of
implementing basic 'device namespace' in userspace (never miss an
opportunity to throw away kernel code). Can anyone point out any
obvious reason why this would not work if we consider bulk of the work
being plain access filtering?

That being said, is there a valid reason why binder is part of device
namespace here instead of IPC?


-- 
Janne

Re: RFC: Device Namespaces

[Eric W. Biederman]

Janne Karhunen <janne.karhunen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> writes:

> That being said, is there a valid reason why binder is part of device
> namespace here instead of IPC?

I think the practical issue with binder was simply that binder only
allows for a single instance and thus is does not play nicely with
containers.

Eric

Re: [lxc-devel] RFC: Device Namespaces

[Jeremy Andrus]

On Sep 25, 2013, at 4:23 PM, Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org> wrote:

> Janne Karhunen <janne.karhunen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> writes:
> 
>> That being said, is there a valid reason why binder is part of device
>> namespace here instead of IPC?
> 
> I think the practical issue with binder was simply that binder only
> allows for a single instance and thus is does not play nicely with
> containers.

It's true that there was a singleton paradigm in binder that had to be
overcome, but I agree with Janne. It really belongs in the IPC namespace,
and I don't see any technical reason not to move it there.

        -Jeremy

Device Namespaces

[Eric W. Biederman]

From conversations at Linux Plumbers Converence it became fairly clear
that one if not the roughest edge on containers today is dealing with
devices.

- Hotplug does not work.
- There seems to be no implementation that does a much beyond creating
  setting up a static set of /dev entries today.
- Containers do not see the appropriate uevents for their container.

One of the more compelling cases I heard was of someone who was running
the a Linux Desktop in container and wanted to just let that container
see the devices needed for his desktop, and not everything else.

Talking with the OpenVZ folks it appears that preserving device numbers
across checkpoint/restart is not currently an issue.  However they reuse
the same loopback minor number when they can which would hide this
issue.   So while it is clear we don't need to worry about migrating
an application that cares about major/minor numbers of filesystems right
now as the set of application that are migrated increases that situation
may change.  As the case with the network device ifindex has shown it is
possible to implement filtering now and later when there is a usecase it
is possible to expand filtering to actual namespace local identifiers.

Thinking about it for the case of container migration the simplest
solution for the rare application that needs something more may be to
figure out how to send a kernel hotplug event.  Something to think about
when we encounter them.

So the big issues for a device namespace to solve are filtering which
devices a container has access to and being able to dynamically change
which devices those are at run time (aka hotplug).

After having thought about this for a bit I don't know if a pure
userspace solution is sufficient or actually a good idea.

- We can manually manage a tmpfs with device nodes in userspace.
  (But that is deprecated functionality in the mainstream kernel).
- We can manually export a subset of sysfs with bind mounts.
  (But that feels hacky, and is essentially incompatible with hotplug).
- We can relay a call of /sbin/hotplug from outside of a container
  to inside of a container based on policy.
  (But no one uses /sbin/hotplug anymore).
- There is no way to fake netlink uevents for a container to see them.
  (The best we could do is replace udev everywhere with something that
   listens on a unix domain socket).
- It would be nice to replace the device cgroup with a comprehensive
  solution that really works. (Among other things the device cgroup
  does not work in terms of struct device the underlying kernel
  abstraction for devices).

We must manage sysfs entries as well device nodes because:
- Seeing more than we should has the real potential to confuse
  userspace, especially a userspace that replays uevents.
- Some device control must happens through writing to sysfs files and
  if we don't remove all root privileges from a container only by
  exporting a subset of sysfs to that container can we limit which
  sysfs nodes can be written to.

The current kernel tagged sysfs entry support does not look like a good
match for the impelementing device filtering.   The common case will
be allowing devices like /dev/zero, and /dev/null that live in
/sys/devices/virtual and are the devices we are most likely to care
about.  Those devices need to live in multiple device namespaces so
everyone can use them.  Perhaps exclusive assignment will be the more
common paradigm for device namespaces like it is for network devices in
the network namespace but from what little I can of this problem right now I
don't think so.

I definitely think we should hold off on a kernel level implementation
until we really understand the issues and are ready to implement device
namespaces correctly.

A userspace implementation looks like it can only do about 95% of what
is really needed, but at the same time looks like an easy way to
experiment until the problem is sufficiently well understood.

At the end of the day we need to filter the devices a set of userspace
processes can use and be able to change that set of devices dynamically.
All of the rest of the infrastructure for that lives in the kernel, and
keeping all of the infrastructure in one place where it can be
maintained together is likely to be most maintainable.  It looks like
the code is just complicated enough and the use cases just boring enough
that spreading the code to perform container device hotplug and
container device filtering between a dozen userspace tools, and a hadful
of userspace device managers will not be particularly managable at the
end of the day.

In summary the situation with device hoptlug and containers sucks today,
and we need to do something.  Running a linux desktop in a container is
a reasonably good example use case.  Having one standard common
maintainable implementation would be very useful and the most logical
place for that would be in the kernel.  For now we should focus on
simple device filtering and hotplug.

Eric

Re: [lxc-devel] RFC: Device Namespaces

[Eric W. Biederman]

Jeremy Andrus <jeremya-eQaUEPhvms7ENvBUuze7eA@public.gmane.org> writes:

> On Sep 25, 2013, at 4:23 PM, Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org> wrote:
>
>> Janne Karhunen <janne.karhunen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> writes:
>> 
>>> That being said, is there a valid reason why binder is part of device
>>> namespace here instead of IPC?
>> 
>> I think the practical issue with binder was simply that binder only
>> allows for a single instance and thus is does not play nicely with
>> containers.
>
> It's true that there was a singleton paradigm in binder that had to be
> overcome, but I agree with Janne. It really belongs in the IPC namespace,
> and I don't see any technical reason not to move it there.

*Blink* I missed the IPC namespace suggestion.

The IPC namespace sounds reasonable.

Of course binder is still in staging because it has implementation and
ABI problems.  Little things like a 64bit kernel and a 32bit userspace
don't work particularly well.  So while fixing those problems it might
be possible to fix the single container problem as well.  It would be a
weird direction for cleanup of binder to come from but I don't see why
that wouldn't work.

Personally until binder is out of staging it seems reasonable to push
for an API that sucks less, or for a more general solution that Androdid
could use instead of binder.

One of the uses of namespaces is to clean up after problematic kernel
design decisions.  If we still have the option I would rather fix the
problems than clean up after them.

Eric

Re: Device Namespaces

[Greg Kroah-Hartman]

On Wed, Sep 25, 2013 at 02:34:54PM -0700, Eric W. Biederman wrote:
> So the big issues for a device namespace to solve are filtering which
> devices a container has access to and being able to dynamically change
> which devices those are at run time (aka hotplug).

As _all_ devices are hotpluggable now (look, there's no CONFIG_HOTPLUG
anymore, because it was redundant), I think you need to really think
this through better (pci, memory, cpus, etc.) before you do anything in
the kernel.

> After having thought about this for a bit I don't know if a pure
> userspace solution is sufficient or actually a good idea.
> 
> - We can manually manage a tmpfs with device nodes in userspace.
>   (But that is deprecated functionality in the mainstream kernel).

Yes, but I'm not going to namespace devtmpfs, as that is going to be an
impossible task, right?

And remember, udev doesn't create device nodes anymore...

> - We can manually export a subset of sysfs with bind mounts.
>   (But that feels hacky, and is essentially incompatible with hotplug).

True.

> - We can relay a call of /sbin/hotplug from outside of a container
>   to inside of a container based on policy.
>   (But no one uses /sbin/hotplug anymore).

That's right, they should be listening to libudev events, so why can't
your daemon shuffle them off to the proper container, all in userspace?

> - There is no way to fake netlink uevents for a container to see them.
>   (The best we could do is replace udev everywhere with something that
>    listens on a unix domain socket).

You shouldn't need to do this.

> - It would be nice to replace the device cgroup with a comprehensive
>   solution that really works. (Among other things the device cgroup
>   does not work in terms of struct device the underlying kernel
>   abstraction for devices).

I didn't even know there was a device cgroup.

Which means that if there is one, odds are it's useless.

> We must manage sysfs entries as well device nodes because:
> - Seeing more than we should has the real potential to confuse
>   userspace, especially a userspace that replays uevents.

You should never replay uevents.  If you don't do that, why can't you
see all of sysfs?

> - Some device control must happens through writing to sysfs files and
>   if we don't remove all root privileges from a container only by
>   exporting a subset of sysfs to that container can we limit which
>   sysfs nodes can be written to.

But you have the issue of controlling devices in a "shared" way, which
isn't going to be usable for almost all devices.

> The current kernel tagged sysfs entry support does not look like a good
> match for the impelementing device filtering.   The common case will
> be allowing devices like /dev/zero, and /dev/null that live in
> /sys/devices/virtual and are the devices we are most likely to care
> about.  Those devices need to live in multiple device namespaces so
> everyone can use them.  Perhaps exclusive assignment will be the more
> common paradigm for device namespaces like it is for network devices in
> the network namespace but from what little I can of this problem right now I
> don't think so.
> 
> I definitely think we should hold off on a kernel level implementation
> until we really understand the issues and are ready to implement device
> namespaces correctly.

I agree, especially as I don't think this will ever work.

> A userspace implementation looks like it can only do about 95% of what
> is really needed, but at the same time looks like an easy way to
> experiment until the problem is sufficiently well understood.

95% is probably way better than what you have today, and will fit the
needs of almost everyone today, so why not do it?

I'd argue that those last 5% either are custom solutions that never get
merged, or candidates for true virtulization.

> In summary the situation with device hoptlug and containers sucks today,
> and we need to do something.  Running a linux desktop in a container is
> a reasonably good example use case.

No it isn't.  I'd argue that this is a horrible use case, one that you
shouldn't do.  Why not just use multi-head machines like people do who
really want to do this, relying on user separation?  That's a workable
solution that is quite common and works very well today.

> Having one standard common maintainable implementation would be very
> useful and the most logical place for that would be in the kernel.
> For now we should focus on simple device filtering and hotplug.

Just listen for libudev stuff, don't try to filter them, or ever
"replay" them, that way lies madness, and lots of nasty race conditions
that is guaranteed to break things.

good luck,

greg k-h

Re: Device Namespaces

[Janne Karhunen]

On Thu, Sep 26, 2013 at 8:33 AM, Greg Kroah-Hartman
<gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:

>> In summary the situation with device hoptlug and containers sucks today,
>> and we need to do something.  Running a linux desktop in a container is
>> a reasonably good example use case.
>
> No it isn't.  I'd argue that this is a horrible use case, one that you
> shouldn't do.  Why not just use multi-head machines like people do who
> really want to do this, relying on user separation?  That's a workable
> solution that is quite common and works very well today.

I suppose so, but now you take the assumption that there is no
need for running multiple Linux variants on the same host (say
Ubuntu and Android side by side). Is this something you would
not like to see done?


-- 
Janne

Re: Device Namespaces

[Greg Kroah-Hartman]

On Thu, Sep 26, 2013 at 11:25:56AM +0300, Janne Karhunen wrote:
> On Thu, Sep 26, 2013 at 8:33 AM, Greg Kroah-Hartman
> <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:
> 
> >> In summary the situation with device hoptlug and containers sucks today,
> >> and we need to do something.  Running a linux desktop in a container is
> >> a reasonably good example use case.
> >
> > No it isn't.  I'd argue that this is a horrible use case, one that you
> > shouldn't do.  Why not just use multi-head machines like people do who
> > really want to do this, relying on user separation?  That's a workable
> > solution that is quite common and works very well today.
> 
> I suppose so, but now you take the assumption that there is no
> need for running multiple Linux variants on the same host (say
> Ubuntu and Android side by side). Is this something you would
> not like to see done?

You can do that today without any need for device namespaces, so why is
this an issue here?

greg k-h

Re: Device Namespaces

[Janne Karhunen]

On Thu, Sep 26, 2013 at 4:56 PM, Greg Kroah-Hartman
<gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:

>> I suppose so, but now you take the assumption that there is no
>> need for running multiple Linux variants on the same host (say
>> Ubuntu and Android side by side). Is this something you would
>> not like to see done?
>
> You can do that today without any need for device namespaces, so why is
> this an issue here?

I think you misunderstood me. I wasn't so much advocating on the
device namespace part, just the issue at hand (device access
filtering based on which ns happens to be 'active'). We are already
trying to do this in userspace, let's see how that goes.

That being said, our wish would be to support any combination of
OS's and frankly, I'd be slightly annoyed to tell the customer that
they can't do two Androids or we magically run out of bits.


-- 
Janne

Re: Device Namespaces

[Greg Kroah-Hartman]

On Thu, Sep 26, 2013 at 08:01:31PM +0300, Janne Karhunen wrote:
> That being said, our wish would be to support any combination of
> OS's and frankly, I'd be slightly annoyed to tell the customer that
> they can't do two Androids or we magically run out of bits.

If you want to support "any" combination of operating systems, then use
a hypervisor, that's what they are there for :)

Re: Device Namespaces

[Janne Karhunen]

On Thu, Sep 26, 2013 at 8:07 PM, Greg Kroah-Hartman
<gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:

>> That being said, our wish would be to support any combination of
>> OS's and frankly, I'd be slightly annoyed to tell the customer that
>> they can't do two Androids or we magically run out of bits.
>
> If you want to support "any" combination of operating systems, then use
> a hypervisor, that's what they are there for :)

Only relevant mobile OS's are of interest ;)


-- 
Janne

Re: [lxc-devel] RFC: Device Namespaces

[Amir Goldstein]

On Thu, Sep 26, 2013 at 12:47 AM, Eric W. Biederman
<ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>wrote:

> Jeremy Andrus <jeremya-eQaUEPhvms7ENvBUuze7eA@public.gmane.org> writes:
>
> > On Sep 25, 2013, at 4:23 PM, Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
> wrote:
> >
> >> Janne Karhunen <janne.karhunen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> writes:
> >>
> >>> That being said, is there a valid reason why binder is part of device
> >>> namespace here instead of IPC?
> >>
> >> I think the practical issue with binder was simply that binder only
> >> allows for a single instance and thus is does not play nicely with
> >> containers.
> >
> > It's true that there was a singleton paradigm in binder that had to be
> > overcome, but I agree with Janne. It really belongs in the IPC namespace,
> > and I don't see any technical reason not to move it there.
>
> *Blink* I missed the IPC namespace suggestion.
>
> The IPC namespace sounds reasonable.
>

Binder rewrite for IPC namespace is in the works (by Oren)
We discussed this with Greg and adding namespace support to binder (in
staging) seemed reasonable to him as well.


> Of course binder is still in staging because it has implementation and
> ABI problems.  Little things like a 64bit kernel and a 32bit userspace
> don't work particularly well.  So while fixing those problems it might
> be possible to fix the single container problem as well.  It would be a
> weird direction for cleanup of binder to come from but I don't see why
> that wouldn't work.
>
> Personally until binder is out of staging it seems reasonable to push
> for an API that sucks less, or for a more general solution that Androdid
> could use instead of binder.
>
> One of the uses of namespaces is to clean up after problematic kernel
> design decisions.  If we still have the option I would rather fix the
> problems than clean up after them.
>
> Eric
>
> _______________________________________________
> Containers mailing list
> Containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
> https://lists.linuxfoundation.org/mailman/listinfo/containers
>

Re: Device Namespaces

[James Bottomley]

On Thu, 2013-09-26 at 10:07 -0700, Greg Kroah-Hartman wrote:
> On Thu, Sep 26, 2013 at 08:01:31PM +0300, Janne Karhunen wrote:
> > That being said, our wish would be to support any combination of
> > OS's and frankly, I'd be slightly annoyed to tell the customer that
> > they can't do two Androids or we magically run out of bits.
> 
> If you want to support "any" combination of operating systems, then use
> a hypervisor, that's what they are there for :)

No that's not quite the right way to think about it: The correct
statement is only use a hypervisor if you need different kernels.  With
Windows, it happens to be true that you need a different kernel for each
different OS version.  However; with Linux, thanks to strong ABI
backwards compatibility, you mostly don't.  The way OpenVZ works today
is that it installs a modified kernel which can then bring up every
Linux OS in a separate container.  Our use case is the hosters that give
you root login to a virtual private server and allow you to upgrade it
on your own.  The reason for using a container rather than a hypervisor
is the old density and elasticity one:  3x the density (i.e. 1/3 the
overhead cost to the hoster) and the boot only needs to start at init,
not bring up of virtual hardware and booting a second kernel.

James

Re: Device Namespaces

[Greg Kroah-Hartman]

On Mon, Sep 30, 2013 at 08:37:19AM -0700, James Bottomley wrote:
> On Thu, 2013-09-26 at 10:07 -0700, Greg Kroah-Hartman wrote:
> > On Thu, Sep 26, 2013 at 08:01:31PM +0300, Janne Karhunen wrote:
> > > That being said, our wish would be to support any combination of
> > > OS's and frankly, I'd be slightly annoyed to tell the customer that
> > > they can't do two Androids or we magically run out of bits.
> > 
> > If you want to support "any" combination of operating systems, then use
> > a hypervisor, that's what they are there for :)
> 
> No that's not quite the right way to think about it: The correct
> statement is only use a hypervisor if you need different kernels.  With
> Windows, it happens to be true that you need a different kernel for each
> different OS version.  However; with Linux, thanks to strong ABI
> backwards compatibility, you mostly don't.  The way OpenVZ works today
> is that it installs a modified kernel which can then bring up every
> Linux OS in a separate container.  Our use case is the hosters that give
> you root login to a virtual private server and allow you to upgrade it
> on your own.  The reason for using a container rather than a hypervisor
> is the old density and elasticity one:  3x the density (i.e. 1/3 the
> overhead cost to the hoster) and the boot only needs to start at init,
> not bring up of virtual hardware and booting a second kernel.

I understand that some people really like the idea of using OpenVZ for
various things like this, but to claim that because of it we need to
hack up the driver core in the kernel into unimaginable pieces is not
necessarily something that I'll agree with.

But all of this is just words, I have yet to see any patches for any of
this, so I'll just wait until that happens before worrying about it...

thanks,

greg k-h

Re: Device Namespaces

[James Bottomley]

On Mon, 2013-09-30 at 09:11 -0700, Greg Kroah-Hartman wrote:
> On Mon, Sep 30, 2013 at 08:37:19AM -0700, James Bottomley wrote:
> > On Thu, 2013-09-26 at 10:07 -0700, Greg Kroah-Hartman wrote:
> > > On Thu, Sep 26, 2013 at 08:01:31PM +0300, Janne Karhunen wrote:
> > > > That being said, our wish would be to support any combination of
> > > > OS's and frankly, I'd be slightly annoyed to tell the customer that
> > > > they can't do two Androids or we magically run out of bits.
> > > 
> > > If you want to support "any" combination of operating systems, then use
> > > a hypervisor, that's what they are there for :)
> > 
> > No that's not quite the right way to think about it: The correct
> > statement is only use a hypervisor if you need different kernels.  With
> > Windows, it happens to be true that you need a different kernel for each
> > different OS version.  However; with Linux, thanks to strong ABI
> > backwards compatibility, you mostly don't.  The way OpenVZ works today
> > is that it installs a modified kernel which can then bring up every
> > Linux OS in a separate container.  Our use case is the hosters that give
> > you root login to a virtual private server and allow you to upgrade it
> > on your own.  The reason for using a container rather than a hypervisor
> > is the old density and elasticity one:  3x the density (i.e. 1/3 the
> > overhead cost to the hoster) and the boot only needs to start at init,
> > not bring up of virtual hardware and booting a second kernel.
> 
> I understand that some people really like the idea of using OpenVZ for
> various things like this, but to claim that because of it we need to
> hack up the driver core in the kernel into unimaginable pieces is not
> necessarily something that I'll agree with.

I don't believe I claimed that.  In fact, from 3.9 we can already bring
up an OpenVZ containerised system running different versions of Linux
that you can give someone root access to with no kernel modifications
whatsoever.  The user space solution currently works for us because
we're handing out server VPSs, so the device configuration is fixed as
we init the container.  However, we do have use cases for dynamic
instead of static device configurations, which is why we're
participating in the debate.

> But all of this is just words, I have yet to see any patches for any of
> this, so I'll just wait until that happens before worrying about it...

Well, that's because we're still debating what the best approach is.  If
you want a historical parallel: the comments you make above (hack up
the ... kernel into unimaginable pieces) is an almost exact mirror of
the comments that were made rejecting the in-kernel Checkpoint/Restore
patches at the 2010 Kernel Summit ... yet we have it fully functional
today in a form that proved acceptable.

James

Re: Device Namespaces

[Janne Karhunen]

On Thu, Sep 26, 2013 at 8:33 AM, Greg Kroah-Hartman
<gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:

>> - We can relay a call of /sbin/hotplug from outside of a container
>>   to inside of a container based on policy.
>>   (But no one uses /sbin/hotplug anymore).
>
> That's right, they should be listening to libudev events, so why can't
> your daemon shuffle them off to the proper container, all in userspace?

Which reminds me, one potential reason being..
http://lists.linuxfoundation.org/pipermail/containers/2013-May/032591.html


-- 
Janne

Re: Device Namespaces

[Andy Lutomirski]

On Tue, Oct 1, 2013 at 7:19 AM, Janne Karhunen <janne.karhunen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> On Thu, Sep 26, 2013 at 8:33 AM, Greg Kroah-Hartman
> <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:
>
>>> - We can relay a call of /sbin/hotplug from outside of a container
>>>   to inside of a container based on policy.
>>>   (But no one uses /sbin/hotplug anymore).
>>
>> That's right, they should be listening to libudev events, so why can't
>> your daemon shuffle them off to the proper container, all in userspace?
>
> Which reminds me, one potential reason being..
> http://lists.linuxfoundation.org/pipermail/containers/2013-May/032591.html
>

Can't the daemon live outside the container and shuffle stuff in?
IOW, there seems to be little point in containerizing things if you're
just going to punch a privilege hole in the namespace.

FWIW, I think that the capability evolution rules are crap, but
changing them is a can of worms, and enough people seem to thing the
status quo is acceptable that this is unlikely to ever get fixed.

--Andy

Re: Device Namespaces

[Greg Kroah-Hartman]

On Tue, Oct 01, 2013 at 09:19:58AM +0300, Janne Karhunen wrote:
> On Thu, Sep 26, 2013 at 8:33 AM, Greg Kroah-Hartman
> <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:
> 
> >> - We can relay a call of /sbin/hotplug from outside of a container
> >>   to inside of a container based on policy.
> >>   (But no one uses /sbin/hotplug anymore).
> >
> > That's right, they should be listening to libudev events, so why can't
> > your daemon shuffle them off to the proper container, all in userspace?
> 
> Which reminds me, one potential reason being..
> http://lists.linuxfoundation.org/pipermail/containers/2013-May/032591.html

I really wish I had never seen that patch, and I am glad it was
rejected.

Re: Device Namespaces

[Serge E. Hallyn]

Quoting Andy Lutomirski (luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org):
> On Tue, Oct 1, 2013 at 7:19 AM, Janne Karhunen <janne.karhunen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > On Thu, Sep 26, 2013 at 8:33 AM, Greg Kroah-Hartman
> > <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:
> >
> >>> - We can relay a call of /sbin/hotplug from outside of a container
> >>>   to inside of a container based on policy.
> >>>   (But no one uses /sbin/hotplug anymore).
> >>
> >> That's right, they should be listening to libudev events, so why can't
> >> your daemon shuffle them off to the proper container, all in userspace?
> >
> > Which reminds me, one potential reason being..
> > http://lists.linuxfoundation.org/pipermail/containers/2013-May/032591.html
> >
> 
> Can't the daemon live outside the container and shuffle stuff in?

That's exactly what Michael Warfield is suggesting, fwiw.

-serge

Re: Device Namespaces

[Janne Karhunen]

On Tue, Oct 1, 2013 at 8:33 PM, Greg Kroah-Hartman
<gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:

>> > That's right, they should be listening to libudev events, so why can't
>> > your daemon shuffle them off to the proper container, all in userspace?
>>
>> Which reminds me, one potential reason being..
>> http://lists.linuxfoundation.org/pipermail/containers/2013-May/032591.html
>
> I really wish I had never seen that patch, and I am glad it was
> rejected.

Thanks, I agree. Just wanted to point out the reason and
bring up the discussion.


-- 
Janne

Re: Device Namespaces

[Janne Karhunen]

On Tue, Oct 1, 2013 at 8:27 PM, Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org> wrote:

>> http://lists.linuxfoundation.org/pipermail/containers/2013-May/032591.html
>
> Can't the daemon live outside the container and shuffle stuff in?
> IOW, there seems to be little point in containerizing things if you're
> just going to punch a privilege hole in the namespace.

Yeah. I will try to experiment just how much can be 'stuffed
in' without effective caps. It certainly would be better this way.


> FWIW, I think that the capability evolution rules are crap, but
> changing them is a can of worms, and enough people seem to thing the
> status quo is acceptable that this is unlikely to ever get fixed.

I have noted (Casey almost tried to strangle me during the
last security summit for even daring to talk about it).


-- 
Janne

Re: Device Namespaces

[Eric W. Biederman]

"Serge E. Hallyn" <serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org> writes:

> Quoting Andy Lutomirski (luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org):
>> On Tue, Oct 1, 2013 at 7:19 AM, Janne Karhunen <janne.karhunen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> > On Thu, Sep 26, 2013 at 8:33 AM, Greg Kroah-Hartman
>> > <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:
>> >
>> >>> - We can relay a call of /sbin/hotplug from outside of a container
>> >>>   to inside of a container based on policy.
>> >>>   (But no one uses /sbin/hotplug anymore).
>> >>
>> >> That's right, they should be listening to libudev events, so why can't
>> >> your daemon shuffle them off to the proper container, all in userspace?
>> >
>> > Which reminds me, one potential reason being..
>> > http://lists.linuxfoundation.org/pipermail/containers/2013-May/032591.html
>> >
>> 
>> Can't the daemon live outside the container and shuffle stuff in?
>
> That's exactly what Michael Warfield is suggesting, fwiw.

Michael Warfields example of dynamically assigning serial ports to
containers is a pretty good test case.  Serial ports are extremely well
known kernel objects who evolution effectively stopped long ago.  When
we need it we have ptys to virtual serial ports when we need it, but in
general unprivileged users are safe to directly use a serial port
device.

Glossing over the details.  The general problem is some policy exists
outside of the container that deciedes if an when a container gets a
serial port and stuffs it in.

The expectation is that system containers will then run the udev
rules and send the libuevent event.  

To make that all work without kernel modifications requires placing
a faux-udev in the container, that listens for a device assignment from
outside the container and then does exactly what udev would have done.

The problems with this that I see are:

- udev is a moving target making it hard to build a faux-udev that will
  work everywhere.

- On distro's running systemd and udev integration is sufficiently tight
  that I am not certain a faux-udev is possible or will continue to be
  possible.

- There are two other widely deployed solutions for managing hotplug
  devices besides udev.

So given these difficulties I do not believe that the evolution of linux
device management is done, and that patches to udev, the kernel or both
will be needed.  While it would be good for testing and understanding
the problem I don't think a faux-udev will be a long term maintainable
solution.

I also understand the point that we aren't talking patches yet and just
discussing ideas.  Right now it is my hope that if we talk this out we
can figure out a general direction that has a hope of working.

From where I am standing faking uevents instead of replacing
udev/mdev/whatever looks simpler and more maintainable.

Eric

Re: Device Namespaces

[Serge Hallyn]

Quoting Eric W. Biederman (ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org):
> "Serge E. Hallyn" <serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org> writes:
> 
> > Quoting Andy Lutomirski (luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org):
> >> On Tue, Oct 1, 2013 at 7:19 AM, Janne Karhunen <janne.karhunen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >> > On Thu, Sep 26, 2013 at 8:33 AM, Greg Kroah-Hartman
> >> > <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:
> >> >
> >> >>> - We can relay a call of /sbin/hotplug from outside of a container
> >> >>>   to inside of a container based on policy.
> >> >>>   (But no one uses /sbin/hotplug anymore).
> >> >>
> >> >> That's right, they should be listening to libudev events, so why can't
> >> >> your daemon shuffle them off to the proper container, all in userspace?
> >> >
> >> > Which reminds me, one potential reason being..
> >> > http://lists.linuxfoundation.org/pipermail/containers/2013-May/032591.html
> >> >
> >> 
> >> Can't the daemon live outside the container and shuffle stuff in?
> >
> > That's exactly what Michael Warfield is suggesting, fwiw.
> 
> Michael Warfields example of dynamically assigning serial ports to
> containers is a pretty good test case.  Serial ports are extremely well
> known kernel objects who evolution effectively stopped long ago.  When
> we need it we have ptys to virtual serial ports when we need it, but in
> general unprivileged users are safe to directly use a serial port
> device.
> 
> Glossing over the details.  The general problem is some policy exists
> outside of the container that deciedes if an when a container gets a
> serial port and stuffs it in.
> 
> The expectation is that system containers will then run the udev
> rules and send the libuevent event.  

I thought the suggestion was that udev on the host would be given
container-specific rules, saying "plop this device into /dev/container1/"
(with /dev/container1 being bind-mounted to $container1_rootfs/dev).

-serge

Re: Device Namespaces

[Greg Kroah-Hartman]

On Tue, Oct 01, 2013 at 12:51:36PM -0700, Eric W. Biederman wrote:
> "Serge E. Hallyn" <serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org> writes:
> 
> > Quoting Andy Lutomirski (luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org):
> >> On Tue, Oct 1, 2013 at 7:19 AM, Janne Karhunen <janne.karhunen-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >> > On Thu, Sep 26, 2013 at 8:33 AM, Greg Kroah-Hartman
> >> > <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:
> >> >
> >> >>> - We can relay a call of /sbin/hotplug from outside of a container
> >> >>>   to inside of a container based on policy.
> >> >>>   (But no one uses /sbin/hotplug anymore).
> >> >>
> >> >> That's right, they should be listening to libudev events, so why can't
> >> >> your daemon shuffle them off to the proper container, all in userspace?
> >> >
> >> > Which reminds me, one potential reason being..
> >> > http://lists.linuxfoundation.org/pipermail/containers/2013-May/032591.html
> >> >
> >> 
> >> Can't the daemon live outside the container and shuffle stuff in?
> >
> > That's exactly what Michael Warfield is suggesting, fwiw.
> 
> Michael Warfields example of dynamically assigning serial ports to
> containers is a pretty good test case.  Serial ports are extremely well
> known kernel objects who evolution effectively stopped long ago.  When
> we need it we have ptys to virtual serial ports when we need it, but in
> general unprivileged users are safe to directly use a serial port
> device.
> 
> Glossing over the details.  The general problem is some policy exists
> outside of the container that deciedes if an when a container gets a
> serial port and stuffs it in.
> 
> The expectation is that system containers will then run the udev
> rules and send the libuevent event.  
> 
> To make that all work without kernel modifications requires placing
> a faux-udev in the container, that listens for a device assignment from
> outside the container and then does exactly what udev would have done.
> 
> The problems with this that I see are:
> 
> - udev is a moving target making it hard to build a faux-udev that will
>   work everywhere.

How is udev a moving target?  Use libudev and all should be fine, that's
an ABI you can rely on, right?

Or, if you don't like/want udev, use mdev in your container.  Or
something else, what does this have to do with the kernel?

> - On distro's running systemd and udev integration is sufficiently tight
>   that I am not certain a faux-udev is possible or will continue to be
>   possible.

That's not a kernel issue, that's a "ouch, this is hard, let's give up"
issue.

Or perhaps it is a "maybe I shouldn't even be trying to do this" type
issue... :)

> - There are two other widely deployed solutions for managing hotplug
>   devices besides udev.

I know of mdev, what's the other one?  The hacked-up shell script that
Android uses?  Or something else?

> So given these difficulties I do not believe that the evolution of linux
> device management is done, and that patches to udev, the kernel or both
> will be needed.  While it would be good for testing and understanding
> the problem I don't think a faux-udev will be a long term maintainable
> solution.

You are saying that for some reason you feel helpless with the way
userspace is going, so we have to change the kernel.  That's horrible,
and is not going to be a reason I accept to change the kernel, sorry.

> I also understand the point that we aren't talking patches yet and just
> discussing ideas.  Right now it is my hope that if we talk this out we
> can figure out a general direction that has a hope of working.
> 
> From where I am standing faking uevents instead of replacing
> udev/mdev/whatever looks simpler and more maintainable.

Have you really looked into this?  Numerous people, who understand this
code path and userspace issues, have said it is not a good idea at all.

But hey, what do I know...

I still have yet to see a reason why you can't use libudev today for
something like this.

Anyway, I'm done discussing this as it's pointless this early, I'm going
to refrain for any more pithy comments until someone posts some code, as
this is just wasting people's time at the moment.

greg k-h

Re: Device Namespaces

[Michael H. Warfield]

[-- Attachment #1.1: Type: text/plain, Size: 5040 bytes --]

On Tue, 2013-10-01 at 12:51 -0700, Eric W. Biederman wrote: 
> "Serge E. Hallyn" <serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org> writes:
> 
> > Quoting Andy Lutomirski (luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org):
> >> On Tue, Oct 1, 2013 at 7:19 AM, Janne Karhunen <janne.karhunen@gmail.com> wrote:
> >> > On Thu, Sep 26, 2013 at 8:33 AM, Greg Kroah-Hartman
> >> > <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:
> >> >
> >> >>> - We can relay a call of /sbin/hotplug from outside of a container
> >> >>>   to inside of a container based on policy.
> >> >>>   (But no one uses /sbin/hotplug anymore).
> >> >>
> >> >> That's right, they should be listening to libudev events, so why can't
> >> >> your daemon shuffle them off to the proper container, all in userspace?
> >> >
> >> > Which reminds me, one potential reason being..
> >> > http://lists.linuxfoundation.org/pipermail/containers/2013-May/032591.html
> >> >
> >> 
> >> Can't the daemon live outside the container and shuffle stuff in?
> >
> > That's exactly what Michael Warfield is suggesting, fwiw.

> Michael Warfields example of dynamically assigning serial ports to
> containers is a pretty good test case.  Serial ports are extremely well
> known kernel objects who evolution effectively stopped long ago.  When
> we need it we have ptys to virtual serial ports when we need it, but in
> general unprivileged users are safe to directly use a serial port
> device.

> Glossing over the details.  The general problem is some policy exists
> outside of the container that deciedes if an when a container gets a
> serial port and stuffs it in.

Actually, I don't necessarily see that as a problem as much as a
necessity.  If a container can decide when it gets a serial port or
other device, I would think that would constitute a security issue and
container isolation violation.  Restricting what container can have
access to what has to be determined in the host and, once you've drunk
that koolaid, you might as well stuff it in somewhere.  Policy has to be
in the host or you will never get the security corner cases right.

Ultimately, it is the host which is in charge of the hardware and is
managing the containers (it can start them up, shut them down, or manage
them) so, at its base level, is is the responsibility of the host to
manage those devices between the containers.

That being said, there is the additional issue of, what does the
container do when we hand it a device and how do we let it know.  That's
now classically the issue of udev and formerly hotplug and their
predecessors...

> The expectation is that system containers will then run the udev
> rules and send the libuevent event.  

Which makes sense.  Something along the line of a socket into the
container to send selected events from the user space daemon in the host
would make some sense there.

> To make that all work without kernel modifications requires placing
> a faux-udev in the container, that listens for a device assignment from
> outside the container and then does exactly what udev would have done.

> The problems with this that I see are:

> - udev is a moving target making it hard to build a faux-udev that will
>   work everywhere.

Well, it is an it isn't.  Yeah the rules have been changing (I'm getting
tired of the "deprecated" rule warnings) but I've seen worse, much
worse.

> - On distro's running systemd and udev integration is sufficiently tight
>   that I am not certain a faux-udev is possible or will continue to be
>   possible.

Actually, I think that's a non-issue.  IIRC, systemd (now) discontinues
its udev operation when it detects it's in a container.  That was at the
heart of the entire Fedora 15/16 in a container meltdown with the broken
versions of systemd trying to run udev in the container.  What do we do
in place of it?  I don't know.

> - There are two other widely deployed solutions for managing hotplug
>   devices besides udev.

> So given these difficulties I do not believe that the evolution of linux
> device management is done, and that patches to udev, the kernel or both
> will be needed.  While it would be good for testing and understanding
> the problem I don't think a faux-udev will be a long term maintainable
> solution.

> I also understand the point that we aren't talking patches yet and just
> discussing ideas.  Right now it is my hope that if we talk this out we
> can figure out a general direction that has a hope of working.

> From where I am standing faking uevents instead of replacing
> udev/mdev/whatever looks simpler and more maintainable.

> Eric

Mike
-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw-BetbSzk+GohWk0Htik3J/w@public.gmane.org
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
 PGP Key: 0x674627FF        | possible worlds.  A pessimist is sure of it!

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Re: [lxc-devel] Device Namespaces

[Michael H. Warfield]

[-- Attachment #1.1: Type: text/plain, Size: 4401 bytes --]

On Tue, 2013-10-01 at 15:46 -0500, Serge Hallyn wrote: 
> Quoting Eric W. Biederman (ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org):
> > "Serge E. Hallyn" <serge-A9i7LUbDfNHQT0dZR+AlfA@public.gmane.org> writes:
> > 
> > > Quoting Andy Lutomirski (luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org):
> > >> On Tue, Oct 1, 2013 at 7:19 AM, Janne Karhunen <janne.karhunen@gmail.com> wrote:
> > >> > On Thu, Sep 26, 2013 at 8:33 AM, Greg Kroah-Hartman
> > >> > <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:
> > >> >
> > >> >>> - We can relay a call of /sbin/hotplug from outside of a container
> > >> >>>   to inside of a container based on policy.
> > >> >>>   (But no one uses /sbin/hotplug anymore).
> > >> >>
> > >> >> That's right, they should be listening to libudev events, so why can't
> > >> >> your daemon shuffle them off to the proper container, all in userspace?
> > >> >
> > >> > Which reminds me, one potential reason being..
> > >> > http://lists.linuxfoundation.org/pipermail/containers/2013-May/032591.html
> > >> >
> > >> 
> > >> Can't the daemon live outside the container and shuffle stuff in?
> > >
> > > That's exactly what Michael Warfield is suggesting, fwiw.
> > 
> > Michael Warfields example of dynamically assigning serial ports to
> > containers is a pretty good test case.  Serial ports are extremely well
> > known kernel objects who evolution effectively stopped long ago.  When
> > we need it we have ptys to virtual serial ports when we need it, but in
> > general unprivileged users are safe to directly use a serial port
> > device.
> > 
> > Glossing over the details.  The general problem is some policy exists
> > outside of the container that deciedes if an when a container gets a
> > serial port and stuffs it in.
> > 
> > The expectation is that system containers will then run the udev
> > rules and send the libuevent event.  

> I thought the suggestion was that udev on the host would be given
> container-specific rules, saying "plop this device into /dev/container1/"
> (with /dev/container1 being bind-mounted to $container1_rootfs/dev).

I think that the "given container-specific rules, saying..." thing was
on my chart of options as the one with the big cloudy shaped object in
the lower right corner labeled "and then a miracle occurs".

The basic part is the mapping from /dev into /dev/lxc/container.  That
should be doable based on the rules in the host and a basic udev trigger
along with a simple mapping configuration.  The "given
container-specific" part becomes a morass if it gets complicated enough.

What I was envisioning was a very simple system of container specific
{match} and {map} objects.  If a name or symlink passed to the daemon
from a udev trigger matched a match, then the name and symlinks and
additional maps would be mapped into the appropriate container
subdirectory.  That works real well if the container and host udev rules
are congruent.

The tough part is the "container-specific" rules which was the part I
specifically mentioned that I had no clue how to make happen.  That's a
non-trivial task if the container is allowed to make arbitrary udev rule
changes based on what they are allowed to receive from the host (and how
do we trigger the changes in the host when a change is made in the
container).

It's easily doable where the container rules are congruent with the host
rules.  Where they are orthogonal gets much more complicated.  But...
All that being said, I will take the congruent solution as a starting
point (and that will not be an 80% solution - it will be more like a 95%
solution) and we can argue about the corner cases and deltas after that.
Doable, yes, for some value of doable.

I like what Greg was saying about using libudev but I'm totally in the
dark as to how to effectively hook that or if it would even work in the
container.  That one is not in my realm.

> -serge

Regards,
Mike
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Re: Device Namespaces

[Eric W. Biederman]

I think libudev is a solution to a completely different problem.  It is
possible I am blind but I just don't see how libudev even attempts to
solve the problem.

The desire is to plop a distro install into a subdirectory.  Fire up a
container around it, and let the distro's userspace do it's thing to
manage hotplug events.

devtmpfs can be faked fairly easily.
I don't know about sysfs.

Sending events that say you have hotplugged is the largest practical
problem.

On the minimal side I think the patch below is enough to let us fake up
uevents for the container and make things work.  I have heard the words
faking uevents and is a bad thing.  But I have not heard a reason or seen
any attempt at explanation.  My guess is that we are simply talking
about different problems.

I would like to see someone wire up all of the userspace bits and see
how well hotplug can be made to work before I walk down the path
represented by this patch but it seems reasonable.  But I do have
anecdotal reports from someone who walked a similar path that this is
enough to bring up a full desktop system in a container.

Eric


diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index 7a6c396a263b..46d05783da82 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -38,6 +38,7 @@ extern void netlink_table_ungrab(void);
 
 #define NL_CFG_F_NONROOT_RECV	(1 << 0)
 #define NL_CFG_F_NONROOT_SEND	(1 << 1)
+#define NL_CFG_F_IMPERSONATE_KERN (1 << 2)
 
 /* optional Netlink kernel configuration parameters */
 struct netlink_kernel_cfg {
diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index 52e5abbc41db..f75e34397df8 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -375,9 +375,12 @@ static int uevent_net_init(struct net *net)
 	struct uevent_sock *ue_sk;
 	struct netlink_kernel_cfg cfg = {
 		.groups	= 1,
-		.flags	= NL_CFG_F_NONROOT_RECV,
+		.flags	= NL_CFG_F_NONROOT_RECV | NL_CFG_F_IMPERSONATE_KERN,
 	};
 
+	if (net->user_ns != &init_user_ns)
+		return 0;
+
 	ue_sk = kzalloc(sizeof(*ue_sk), GFP_KERNEL);
 	if (!ue_sk)
 		return -ENOMEM;
@@ -399,6 +402,9 @@ static void uevent_net_exit(struct net *net)
 {
 	struct uevent_sock *ue_sk;
 
+	if (net->user_ns != &init_user_ns)
+		return;
+
 	mutex_lock(&uevent_sock_mutex);
 	list_for_each_entry(ue_sk, &uevent_sock_list, list) {
 		if (sock_net(ue_sk->sk) == net)
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 0c61b59175dc..71863cc465eb 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -1252,7 +1252,7 @@ static int netlink_release(struct socket *sock)
 
 	skb_queue_purge(&sk->sk_write_queue);
 
-	if (nlk->portid) {
+	if (sk_hashed(sk)) {
 		struct netlink_notify n = {
 						.net = sock_net(sk),
 						.protocol = sk->sk_protocol,
@@ -1409,11 +1409,21 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
 			return err;
 	}
 
-	if (nlk->portid) {
+	if (sk_hashed(sk)) {
 		if (nladdr->nl_pid != nlk->portid)
 			return -EINVAL;
 	} else {
-		err = nladdr->nl_pid ?
+		bool autobind = nladdr->nl_pid == 0;
+		if (nladdr->nl_pid == 0 && (nladdr->nl_pad == 0xffff)) {
+			if (!(nl_table[sk->sk_protocol].flags & NL_CFG_F_IMPERSONATE_KERN))
+				return -EPERM;
+			if (net->user_ns == &init_user_ns)
+				return -EPERM;
+			if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
+				return -EPERM;
+			autobind = false;
+		}
+		err = !autobind ?
 			netlink_insert(sk, net, nladdr->nl_pid) :
 			netlink_autobind(sock);
 		if (err)
@@ -1467,7 +1477,7 @@ static int netlink_connect(struct socket *sock, struct sockaddr *addr,
 	if (nladdr->nl_groups && !netlink_capable(sock, NL_CFG_F_NONROOT_SEND))
 		return -EPERM;
 
-	if (!nlk->portid)
+	if (!sk_hashed(sk))
 		err = netlink_autobind(sock);
 
 	if (err == 0) {
@@ -2228,7 +2238,7 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock,
 		dst_group = nlk->dst_group;
 	}
 
-	if (!nlk->portid) {
+	if (!sk_hashed(sk)) {
 		err = netlink_autobind(sock);
 		if (err)
 			goto out;

Re: Device Namespaces

[Eric W. Biederman]

Serge Hallyn <serge.hallyn-GeWIH/nMZzLQT0dZR+AlfA@public.gmane.org> writes:

>> Glossing over the details.  The general problem is some policy exists
>> outside of the container that deciedes if an when a container gets a
>> serial port and stuffs it in.
>> 
>> The expectation is that system containers will then run the udev
>> rules and send the libuevent event.  
>
> I thought the suggestion was that udev on the host would be given
> container-specific rules, saying "plop this device into /dev/container1/"
> (with /dev/container1 being bind-mounted to $container1_rootfs/dev).

That is what I was trying to describe.  We still need something that
lets the software in the container know it needs to do something.

I may be blind but right now short of replacing the internal udev, or
modifying the kernel I don't see a solution for letting software in a
container know there is a new device it can use.

Once we get the notification issue sorted out I think we have enough to
bring up a full desktop environment in a container and be able to say we
don't need anything else from devices unless someone discovers that
checkpoint/restart actually needs minor numbers to be preserved.

Eric

Re: Device Namespaces

[Andrey Wagin]

2013/9/26 Eric W. Biederman <ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org>
>
>
> From conversations at Linux Plumbers Converence it became fairly clear
> that one if not the roughest edge on containers today is dealing with
> devices.
>
> - Hotplug does not work.
> - There seems to be no implementation that does a much beyond creating
>   setting up a static set of /dev entries today.
> - Containers do not see the appropriate uevents for their container.
>
> One of the more compelling cases I heard was of someone who was running
> the a Linux Desktop in container and wanted to just let that container
> see the devices needed for his desktop, and not everything else.

I had experience of implementing this functionality in OpenVZ kernel.
I had requirements to not modify user-space tools, so that
implementations looks as dirty hack, but even hotplug of devices are
workin there.

....

>
> So the big issues for a device namespace to solve are filtering which
> devices a container has access to and being able to dynamically change
> which devices those are at run time (aka hotplug).
>
> After having thought about this for a bit I don't know if a pure
> userspace solution is sufficient or actually a good idea.

I would prefer to think a bit more about userspace solution. We can
try to expand udev functionality.

>
> - We can manually manage a tmpfs with device nodes in userspace.
>   (But that is deprecated functionality in the mainstream kernel).
> - We can manually export a subset of sysfs with bind mounts.
>   (But that feels hacky, and is essentially incompatible with hotplug).
> - We can relay a call of /sbin/hotplug from outside of a container
>   to inside of a container based on policy.
>   (But no one uses /sbin/hotplug anymore).
> - There is no way to fake netlink uevents for a container to see them.
>   (The best we could do is replace udev everywhere with something that
>    listens on a unix domain socket).

or we can teach udev to listens on a unix domain socket.

The host udev listens netlink. When it gets an event about a new
device, it decides for which containers it must be avaliable, does all
required actions and sends events in containers. Probably the protocol
of notifications must be unified for all udev-like services.

>
> - It would be nice to replace the device cgroup with a comprehensive
>   solution that really works. (Among other things the device cgroup
>   does not work in terms of struct device the underlying kernel
>   abstraction for devices).
>
> We must manage sysfs entries as well device nodes because:
> - Seeing more than we should has the real potential to confuse
>   userspace, especially a userspace that replays uevents.
> - Some device control must happens through writing to sysfs files and
>   if we don't remove all root privileges from a container only by
>   exporting a subset of sysfs to that container can we limit which
>   sysfs nodes can be written to.

Sorry if a following idea will sound crazy. Can we use fuse
filesystems for filtering sysfs and devtmpfs? When a CT mounts sysfs,
it will mount fuse-sysfs, which is implemented by userspace program on
host system.

* This way allows to emulate the behavior of uevent files in
containers, if we will use unix sockets between udev services.
* Probably a userspace daemon will be more flexible and customizable
than something in kernel

Do we have a use case when a perfomance of sysfs is critical?

Thanks,
Andrey