[Lxc-users] usb devices

[C Anthony Risinger]

On Thu, Aug 5, 2010 at 4:47 PM, Nirmal Guhan <vavatutu at gmail.com> wrote:
> On Tue, Aug 3, 2010 at 1:22 AM, Toby Corkindale
> <toby.corkindale at strategicdata.com.au> wrote:
>> On 03/08/10 17:44, Nirmal Guhan wrote:
>>> On Mon, Aug 2, 2010 at 6:07 PM, Toby Corkindale
>>> <toby.corkindale at strategicdata.com.au>  wrote:
>>>> On 03/08/10 09:04, Nirmal Guhan wrote:
>>>>> 4) Hot swap does not work within the container. After usb device is
>>>>> reinserted, container cannot recognize it but host can.
>>>>> 5) "mount" within the container  always displays just one single line
>>>>> while I have few more in fstab including the above /media stuff.
>>>>>        none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
>>>>
>>>> Again, that's because of the way LXC works with the filesystem.
>>>>
>>>> Perhaps you could just bind-mount the whole /media directory into the
>>>> guest containers, to their /media directory? That might work better for
>>>> you, although still not quite what you want.
>>>
>>> Thanks Toby. I doubt if this will address #1 and #4 above. Basically,
>>> how to make hot swap work? Or what are the workaround to get
>>> notifications if I have to manually mount/umount.
>>
>>
>> I think you would need to adjust the devices permissions for your
>> container, for the usb nodes.. but I'm not sure.. then the container
>> could talk to the USB devices over USB, and handle the hotswapping.
>> However I'd expect conflicts to occur with the host trying to talk to
>> the same device.
>> Try adding this to your config file?
>>
>> lxc.cgroup.devices.allow = c 189:* rwm
>>
>> I'm no expert and I haven't tried this myself, mind, so you might prefer
>> to wait for someone more qualified to answer.
>>
>> -Toby
>>
> Can you explain what this config means and 189 in particular? I tried
> this but did not help in hot swap. I believe that is because udev is
> not supported within the container and yes, you are correct about
> host/guest accessing the same device.

the 189:* corresponds to some device with a major number 189, and any
minor number.  i'm guessing 189 must correspond to USB drivers.  that
config option is basically saying "allow the container create
character device nodes matching 189:*"  check out "man mknod" for more
info.

> Any plans to support udev and usb pass-through in lxc ?

IMO "lxc" itself is a very specific technology: to add namespaces to
processes/users/network/etc... it really doesn't have anything to do
with full blown virtualization, it's just a use case.  to support
udev, a daemon (or is it kernel?) on the host needs to send uevents to
the container namespace to "fake" shared and private devices intended
for the container.  this probably needs a lot of config... in the *nix
spirit, that should be handled by a separate specialized app... i
think the last paragraph is correct :-)

anyways, you could try to use shared/slave mounts along with the bind
mount to accomplish what you want.  from mount(8):

"Since Linux 2.6.15 it is possible to mark a mount and its submounts
as shared, private, slave or unbindable. A shared mount provides
ability to create mirrors of that mount such that mounts and umounts
within any of the mirrors propagate to the other mirror. A slave mount
receives propagation from its master, but any not vice-versa. A
private mount carries no propagation abilities. A unbindable mount is
a private mount which cannot cloned through a bind operation. Detailed
semantics is documented in Documentation/sharedsubtree.txt file in the
kernel source tree."

it might be as easy as:

mount --make-shared /media

providing /media itself is a mount... else you might have to:

mount --make-shared /

let us know if/how it goes.

C Anthony