[Lxc-users] usb devices

[Nirmal Guhan]

On Thu, Aug 5, 2010 at 3:32 PM, C Anthony Risinger <anthony at extof.me> wrote:
> 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.

Actually, /proc/bus/usb/devices was working within the container. So I
tried mount -t vfat /dev/sdb1 /myusbdir within container and it was
able to mount the usb disk. This is on Fedora 12. Hope this is right
thing to do :=)

-Nirmal

>
> C Anthony
>