[Lxc-users] Dynamic devices...

C Anthony Risinger extofme at gmail.com
Sun Mar 7 05:21:44 UTC 2010

What does udev listen to while under container (or host)?  Is it  
possible to generate events from a host process to each containerized  
udevd, and let udevd do it's job?  I'm not familiar; a "spoofed"  
kernel event generator of sorts

On Mar 6, 2010, at 11:49 AM, "Michael H. Warfield" <mhw at WittsEnd.com>  

> Hey all,
> This is sort of a jump ball for both the OpenVZ camp and the LXC camp.
> Maybe some food for thought as well.  I think it's something that  
> needs
> to be thought out.
> I know udev does not work in containers.  Neither OpenVZ nor LXC.  Ok,
> fine.  So devices are static.  Problem is that I've got a situation
> where I need dynamic devices, specifically some USB devices.
> I have an 8 port serial to USB converter used for controlling the  
> serial
> consoles of a cluster of remote servers.  So ttyS0 on each server is
> hooked to a port on the controller and configured for serial console
> (they also have serial BIOS console redirection as well - very VERY  
> nice
> for remote management where you don't have a remote IP KVM).
> That converter then plugs into a USB sharing device which shares the
> converter between 4 of the servers.  So...  Any one of the four  
> servers
> can take control of the converter and can then access all of the 8
> serial consoles for all of the servers.  Nice redundancy.
> I want to grant access to that subsystem to selected containers so
> certain administrators can be given their very own container and be  
> able
> to access the host consoles over serial ports, then.  Simple so far.
> Just allow those containers access to the usbsharing device and the
> ttyUSB* devices.
> Here's where the rub comes in.  The way the USB sharing device works.
> Any server which does NOT have the consoles sees a USB hiddev device  
> (it
> looks like an USB human input device).  It accesses that device to
> request (or demand) control of the controlled USB devices.  The server
> with the consoles, does NOT see that device at all.  What it does see
> are the controlled USB devices (the ttyUSB* devices in this case)  
> which
> the other servers do NOT see.  So the logic goes that if you see the
> usbsharing device, you do not have the consoles but may request  
> them. If
> you do NOT have the usb sharing device you should have the ttyUSB*
> devices and may access them.  So those devices come and go  
> dynamically.
> How to do this in a container?
> (Yes, obviously, I can try to open the device and get an error.  But,
> really...  That's an ugly answer.)
> I suppose I can apply the dynamics in the udev rules in the host  
> machine
> and create matching devices in the container's dev directory using a  
> hot
> plug run script.  That's what I'm working on now.  Is that really the
> answer though?
> Just food for thought for developers and users alike.  There has to be
> more situations that just this.
> Regards,
> Mike
> -- 
> Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
>   /\/\|=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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