Re: port-xen/47899: xen block script does not create vnd devices when needed.

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Thu, Jun 06, 2013 at 02:05:00AM +0000, Pierre Pronchery wrote:
> The following reply was made to PR port-xen/47899; it has been noted by GNATS.
> 
> From: Pierre Pronchery <khorben%defora.org@localhost>
> To: gnats-bugs%NetBSD.org@localhost
> Cc: 
> Subject: Re: port-xen/47899: xen block script does not create vnd devices
>  when needed.
> Date: Thu, 06 Jun 2013 04:00:34 +0200
> 
>  This is a multi-part message in MIME format.
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>  
>                       Hi 7heo,
>  
>  On 05/06/2013 22:30, 7heo%7heo.tk@localhost wrote:
>  > [...]
>  > By default, NetBSD has 4 (four) vnd devices, /dev/vnd0, /dev/vnd1,
>  > /dev/vnd2 and /dev/vnd3.
>  > 
>  > When one creates a virtual machine with a disk from a file, the
>  > block script uses vnconfig to "mount" the image on a vnd loopback device.
>  > 
>  > When the Xen toolstack (xm) needs to mount more than 4 images at the
>  > same time, it fails, instead of increasing the number of vnd devices to
>  > a suited quantity.
>  
>  Good catch.
>  
>  Can you try the patch attached? It should attempt to create the missing
>  nodes automatically.

I'm not sure it's the right thing to do. If things go wrong (e.g.
a domU being repeteadly restarted without the previous one being
properly destroyed, as with on_crash = rename-restart)
you can fill up /dev, and probably more bad things will happen.

I think it's up to the admin to make sure he has enough vnd devices
created.

The real problem may be that 'xm create' doens't report the real
reason for the failure; the real reason is in xenbackendd.log.
I'm not sure if this can easily be fixed.

>  
>  For some reason "vnconfig -l" seems to only ever lists the four first
>  vnd devices, regardless of the existence of the corresponding device
>  nodes, but that's a separate issue.

vnconfig -l works fine for me:
ragga:/domains#vnconfig -l
vnd0: not in use
vnd1: /domains (/dev/raid1f) inode 4
vnd2: /domains (/dev/raid1f) inode 11
vnd3: /domains (/dev/raid1f) inode 12
vnd4: not in use
vnd5: not in use
vnd6: not in use
[...]
vnd29: not in use
vnd30: not in use
vnd31: not in use

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--