[Qemu-devel] Reopen file descriptors on 'cont' command

[Qemu-devel] Reopen file descriptors on 'cont' command

[Christopher Pereira]

Hi,

Does qemu reopen files on a 'cont' command?

When working with images on a gluster volume, file descriptors may get 
into a bad state because of network timeouts, remounting a share, 
etc...and reinitializing file descriptors may be usefull to get paused 
VMs up again.

Related BZ:
https://bugzilla.redhat.com/show_bug.cgi?id=1058300

Re: [Qemu-devel] Reopen file descriptors on 'cont' command

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 734 bytes --]

On Wed, Feb 25, 2015 at 09:32:18PM -0300, Christopher Pereira wrote:
> Does qemu reopen files on a 'cont' command?
> 
> When working with images on a gluster volume, file descriptors may get into
> a bad state because of network timeouts, remounting a share, etc...and
> reinitializing file descriptors may be usefull to get paused VMs up again.
> 
> Related BZ:
> https://bugzilla.redhat.com/show_bug.cgi?id=1058300

No, QEMU doesn't reopen file descriptors.

This can be challenging because QEMU supports file descriptor passing,
which is used when the QEMU process is isolated using SELinux so it
cannot open files itself.  Reopening would require new file descriptors
passed in from the management tool.

Stefan

[-- Attachment #2: Type: application/pgp-signature, Size: 473 bytes --]

Re: [Qemu-devel] Reopen file descriptors on 'cont' command

[Christopher Pereira]

On 06-03-2015 14:19, Stefan Hajnoczi wrote:
> On Wed, Feb 25, 2015 at 09:32:18PM -0300, Christopher Pereira wrote:
>> Does qemu reopen files on a 'cont' command?
>>
>> When working with images on a gluster volume, file descriptors may get into
>> a bad state because of network timeouts, remounting a share, etc...and
>> reinitializing file descriptors may be usefull to get paused VMs up again.
>>
>> Related BZ:
>> https://bugzilla.redhat.com/show_bug.cgi?id=1058300
> No, QEMU doesn't reopen file descriptors.
>
> This can be challenging because QEMU supports file descriptor passing,
> which is used when the QEMU process is isolated using SELinux so it
> cannot open files itself.  Reopening would require new file descriptors
> passed in from the management tool.

Thanks Stefan.

I confirmed that libvirtd is not passing a FD to QEMU, but an image path.
Is QEMU reopening this image file when the VM is resumed?
QEMU must check if the FD (initialized by QEMU) is still valid, 
especially after resuming a paused VM.