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Re: [libvirt] [Qemu-devel] [PATCH v2 3/3] raw-posix: Re-open host CD-ROM after media change



On (Mon) 04 Apr 2011 [16:09:05], Stefan Hajnoczi wrote:
> On Mon, Apr 4, 2011 at 2:49 PM, Avi Kivity <avi redhat com> wrote:
> > On 04/04/2011 04:38 PM, Anthony Liguori wrote:
> >>
> >> On 04/04/2011 08:22 AM, Avi Kivity wrote:
> >>>
> >>> On 04/03/2011 02:57 PM, Stefan Hajnoczi wrote:
> >>>>
> >>>> In order for media change to work with Linux host CD-ROM it is
> >>>> necessary to reopen the file (otherwise the inode size will not
> >>>> refresh, this is an issue with existing kernels).
> >>>>
> >>>
> >>> Maybe we should fix the bug in Linux (and backport as necessary)?
> >>>
> >>> I think cd-rom assignment is sufficiently obscure that we can require a
> >>> fixed kernel instead of providing a workaround.
> >>
> >> Do reads fail after CD change?  Or do they succeed and the size is just
> >> reported incorrectly?
> >>
> >> If it's the later, I'd agree that it needs fixing in the kernel.  If it's
> >> the former, I'd say it's clearly a feature.
> >>
> >
> > Even if it's a documented or intentional feature, we can add an ioctl to
> > "refresh" the device with up-to-date data.
> 
> It's possible to fix this in the kernel.  I just haven't written the
> patch yet.  The inode size needs to be updated when the new medium is
> detected.
> 
> I haven't tested but I suspect reads within the size of the previous
> medium will succeed.  But if the new medium is larger then reads
> beyond the old medium size will fail.

See http://www.spinics.net/lists/linux-scsi/msg51504.html

		Amit


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