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

[Avi Kivity <avi@redhat.com>]

On 04/04/2011 06:09 PM, 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.
>
> The size reported by lseek(fd, 0, SEEK_END) is outdated.

I believe a kernel fix is best in that case, leaving qemu alone.

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