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(a)redhat.com&gt; 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