Re: CD-ROM size not updated when switching CD-ROM images.

[Alex Davis <alex14641@yahoo.com>]

I code, therefore I am


--- On Tue, 10/19/10, Stefan Hajnoczi <stefanha@gmail.com> wrote:

> From: Stefan Hajnoczi <stefanha@gmail.com>
> Subject: Re: CD-ROM size not updated when switching CD-ROM images.
> To: "Alex Davis" <alex14641@yahoo.com>
> Cc: kvm@vger.kernel.org
> Date: Tuesday, October 19, 2010, 4:31 AM
> On Tue, Oct 19, 2010 at 4:43 AM, Alex
> Davis <alex14641@yahoo.com>
> wrote:
> > Steps to reproduce:
> > ) Download the first two Slackware-13.1 32-bit CD-ROM
> ISO images.
> > ) Start KVM with the following command
> >   qemu-system-x86_64 -m 1024M \
> >     -cdrom < full path of 1st install disk >
> \
> >     -boot d
> > ) Hit return when prompted for extra boot parameters.
> > ) Hit return when asked to select a keyboard map.
> > ) Hit return at the login prompt.
> > ) cat /sys/block/sr0/size: this should return
> 1209360.
> > ) Press Alt-Ctrl-2 to access the monitor
> > ) eject ide1-cd0
> > ) change ide1-cd0 < full path name of 2nd install
> disk >
> > ) Press Alt-Ctrl-1 to return to the guest.
> > ) dd if=/dev/sr0 of=/dev/null bs=512 skip=1209360
> count=3
> >  this should return
> >   3+0 records in
> >   3+0 records out.
> >  instead it returns 0+0....
> > ) cat /sys/block/sr0/size: this still returns 1209360;
> it should return 1376736.
> >
> > Oddly, when "mount /dev/sr0 ...." is  executed in the
> guest, ls of the mounted directory shows the correct
> contents for the 2nd CD.
> 
> After changing the CD-ROM, does running "blockdev
> --rereadpt /dev/sr0"
> update the size as expected?
The install CD does not have the blockdev command.

> You ejected the CD-ROM on the QEMU side, the guest doesn't
> necessarily
> know about the medium change.  What happens when you
> use "eject
> /dev/sr0" inside the guest instead?
I get a 'no medium found' error from the 'dd..' command. After
going into the the monitor, ejecting and reloading the disk, 
I still get the size of the first disk in the guest.
> 
> I don't know how CD-ROM media change works on real
> hardware, but that
> is the behavior that QEMU should be following.
> 
> Stefan