Since pretty much every cdrom drive use scsi today, shouldnt the readonly/writeable flag for MMC devices rather be done down in the hw/scsi* code rather than the generic block code? If/when/ever I get enough time I would like to port the writeable dvd+r emulation I wrote for STGT to qemu. In STGT, MMC/DVD devices can be either read-only or read-write. If the filesize for the backing file is >0 bytes, it is assumed the file is an iso image and that the file is a read-only iso image. If filesize is ==0, then the file is opened read-write and is treated as a "blank dvd+r disk that the initiator can write/burn to" regards ronnie sahlberg On Tue, Aug 7, 2012 at 6:47 PM, Markus Armbruster <armbru@redhat.com> wrote:
Kevin Wolf <kwolf@redhat.com> writes:
Am 02.08.2012 09:20, schrieb Kevin Shanahan:
On Thu, Aug 02, 2012 at 02:49:52PM +0930, Kevin Shanahan wrote:
On Thu, Aug 02, 2012 at 11:46:13AM +0930, Kevin Shanahan wrote:
On Thu, Aug 02, 2012 at 11:02:42AM +0930, Kevin Shanahan wrote:
Set the block driver read_only flag for cdrom devices so that qmp_change_blockdev does not attempt to open cdrom files in read-write mode when changing media.
Hrm, this fixes my simple test case using the kvm monitor directly but changing media via libvirt still has the same issue (fails for RO files, succeeds for writable files).
$ virsh attach-disk --type cdrom --mode readonly test1 /srv/kvm/iso/ubuntu-12.04-server-amd64.iso hdc error: Failed to attach disk error: internal error unable to execute QEMU command 'change': Could not open '/srv/kvm/iso/ubuntu-12.04-server-amd64.iso'
I'll keep looking into it.
In the libvirt case, it seems libvirt is failing to add media=cdrom to the commandline, so in this case qemu is defaulting to media=disk and my proposed fix has no effect. Diving into libvirt now to see why no media=disk is getting added...
Common test case has this xml (generated by virt-install):
<disk type='block' device='cdrom'> <driver name='qemu' type='raw'/> <target dev='hdc' bus='ide'/> <readonly/> <alias name='ide0-1-0'/> <address type='drive' controller='0' bus='1' target='0' unit='0'/> </disk>
Ok, looks like libvirt is intentionally leaving media=cdrom off the command line in the case that "-device ide-cd,..." is supported. Presumably by specifying the device this way, qemu is supposed to work out that the media type is cdrom automatically (but it doesn't, it defaults to disk).
Libvirt wants to use:
qemu-kvm ... \ -drive if=none,id=drive-ide0-1-0,readonly=on,format=raw \ -device ide-cd,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 ...
If I hack qemu/qemu_command.c::qemuBuildDriveStr() to ignore the check for QEMU_CAPS_IDE_CD and always add media=cdrom, then (with my qemu as well patch) qemu will open cdrom media files read-only.
There's probably a neater way to just get qemu to set the media type if "-device ide-cd,..." is used, but I haven't worked it out yet.
Anyway, apologies for the rambling conversation with myself on your lists. Hope this is helpful in some way.
Thanks, that's some good information.
However, I don't think you should start from media=cdrom. libvirt already does specify readonly=on and that is the property you're really interested in. Since commit 528f7663 (released with 0.13) the 'change' command should keep the read-only flag for all kinds of media.
Correct.
Now I'm not sure where you lost the read-only flag. At least on git master it doesn't seem to reproduce for me.
I can:
$ qemu --enable-kvm -S -m 384 -vnc localhost:5500 -monitor stdio \ -drive if=none,id=cd,readonly=on,format=raw \ -device ide-cd,bus=ide.1,unit=0,drive=cd QEMU 1.1.50 monitor - type 'help' for more information (qemu) change cd r5.iso Could not open 'r5.iso' (qemu) q armbru@blackfin:~/work/images$ ls -l r5.iso -r--r--r--. 1 armbru armbru 2872639488 Mar 31 2011 r5.iso
Looks like a QEMU bug to me.