Re: [PATCH V2] libxl: relax readonly check introduced by XSA-142 fix

[Ian Campbell <ian.campbell@citrix.com>]

On Fri, 2015-11-13 at 09:56 -0700, Jim Fehlig wrote:
> On 11/12/2015 07:40 PM, Jim Fehlig wrote:
> > The fix for XSA-142 is quite a big hammer, rejecting readonly
> > disk configuration even when the requested backend is known to
> > support readonly. While it is true that qemu doesn't support
> > readonly for emulated IDE or AHCI disks
> > 
> > $ /usr/lib/xen/bin/qemu-system-i386 \
> >  -drive file=/tmp/disk.raw,if=ide,media=disk,format=raw,readonly=on
> > qemu-system-i386: Can't use a read-only drive
> > 
> > $ /usr/lib/xen/bin/qemu-system-i386 -device ahci,id=ahci0 \
> >  -drive file=/tmp/disk.raw,if=none,id=ahcidisk-0,format=raw,readonly=on 
> > \
> >  -device ide-hd,bus=ahci0.0,unit=0,drive=ahcidisk-0
> > qemu-system-i386: -device ide-hd,bus=ahci0.0,unit=0,drive=ahcidisk-0:
> > Can't use a read-only drive
> > 
> > It does support readonly SCSI disks
> > 
> > $ /usr/lib/xen/bin/qemu-system-i386 \
> >  -drive file=/tmp/disk.raw,if=scsi,media=disk,format=raw,readonly=on
> > [ok]
> > 
> > Inside a guest using such a disk, the SCSI kernel driver sees write
> > protect on
> > 
> > [   7.339232] sd 2:0:1:0: [sdb] Write Protect is on
> > 
> > Also, PV drivers support readonly, but the patch rejects such
> > configuration even when PV drivers (vdev=xvd*) have been explicitly
> > specified and creation of an emulated twin is skiped.
> > 
> > This follow-up patch loosens the restriction to reject readonly when
> > creating and emulated IDE or AHCI disk, but allows it when the backend
> 
> s/and/an/. I can fix this typo if a V3 is needed.

I fixed it upon commit.

Thanks,
Ian.


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