Re: [Qemu-devel] read-only IDE drives in qemu

["Frédéric Dreier" <frederic.dreier@gmail.com>]

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Hi,

Now I understand why read-only IDE support was dropped. I will investigate
if I could use read-only virtio disks for my purpose.

Thank you for your response and for the hints,

Best regards,

Frederic



Le 4 août 2011 20:20, Markus Armbruster <armbru@redhat.com> a écrit :

> Frédéric Dreier <frederic.dreier@gmail.com> writes:
>
> > Hi,
> >
> > We are updating some machines in our server farm to Ubuntu natty (KVM /
> > Opennebula cluster). Since then we used to have some VM with shared
> > read-only IDE disks to mirror software repositories through several
> isolated
> > networks (one-way data diode).
> >
> > The updated qemu does not allow it. It failed to start the VM with a
> 'Can't
> > use a read-only drive' error. After checking in the qemu git, it seems
> that
> > this has been forbidden by this commit
> > '7aa9c811ca0761918a0252d0f923a80224953fa6' :
> >
> > -----------------------------
> > Author: Markus Armbruster <armbru@redhat.com>  2010-06-28 19:10:36
> > Committer: Kevin Wolf <kwolf@redhat.com>  2010-07-06 17:05:50
> > Parent: c4d74df726cb3791d9f1661b58067df5608b627e (ide: Make
> ide_init_drive()
> > return success)
> > Child:  dce9e92834cc4f962e547cae46b73ca559d05b0c (ide: Reject invalid CHS
> > geometry)
> > Branches: master, remotes/origin/master, remotes/origin/stable-0.13,
> > remotes/origin/stable-0.14, remotes/origin/stable-0.15
> > Follows: v0.12.0-rc0
> > Precedes: v0.13.0-rc0
> >
> >     ide: Reject readonly drives unless CD-ROM
> >
> >     drive_init() doesn't permit option readonly for if=ide, but that's
> >     worthless: we get it via if=none and -device.
> >
> >     Signed-off-by: Markus Armbruster <armbru@redhat.com>
> >     Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > -----------------------------
> >
> > I do not understand the comment, if there is a workaround or if it
> something
> > to avoid.
> >
> > May you help me to understand it?
>
> Real IDE disks can't do read-only.
>
> -drive if=ide rejects readonly unless you also supply media=cdrom, which
> turns the drive into a CD-ROM.
>
> When -drive if=none got added, we inadvertedly created a loophole: the
> reject covered only if=ide, not if=none when used for a -device
> ide-drive.  The commit you quoted fixed that.
>
> Can you use an IDE CD-ROM instead?  Or virtio-blk-pci?
>

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