[libvirt] libvirt disk labels and QEMU drive host alias generation

[Kashyap Chamarthy]

On Tue, Jun 14, 2016 at 12:01:52PM +0100, Daniel P. Berrange wrote:
> On Tue, Jun 14, 2016 at 12:50:09PM +0200, Kashyap Chamarthy wrote:
> > Summary
> > -------
> > 
> > It seems like libvirt is generating the same QEMU drive host
> > alias ('drive-virtio-disk%d') for different two disk labels (vdb, vdb1).
> > 
> > [Refer the contextual root cause analysis discussion at the end with
> > Laine & Peter.]
> > 
> > Let's take a quick example to demonstrate the issue.
> > 
> > On a guest that is shut down, attach a couplee of disks with labels
> > 'vdb', and 'vdb1'
> > 
> >     $ sudo virsh attach-disk cvm1 \
> >          /export/vmimages/1.raw vdb --config
> > 
> >     $ sudo virsh attach-disk cvm1 \
> >          /export/vmimages/1.raw vdb1 --config
> 
> That second command is user error - hotplugging a disk partition
> is nonsensical, except with Xen which allows that for paravirtualized
> disks. We should reject such disk names with an error right away in
> all other cases.

Okay, filed this upstream bug:

    https://bugzilla.redhat.com/show_bug.cgi?id=1346265 --
    Disallow disk hot-plugging with invalid target labels (e.g. disk
    partition number for non-paravirt disks)

I realized supplying disk partition numbers as targets is not sensible,
but virDiskNameParse() parses partition numbers too:

    $ less -N src/util/virutil.c
    [...]
    543 /* Translates a device name of the form (regex) /^[fhv]d[a-z]+[0-9]*$/
    544  * into the corresponding index and partition number
    545  * (e.g. sda0 => (0,0), hdz2 => (25,2), vdaa12 => (26,12))
    546  * @param name The name of the device
    547  * @param disk The disk index to be returned
    548  * @param partition The partition index to be returned
    549  * @return 0 on success, or -1 on failure
    550  */
    551 int virDiskNameParse(const char *name, int *disk, int *partition)
    552 {
    [...]


-- 
/kashyap