Re: [Qemu-devel] [PATCH RFC v3 for-2.9 02/11] rbd: Fix to cleanly reject -drive without pool or image

[Jeff Cody <jcody@redhat.com>]

On Tue, Mar 28, 2017 at 09:54:53AM +0200, Markus Armbruster wrote:
> Jeff Cody <jcody@redhat.com> writes:
> 
> > On Mon, Mar 27, 2017 at 08:58:28PM +0200, Markus Armbruster wrote:
> >> Markus Armbruster <armbru@redhat.com> writes:
> >> 
> >> > Max Reitz <mreitz@redhat.com> writes:
> >> >
> >> >> On 27.03.2017 18:10, Max Reitz wrote:
> >> >>> On 27.03.2017 15:26, Markus Armbruster wrote:
> >> >>>> qemu_rbd_open() neglects to check pool and image are present.
> >> >>>> Reproducer:
> >> >>>>
> >> >>>>     $ qemu-system-x86_64 -nodefaults -drive if=none,driver=rbd,pool=p
> >> >>>>     Segmentation fault (core dumped)
> >> >>>>     $ qemu-system-x86_64 -nodefaults -drive if=none,driver=rbd,image=i
> >> >>>>     qemu-system-x86_64: -drive if=none,driver=rbd,image=i: error opening pool (null)
> >> >>>>
> >> >>>> Doesn't affect -drive with file=..., because qemu_rbd_parse_filename()
> >> >>>> always sets both pool and image.
> >> >>>>
> >> >>>> Doesn't affect -blockdev, because pool and image are mandatory in the
> >> >>>> QAPI schema.
> >> >>>>
> >> >>>> Fix by adding the missing checks.
> >> >>>>
> >> >>>> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> >> >>>> Reviewed-by: Eric Blake <eblake@redhat.com>
> >> >>>> ---
> >> >>>>  block/rbd.c | 10 +++++++---
> >> >>>>  1 file changed, 7 insertions(+), 3 deletions(-)
> >> >>> 
> >> >>> Reviewed-by: Max Reitz <mreitz@redhat.com>
> >> >>
> >> >> That said, don't we have a similar issue with qemu_rbd_create()? It too
> >> >> doesn't check whether those options are given but I guess they're just
> >> >> as mandatory.
> >> >
> >> > Looks like it.  I'll try to stick a fix into v4.
> >> 
> >> Hmm, ignorant question: how can I reach qemu_rbd_create() without going
> >> through qemu_rbd_parse_filename()?
> >
> > You can't -- commit c7cacb3e7 forces qemu_rbd_create() to call
> > qemu_rbd_parse_filename().  And in qemu_rbd_parse_filename(), it will
> > complain if pool is not provided (and that is what causes the abort, not the
> > missing image parameter).  So I think we are safe, but a nicer error message
> > for a missing 'image' parameter might be nice anyway.
> 
> I now see the "we are safe" part, but not the "want a nicer error
> message for a missing 'image'" part.  How can 'image' be missing?
> 
> qemu_rbd_parse_filename() parses a pseudo-filename of the form
> 
>     rbd:POOL/IMAGE[@SNAP][:KEY=VALUE:...]
> 
> It fails if
> 
> * the pseudo-filename doesn't start with "rbd:"
> 
> * doesn't contain '/' ("Pool name is required")
> 
> * POOL, IMAGE, SNAP, the KEY=VALUE:... part or any KEY in it is empty or
>   too long (until the next commit)
> 
> * a KEY=VALUE doesn't contain '='
> 
> If it succeeds, "pool" and "image" are both set in @options.
> 
> Can you give me a reproducer for the error message you'd like me to
> improve?


Sure: qemu-img info rbd:mypool/:mon_host=192.168.15.180

'image' is technically present in the options, but it is an empty string.

My thought was that it'd be nice to throw a similar error message for an
empty string for 'image'.  As it is, the rbd library catches it, so it isn't
catastrophic, but a nicer message would be helpful.

(My comment here assumes an empty string is not an acceptable image name for
rbd)