[Libguestfs] [nbdkit PATCH 2/4] nbd: Normalize return values of can_*

[Richard W.M. Jones]

On Tue, Mar 17, 2020 at 06:59:09AM -0500, Eric Blake wrote:
> On 3/17/20 3:12 AM, Richard W.M. Jones wrote:
> >On Mon, Mar 16, 2020 at 10:36:15PM -0500, Eric Blake wrote:
> >>Although nbdkit documents that any positive value should be treated as
> >>success to the .can_* callbacks, we had a window of releases where
> >>anything other than 1 could trigger an assertion failure, fixed in the
> >>previous patch.  Update what we return to avoid tripping the bug in
> >>broken nbdkit.
> >>
> >>Our return value has been latent since 0e8e8eb11d (v1.1.17), but the
> >>assertion failures did not occur until c306fa93ab and neighboring
> >>commits (v1.15.1).  As v1.13.6 was the point where we started
> >>preferring builds against libnbd, where we always returned 1 on
> >>success, the problem was not detected until now; but it is still in
> >>the wild for any user mixing old plugins with new libnbd.
> >>
> >>Signed-off-by: Eric Blake <eblake at redhat.com>
> >>---
> >>  plugins/nbd/nbd-standalone.c | 12 ++++++------
> >>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> >While I don't like the idea of modifying plugins to fix broken nbdkit
> >behaviour, you make a good case for this being safer, so:
> >
> >ACK
> 
> Think of it as working around broken nbdkit behavior, rather than
> fixing it (as the fix is in patch 1/4).  How many stable branches
> should we backport this to?  Going all the way back to stable-1.2
> seems like it might be overkill; maybe back to stable-1.14 (where
> nbd-standalone was first split off) or stable-1.12 (the last release
> that did not use libnbd) is sufficient?

I'm routinely backporting only to 1.16 and 1.18.

And then backporting to other branches only as-needed.  For example I
backported something to 1.4 yesterday, but that was only because I was
trying to check for a bug which had been reported against 1.4 and I
needed the backport to make the branch compile on a modern distro.

By the way I'm happy to do these cherry picks (just for 1.16 and 1.18)
because I find it helps me to keep the commits in their original order
so I know which ones have been applied and which ones have been
skipped.  Unless there is tooling which does this, which I've
occasionally looked for but never found.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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