Re: [Libguestfs] [nbdkit PATCH 2/4] nbd: Normalize return values of can_*
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(a)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?
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
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