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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 oc...

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....

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 >...

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...

The documentation for .can_write and friends mentioned merely that the callback must return a boolean value, or -1 on failure. Historically, we have treated any non-zero value other than -1 as true, and some plugins have sloppily relied on this behavior, including the standalone nbd plugin prior to the use of libnbd in v1.14...

The idea and patch is fine, but I wonder if it would be more useful to callers if it was exposed as two separate APIs. Callers would then not need to deal with masking out unknown flags, and it works more like the other is_* / can_* ("flag calls") we already have. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the netwo...

On Mon, Mar 16, 2020 at 10:36:14PM -0500, Eric Blake wrote: > The documentation for .can_write and friends mentioned merely that the > callback must return a boolean value, or -1 on failure. Historically, > we have treated any non-zero value other than -1 as true, and some > plugins have sloppily relied on this behavior, including the > standalone nbd plugin prior to the us...

...t to tell the drivers if silent deflation is actually supported. The meaning of the feature bit is reversed compared to the original, because the original meaning was not safe against migration. For features to be safe against migration, they have to be defined as "this is true if the guest _can_ do X". For such a "positive" feature, migration is possible if the destination supports it, or the source didn't set it: dest support source set ok? T T T T F T F...

Here is the series, split in two patches, with small edits and new commit messages. Paolo Bonzini (2): virtio-balloon spec: rewrite description of VIRTIO_BALLOON_F_MUST_TELL_HOST virtio-balloon spec: reintroduce "silent deflation" feature virtio-spec.lyx | 238 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 233 insertions(+), 5 deletions(-) --

It's easy to expose new callbacks to sh plugins, by borrowing tri-state code from can_fua. It's possible that nbdkit emulate will actually work well (in our example.sh script, the kernel caching a pread from one dd invocation may indeed speed up the next access), but for the sake of the example, I demonstrated advertising a no-op handler. The shell plugin, coupled with Rich'...

...t > deflation is actually supported. The meaning of the feature bit is > reversed compared to the original, because the original meaning was > not safe against migration. > > For features to be safe against migration, they have to be defined as > "this is true if the guest _can_ do X". For such a "positive" feature, > migration is possible if the destination supports it, or the source > didn't set it: > > dest support source set ok? > T T T > T F...

b_conn_handle fields exportsize and can_* have a special meaning when they are -1. It means that the value of the field has not been computed and cached yet. The struct was being initialized using memset (_, -1, _) which does indeed have the effect of setting all the fields to -1, although it's somewhat non-obvious to say the least....

Some feature additions to the shell script plugin allow us to test the export flags field reasonably easily. Rich.

Previously we lazily requested the server options in the can_* callbacks. The can_* callbacks are always called by nbdkit straight after open, so this just adds complexity for no benefit. This change simply makes the code always fetch the server options during the open callback. This is — functionally at least — mostly just refactoring. However I also add...

Previously we lazily requested the server options in the can_* callbacks. The can_* callbacks are always called by nbdkit straight after open, so this just adds complexity for no benefit. This change simply makes the code always fetch the server options during the open callback. This is — functionally at least — mostly just refactoring. However I also add...

...m> > Date: Thu, 9 Apr 2020 12:45:10 +0100 > Subject: [PATCH] Add the ability to write plugins in golang. > MIME-Version: 1.0 > Content-Type: text/plain; charset=UTF-8 > Content-Transfer-Encoding: 8bit > > Thanks: Dan Berrangé > > XXX UNFINISHED: > > - Default can_* methods are hard to implement. Ideally we would be > able to test if a user plugin implements a particular callback > (eg. TestPlugin.PWrite) or else defaults to the default callback, > but even with reflection I don't think this is possible in golang. > [Discussed on...

On Wed, May 15, 2019 at 10:57:57PM -0500, Eric Blake wrote: > It's easy to expose new callbacks to sh plugins, by borrowing > tri-state code from can_fua. It's possible that nbdkit emulate will > actually work well (in our example.sh script, the kernel caching a > pread from one dd invocation may indeed speed up the next access), but > for the sake of the example, I demonstrated advertising a no-op > handler. > > The shell...

On Fri, Jun 22, 2018 at 2:59 PM Richard W.M. Jones <rjones@redhat.com> wrote: > Previously we lazily requested the server options in the can_* > callbacks. The can_* callbacks are always called by nbdkit straight > after open, so this just adds complexity for no benefit. This change > simply makes the code always fetch the server options during the open > callback. > I agree, the simple way is much better. > > T...

..."script=-" and use it in the test; and verify this also works on FreeBSD; and verify that it doesn't depend on the particular behaviour of our wrapper script and should work with installed nbdkit too. - Fix handling of zero flags parameter. - Add "to stdout" for can_fua. - "In future" -> "In the future," in various places. - Make the test work on FreeBSD by avoiding use of endian swaps. - Use socat "cool-write" to avoid occasional EPIPE error seen in tests. - Retest on Linux & FreeBSD. - Extra commit for a small do...

v1 was here: https://www.redhat.com/archives/libguestfs/2018-June/msg00099.html v2: - Just fixes the two problems noted in the review of the previous version. Rich.