Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes:
On 17.10.23 18:00, Markus Armbruster wrote:
Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru> writes:
Send a new event when guest reads virtio-pci config after
virtio_notify_config() call.
That's useful to check that guest fetched modified config, for example
after resizing disk backend.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
[...]
diff --git a/qapi/qdev.json b/qapi/qdev.json
index 2468f8bddf..37a8785b81 100644
--- a/qapi/qdev.json
+++ b/qapi/qdev.json
@@ -329,3 +329,25 @@
# Since: 8.2
##
{ 'command': 'x-device-sync-config', 'data': {'id': 'str'} }
+
+##
+# @X_CONFIG_READ:
+#
+# Emitted whenever guest reads virtio device config after config change.
+#
+# @device: device name
+#
+# @path: device path
+#
+# Since: 5.0.1-24
+#
+# Example:
+#
+# <- { "event": "X_CONFIG_READ",
+# "data": { "device": "virtio-net-pci-0",
+# "path": "/machine/peripheral/virtio-net-pci-0" },
+# "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }
+#
+##
+{ 'event': 'X_CONFIG_READ',
+ 'data': { '*device': 'str', 'path': 'str' } }
The commit message talks about event CONFIG_READ, but you actually name
it x-device-sync-config.
will fix
I figure you use x- to signify "unstable". Please use feature flag
'unstable' for that. See docs/devel/qapi-code-gen.rst section
"Features", in particular "Special features", and also the note on x- in
section "Naming rules and reserved names".
OK, will do.
Hmm, it say
Names beginning with ``x-`` used to signify "experimental". This
convention has been replaced by special feature "unstable".
"replaced".. So, I should use "unstable" flag without "x-" prefix? Can't find an example. Seems
"unstable" always used together with "x-".
True.
The "x-" prefix originated with qdev properties. First use might be
commit f0c07c7c7b4. The convention wasn't documented then, but QOM/qdev
properties have always been a documentation wasteland. It then spread
to other places, and eventually to the QAPI schema. Where we try pretty
hard to document things properly. We documented the "x-" prefix in
commit e790e666518:
Any name (command, event, type, field, or enum value) beginning with
"x-" is marked experimental, and may be withdrawn or changed
incompatibly in a future release.
Minor pain point: when things grow up from experimental to stable, we
have to rename.
The convention didn't stop us from naming non-experimental things x-FOO,
e.g. QOM property "x-origin" in commit 6105683da35. Made it to the QAPI
schema in commit 8825587b53c. Point is: the prefix isn't a reliable
marker for "unstable".
Since I needed a reliable marker for my "set policy for unstable
interfaces" feature (see CLI option -compat), I created special feature
flag "unstable", and dropped the "x-" convention for the QAPI schema.
Renaming existing "x-" names felt like pointless churn, so I didn't.
I'm not objecting to new names starting with "x-". Nor am I objecting
to feature 'unstable' on names that don't start with "x-".
I guess "x-" remains just fine for things we don't intend to make stable
at some point. The "x-" can remind humans "this is unstable" better
than a feature flag can (for machines, it's the other way round).
For things we do intend (hope?) to make stable, I wouldn't bother with
the "x-".
Clearer now?
Also, nothing said about events. Is using "X_" wrong idea? Should it be
x-SOME_EVENT instead?
Since this is the first unstable event, there is no precedent. Let's
use no prefix, and move on.
The name CONFIG_READ feels overly generic for something that makes sense
only with virtio devices.
Hmm, right.. I think, we can say same thing about DEVICE_UNPLUG_GUEST_ERROR.
That one came to be as a generalization of existing MEM_UNPLUG_ERROR and
a concrete need to signal CPU unplug errors. Demonstrates "unplug guest
errors" can happen for different kinds of devices. So we went with a
generic event we can use for all of them.
This doesn't seem to be the case for this patch's event. Thoughts?