In QAPI, absent optional members are distinct from any present value.
We thus represent an optional schema member FOO as two C members: a
FOO with the member's type, and a bool has_FOO. Likewise for function
arguments.
However, has_FOO is actually redundant for a pointer-valued FOO, which
can be null only when has_FOO is false, i.e. has_FOO == !!FOO. Except
for arrays, where we a null FOO can also be a present empty array.
The redundant has_FOO are a nuisance to work with. Improve the
generator to elide them. Uses of has_FOO need to be replaced as
follows.
Tests of has_FOO become the equivalent comparison of FOO with null.
For brevity, this is commonly done by implicit conversion to bool.
Assignments to has_FOO get dropped.
Likewise for arguments to has_FOO parameters.
Beware: code may violate the invariant has_FOO == !!FOO before the
transformation, and get away with it. The above transformation can
then break things. Two cases:
* Absent: if code ignores FOO entirely when !has_FOO (except for
freeing it if necessary), even non-null / uninitialized FOO works.
Such code is known to exist.
* Present: if code ignores FOO entirely when has_FOO, even null FOO
works. Such code should not exist.
In both cases, replacing tests of has_FOO by FOO reverts their sense.
We have to fix the value of FOO then.
To facilitate review of the necessary updates to handwritten code, add
means to opt out of this change, and opt out for all QAPI schema
modules where the change requires updates to handwritten code. The
next few commits will remove these opt-outs in reviewable chunks, then
drop the means to opt out.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20221104160712.3005652-5-armbru@redhat.com>
The next commit will change the code generated for some optional
members. The example schema contains an optional member affected by
the change. Add one that is not affected.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20221104160712.3005652-4-armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20221104160712.3005652-3-armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20221104160712.3005652-2-armbru@redhat.com>
Commit 4e99f4b12c dropped simple unions and updated most
documentation accordingly, but in one case we still claim that
there are "two flavors of unions".
Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Message-Id: <20220420153408.243584-2-abologna@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Previous commits enabled trace events generation for most of QAPI
generated code (except for tests/ and qga/). Let's update documentation
to illustrate it.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20220126161130.3240892-6-vsementsov@virtuozzo.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Move error_propagate() to if (err) and make "if (err)" block mandatory.
This is to simplify further commit, which will bring trace events
generation for QMP commands.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20220126161130.3240892-3-vsementsov@virtuozzo.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Commit 6a8c0b5102 "qapi: Add feature flags to struct types" neglected
to document how to document feature flags. Make up for that.
Cc: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20211026111023.76937-3-armbru@redhat.com>
[Editing accident fixed]
Commit 55ec69f8b1 "docs/devel/qapi-code-gen.txt: Update to new rST
backend conventions" accidentally duplicated a paragraph. Drop it.
Cc: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20211026111023.76937-2-armbru@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
By convention, names starting with "x-" are experimental. The parts
of external interfaces so named may be withdrawn or changed
incompatibly in future releases.
The naming convention makes unstable interfaces easy to recognize.
Promoting something from experimental to stable involves a name
change. Client code needs to be updated. Occasionally bothersome.
Worse, the convention is not universally observed:
* QOM type "input-barrier" has properties "x-origin", "y-origin".
Looks accidental, but it's ABI since 4.2.
* QOM types "memory-backend-file", "memory-backend-memfd",
"memory-backend-ram", and "memory-backend-epc" have a property
"x-use-canonical-path-for-ramblock-id" that is documented to be
stable despite its name.
We could document these exceptions, but documentation helps only
humans. We want to recognize "unstable" in code, like "deprecated".
So support recognizing it the same way: introduce new special feature
flag "unstable". It will be treated specially by the QAPI generator,
like the existing feature flag "deprecated", and unlike regular
feature flags.
This commit updates documentation and prepares tests. The next commit
updates the QAPI schema. The remaining patches update the QAPI
generator and wire up -compat policy checking.
Management applications can then use query-qmp-schema and -compat to
manage or guard against use of unstable interfaces the same way as for
deprecated interfaces.
docs/devel/qapi-code-gen.txt no longer mandates the naming convention.
Using it anyway might help writers of programs that aren't
full-fledged management applications. Not using it can save us
bothersome renames. We'll see how that shakes out.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-Id: <20211028102520.747396-2-armbru@redhat.com>
This is quite similar to commit 84ab008687 "qapi: Add feature flags to
struct members", only for enums instead of structs.
Special feature flag 'deprecated' is silently ignored there. This is
okay only because it will be implemented shortly.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20211025042405.3762351-3-armbru@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
The next commit will add feature flags to enum members. There's a
problem, though: query-qmp-schema shows an enum type's members as an
array of member names (SchemaInfoEnum member @values). If it showed
an array of objects with a name member, we could simply add more
members to these objects. Since it's just strings, we can't.
I can see three ways to correct this design mistake:
1. Do it the way we should have done it, plus compatibility goo.
We want a ['SchemaInfoEnumMember'] member in SchemaInfoEnum. Since
changing @values would be a compatibility break, add a new member
@members instead.
@values is now redundant. In my testing, output of
qemu-system-x86_64's query-qmp-schema grows by 11% (18.5KiB).
We can deprecate @values now and drop it later. This will break
outmoded clients. Well-behaved clients such as libvirt are
expected to break cleanly.
2. Like 1, but omit "boring" elements of @member, and empty @member.
@values does not become redundant. @members augments it. Somewhat
cumbersome, but output of query-qmp-schema grows only as we make
enum members non-boring.
There is nothing to deprecate here.
3. Versioned query-qmp-schema.
query-qmp-schema provides either @values or @members. The QMP
client can select which version it wants. There is no redundant
output.
We can deprecate old versions and eventually drop them. This will
break outmoded clients. Breaking cleanly is easier than for 1.
While 1 and 2 operate within the common rules for compatible
evolution apply (section "Compatibility considerations" in
docs/devel/qapi-code-gen.rst), 3 bypasses them. Attractive when
operating within the rules is just too awkward. Not the case here.
This commit implements 1. Libvirt developers prefer it.
Deprecate @values in favour of @members. Since query-qmp-schema
compatibility is pretty fundamental for management applications, an
extended grace period is advised.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Tested-by: Peter Krempa <pkrempa@redhat.com>
Acked-by: Peter Krempa <pkrempa@redhat.com>
Message-Id: <20211025042405.3762351-2-armbru@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Simple unions predate flat unions. Having both complicates the QAPI
schema language and the QAPI generator. We haven't been using simple
unions in new code for a long time, because they are less flexible and
somewhat awkward on the wire.
The previous commits eliminated simple union from the tree. Now drop
them from the QAPI schema language entirely, and update mentions of
"flat union" to just "union".
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20210917143134.412106-22-armbru@redhat.com>
Break lines between members instead of within members.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20210917143134.412106-2-armbru@redhat.com>
Update the documentation describing the changes in this series.
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Tested-by: John Snow <jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20210804083105.97531-2-marcandre.lureau@redhat.com>
[Rebased with straightforward conflicts]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Add clickables to many places.
Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20210720235619.2048797-4-jsnow@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Mostly, add ``literal`` markers to a lot of things like C types, add
code blocks, and fix the way a few things render.
Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20210720235619.2048797-3-jsnow@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
This is a very rudimentary conversion from .txt to .rst changing as
little as possible, but getting it to render somewhat nicely; without
using any Sphinx directives. (It is 'native' ReST.)
Further patches will add cross-references and Sphinx-specific extensions
to make it sparkle.
Signed-off-by: John Snow <jsnow@redhat.com>
Message-Id: <20210720235619.2048797-2-jsnow@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
