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>
This helps us construct strings elsewhere before echoing to the
monitor. It avoids having to jump through hoops like:
monitor_printf(mon, "%s", s->str);
It will be useful in following patches but for now convert all
existing plain "%s" printfs to use the _puts api.
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220929114231.583801-33-alex.bennee@linaro.org>
STEXI and ETEXI is not used anymore since we switched to Sphinx.
Replace them in the example with SRST and ERST, too.
Message-Id: <20220506150146.564244-1-thuth@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Stefan Weil <sw@weilnetz.de>
Message-Id: <20211117210702.1393570-1-sw@weilnetz.de>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
[thuth: "what's" --> "what is" as suggested by philmd]
Signed-off-by: Thomas Huth <thuth@redhat.com>
We no longer wish to have commands implemented in HMP only. All commands
should start with a QMP implementation and the HMP merely be a shim
around this. To reduce the burden of implementing QMP commands where
there is low expectation of machine usage, requirements for QAPI
modelling are relaxed provided the command is under the "x-" name
prefix.
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
This illustrates how to add a QMP command returning unstructured text,
following the guidelines added in the previous patch. The example uses
a simplified version of 'info roms'.
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Traditionally we have required that newly added QMP commands will model
any returned data using fine grained QAPI types. This is good for
commands that are intended to be consumed by machines, where clear data
representation is very important. Commands that don't satisfy this have
generally been added to HMP only.
In effect the decision of whether to add a new command to QMP vs HMP has
been used as a proxy for the decision of whether the cost of designing a
fine grained QAPI type is justified by the potential benefits.
As a result the commands present in QMP and HMP are non-overlapping
sets, although HMP comamnds can be accessed indirectly via the QMP
command 'human-monitor-command'.
One of the downsides of 'human-monitor-command' is that the QEMU monitor
APIs remain tied into various internal parts of the QEMU code. For
example any exclusively HMP command will need to use 'monitor_printf'
to get data out. It would be desirable to be able to fully isolate the
monitor implementation from QEMU internals, however, this is only
possible if all commands are exclusively based on QAPI with direct
QMP exposure.
The way to achieve this desired end goal is to finese the requirements
for QMP command design. For cases where the output of a command is only
intended for human consumption, it is reasonable to want to simplify
the implementation by returning a plain string containing formatted
data instead of designing a fine grained QAPI data type. This can be
permitted if-and-only-if the command is exposed under the 'x-' name
prefix. This indicates that the command data format is liable to
future change and that it is not following QAPI design best practice.
The poster child example for this would be the 'info registers' HMP
command which returns printf formatted data representing CPU state.
This information varies enourmously across target architectures and
changes relatively frequently as new CPU features are implemented.
It is there as debugging data for human operators, and any machine
usage would treat it as an opaque blob. It is thus reasonable to
expose this in QMP as 'x-query-registers' returning a 'str' field.
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Best practice is to use the 'hmp_handle_error' function, not
'monitor_printf' or 'error_report_err'. This ensures that the
message always gets an 'Error: ' prefix, distinguishing it
from normal command output.
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
The new headings reflect the intended structure of the document and will
better suit additions that follow.
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
The file already covers writing HMP commands, in addition to
the QMP commands, so it deserves a more general name.
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
