error_propagate_prepend() "behaves like error_prepend()", and
error_prepend() uses "formatting @fmt, ... like printf()".
error_prepend() checks its format string argument, but
error_propagate_prepend() does not. Fix by addint the format
attribute to error_propagate_prepend() and error_vprepend().
This would have caught the bug fixed in the previous commit.
Missed in commit 4b5766488f "error: Fix use of error_prepend() with
&error_fatal, &error_abort".
Inspired-by: Stefan Weil <sw@weilnetz.de>
Suggested-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200723171205.14949-1-philmd@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Commit message tweaked]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Script adds ERRP_GUARD() macro invocations where appropriate and
does corresponding changes in code (look for details in
include/qapi/error.h)
Usage example:
spatch --sp-file scripts/coccinelle/errp-guard.cocci \
--macro-file scripts/cocci-macro-file.h --in-place --no-show-diff \
--max-width 80 FILES...
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200707165037.1026246-3-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[ERRP_AUTO_PROPAGATE() renamed to ERRP_GUARD(), and
auto-propagated-errp.cocci to errp-guard.cocci]
Introduce a new ERRP_GUARD() macro, to be used at start of functions
with an errp OUT parameter.
It has three goals:
1. Fix issue with error_fatal and error_prepend/error_append_hint: the
user can't see this additional information, because exit() happens in
error_setg earlier than information is added. [Reported by Greg Kurz]
2. Fix issue with error_abort and error_propagate: when we wrap
error_abort by local_err+error_propagate, the resulting coredump will
refer to error_propagate and not to the place where error happened.
(the macro itself doesn't fix the issue, but it allows us to [3.] drop
the local_err+error_propagate pattern, which will definitely fix the
issue) [Reported by Kevin Wolf]
3. Drop local_err+error_propagate pattern, which is used to workaround
void functions with errp parameter, when caller wants to know resulting
status. (Note: actually these functions could be merely updated to
return int error code).
To achieve these goals, later patches will add invocations
of this macro at the start of functions with either use
error_prepend/error_append_hint (solving 1) or which use
local_err+error_propagate to check errors, switching those
functions to use *errp instead (solving 2 and 3).
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
[Merge comments properly with recent commit "error: Document Error API
usage rules", and edit for clarity. Put ERRP_AUTO_PROPAGATE() before
its helpers, and touch up style. Tweak commit message.]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200707165037.1026246-2-armbru@redhat.com>
[Rename ERRP_AUTO_PROPAGATE() to ERRP_GUARD(), tweak commit message
again]
This merely codifies existing practice, with one exception: the rule
advising against returning void, where existing practice is mixed.
When the Error API was created, we adopted the (unwritten) rule to
return void when the function returns no useful value on success,
unlike GError, which recommends to return true on success and false on
error then.
When a function returns a distinct error value, say false, a checked
call that passes the error up looks like
if (!frobnicate(..., errp)) {
handle the error...
}
When it returns void, we need
Error *err = NULL;
frobnicate(..., &err);
if (err) {
handle the error...
error_propagate(errp, err);
}
Not only is this more verbose, it also creates an Error object even
when @errp is null, &error_abort or &error_fatal.
People got tired of the additional boilerplate, and started to ignore
the unwritten rule. The result is confusion among developers about
the preferred usage.
Make the rule advising against returning void official by putting it
in writing. This will hopefully reduce confusion.
Update the examples accordingly.
The remainder of this series will update a substantial amount of code
to honor the rule.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <20200707160613.848843-4-armbru@redhat.com>
[Tweak prose as per advice from Eric]
The previous few commits have made this more obvious, and removed the
one exception. Time to clarify the documentation, and drop dead error
checking.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200424084338.26803-13-armbru@redhat.com>
The contract demands v->start_alternate() for input and dealloc
visitors, but visit_start_alternate() actually requires it for input
and clone visitors. Fix the contract, and delete superfluous
qapi_dealloc_start_alternate().
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200424084338.26803-8-armbru@redhat.com>
Mostly, Error ** is for returning error from the function, so the
callee sets it. However these three functions get already filled errp
parameter. They don't change the pointer itself, only change the
internal state of referenced Error object. So we can make it
Error *const * errp, to stress the behavior. It will also help
coccinelle script (in future) to distinguish such cases from common
errp usage.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20191205174635.18758-4-vsementsov@virtuozzo.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Commit message typo fixed]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
visit_next_list() returns non-null on success, null on failure. The
comment's phrasing "until NULL return or error occurs" is needlessly
confusing. Scratch the "or error occurs" part.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190802122325.16520-1-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
In my "build everything" tree, changing a type in qapi/common.json
triggers a recompile of some 3600 out of 6600 objects (not counting
tests and objects that don't depend on qemu/osdep.h).
One common dependency is QapiErrorClass: it's used only in in
qapi/error.h, which uses nothing else, and is widely included.
Move QapiErrorClass from common.json to new error.json. Touching
common.json now recompiles only some 2900 objects.
Cc: Eric Blake <eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190812052359.30071-4-armbru@redhat.com>
The qapi_event_send_FOO() functions emit events like this:
QMPEventFuncEmit emit;
emit = qmp_event_get_func_emit();
if (!emit) {
return;
}
qmp = qmp_event_build_dict("FOO");
[put event arguments into @qmp...]
emit(QAPI_EVENT_FOO, qmp);
The value of qmp_event_get_func_emit() depends only on the program:
* In qemu-system-FOO, it's always monitor_qapi_event_queue.
* In tests/test-qmp-event, it's always event_test_emit.
* In all other programs, it's always null.
This is exactly the kind of dependence the linker is supposed to
resolve; we don't actually need an indirection.
Note that things would fall apart if we linked more than one QAPI
schema into a single program: each set of qapi_event_send_FOO() uses
its own event enumeration, yet they share a single emit function.
Which takes the event enumeration as an argument. Which one if
there's more than one?
More seriously: how does this work even now? qemu-system-FOO wants
QAPIEvent, and passes a function taking that to
qmp_event_set_func_emit(). test-qmp-event wants test_QAPIEvent, and
passes a function taking that to qmp_event_set_func_emit().
It works by type trickery, of course:
typedef void (*QMPEventFuncEmit)(unsigned event, QDict *dict);
void qmp_event_set_func_emit(QMPEventFuncEmit emit);
QMPEventFuncEmit qmp_event_get_func_emit(void);
We use unsigned instead of the enumeration type. Relies on both
enumerations boiling down to unsigned, which happens to be true for
the compilers we use.
Clean this up as follows:
* Generate qapi_event_send_FOO() that call PREFIX_qapi_event_emit()
instead of the value of qmp_event_set_func_emit().
* Generate a prototype for PREFIX_qapi_event_emit() into
qapi-events.h.
* PREFIX_ is empty for qapi/qapi-schema.json, and test_ for
tests/qapi-schema/qapi-schema-test.json. It's qga_ for
qga/qapi-schema.json, and doc-good- for
tests/qapi-schema/doc-good.json, but those don't define any events.
* Rename monitor_qapi_event_queue() to qapi_event_emit() instead of
passing it to qmp_event_set_func_emit(). This takes care of
qemu-system-FOO.
* Rename event_test_emit() to test_qapi_event_emit() instead of
passing it to qmp_event_set_func_emit(). This takes care of
tests/test-qmp-event.
* Add a qapi_event_emit() that does nothing to stubs/monitor.c. This
takes care of all other programs that link code emitting QMP events.
* Drop qmp_event_set_func_emit(), qmp_event_get_func_emit().
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20181218182234.28876-3-armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
[Commit message typos fixed]
