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Eric Blake 12dabf0640
qapi: Don't box struct branch of alternate
There's no reason to do two malloc's for an alternate type visiting
a QAPI struct; let's just inline the struct directly as the C union
branch of the struct.

Surprisingly, no clients were actually using the struct member prior
to this patch outside of the testsuite; an earlier patch in the series
added some testsuite coverage to make the effect of this patch more
obvious.

In qapi.py, c_type() gains a new is_unboxed flag to control when we
are emitting a C struct unboxed within the context of an outer
struct (different from our other two modes of usage with no flags
for normal local variable declarations, and with is_param for adding
'const' in a parameter list). I don't know if there is any more
pythonic way of collapsing the two flags into a single parameter,
as we never have a caller setting both flags at once.

Ultimately, we want to also unbox branches for QAPI unions, but as
that touches a lot more client code, it is better as separate
patches. But since unions and alternates share gen_variants(), I
had to hack in a way to test if we are visiting an alternate type
for setting the is_unboxed flag: look for a non-object branch.
This works because alternates have at least two branches, with at
most one object branch, while unions have only object branches.
The hack will go away in a later patch.

The generated code difference to qapi-types.h is relatively small:

| struct BlockdevRef {
| QType type;
| union { /* union tag is @type */
| void *data;
|- BlockdevOptions *definition;
|+ BlockdevOptions definition;
| char *reference;
| } u;
| };

The corresponding spot in qapi-visit.c calls visit_type_FOO(), which
first calls visit_start_struct() to allocate or deallocate the member
and handle a layer of {} from the JSON stream, then visits the
members. To peel off the indirection and the memory management that
comes with it, we inline this call, then suppress allocation /
deallocation by passing NULL to visit_start_struct(), and adjust the
member visit:

| switch ((*obj)->type) {
| case QTYPE_QDICT:
|- visit_type_BlockdevOptions(v, name, &(*obj)->u.definition, &err);
|+ visit_start_struct(v, name, NULL, 0, &err);
|+ if (err) {
|+ break;
|+ }
|+ visit_type_BlockdevOptions_fields(v, &(*obj)->u.definition, &err);
|+ error_propagate(errp, err);
|+ err = NULL;
|+ visit_end_struct(v, &err);
| break;
| case QTYPE_QSTRING:
| visit_type_str(v, name, &(*obj)->u.reference, &err);

The visit of non-object fields is unchanged.

Backports commit becceedc4d9bc1435099c90a0514945a89844d3a from qemu
2018-02-20 16:32:11 -05:00
bindings
docs
include include: Move RAMList to ramlist.h 2018-02-20 08:47:51 -05:00
msvc qapi-visit: Less indirection in visit_type_Foo_fields() 2018-02-20 16:00:37 -05:00
qemu qapi: Don't box struct branch of alternate 2018-02-20 16:32:11 -05:00
samples
tests
.appveyor.yml
.gitignore
.travis.yml
AUTHORS.TXT
Brewfile
ChangeLog
config.mk
COPYING
COPYING.LGPL2
COPYING_GLIB
CREDITS.TXT
install-cmocka-linux.sh
list.c
make.sh
Makefile crypto: introduce new module for computing hash digests 2018-02-17 15:23:17 -05:00
msvc.bat
pkgconfig.mk
README.md
uc.c uc: Handle freeing of multiple address spaces 2018-02-18 21:36:50 -05:00
windows_export.bat

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