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e65d89bf1a
By sticking the next pointer first, we don't need a union with
64-bit padding for smaller types. On 32-bit platforms, this
can reduce the size of uint8List from 16 bytes (or 12, depending
on whether 64-bit ints can tolerate 4-byte alignment) down to 8.
It has no effect on 64-bit platforms (where alignment still
dictates a 16-byte struct); but fewer anonymous unions is still
a win in my book.
It requires visit_next_list() to gain a size parameter, to know
what size element to allocate; comparable to the size parameter
of visit_start_struct().
I debated about going one step further, to allow for fewer casts,
by doing:
typedef GenericList GenericList;
struct GenericList {
GenericList *next;
};
struct FooList {
GenericList base;
Foo *value;
};
so that you convert to 'GenericList *' by '&foolist->base', and
back by 'container_of(generic, GenericList, base)' (as opposed to
the existing '(GenericList *)foolist' and '(FooList *)generic').
But doing that would require hoisting the declaration of
GenericList prior to inclusion of qapi-types.h, rather than its
current spot in visitor.h; it also makes iteration a bit more
verbose through 'foolist->base.next' instead of 'foolist->next'.
Note that for lists of objects, the 'value' payload is still
hidden behind a boxed pointer. Someday, it would be nice to do:
struct FooList {
FooList *next;
Foo value;
};
for one less level of malloc for each list element. This patch
is a step in that direction (now that 'next' is no longer at a
fixed non-zero offset within the struct, we can store more than
just a pointer's-worth of data as the value payload), but the
actual conversion would be a task for another series, as it will
touch a lot of code.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1455778109-6278-10-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
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| .. | ||
| kvm | ||
| qemu-guest-agent | ||
| qemugdb | ||
| qmp | ||
| tracetool | ||
| analyse-9p-simpletrace.py | ||
| analyze-migration.py | ||
| check-qerror.sh | ||
| checkpatch.pl | ||
| clean-includes | ||
| cleanup-trace-events.pl | ||
| cocci-macro-file.h | ||
| coverity-model.c | ||
| create_config | ||
| disas-objdump.pl | ||
| dump-guest-memory.py | ||
| extract-vsssdk-headers | ||
| feature_to_c.sh | ||
| get_maintainer.pl | ||
| gtester-cat | ||
| hxtool | ||
| make-release | ||
| make_device_config.sh | ||
| ordereddict.py | ||
| qapi-commands.py | ||
| qapi-event.py | ||
| qapi-introspect.py | ||
| qapi-types.py | ||
| qapi-visit.py | ||
| qapi.py | ||
| qemu-binfmt-conf.sh | ||
| qemu-gdb.py | ||
| qtest.py | ||
| refresh-pxe-roms.sh | ||
| shaderinclude.pl | ||
| signrom.py | ||
| simpletrace.py | ||
| switch-timer-api | ||
| texi2pod.pl | ||
| tracetool.py | ||
| update-linux-headers.sh | ||
| vmstate-static-checker.py | ||