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3cf7b6dd3b
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.
Backports commit e65d89bf1a4484e0db0f3dc820a8b209f2fb1e8b from qemu
71 lines
2.3 KiB
C
71 lines
2.3 KiB
C
/*
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* Core Definitions for QAPI Visitor implementations
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*
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* Copyright (C) 2012-2016 Red Hat, Inc.
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*
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* Author: Paolo Bonizni <pbonzini@redhat.com>
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*
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* This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
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* See the COPYING.LIB file in the top-level directory.
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*
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*/
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#ifndef QAPI_VISITOR_IMPL_H
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#define QAPI_VISITOR_IMPL_H
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#include "qapi/error.h"
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#include "qapi/visitor.h"
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/*
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* There are three classes of visitors; setting the class determines
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* how QAPI enums are visited, as well as what additional restrictions
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* can be asserted.
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*/
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typedef enum VisitorType {
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VISITOR_INPUT,
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VISITOR_OUTPUT,
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VISITOR_DEALLOC,
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} VisitorType;
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struct Visitor
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{
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/* Must be set */
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void (*start_struct)(Visitor *v, const char *name, void **obj,
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size_t size, Error **errp);
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void (*end_struct)(Visitor *v, Error **errp);
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void (*start_implicit_struct)(Visitor *v, void **obj, size_t size,
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Error **errp);
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void (*end_implicit_struct)(Visitor *v);
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void (*start_list)(Visitor *v, const char *name, Error **errp);
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GenericList *(*next_list)(Visitor *v, GenericList **list, size_t size);
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void (*end_list)(Visitor *v);
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/* May be NULL; only needed for input visitors. */
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void (*get_next_type)(Visitor *v, const char *name, QType *type,
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bool promote_int, Error **errp);
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void (*type_int64)(Visitor *v, const char *name, int64_t *obj,
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Error **errp);
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/* Must be set. */
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void (*type_uint64)(Visitor *v, const char *name, uint64_t *obj,
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Error **errp);
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/* Optional; fallback is type_uint64(). */
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void (*type_size)(Visitor *v, const char *name, uint64_t *obj,
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Error **errp);
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/* Must be set. */
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void (*type_bool)(Visitor *v, const char *name, bool *obj, Error **errp);
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void (*type_str)(Visitor *v, const char *name, char **obj, Error **errp);
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void (*type_number)(Visitor *v, const char *name, double *obj,
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Error **errp);
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void (*type_any)(Visitor *v, const char *name, QObject **obj,
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Error **errp);
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/* May be NULL; most useful for input visitors. */
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void (*optional)(Visitor *v, const char *name, bool *present);
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/* Must be set */
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VisitorType type;
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};
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#endif
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