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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
209 lines
5.1 KiB
C
209 lines
5.1 KiB
C
/*
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* Dealloc Visitor
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*
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* Copyright IBM, Corp. 2011
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*
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* Authors:
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* Michael Roth <mdroth@linux.vnet.ibm.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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#include "qemu/osdep.h"
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#include "qapi/error.h"
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#include "qapi/dealloc-visitor.h"
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#include "qemu/queue.h"
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#include "qemu-common.h"
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#include "qapi/qmp/types.h"
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#include "qapi/visitor-impl.h"
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typedef struct StackEntry
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{
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void *value;
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bool is_list_head;
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QTAILQ_ENTRY(StackEntry) node;
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} StackEntry;
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struct QapiDeallocVisitor
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{
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Visitor visitor;
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QTAILQ_HEAD(, StackEntry) stack;
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bool is_list_head;
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};
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static QapiDeallocVisitor *to_qov(Visitor *v)
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{
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return container_of(v, QapiDeallocVisitor, visitor);
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}
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static void qapi_dealloc_push(QapiDeallocVisitor *qov, void *value)
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{
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StackEntry *e = g_malloc0(sizeof(*e));
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e->value = value;
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/* see if we're just pushing a list head tracker */
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if (value == NULL) {
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e->is_list_head = true;
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}
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QTAILQ_INSERT_HEAD(&qov->stack, e, node);
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}
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static void *qapi_dealloc_pop(QapiDeallocVisitor *qov)
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{
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StackEntry *e = QTAILQ_FIRST(&qov->stack);
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QObject *value;
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QTAILQ_REMOVE(&qov->stack, e, node);
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value = e->value;
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g_free(e);
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return value;
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}
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static void qapi_dealloc_start_struct(Visitor *v, const char *name, void **obj,
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size_t unused, Error **errp)
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{
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QapiDeallocVisitor *qov = to_qov(v);
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qapi_dealloc_push(qov, obj);
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}
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static void qapi_dealloc_end_struct(Visitor *v, Error **errp)
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{
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QapiDeallocVisitor *qov = to_qov(v);
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void **obj = qapi_dealloc_pop(qov);
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if (obj) {
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g_free(*obj);
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}
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}
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static void qapi_dealloc_start_implicit_struct(Visitor *v,
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void **obj,
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size_t size,
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Error **errp)
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{
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QapiDeallocVisitor *qov = to_qov(v);
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qapi_dealloc_push(qov, obj);
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}
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static void qapi_dealloc_end_implicit_struct(Visitor *v)
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{
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QapiDeallocVisitor *qov = to_qov(v);
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void **obj = qapi_dealloc_pop(qov);
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if (obj) {
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g_free(*obj);
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}
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}
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static void qapi_dealloc_start_list(Visitor *v, const char *name, Error **errp)
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{
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QapiDeallocVisitor *qov = to_qov(v);
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qapi_dealloc_push(qov, NULL);
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}
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static GenericList *qapi_dealloc_next_list(Visitor *v, GenericList **listp,
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size_t size)
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{
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GenericList *list = *listp;
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QapiDeallocVisitor *qov = to_qov(v);
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StackEntry *e = QTAILQ_FIRST(&qov->stack);
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if (e && e->is_list_head) {
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e->is_list_head = false;
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return list;
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}
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if (list) {
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list = list->next;
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g_free(*listp);
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return list;
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}
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return NULL;
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}
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static void qapi_dealloc_end_list(Visitor *v)
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{
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QapiDeallocVisitor *qov = to_qov(v);
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void *obj = qapi_dealloc_pop(qov);
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assert(obj == NULL); /* should've been list head tracker with no payload */
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}
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static void qapi_dealloc_type_str(Visitor *v, const char *name, char **obj,
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Error **errp)
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{
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if (obj) {
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g_free(*obj);
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}
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}
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static void qapi_dealloc_type_int64(Visitor *v, const char *name, int64_t *obj,
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Error **errp)
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{
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}
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static void qapi_dealloc_type_uint64(Visitor *v, const char *name,
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uint64_t *obj, Error **errp)
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{
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}
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static void qapi_dealloc_type_bool(Visitor *v, const char *name, bool *obj,
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Error **errp)
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{
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}
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static void qapi_dealloc_type_number(Visitor *v, const char *name, double *obj,
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Error **errp)
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{
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}
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static void qapi_dealloc_type_anything(Visitor *v, const char *name,
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QObject **obj, Error **errp)
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{
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if (obj) {
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qobject_decref(*obj);
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}
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}
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static void qapi_dealloc_type_size(Visitor *v, const char *name, uint64_t *obj,
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Error **errp)
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{
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}
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Visitor *qapi_dealloc_get_visitor(QapiDeallocVisitor *v)
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{
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return &v->visitor;
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}
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void qapi_dealloc_visitor_cleanup(QapiDeallocVisitor *v)
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{
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g_free(v);
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}
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QapiDeallocVisitor *qapi_dealloc_visitor_new(void)
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{
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QapiDeallocVisitor *v;
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v = g_malloc0(sizeof(*v));
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v->visitor.type = VISITOR_DEALLOC;
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v->visitor.start_struct = qapi_dealloc_start_struct;
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v->visitor.end_struct = qapi_dealloc_end_struct;
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v->visitor.start_implicit_struct = qapi_dealloc_start_implicit_struct;
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v->visitor.end_implicit_struct = qapi_dealloc_end_implicit_struct;
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v->visitor.start_list = qapi_dealloc_start_list;
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v->visitor.next_list = qapi_dealloc_next_list;
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v->visitor.end_list = qapi_dealloc_end_list;
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v->visitor.type_int64 = qapi_dealloc_type_int64;
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v->visitor.type_uint64 = qapi_dealloc_type_uint64;
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v->visitor.type_bool = qapi_dealloc_type_bool;
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v->visitor.type_str = qapi_dealloc_type_str;
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v->visitor.type_number = qapi_dealloc_type_number;
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v->visitor.type_any = qapi_dealloc_type_anything;
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v->visitor.type_size = qapi_dealloc_type_size;
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QTAILQ_INIT(&v->stack);
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return v;
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}
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