unicorn/qemu/qapi/qapi-dealloc-visitor.c
Eric Blake 3cf7b6dd3b
qapi: Adjust layout of FooList types
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
2018-02-23 14:49:06 -05:00

209 lines
5.1 KiB
C

/*
* Dealloc Visitor
*
* Copyright IBM, Corp. 2011
*
* Authors:
* Michael Roth <mdroth@linux.vnet.ibm.com>
*
* This work is licensed under the terms of the GNU LGPL, version 2.1 or later.
* See the COPYING.LIB file in the top-level directory.
*
*/
#include "qemu/osdep.h"
#include "qapi/error.h"
#include "qapi/dealloc-visitor.h"
#include "qemu/queue.h"
#include "qemu-common.h"
#include "qapi/qmp/types.h"
#include "qapi/visitor-impl.h"
typedef struct StackEntry
{
void *value;
bool is_list_head;
QTAILQ_ENTRY(StackEntry) node;
} StackEntry;
struct QapiDeallocVisitor
{
Visitor visitor;
QTAILQ_HEAD(, StackEntry) stack;
bool is_list_head;
};
static QapiDeallocVisitor *to_qov(Visitor *v)
{
return container_of(v, QapiDeallocVisitor, visitor);
}
static void qapi_dealloc_push(QapiDeallocVisitor *qov, void *value)
{
StackEntry *e = g_malloc0(sizeof(*e));
e->value = value;
/* see if we're just pushing a list head tracker */
if (value == NULL) {
e->is_list_head = true;
}
QTAILQ_INSERT_HEAD(&qov->stack, e, node);
}
static void *qapi_dealloc_pop(QapiDeallocVisitor *qov)
{
StackEntry *e = QTAILQ_FIRST(&qov->stack);
QObject *value;
QTAILQ_REMOVE(&qov->stack, e, node);
value = e->value;
g_free(e);
return value;
}
static void qapi_dealloc_start_struct(Visitor *v, const char *name, void **obj,
size_t unused, Error **errp)
{
QapiDeallocVisitor *qov = to_qov(v);
qapi_dealloc_push(qov, obj);
}
static void qapi_dealloc_end_struct(Visitor *v, Error **errp)
{
QapiDeallocVisitor *qov = to_qov(v);
void **obj = qapi_dealloc_pop(qov);
if (obj) {
g_free(*obj);
}
}
static void qapi_dealloc_start_implicit_struct(Visitor *v,
void **obj,
size_t size,
Error **errp)
{
QapiDeallocVisitor *qov = to_qov(v);
qapi_dealloc_push(qov, obj);
}
static void qapi_dealloc_end_implicit_struct(Visitor *v)
{
QapiDeallocVisitor *qov = to_qov(v);
void **obj = qapi_dealloc_pop(qov);
if (obj) {
g_free(*obj);
}
}
static void qapi_dealloc_start_list(Visitor *v, const char *name, Error **errp)
{
QapiDeallocVisitor *qov = to_qov(v);
qapi_dealloc_push(qov, NULL);
}
static GenericList *qapi_dealloc_next_list(Visitor *v, GenericList **listp,
size_t size)
{
GenericList *list = *listp;
QapiDeallocVisitor *qov = to_qov(v);
StackEntry *e = QTAILQ_FIRST(&qov->stack);
if (e && e->is_list_head) {
e->is_list_head = false;
return list;
}
if (list) {
list = list->next;
g_free(*listp);
return list;
}
return NULL;
}
static void qapi_dealloc_end_list(Visitor *v)
{
QapiDeallocVisitor *qov = to_qov(v);
void *obj = qapi_dealloc_pop(qov);
assert(obj == NULL); /* should've been list head tracker with no payload */
}
static void qapi_dealloc_type_str(Visitor *v, const char *name, char **obj,
Error **errp)
{
if (obj) {
g_free(*obj);
}
}
static void qapi_dealloc_type_int64(Visitor *v, const char *name, int64_t *obj,
Error **errp)
{
}
static void qapi_dealloc_type_uint64(Visitor *v, const char *name,
uint64_t *obj, Error **errp)
{
}
static void qapi_dealloc_type_bool(Visitor *v, const char *name, bool *obj,
Error **errp)
{
}
static void qapi_dealloc_type_number(Visitor *v, const char *name, double *obj,
Error **errp)
{
}
static void qapi_dealloc_type_anything(Visitor *v, const char *name,
QObject **obj, Error **errp)
{
if (obj) {
qobject_decref(*obj);
}
}
static void qapi_dealloc_type_size(Visitor *v, const char *name, uint64_t *obj,
Error **errp)
{
}
Visitor *qapi_dealloc_get_visitor(QapiDeallocVisitor *v)
{
return &v->visitor;
}
void qapi_dealloc_visitor_cleanup(QapiDeallocVisitor *v)
{
g_free(v);
}
QapiDeallocVisitor *qapi_dealloc_visitor_new(void)
{
QapiDeallocVisitor *v;
v = g_malloc0(sizeof(*v));
v->visitor.type = VISITOR_DEALLOC;
v->visitor.start_struct = qapi_dealloc_start_struct;
v->visitor.end_struct = qapi_dealloc_end_struct;
v->visitor.start_implicit_struct = qapi_dealloc_start_implicit_struct;
v->visitor.end_implicit_struct = qapi_dealloc_end_implicit_struct;
v->visitor.start_list = qapi_dealloc_start_list;
v->visitor.next_list = qapi_dealloc_next_list;
v->visitor.end_list = qapi_dealloc_end_list;
v->visitor.type_int64 = qapi_dealloc_type_int64;
v->visitor.type_uint64 = qapi_dealloc_type_uint64;
v->visitor.type_bool = qapi_dealloc_type_bool;
v->visitor.type_str = qapi_dealloc_type_str;
v->visitor.type_number = qapi_dealloc_type_number;
v->visitor.type_any = qapi_dealloc_type_anything;
v->visitor.type_size = qapi_dealloc_type_size;
QTAILQ_INIT(&v->stack);
return v;
}