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>
void (*start_list)(Visitor *v, const char *name, Error **errp);
/* Must be set */
- GenericList *(*next_list)(Visitor *v, GenericList **list);
+ GenericList *(*next_list)(Visitor *v, GenericList **list, size_t size);
/* Must be set */
void (*end_list)(Visitor *v);
#include "qapi/error.h"
#include <stdlib.h>
-typedef struct GenericList
-{
- union {
- void *value;
- uint64_t padding;
- };
+/* This struct is layout-compatible with all other *List structs
+ * created by the qapi generator. It is used as a typical
+ * singly-linked list. */
+typedef struct GenericList {
struct GenericList *next;
+ char padding[];
} GenericList;
void visit_start_struct(Visitor *v, const char *name, void **obj,
void visit_end_implicit_struct(Visitor *v);
void visit_start_list(Visitor *v, const char *name, Error **errp);
-GenericList *visit_next_list(Visitor *v, GenericList **list);
+GenericList *visit_next_list(Visitor *v, GenericList **list, size_t size);
void visit_end_list(Visitor *v);
/**
static GenericList *
-opts_next_list(Visitor *v, GenericList **list)
+opts_next_list(Visitor *v, GenericList **list, size_t size)
{
OptsVisitor *ov = to_ov(v);
GenericList **link;
abort();
}
- *link = g_malloc0(sizeof **link);
+ *link = g_malloc0(size);
return *link;
}
qapi_dealloc_push(qov, NULL);
}
-static GenericList *qapi_dealloc_next_list(Visitor *v, GenericList **listp)
+static GenericList *qapi_dealloc_next_list(Visitor *v, GenericList **listp,
+ size_t size)
{
GenericList *list = *listp;
QapiDeallocVisitor *qov = to_qov(v);
v->start_list(v, name, errp);
}
-GenericList *visit_next_list(Visitor *v, GenericList **list)
+GenericList *visit_next_list(Visitor *v, GenericList **list, size_t size)
{
- return v->next_list(v, list);
+ assert(list && size >= sizeof(GenericList));
+ return v->next_list(v, list, size);
}
void visit_end_list(Visitor *v)
qmp_input_push(qiv, qobj, errp);
}
-static GenericList *qmp_input_next_list(Visitor *v, GenericList **list)
+static GenericList *qmp_input_next_list(Visitor *v, GenericList **list,
+ size_t size)
{
QmpInputVisitor *qiv = to_qiv(v);
GenericList *entry;
return NULL;
}
- entry = g_malloc0(sizeof(*entry));
+ entry = g_malloc0(size);
if (first) {
*list = entry;
} else {
qmp_output_push(qov, list);
}
-static GenericList *qmp_output_next_list(Visitor *v, GenericList **listp)
+static GenericList *qmp_output_next_list(Visitor *v, GenericList **listp,
+ size_t size)
{
GenericList *list = *listp;
QmpOutputVisitor *qov = to_qov(v);
}
}
-static GenericList *next_list(Visitor *v, GenericList **list)
+static GenericList *next_list(Visitor *v, GenericList **list, size_t size)
{
StringInputVisitor *siv = to_siv(v);
GenericList **link;
link = &(*list)->next;
}
- *link = g_malloc0(sizeof **link);
+ *link = g_malloc0(size);
return *link;
}
sov->head = true;
}
-static GenericList *next_list(Visitor *v, GenericList **list)
+static GenericList *next_list(Visitor *v, GenericList **list, size_t size)
{
StringOutputVisitor *sov = to_sov(v);
GenericList *ret = NULL;
return mcgen('''
struct %(c_name)s {
- union {
- %(c_type)s value;
- uint64_t padding;
- };
%(c_name)s *next;
+ %(c_type)s value;
};
''',
c_name=c_name(name), c_type=element_type.c_type())
}
for (prev = (GenericList **)obj;
- !err && (i = visit_next_list(v, prev)) != NULL;
+ !err && (i = visit_next_list(v, prev, sizeof(**obj))) != NULL;
prev = &i) {
%(c_name)s *native_i = (%(c_name)s *)i;
visit_type_%(c_elt_type)s(v, NULL, &native_i->value, &err);
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