d9f62dde13
The semantics of the list visit are somewhat baroque, with the
following pseudocode when FooList is used:
start()
for (prev = head; cur = next(prev); prev = &cur) {
visit(&cur->value)
}
Note that these semantics (advance before visit) requires that
the first call to next() return the list head, while all other
calls return the next element of the list; that is, every visitor
implementation is required to track extra state to decide whether
to return the input as-is, or to advance. It also requires an
argument of 'GenericList **' to next(), solely because the first
iteration might need to modify the caller's GenericList head, so
that all other calls have to do a layer of dereferencing.
Thankfully, we only have two uses of list visits in the entire
code base: one in spapr_drc (which completely avoids
visit_next_list(), feeding in integers from a different source
than uint8List), and one in qapi-visit.py. That is, all other
list visitors are generated in qapi-visit.c, and share the same
paradigm based on a qapi FooList type, so we can refactor how
lists are laid out with minimal churn among clients.
We can greatly simplify things by hoisting the special case
into the start() routine, and flipping the order in the loop
to visit before advance:
start(head)
for (tail = *head; tail; tail = next(tail)) {
visit(&tail->value)
}
With the simpler semantics, visitors have less state to track,
the argument to next() is reduced to 'GenericList *', and it
also becomes obvious whether an input visitor is allocating a
FooList during visit_start_list() (rather than the old way of
not knowing if an allocation happened until the first
visit_next_list()). As a minor drawback, we now allocate in
two functions instead of one, and have to pass the size to
both functions (unless we were to tweak the input visitors to
cache the size to start_list for reuse during next_list, but
that defeats the goal of less visitor state).
The signature of visit_start_list() is chosen to match
visit_start_struct(), with the new parameters after 'name'.
The spapr_drc case is a virtual visit, done by passing NULL for
list, similarly to how NULL is passed to visit_start_struct()
when a qapi type is not used in those visits. It was easy to
provide these semantics for qmp-output and dealloc visitors,
and a bit harder for qmp-input (several prerequisite patches
refactored things to make this patch straightforward). But it
turned out that the string and opts visitors munge enough other
state during visit_next_list() to make it easier to just
document and require a GenericList visit for now; an assertion
will remind us to adjust things if we need the semantics in the
future.
Several pre-requisite cleanup patches made the reshuffling of
the various visitors easier; particularly the qmp input visitor.
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1461879932-9020-24-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
185 lines
4.5 KiB
C
185 lines
4.5 KiB
C
/*
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* Dealloc Visitor
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*
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* Copyright (C) 2012-2016 Red Hat, Inc.
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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/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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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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};
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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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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)
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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_alternate(Visitor *v, const char *name,
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GenericAlternate **obj, size_t size,
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bool promote_int, 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_alternate(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,
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GenericList **list, size_t size,
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Error **errp)
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{
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}
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static GenericList *qapi_dealloc_next_list(Visitor *v, GenericList *tail,
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size_t size)
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{
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GenericList *next = tail->next;
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g_free(tail);
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return next;
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}
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static void qapi_dealloc_end_list(Visitor *v)
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{
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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_null(Visitor *v, const char *name, 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_alternate = qapi_dealloc_start_alternate;
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v->visitor.end_alternate = qapi_dealloc_end_alternate;
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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_null = qapi_dealloc_type_null;
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QTAILQ_INIT(&v->stack);
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return v;
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}
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