qemu/qapi/qapi-dealloc-visitor.c

142 lines
3.6 KiB
C
Raw Normal View History

/*
* Dealloc Visitor
*
* Copyright (C) 2012-2016 Red Hat, Inc.
* 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/dealloc-visitor.h"
#include "qapi/qmp/qnull.h"
#include "qapi/visitor-impl.h"
struct QapiDeallocVisitor
{
Visitor visitor;
};
static void qapi_dealloc_start_struct(Visitor *v, const char *name, void **obj,
size_t unused, Error **errp)
{
}
2016-06-10 00:48:34 +08:00
static void qapi_dealloc_end_struct(Visitor *v, void **obj)
{
if (obj) {
g_free(*obj);
}
}
static void qapi_dealloc_start_alternate(Visitor *v, const char *name,
GenericAlternate **obj, size_t size,
Error **errp)
{
}
2016-06-10 00:48:34 +08:00
static void qapi_dealloc_end_alternate(Visitor *v, void **obj)
{
if (obj) {
g_free(*obj);
}
}
qapi: Simplify semantics of visit_next_list() 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>
2016-04-29 05:45:31 +08:00
static void qapi_dealloc_start_list(Visitor *v, const char *name,
GenericList **list, size_t size,
Error **errp)
{
}
qapi: Simplify semantics of visit_next_list() 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>
2016-04-29 05:45:31 +08:00
static GenericList *qapi_dealloc_next_list(Visitor *v, GenericList *tail,
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. 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>
2016-02-18 14:48:23 +08:00
size_t size)
{
qapi: Simplify semantics of visit_next_list() 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>
2016-04-29 05:45:31 +08:00
GenericList *next = tail->next;
g_free(tail);
return next;
}
2016-06-10 00:48:34 +08:00
static void qapi_dealloc_end_list(Visitor *v, void **obj)
{
}
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_unref(*obj);
}
}
static void qapi_dealloc_type_null(Visitor *v, const char *name,
QNull **obj, Error **errp)
2016-04-29 05:45:22 +08:00
{
if (obj) {
qobject_unref(*obj);
}
2016-04-29 05:45:22 +08:00
}
static void qapi_dealloc_free(Visitor *v)
{
g_free(container_of(v, QapiDeallocVisitor, visitor));
}
Visitor *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_alternate = qapi_dealloc_start_alternate;
v->visitor.end_alternate = qapi_dealloc_end_alternate;
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;
2016-04-29 05:45:22 +08:00
v->visitor.type_null = qapi_dealloc_type_null;
v->visitor.free = qapi_dealloc_free;
return &v->visitor;
}