From e65d89bf1a4484e0db0f3dc820a8b209f2fb1e8b Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Wed, 17 Feb 2016 23:48:23 -0700 Subject: 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 Message-Id: <1455778109-6278-10-git-send-email-eblake@redhat.com> Signed-off-by: Markus Armbruster --- qapi/opts-visitor.c | 4 ++-- qapi/qapi-dealloc-visitor.c | 3 ++- qapi/qapi-visit-core.c | 5 +++-- qapi/qmp-input-visitor.c | 5 +++-- qapi/qmp-output-visitor.c | 3 ++- qapi/string-input-visitor.c | 4 ++-- qapi/string-output-visitor.c | 2 +- 7 files changed, 15 insertions(+), 11 deletions(-) (limited to 'qapi') diff --git a/qapi/opts-visitor.c b/qapi/opts-visitor.c index ae5b9553fa..73e4acea7b 100644 --- a/qapi/opts-visitor.c +++ b/qapi/opts-visitor.c @@ -215,7 +215,7 @@ opts_start_list(Visitor *v, const char *name, Error **errp) 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; @@ -258,7 +258,7 @@ opts_next_list(Visitor *v, GenericList **list) abort(); } - *link = g_malloc0(sizeof **link); + *link = g_malloc0(size); return *link; } diff --git a/qapi/qapi-dealloc-visitor.c b/qapi/qapi-dealloc-visitor.c index 2659d3fcca..6667e8ca43 100644 --- a/qapi/qapi-dealloc-visitor.c +++ b/qapi/qapi-dealloc-visitor.c @@ -100,7 +100,8 @@ static void qapi_dealloc_start_list(Visitor *v, const char *name, Error **errp) 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); diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c index f856286461..b4a0f21b36 100644 --- a/qapi/qapi-visit-core.c +++ b/qapi/qapi-visit-core.c @@ -50,9 +50,10 @@ void visit_start_list(Visitor *v, const char *name, Error **errp) 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) diff --git a/qapi/qmp-input-visitor.c b/qapi/qmp-input-visitor.c index 2f48b95515..26216604cc 100644 --- a/qapi/qmp-input-visitor.c +++ b/qapi/qmp-input-visitor.c @@ -165,7 +165,8 @@ static void qmp_input_start_list(Visitor *v, const char *name, Error **errp) 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; @@ -184,7 +185,7 @@ static GenericList *qmp_input_next_list(Visitor *v, GenericList **list) return NULL; } - entry = g_malloc0(sizeof(*entry)); + entry = g_malloc0(size); if (first) { *list = entry; } else { diff --git a/qapi/qmp-output-visitor.c b/qapi/qmp-output-visitor.c index f47eefa626..d44c676317 100644 --- a/qapi/qmp-output-visitor.c +++ b/qapi/qmp-output-visitor.c @@ -126,7 +126,8 @@ static void qmp_output_start_list(Visitor *v, const char *name, Error **errp) 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); diff --git a/qapi/string-input-visitor.c b/qapi/string-input-visitor.c index 18b9339768..59eb5dc4e3 100644 --- a/qapi/string-input-visitor.c +++ b/qapi/string-input-visitor.c @@ -139,7 +139,7 @@ start_list(Visitor *v, const char *name, Error **errp) } } -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; @@ -173,7 +173,7 @@ static GenericList *next_list(Visitor *v, GenericList **list) link = &(*list)->next; } - *link = g_malloc0(sizeof **link); + *link = g_malloc0(size); return *link; } diff --git a/qapi/string-output-visitor.c b/qapi/string-output-visitor.c index b980bd3265..c2e5c5b92b 100644 --- a/qapi/string-output-visitor.c +++ b/qapi/string-output-visitor.c @@ -276,7 +276,7 @@ start_list(Visitor *v, const char *name, Error **errp) 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; -- cgit v1.2.3-55-g7522