From patchwork Thu Feb 18 06:48:23 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Blake X-Patchwork-Id: 8346691 Return-Path: X-Original-To: patchwork-qemu-devel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id E6677C0553 for ; Thu, 18 Feb 2016 06:55:34 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id EFE4320386 for ; Thu, 18 Feb 2016 06:55:33 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C69CE20384 for ; Thu, 18 Feb 2016 06:55:32 +0000 (UTC) Received: from localhost ([::1]:37715 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aWIUu-0001TF-1z for patchwork-qemu-devel@patchwork.kernel.org; Thu, 18 Feb 2016 01:55:32 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40270) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aWIOH-0005NM-6t for qemu-devel@nongnu.org; Thu, 18 Feb 2016 01:48:42 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aWIOE-00020h-Mk for qemu-devel@nongnu.org; Thu, 18 Feb 2016 01:48:41 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57127) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aWIOE-00020U-9d for qemu-devel@nongnu.org; Thu, 18 Feb 2016 01:48:38 -0500 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (Postfix) with ESMTPS id DD4A67F6A2; Thu, 18 Feb 2016 06:48:37 +0000 (UTC) Received: from red.redhat.com (ovpn-113-75.phx2.redhat.com [10.3.113.75]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u1I6mXAe023855; Thu, 18 Feb 2016 01:48:37 -0500 From: Eric Blake To: qemu-devel@nongnu.org Date: Wed, 17 Feb 2016 23:48:23 -0700 Message-Id: <1455778109-6278-10-git-send-email-eblake@redhat.com> In-Reply-To: <1455778109-6278-1-git-send-email-eblake@redhat.com> References: <1455778109-6278-1-git-send-email-eblake@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 209.132.183.28 Cc: armbru@redhat.com, Michael Roth Subject: [Qemu-devel] [PATCH v11 09/15] qapi: Adjust layout of FooList types X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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 --- v11: assert that size is sane, improve commit message v10: hoist earlier in series v9: no change v8: rebase to earlier changes v7: new patch; probably too invasive to be worth it, especially if we can't prove that our current size for uint8List is a bottleneck --- include/qapi/visitor.h | 13 ++++++------- include/qapi/visitor-impl.h | 2 +- scripts/qapi-types.py | 5 +---- scripts/qapi-visit.py | 2 +- qapi/qapi-visit-core.c | 5 +++-- qapi/opts-visitor.c | 4 ++-- qapi/qapi-dealloc-visitor.c | 3 ++- qapi/qmp-input-visitor.c | 5 +++-- qapi/qmp-output-visitor.c | 3 ++- qapi/string-input-visitor.c | 4 ++-- qapi/string-output-visitor.c | 2 +- 11 files changed, 24 insertions(+), 24 deletions(-) diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h index 5e581dc..8a2d5cc 100644 --- a/include/qapi/visitor.h +++ b/include/qapi/visitor.h @@ -19,13 +19,12 @@ #include "qapi/error.h" #include -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, @@ -36,7 +35,7 @@ void visit_start_implicit_struct(Visitor *v, void **obj, size_t size, 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); /** diff --git a/include/qapi/visitor-impl.h b/include/qapi/visitor-impl.h index ea252f8..7905a28 100644 --- a/include/qapi/visitor-impl.h +++ b/include/qapi/visitor-impl.h @@ -29,7 +29,7 @@ struct Visitor 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); diff --git a/scripts/qapi-types.py b/scripts/qapi-types.py index 7b0dca8..83f230a 100644 --- a/scripts/qapi-types.py +++ b/scripts/qapi-types.py @@ -26,11 +26,8 @@ def gen_array(name, element_type): 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()) diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py index 231e424..48ebd2b 100644 --- a/scripts/qapi-visit.py +++ b/scripts/qapi-visit.py @@ -173,7 +173,7 @@ void visit_type_%(c_name)s(Visitor *v, const char *name, %(c_name)s **obj, Error } 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); diff --git a/qapi/qapi-visit-core.c b/qapi/qapi-visit-core.c index f856286..b4a0f21 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/opts-visitor.c b/qapi/opts-visitor.c index ae5b955..73e4ace 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 2659d3f..6667e8c 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/qmp-input-visitor.c b/qapi/qmp-input-visitor.c index 2f48b95..2621660 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 f47eefa..d44c676 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 18b9339..59eb5dc 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 b980bd3..c2e5c5b 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;