From nobody Sun Feb 8 11:15:14 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=virtuozzo.com Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 154953564051775.00672972339964; Thu, 7 Feb 2019 02:34:00 -0800 (PST) Received: from localhost ([127.0.0.1]:37382 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1grh0I-0001AV-D1 for importer@patchew.org; Thu, 07 Feb 2019 05:33:58 -0500 Received: from eggs.gnu.org ([209.51.188.92]:37037) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1grgru-0002z6-Ko for qemu-devel@nongnu.org; Thu, 07 Feb 2019 05:25:19 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1grgrt-00025M-O3 for qemu-devel@nongnu.org; Thu, 07 Feb 2019 05:25:18 -0500 Received: from relay.sw.ru ([185.231.240.75]:43058) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1grgrt-0001dX-FO; Thu, 07 Feb 2019 05:25:17 -0500 Received: from [10.28.8.145] (helo=kvm.sw.ru) by relay.sw.ru with esmtp (Exim 4.91) (envelope-from ) id 1grgrO-0005bY-GD; Thu, 07 Feb 2019 13:24:46 +0300 From: Vladimir Sementsov-Ogievskiy To: qemu-devel@nongnu.org, qemu-block@nongnu.org Date: Thu, 7 Feb 2019 13:24:29 +0300 Message-Id: <20190207102445.71998-2-vsementsov@virtuozzo.com> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20190207102445.71998-1-vsementsov@virtuozzo.com> References: <20190207102445.71998-1-vsementsov@virtuozzo.com> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 185.231.240.75 Subject: [Qemu-devel] [PATCH v3 01/17] block: enhance QEMUIOVector structure X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: fam@euphon.net, kwolf@redhat.com, vsementsov@virtuozzo.com, quintela@redhat.com, jcody@redhat.com, dgilbert@redhat.com, mreitz@redhat.com, stefanha@redhat.com, den@openvz.org, jsnow@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Add a possibility of embedded iovec, for cases when we need only one local iov. Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Eric Blake --- include/qemu/iov.h | 64 ++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 62 insertions(+), 2 deletions(-) diff --git a/include/qemu/iov.h b/include/qemu/iov.h index 5f433c7768..034b9ae080 100644 --- a/include/qemu/iov.h +++ b/include/qemu/iov.h @@ -133,10 +133,70 @@ size_t iov_discard_back(struct iovec *iov, unsigned i= nt *iov_cnt, typedef struct QEMUIOVector { struct iovec *iov; int niov; - int nalloc; - size_t size; + + /* + * For external @iov (qemu_iovec_init_external()) or allocated @iov + * (qemu_iovec_init()), @size is the cumulative size of iovecs and + * @local_iov is invalid and unused. + * + * For embedded @iov (QEMU_IOVEC_INIT_BUF() or qemu_iovec_init_buf()), + * @iov is equal to &@local_iov, and @size is valid, as it has same + * offset and type as @local_iov.iov_len, which is guaranteed by + * static assertion below. + * + * @nalloc is always valid and is -1 both for embedded and external + * cases. It is included in the union only to ensure the padding prior + * to the @size field will not result in a 0-length array. + */ + union { + struct { + int nalloc; + struct iovec local_iov; + }; + struct { + char __pad[sizeof(int) + offsetof(struct iovec, iov_len)]; + size_t size; + }; + }; } QEMUIOVector; =20 +QEMU_BUILD_BUG_ON(offsetof(QEMUIOVector, size) !=3D + offsetof(QEMUIOVector, local_iov.iov_len)); + +#define QEMU_IOVEC_INIT_BUF(self, buf, len) \ +{ \ + .iov =3D &(self).local_iov, \ + .niov =3D 1, \ + .nalloc =3D -1, \ + .local_iov =3D { \ + .iov_base =3D (void *)(buf), /* cast away const */ \ + .iov_len =3D (len), \ + }, \ +} + +/* + * qemu_iovec_init_buf + * + * Initialize embedded QEMUIOVector. + * + * Note: "const" is used over @buf pointer to make it simple to pass + * const pointers, appearing in read functions. Then this "const" is + * casted away by QEMU_IOVEC_INIT_BUF(). + */ +static inline void qemu_iovec_init_buf(QEMUIOVector *qiov, + const void *buf, size_t len) +{ + *qiov =3D (QEMUIOVector) QEMU_IOVEC_INIT_BUF(*qiov, buf, len); +} + +static inline void *qemu_iovec_get_buf(QEMUIOVector *qiov) +{ + /* Only supports embedded iov */ + assert(qiov->niov =3D=3D -1 && qiov->iov =3D=3D &(qiov->local_iov)); + + return qiov->local_iov.iov_base; +} + void qemu_iovec_init(QEMUIOVector *qiov, int alloc_hint); void qemu_iovec_init_external(QEMUIOVector *qiov, struct iovec *iov, int n= iov); void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len); --=20 2.18.0