From nobody Fri Nov 7 23:00:33 2025 Delivered-To: importer@patchew.org Received-SPF: temperror (zoho.com: Error in retrieving data from DNS) 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=temperror (zoho.com: Error in retrieving data from DNS) 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 (209.51.188.17 [209.51.188.17]) by mx.zohomail.com with SMTPS id 1549472161494978.9785218208049; Wed, 6 Feb 2019 08:56:01 -0800 (PST) Received: from localhost ([127.0.0.1]:53856 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1grQUI-0002OT-E0 for importer@patchew.org; Wed, 06 Feb 2019 11:55:50 -0500 Received: from eggs.gnu.org ([209.51.188.92]:48345) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1grQSL-00010I-97 for qemu-devel@nongnu.org; Wed, 06 Feb 2019 11:53:50 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1grQSK-00027r-8O for qemu-devel@nongnu.org; Wed, 06 Feb 2019 11:53:49 -0500 Received: from relay.sw.ru ([185.231.240.75]:38120) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1grQSI-00025f-Dl; Wed, 06 Feb 2019 11:53:46 -0500 Received: from [10.28.8.145] (helo=kvm.sw.ru) by relay.sw.ru with esmtp (Exim 4.91) (envelope-from ) id 1grQSE-0002UR-Gk; Wed, 06 Feb 2019 19:53:42 +0300 From: Vladimir Sementsov-Ogievskiy To: qemu-devel@nongnu.org, qemu-block@nongnu.org Date: Wed, 6 Feb 2019 19:53:41 +0300 Message-Id: <20190206165342.219192-2-vsementsov@virtuozzo.com> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20190206165342.219192-1-vsementsov@virtuozzo.com> References: <20190206165342.219192-1-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 v2 1/2] 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: kwolf@redhat.com, fam@euphon.net, vsementsov@virtuozzo.com, mreitz@redhat.com, stefanha@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 --- include/qemu/iov.h | 47 ++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 45 insertions(+), 2 deletions(-) diff --git a/include/qemu/iov.h b/include/qemu/iov.h index 5f433c7768..3753b63558 100644 --- a/include/qemu/iov.h +++ b/include/qemu/iov.h @@ -133,10 +133,53 @@ 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 assertions below. + * + * @nalloc is valid always and is -1 both for embedded and external + * cases. It included into union only to make appropriate padding for + * @size field avoiding creation of 0-length array in the worst case. + */ + 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), \ + }, \ +} + +static inline void qemu_iovec_init_buf(QEMUIOVector *qiov, + void *buf, size_t len) +{ + *qiov =3D (QEMUIOVector) QEMU_IOVEC_INIT_BUF(*qiov, buf, len); +} + 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