From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:49812) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1goUqN-0006Fb-1m for qemu-devel@nongnu.org; Tue, 29 Jan 2019 09:58:38 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1goUXr-00007e-OV for qemu-devel@nongnu.org; Tue, 29 Jan 2019 09:39:29 -0500 From: Vladimir Sementsov-Ogievskiy Date: Tue, 29 Jan 2019 17:37:59 +0300 Message-Id: <20190129143800.88563-2-vsementsov@virtuozzo.com> In-Reply-To: <20190129143800.88563-1-vsementsov@virtuozzo.com> References: <20190129143800.88563-1-vsementsov@virtuozzo.com> Subject: [Qemu-devel] [PATCH 1/2] block: enhance QEMUIOVector structure List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-block@nongnu.org, qemu-devel@nongnu.org Cc: mreitz@redhat.com, kwolf@redhat.com, fam@euphon.net, stefanha@redhat.com, vsementsov@virtuozzo.com 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 | 41 ++++++++++++++++++++++++++++++++++++++++- 1 file changed, 40 insertions(+), 1 deletion(-) diff --git a/include/qemu/iov.h b/include/qemu/iov.h index 5f433c7768..f739cff97d 100644 --- a/include/qemu/iov.h +++ b/include/qemu/iov.h @@ -134,9 +134,48 @@ 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. + */ + union { + struct { + void *__unused_iov_base; + size_t size; + }; + struct iovec local_iov; + }; } QEMUIOVector; +G_STATIC_ASSERT(offsetof(QEMUIOVector, size) == + offsetof(QEMUIOVector, local_iov.iov_len)); +G_STATIC_ASSERT(sizeof(((QEMUIOVector *)NULL)->size) == + sizeof(((QEMUIOVector *)NULL)->local_iov.iov_len)); + +#define QEMU_IOVEC_INIT_BUF(self, buf, len) \ +{ \ + .iov = &(self).local_iov, \ + .niov = 1, \ + .nalloc = -1, \ + .local_iov = { \ + .iov_base = (void *)(buf), \ + .iov_len = len \ + } \ +} + +static inline void qemu_iovec_init_buf(QEMUIOVector *qiov, + void *buf, size_t len) +{ + *qiov = (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 niov); void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len); -- 2.18.0