From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:32828) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dwqkQ-0001Qg-Am for qemu-devel@nongnu.org; Tue, 26 Sep 2017 10:22:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dwqkK-0005Kk-OX for qemu-devel@nongnu.org; Tue, 26 Sep 2017 10:22:06 -0400 From: Kevin Wolf Date: Tue, 26 Sep 2017 16:21:12 +0200 Message-Id: <20170926142133.2498-4-kwolf@redhat.com> In-Reply-To: <20170926142133.2498-1-kwolf@redhat.com> References: <20170926142133.2498-1-kwolf@redhat.com> Subject: [Qemu-devel] [PULL 03/24] file-posix: Clear out first sector in hdev_create List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-block@nongnu.org Cc: kwolf@redhat.com, peter.maydell@linaro.org, qemu-devel@nongnu.org From: Fam Zheng People get surprised when, after "qemu-img create -f raw /dev/sdX", they still see qcow2 with "qemu-img info", if previously the bdev had a qcow2 header. While this is natural because raw doesn't need to write any magic bytes during creation, hdev_create is free to clear out the first sector to make sure the stale qcow2 header doesn't cause such confusion. Signed-off-by: Fam Zheng Signed-off-by: Kevin Wolf --- block/file-posix.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/block/file-posix.c b/block/file-posix.c index ab12a2b591..36ee89e940 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -2730,6 +2730,16 @@ static int hdev_create(const char *filename, QemuOpts *opts, ret = -ENOSPC; } + if (!ret && total_size) { + uint8_t buf[BDRV_SECTOR_SIZE] = { 0 }; + int64_t zero_size = MIN(BDRV_SECTOR_SIZE, total_size); + if (lseek(fd, 0, SEEK_SET) == -1) { + ret = -errno; + } else { + ret = qemu_write_full(fd, buf, zero_size); + ret = ret == zero_size ? 0 : -errno; + } + } qemu_close(fd); return ret; } -- 2.13.5