From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59530) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dfiPF-0007TL-7Y for qemu-devel@nongnu.org; Thu, 10 Aug 2017 04:01:26 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dfiPE-0001bb-8Y for qemu-devel@nongnu.org; Thu, 10 Aug 2017 04:01:25 -0400 From: Fam Zheng Date: Thu, 10 Aug 2017 16:01:08 +0800 Message-Id: <20170810080108.31047-1-famz@redhat.com> Subject: [Qemu-devel] [PATCH] file-posix: Clear out first sector in hdev_create List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Kevin Wolf , Max Reitz , qemu-block@nongnu.org People get surprised when, after "qemu-imc 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 a confusion. Signed-off-by: Fam Zheng --- block/file-posix.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/block/file-posix.c b/block/file-posix.c index f4de022ae0..1d8ef6f873 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -2703,6 +2703,17 @@ static int hdev_create(const char *filename, QemuOpts *opts, ret = -ENOSPC; } + if (total_size) { + int64_t zero_size = MIN(BDRV_SECTOR_SIZE, total_size); + uint8_t *buf; + if (lseek(fd, 0, SEEK_SET) == -1) { + ret = -errno; + } else { + buf = g_malloc0(zero_size); + ret = qemu_write_full(fd, buf, zero_size); + g_free(buf); + } + } qemu_close(fd); return ret; } -- 2.13.3