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 <f...@redhat.com> --- v2: Use stack allocated buffer. [Eric] Fix return value. (Keep qemu_write_full instead of switching to qemu_pwritev because the former handles short writes.) Fix typo "qemu-img". [Changlong] --- block/file-posix.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/block/file-posix.c b/block/file-posix.c index f4de022ae0..a63bbf2b90 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -2703,6 +2703,16 @@ static int hdev_create(const char *filename, QemuOpts *opts, ret = -ENOSPC; } + if (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; } -- 2.13.4