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file-posix: Clear out first sector in hdev_create 

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 <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Fam Zheng 2017-09-08 17:44:57 +08:00 committed by Kevin Wolf
parent a16efd5340
commit 97ec9117c3
1 changed files with 10 additions and 0 deletions
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10
block/file-posix.c
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@ -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;
}