qemu-img: conditionally zero out target on convert
If the target has_zero_init = 0, but supports efficiently
writing zeroes by unmapping we call bdrv_make_zero to
avoid fully allocating the target. This currently works
only for iscsi. It can be extended to raw with
BLKDISCARDZEROES for example.
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/qemu-img.c b/qemu-img.c
index cc3fed7..dc0c2f0 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1355,7 +1355,7 @@
}
}
- flags = BDRV_O_RDWR;
+ flags = min_sparse ? (BDRV_O_RDWR | BDRV_O_UNMAP) : BDRV_O_RDWR;
ret = bdrv_parse_cache_flags(cache, &flags);
if (ret < 0) {
error_report("Invalid cache option: %s", cache);
@@ -1471,6 +1471,14 @@
} else {
int has_zero_init = min_sparse ? bdrv_has_zero_init(out_bs) : 0;
+ if (!has_zero_init && bdrv_can_write_zeroes_with_unmap(out_bs)) {
+ ret = bdrv_make_zero(out_bs, BDRV_REQ_MAY_UNMAP);
+ if (ret < 0) {
+ goto out;
+ }
+ has_zero_init = 1;
+ }
+
sector_num = 0; // total number of sectors converted so far
nb_sectors = total_sectors - sector_num;
if (nb_sectors != 0) {
