@@ -3431,6 +3431,8 @@ static int img_rebase(int argc, char **argv)
}
for (offset = 0; offset < size; offset += n) {
+ bool buf_old_is_zero = false;
+
/* How many bytes can we handle with the next read? */
n = MIN(IO_BUF_SIZE, size - offset);
@@ -3451,6 +3453,7 @@ static int img_rebase(int argc, char **argv)
*/
if (offset >= old_backing_size) {
memset(buf_old, 0, n);
+ buf_old_is_zero = true;
} else {
if (offset + n > old_backing_size) {
n = old_backing_size - offset;
@@ -3486,8 +3489,12 @@ static int img_rebase(int argc, char **argv)
if (compare_buffers(buf_old + written, buf_new + written,
n - written, &pnum))
{
- ret = blk_pwrite(blk, offset + written,
- buf_old + written, pnum, 0);
+ if (buf_old_is_zero) {
+ ret = blk_pwrite_zeroes(blk, offset + written, pnum, 0);
+ } else {
+ ret = blk_pwrite(blk, offset + written,
+ buf_old + written, pnum, 0);
+ }
if (ret < 0) {
error_report("Error while writing to COW image: %s",
strerror(-ret));