Commit 1c6e8779 authored by Max Reitz's avatar Max Reitz Committed by Kevin Wolf
Browse files

qemu-img: Use zero writes after source backing EOF 



Past the end of the source backing file, we memset() buf_old to zero, so
it is clearly easy to use blk_pwrite_zeroes() instead of blk_pwrite()
then.

Signed-off-by: default avatarMax Reitz <mreitz@redhat.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent 35ddd930

qemu-img.c

+9 −2
Original line number Diff line number Diff line
@@ -3432,6 +3432,8 @@ 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);
@@ -3452,6 +3454,7 @@ 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;
@@ -3487,8 +3490,12 @@ static int img_rebase(int argc, char **argv) 
                if (compare_buffers(buf_old + written, buf_new + written,

                                    n - written, &pnum))

                {

                    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));