ShuriZma
/
xemu
mirror of https://github.com/xemu-project/xemu.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

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: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Max Reitz 2019-05-09 19:52:36 +02:00 committed by Kevin Wolf
parent 35ddd9300b
commit 1c6e877992
1 changed files with 9 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
qemu-img.c
View File

@ -3432,6 +3432,8 @@ static int img_rebase(int argc, char **argv)
} }
for (offset = 0; offset < size; offset += n) { for (offset = 0; offset < size; offset += n) {
bool buf_old_is_zero = false;
/* How many bytes can we handle with the next read? */ /* How many bytes can we handle with the next read? */
n = MIN(IO_BUF_SIZE, size - offset); n = MIN(IO_BUF_SIZE, size - offset);
@ -3452,6 +3454,7 @@ static int img_rebase(int argc, char **argv)
*/ */
if (offset >= old_backing_size) { if (offset >= old_backing_size) {
memset(buf_old, 0, n); memset(buf_old, 0, n);
buf_old_is_zero = true;
} else { } else {
if (offset + n > old_backing_size) { if (offset + n > old_backing_size) {
n = old_backing_size - offset; 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, if (compare_buffers(buf_old + written, buf_new + written,
n - written, &pnum)) n - written, &pnum))
{ {
ret = blk_pwrite(blk, offset + written, if (buf_old_is_zero) {
buf_old + written, pnum, 0); ret = blk_pwrite_zeroes(blk, offset + written, pnum, 0);
} else {
ret = blk_pwrite(blk, offset + written,
buf_old + written, pnum, 0);
}
if (ret < 0) { if (ret < 0) {
error_report("Error while writing to COW image: %s", error_report("Error while writing to COW image: %s",
strerror(-ret)); strerror(-ret));