On 5/6/20 4:25 AM, Vladimir Sementsov-Ogievskiy wrote:
qemu-img convert wants to distinguish ZERO which comes from short
backing files. unallocated_blocks_are_zero field of bdi is unrelated:
space after EOF is always considered to be zero anyway. So, just make
post_backing_zero true in case of short backing file.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
---
qemu-img.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
This patch should come first in the series. It would have saved me a
lot of time in reviewing 1/8.
diff --git a/qemu-img.c b/qemu-img.c
index 6a4327aaba..4fe751878b 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1632,7 +1632,6 @@ typedef struct ImgConvertState {
BlockBackend *target;
bool has_zero_init;
bool compressed;
- bool unallocated_blocks_are_zero;
bool target_is_new;
bool target_has_backing;
int64_t target_backing_sectors; /* negative if unknown */
@@ -1677,7 +1676,7 @@ static int convert_iteration_sectors(ImgConvertState *s,
int64_t sector_num)
if (s->target_backing_sectors >= 0) {
if (sector_num >= s->target_backing_sectors) {
- post_backing_zero = s->unallocated_blocks_are_zero;
+ post_backing_zero = true;
} else if (sector_num + n > s->target_backing_sectors) {
/* Split requests around target_backing_sectors (because
* starting from there, zeros are handled differently) */
@@ -2580,7 +2579,6 @@ static int img_convert(int argc, char **argv)
} else {
s.compressed = s.compressed || bdi.needs_compressed_writes;
s.cluster_sectors = bdi.cluster_size / BDRV_SECTOR_SIZE;
- s.unallocated_blocks_are_zero = bdi.unallocated_blocks_are_zero;
}
My question in 1/8 about whether we have iotest coverage of this
optimization remains, but I concur that the block layer takes care of
reading zero when encountering unallocated blocks beyond EOF of a short
backing file, and therefore performing this optimization always rather
than just when the driver claims that unallocated blocks read as zero
should be safe.
Reviewed-by: Eric Blake <ebl...@redhat.com>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
