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[PATCH v10 27/34] qcow2: Add subcluster support to handle_alloc_space()
From: |
Alberto Garcia |
Subject: |
[PATCH v10 27/34] qcow2: Add subcluster support to handle_alloc_space() |
Date: |
Fri, 3 Jul 2020 17:58:13 +0200 |
The bdrv_co_pwrite_zeroes() call here fills complete clusters with
zeroes, but it can happen that some subclusters are not part of the
write request or the copy-on-write. This patch makes sure that only
the affected subclusters are overwritten.
A potential improvement would be to also fill with zeroes the other
subclusters if we can guarantee that we are not overwriting existing
data. However this would waste more disk space, so we should first
evaluate if it's really worth doing.
Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
block/qcow2.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/block/qcow2.c b/block/qcow2.c
index a3481cd85b..86258fbc22 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2411,6 +2411,9 @@ static int handle_alloc_space(BlockDriverState *bs,
QCowL2Meta *l2meta)
for (m = l2meta; m != NULL; m = m->next) {
int ret;
+ uint64_t start_offset = m->alloc_offset + m->cow_start.offset;
+ unsigned nb_bytes = m->cow_end.offset + m->cow_end.nb_bytes -
+ m->cow_start.offset;
if (!m->cow_start.nb_bytes && !m->cow_end.nb_bytes) {
continue;
@@ -2425,16 +2428,14 @@ static int handle_alloc_space(BlockDriverState *bs,
QCowL2Meta *l2meta)
* efficiently zero out the whole clusters
*/
- ret = qcow2_pre_write_overlap_check(bs, 0, m->alloc_offset,
- m->nb_clusters * s->cluster_size,
+ ret = qcow2_pre_write_overlap_check(bs, 0, start_offset, nb_bytes,
true);
if (ret < 0) {
return ret;
}
BLKDBG_EVENT(bs->file, BLKDBG_CLUSTER_ALLOC_SPACE);
- ret = bdrv_co_pwrite_zeroes(s->data_file, m->alloc_offset,
- m->nb_clusters * s->cluster_size,
+ ret = bdrv_co_pwrite_zeroes(s->data_file, start_offset, nb_bytes,
BDRV_REQ_NO_FALLBACK);
if (ret < 0) {
if (ret != -ENOTSUP && ret != -EAGAIN) {
--
2.20.1
- [PATCH v10 21/34] qcow2: Add subcluster support to qcow2_get_host_offset(), (continued)
- [PATCH v10 21/34] qcow2: Add subcluster support to qcow2_get_host_offset(), Alberto Garcia, 2020/07/03
- [PATCH v10 20/34] qcow2: Add subcluster support to calculate_l2_meta(), Alberto Garcia, 2020/07/03
- [PATCH v10 23/34] qcow2: Add subcluster support to discard_in_l2_slice(), Alberto Garcia, 2020/07/03
- [PATCH v10 30/34] qcow2: Add prealloc field to QCowL2Meta, Alberto Garcia, 2020/07/03
- [PATCH v10 28/34] qcow2: Add subcluster support to qcow2_co_pwrite_zeroes(), Alberto Garcia, 2020/07/03
- [PATCH v10 13/34] qcow2: Update get/set_l2_entry() and add get/set_l2_bitmap(), Alberto Garcia, 2020/07/03
- [PATCH v10 17/34] qcow2: Add cluster type parameter to qcow2_get_host_offset(), Alberto Garcia, 2020/07/03
- [PATCH v10 22/34] qcow2: Add subcluster support to zero_in_l2_slice(), Alberto Garcia, 2020/07/03
- [PATCH v10 27/34] qcow2: Add subcluster support to handle_alloc_space(),
Alberto Garcia <=
- [PATCH v10 32/34] qcow2: Allow preallocation and backing files if extended_l2 is set, Alberto Garcia, 2020/07/03
- [PATCH v10 29/34] qcow2: Add subcluster support to qcow2_measure(), Alberto Garcia, 2020/07/03
- [PATCH v10 34/34] iotests: Add tests for qcow2 images with extended L2 entries, Alberto Garcia, 2020/07/03
- [PATCH v10 31/34] qcow2: Add the 'extended_l2' option and the QCOW2_INCOMPAT_EXTL2 bit, Alberto Garcia, 2020/07/03