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[PATCH v11 27/34] qcow2: Add subcluster support to handle_alloc_space()
From: |
Alberto Garcia |
Subject: |
[PATCH v11 27/34] qcow2: Add subcluster support to handle_alloc_space() |
Date: |
Fri, 10 Jul 2020 18:13:09 +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 854a2fbd9b..b58c421c28 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2421,6 +2421,9 @@ 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;
@@ -2435,16 +2438,14 @@ 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 v11 12/34] qcow2: Add l2_entry_size(), (continued)
- [PATCH v11 12/34] qcow2: Add l2_entry_size(), Alberto Garcia, 2020/07/10
- [PATCH v11 26/34] qcow2: Clear the L2 bitmap when allocating a compressed cluster, Alberto Garcia, 2020/07/10
- [PATCH v11 28/34] qcow2: Add subcluster support to qcow2_co_pwrite_zeroes(), Alberto Garcia, 2020/07/10
- [PATCH v11 21/34] qcow2: Add subcluster support to qcow2_get_host_offset(), Alberto Garcia, 2020/07/10
- [PATCH v11 29/34] qcow2: Add subcluster support to qcow2_measure(), Alberto Garcia, 2020/07/10
- [PATCH v11 34/34] iotests: Add tests for qcow2 images with extended L2 entries, Alberto Garcia, 2020/07/10
- [PATCH v11 23/34] qcow2: Add subcluster support to discard_in_l2_slice(), Alberto Garcia, 2020/07/10
- [PATCH v11 16/34] qcow2: Add qcow2_cluster_is_allocated(), Alberto Garcia, 2020/07/10
- [PATCH v11 33/34] qcow2: Assert that expand_zero_clusters_in_l1() does not support subclusters, Alberto Garcia, 2020/07/10
- [PATCH v11 30/34] qcow2: Add prealloc field to QCowL2Meta, Alberto Garcia, 2020/07/10
- [PATCH v11 27/34] qcow2: Add subcluster support to handle_alloc_space(),
Alberto Garcia <=
- [PATCH v11 31/34] qcow2: Add the 'extended_l2' option and the QCOW2_INCOMPAT_EXTL2 bit, Alberto Garcia, 2020/07/10
- Re: [PATCH v11 00/34] Add subcluster allocation to qcow2, no-reply, 2020/07/10
- Re: [PATCH v11 00/34] Add subcluster allocation to qcow2, no-reply, 2020/07/10
- Re: [PATCH v11 00/34] Add subcluster allocation to qcow2, Max Reitz, 2020/07/14