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[PATCH v7 27/32] qcow2: Add subcluster support to handle_alloc_space()
From: |
Alberto Garcia |
Subject: |
[PATCH v7 27/32] qcow2: Add subcluster support to handle_alloc_space() |
Date: |
Mon, 25 May 2020 20:08:52 +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 <address@hidden>
Reviewed-by: Max Reitz <address@hidden>
Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
---
block/qcow2.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/block/qcow2.c b/block/qcow2.c
index 8126ad8fa0..430b4e423a 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 v7 13/32] qcow2: Update get/set_l2_entry() and add get/set_l2_bitmap(), (continued)
- [PATCH v7 08/32] qcow2: Add dummy has_subclusters() function, Alberto Garcia, 2020/05/25
- [PATCH v7 27/32] qcow2: Add subcluster support to handle_alloc_space(),
Alberto Garcia <=
- [PATCH v7 24/32] qcow2: Add subcluster support to check_refcounts_l2(), Alberto Garcia, 2020/05/25
- [PATCH v7 11/32] qcow2: Add offset_into_subcluster() and size_to_subclusters(), Alberto Garcia, 2020/05/25
- [PATCH v7 10/32] qcow2: Add offset_to_sc_index(), Alberto Garcia, 2020/05/25
- [PATCH v7 29/32] qcow2: Add subcluster support to qcow2_measure(), Alberto Garcia, 2020/05/25
- [PATCH v7 04/32] qcow2: Split cluster_needs_cow() out of count_cow_clusters(), Alberto Garcia, 2020/05/25
- [PATCH v7 31/32] qcow2: Assert that expand_zero_clusters_in_l1() does not support subclusters, Alberto Garcia, 2020/05/25
- [PATCH v7 25/32] qcow2: Update L2 bitmap in qcow2_alloc_cluster_link_l2(), Alberto Garcia, 2020/05/25
- [PATCH v7 18/32] qcow2: Replace QCOW2_CLUSTER_* with QCOW2_SUBCLUSTER_*, Alberto Garcia, 2020/05/25
- [PATCH v7 19/32] qcow2: Handle QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC, Alberto Garcia, 2020/05/25