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[RFC PATCH v2 22/26] qcow2: Add subcluster support to handle_alloc_space
From: |
Alberto Garcia |
Subject: |
[RFC PATCH v2 22/26] qcow2: Add subcluster support to handle_alloc_space() |
Date: |
Sun, 27 Oct 2019 00:25:24 +0300 |
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>
---
block/qcow2.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/block/qcow2.c b/block/qcow2.c
index 0261e87709..01322ca449 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2304,6 +2304,9 @@ 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;
+ uint64_t 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;
@@ -2318,16 +2321,14 @@ 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
- Re: [RFC PATCH v2 01/26] qcow2: Add calculate_l2_meta(), (continued)
- [RFC PATCH v2 25/26] qcow2: Allow preallocation and backing files if extended_l2 is set, Alberto Garcia, 2019/10/26
- [RFC PATCH v2 13/26] qcow2: Add subcluster support to calculate_l2_meta(), Alberto Garcia, 2019/10/26
- [RFC PATCH v2 21/26] qcow2: Clear the L2 bitmap when allocating a compressed cluster, Alberto Garcia, 2019/10/26
- [RFC PATCH v2 08/26] qcow2: Add offset_to_sc_index(), Alberto Garcia, 2019/10/26
- [RFC PATCH v2 06/26] qcow2: Add dummy has_subclusters() function, Alberto Garcia, 2019/10/26
- [RFC PATCH v2 10/26] qcow2: Update get/set_l2_entry() and add get/set_l2_bitmap(), Alberto Garcia, 2019/10/26
- [RFC PATCH v2 22/26] qcow2: Add subcluster support to handle_alloc_space(),
Alberto Garcia <=
- [RFC PATCH v2 05/26] qcow2: Document the Extended L2 Entries feature, Alberto Garcia, 2019/10/26
- [RFC PATCH v2 14/26] qcow2: Add subcluster support to qcow2_get_cluster_offset(), Alberto Garcia, 2019/10/26
- [RFC PATCH v2 20/26] qcow2: Update L2 bitmap in qcow2_alloc_cluster_link_l2(), Alberto Garcia, 2019/10/26
- [RFC PATCH v2 19/26] qcow2: Fix offset calculation in handle_dependencies(), Alberto Garcia, 2019/10/26
- [RFC PATCH v2 18/26] qcow2: Add subcluster support to expand_zero_clusters_in_l1(), Alberto Garcia, 2019/10/26
- [RFC PATCH v2 07/26] qcow2: Add subcluster-related fields to BDRVQcow2State, Alberto Garcia, 2019/10/26
- [RFC PATCH v2 12/26] qcow2: Handle QCOW2_CLUSTER_UNALLOCATED_SUBCLUSTER, Alberto Garcia, 2019/10/26
- [RFC PATCH v2 23/26] qcow2: Restrict qcow2_co_pwrite_zeroes() to full clusters only, Alberto Garcia, 2019/10/26