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[PATCH v6 27/32] qcow2: Add subcluster support to handle_alloc_space()
From: |
Alberto Garcia |
Subject: |
[PATCH v6 27/32] qcow2: Add subcluster support to handle_alloc_space() |
Date: |
Sun, 24 May 2020 16:51:47 +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 v6 23/32] qcow2: Add subcluster support to discard_in_l2_slice(), (continued)
- [PATCH v6 23/32] qcow2: Add subcluster support to discard_in_l2_slice(), Alberto Garcia, 2020/05/24
- [PATCH v6 12/32] qcow2: Add l2_entry_size(), Alberto Garcia, 2020/05/24
- [PATCH v6 16/32] qcow2: Add qcow2_cluster_is_allocated(), Alberto Garcia, 2020/05/24
- [PATCH v6 09/32] qcow2: Add subcluster-related fields to BDRVQcow2State, Alberto Garcia, 2020/05/24
- [PATCH v6 02/32] qcow2: Convert qcow2_get_cluster_offset() into qcow2_get_host_offset(), Alberto Garcia, 2020/05/24
- [PATCH v6 22/32] qcow2: Add subcluster support to zero_in_l2_slice(), Alberto Garcia, 2020/05/24
- [PATCH v6 17/32] qcow2: Add cluster type parameter to qcow2_get_host_offset(), Alberto Garcia, 2020/05/24
- [PATCH v6 24/32] qcow2: Add subcluster support to check_refcounts_l2(), Alberto Garcia, 2020/05/24
- [PATCH v6 26/32] qcow2: Clear the L2 bitmap when allocating a compressed cluster, Alberto Garcia, 2020/05/24
- [PATCH v6 28/32] qcow2: Add subcluster support to qcow2_co_pwrite_zeroes(), Alberto Garcia, 2020/05/24
- [PATCH v6 27/32] qcow2: Add subcluster support to handle_alloc_space(),
Alberto Garcia <=
- [PATCH v6 19/32] qcow2: Handle QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC, Alberto Garcia, 2020/05/24
- [PATCH v6 25/32] qcow2: Update L2 bitmap in qcow2_alloc_cluster_link_l2(), Alberto Garcia, 2020/05/24
- [PATCH v6 11/32] qcow2: Add offset_into_subcluster() and size_to_subclusters(), Alberto Garcia, 2020/05/24
- [PATCH v6 15/32] qcow2: Add qcow2_get_subcluster_range_type(), Alberto Garcia, 2020/05/24
- [PATCH v6 07/32] qcow2: Document the Extended L2 Entries feature, Alberto Garcia, 2020/05/24
- [PATCH v6 13/32] qcow2: Update get/set_l2_entry() and add get/set_l2_bitmap(), Alberto Garcia, 2020/05/24
- [PATCH v6 04/32] qcow2: Split cluster_needs_cow() out of count_cow_clusters(), Alberto Garcia, 2020/05/24
- [PATCH v6 31/32] qcow2: Assert that expand_zero_clusters_in_l1() does not support subclusters, Alberto Garcia, 2020/05/24
- [PATCH v6 32/32] iotests: Add tests for qcow2 images with extended L2 entries, Alberto Garcia, 2020/05/24