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[RFC PATCH v3 23/27] qcow2: Add subcluster support to handle_alloc_space
From: |
Alberto Garcia |
Subject: |
[RFC PATCH v3 23/27] qcow2: Add subcluster support to handle_alloc_space() |
Date: |
Sun, 22 Dec 2019 12:37:04 +0100 |
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 1d3da0ccf6..242001afa2 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2354,6 +2354,9 @@ 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;
@@ -2368,16 +2371,14 @@ 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
- [RFC PATCH v3 11/27] qcow2: Add QCow2SubclusterType and qcow2_get_subcluster_type(), (continued)
- [RFC PATCH v3 11/27] qcow2: Add QCow2SubclusterType and qcow2_get_subcluster_type(), Alberto Garcia, 2019/12/22
- [RFC PATCH v3 03/27] qcow2: Process QCOW2_CLUSTER_ZERO_ALLOC clusters in handle_copied(), Alberto Garcia, 2019/12/22
- [RFC PATCH v3 27/27] iotests: Add tests for qcow2 images with extended L2 entries, Alberto Garcia, 2019/12/22
- [RFC PATCH v3 21/27] qcow2: Update L2 bitmap in qcow2_alloc_cluster_link_l2(), Alberto Garcia, 2019/12/22
- [RFC PATCH v3 13/27] qcow2: Handle QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC, Alberto Garcia, 2019/12/22
- [RFC PATCH v3 19/27] qcow2: Add subcluster support to expand_zero_clusters_in_l1(), Alberto Garcia, 2019/12/22
- [RFC PATCH v3 22/27] qcow2: Clear the L2 bitmap when allocating a compressed cluster, Alberto Garcia, 2019/12/22
- [RFC PATCH v3 08/27] qcow2: Add offset_to_sc_index(), Alberto Garcia, 2019/12/22
- [RFC PATCH v3 06/27] qcow2: Add dummy has_subclusters() function, Alberto Garcia, 2019/12/22
- [RFC PATCH v3 02/27] qcow2: Split cluster_needs_cow() out of count_cow_clusters(), Alberto Garcia, 2019/12/22
- [RFC PATCH v3 23/27] qcow2: Add subcluster support to handle_alloc_space(),
Alberto Garcia <=
- [RFC PATCH v3 14/27] qcow2: Add subcluster support to calculate_l2_meta(), Alberto Garcia, 2019/12/22
- [RFC PATCH v3 26/27] qcow2: Add subcluster support to qcow2_measure(), Alberto Garcia, 2019/12/22
- [RFC PATCH v3 09/27] qcow2: Add l2_entry_size(), Alberto Garcia, 2019/12/22
- [RFC PATCH v3 05/27] qcow2: Document the Extended L2 Entries feature, Alberto Garcia, 2019/12/22
- [RFC PATCH v3 12/27] qcow2: Replace QCOW2_CLUSTER_* with QCOW2_SUBCLUSTER_*, Alberto Garcia, 2019/12/22
- [RFC PATCH v3 20/27] qcow2: Fix offset calculation in handle_dependencies(), Alberto Garcia, 2019/12/22
- [RFC PATCH v3 15/27] qcow2: Add subcluster support to qcow2_get_cluster_offset(), Alberto Garcia, 2019/12/22
- [RFC PATCH v3 04/27] qcow2: Add get_l2_entry() and set_l2_entry(), Alberto Garcia, 2019/12/22
- [RFC PATCH v3 25/27] qcow2: Add the 'extended_l2' option and the QCOW2_INCOMPAT_EXTL2 bit, Alberto Garcia, 2019/12/22