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[RFC PATCH 21/23] qcow2: Add subcluster support to handle_alloc_space()
From: |
Alberto Garcia |
Subject: |
[RFC PATCH 21/23] qcow2: Add subcluster support to handle_alloc_space() |
Date: |
Tue, 15 Oct 2019 18:23:32 +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 c222cd261d..c54278ab0b 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2194,6 +2194,9 @@ 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;
@@ -2208,16 +2211,14 @@ 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 22/23] qcow2: Restrict qcow2_co_pwrite_zeroes() to full clusters only, (continued)
- [RFC PATCH 22/23] qcow2: Restrict qcow2_co_pwrite_zeroes() to full clusters only, Alberto Garcia, 2019/10/15
- [RFC PATCH 07/23] qcow2: Add subcluster-related fields to BDRVQcow2State, Alberto Garcia, 2019/10/15
- [RFC PATCH 20/23] qcow2: Update L2 bitmap in qcow2_alloc_cluster_link_l2(), Alberto Garcia, 2019/10/15
- [RFC PATCH 02/23] qcow2: Split cluster_needs_cow() out of count_cow_clusters(), Alberto Garcia, 2019/10/15
- [RFC PATCH 14/23] qcow2: Add subcluster support to qcow2_get_cluster_offset(), Alberto Garcia, 2019/10/15
- [RFC PATCH 18/23] qcow2: Add subcluster support to expand_zero_clusters_in_l1(), Alberto Garcia, 2019/10/15
- [RFC PATCH 19/23] qcow2: Fix offset calculation in handle_dependencies(), Alberto Garcia, 2019/10/15
- [RFC PATCH 23/23] qcow2: Add the 'extended_l2' option and the QCOW2_INCOMPAT_EXTL2 bit, Alberto Garcia, 2019/10/15
- [RFC PATCH 13/23] qcow2: Add subcluster support to calculate_l2_meta(), Alberto Garcia, 2019/10/15
- [RFC PATCH 21/23] qcow2: Add subcluster support to handle_alloc_space(),
Alberto Garcia <=
- [RFC PATCH 17/23] qcow2: Add subcluster support to check_refcounts_l2(), Alberto Garcia, 2019/10/15
- Re: [RFC PATCH 00/23] Add subcluster allocation to qcow2, Eric Blake, 2019/10/15
- Re: [RFC PATCH 00/23] Add subcluster allocation to qcow2, Vladimir Sementsov-Ogievskiy, 2019/10/23