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[PATCH v7 23/32] qcow2: Add subcluster support to discard_in_l2_slice()
From: |
Alberto Garcia |
Subject: |
[PATCH v7 23/32] qcow2: Add subcluster support to discard_in_l2_slice() |
Date: |
Mon, 25 May 2020 20:08:48 +0200 |
Two things need to be taken into account here:
1) With full_discard == true the L2 entry must be cleared completely.
This also includes the L2 bitmap if the image has extended L2
entries.
2) With full_discard == false we have to make the discarded cluster
read back as zeroes. With normal L2 entries this is done with the
QCOW_OFLAG_ZERO bit, whereas with extended L2 entries this is done
with the individual 'all zeroes' bits for each subcluster.
Note however that QCOW_OFLAG_ZERO is not supported in v2 qcow2
images so, if there is a backing file, discard cannot guarantee
that the image will read back as zeroes. If this is important for
the caller it should forbid it as qcow2_co_pdiscard() does (see
80f5c01183 for more details).
Signed-off-by: Alberto Garcia <address@hidden>
---
block/qcow2-cluster.c | 52 +++++++++++++++++++------------------------
1 file changed, 23 insertions(+), 29 deletions(-)
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index 4e59bbd545..edfc8ea91c 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1847,11 +1847,17 @@ static int discard_in_l2_slice(BlockDriverState *bs,
uint64_t offset,
assert(nb_clusters <= INT_MAX);
for (i = 0; i < nb_clusters; i++) {
- uint64_t old_l2_entry;
-
- old_l2_entry = get_l2_entry(s, l2_slice, l2_index + i);
+ uint64_t old_l2_entry = get_l2_entry(s, l2_slice, l2_index + i);
+ uint64_t old_l2_bitmap = get_l2_bitmap(s, l2_slice, l2_index + i);
+ uint64_t new_l2_entry = old_l2_entry;
+ uint64_t new_l2_bitmap = old_l2_bitmap;
+ QCow2ClusterType cluster_type =
+ qcow2_get_cluster_type(bs, old_l2_entry);
/*
+ * If full_discard is true, the cluster should not read back as zeroes,
+ * but rather fall through to the backing file.
+ *
* If full_discard is false, make sure that a discarded area reads back
* as zeroes for v3 images (we cannot do it for v2 without actually
* writing a zero-filled buffer). We can skip the operation if the
@@ -1860,40 +1866,28 @@ static int discard_in_l2_slice(BlockDriverState *bs,
uint64_t offset,
*
* TODO We might want to use bdrv_block_status(bs) here, but we're
* holding s->lock, so that doesn't work today.
- *
- * If full_discard is true, the sector should not read back as zeroes,
- * but rather fall through to the backing file.
*/
- switch (qcow2_get_cluster_type(bs, old_l2_entry)) {
- case QCOW2_CLUSTER_UNALLOCATED:
- if (full_discard || !bs->backing) {
- continue;
+ if (full_discard) {
+ new_l2_entry = new_l2_bitmap = 0;
+ } else if (bs->backing || qcow2_cluster_is_allocated(cluster_type)) {
+ if (has_subclusters(s)) {
+ new_l2_entry = 0;
+ new_l2_bitmap = QCOW_L2_BITMAP_ALL_ZEROES;
+ } else {
+ new_l2_entry = s->qcow_version >= 3 ? QCOW_OFLAG_ZERO : 0;
}
- break;
+ }
- case QCOW2_CLUSTER_ZERO_PLAIN:
- if (!full_discard) {
- continue;
- }
- break;
-
- case QCOW2_CLUSTER_ZERO_ALLOC:
- case QCOW2_CLUSTER_NORMAL:
- case QCOW2_CLUSTER_COMPRESSED:
- break;
-
- default:
- abort();
+ if (old_l2_entry == new_l2_entry && old_l2_bitmap == new_l2_bitmap) {
+ continue;
}
/* First remove L2 entries */
qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_slice);
- if (!full_discard && s->qcow_version >= 3) {
- set_l2_entry(s, l2_slice, l2_index + i, QCOW_OFLAG_ZERO);
- } else {
- set_l2_entry(s, l2_slice, l2_index + i, 0);
+ set_l2_entry(s, l2_slice, l2_index + i, new_l2_entry);
+ if (has_subclusters(s)) {
+ set_l2_bitmap(s, l2_slice, l2_index + i, new_l2_bitmap);
}
-
/* Then decrease the refcount */
qcow2_free_any_clusters(bs, old_l2_entry, 1, type);
}
--
2.20.1
- [PATCH v7 00/32] Add subcluster allocation to qcow2, Alberto Garcia, 2020/05/25
- [PATCH v7 07/32] qcow2: Document the Extended L2 Entries feature, Alberto Garcia, 2020/05/25
- [PATCH v7 28/32] qcow2: Add subcluster support to qcow2_co_pwrite_zeroes(), Alberto Garcia, 2020/05/25
- [PATCH v7 15/32] qcow2: Add qcow2_get_subcluster_range_type(), Alberto Garcia, 2020/05/25
- [PATCH v7 06/32] qcow2: Add get_l2_entry() and set_l2_entry(), Alberto Garcia, 2020/05/25
- [PATCH v7 09/32] qcow2: Add subcluster-related fields to BDRVQcow2State, Alberto Garcia, 2020/05/25
- [PATCH v7 23/32] qcow2: Add subcluster support to discard_in_l2_slice(),
Alberto Garcia <=
- [PATCH v7 01/32] qcow2: Make Qcow2AioTask store the full host offset, Alberto Garcia, 2020/05/25
- [PATCH v7 22/32] qcow2: Add subcluster support to zero_in_l2_slice(), Alberto Garcia, 2020/05/25
- [PATCH v7 13/32] qcow2: Update get/set_l2_entry() and add get/set_l2_bitmap(), Alberto Garcia, 2020/05/25
- [PATCH v7 16/32] qcow2: Add qcow2_cluster_is_allocated(), 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 14/32] qcow2: Add QCow2SubclusterType and qcow2_get_subcluster_type(), Alberto Garcia, 2020/05/25