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[PATCH v10 30/34] qcow2: Add prealloc field to QCowL2Meta
From: |
Alberto Garcia |
Subject: |
[PATCH v10 30/34] qcow2: Add prealloc field to QCowL2Meta |
Date: |
Fri, 3 Jul 2020 17:58:16 +0200 |
This field allows us to indicate that the L2 metadata update does not
come from a write request with actual data but from a preallocation
request.
For traditional images this does not make any difference, but for
images with extended L2 entries this means that the clusters are
allocated normally in the L2 table but individual subclusters are
marked as unallocated.
This will allow preallocating images that have a backing file.
There is one special case: when we resize an existing image we can
also request that the new clusters are preallocated. If the image
already had a backing file then we have to hide any possible stale
data and zero out the new clusters (see commit 955c7d6687 for more
details).
In this case the subclusters cannot be left as unallocated so the L2
bitmap must be updated.
Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
---
block/qcow2.h | 8 ++++++++
block/qcow2-cluster.c | 2 +-
block/qcow2.c | 6 ++++++
3 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/block/qcow2.h b/block/qcow2.h
index 4ef4ae4ab0..f3499e53bf 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -463,6 +463,14 @@ typedef struct QCowL2Meta
*/
bool skip_cow;
+ /**
+ * Indicates that this is not a normal write request but a preallocation.
+ * If the image has extended L2 entries this means that no new individual
+ * subclusters will be marked as allocated in the L2 bitmap (but any
+ * existing contents of that bitmap will be kept).
+ */
+ bool prealloc;
+
/**
* The I/O vector with the data from the actual guest write request.
* If non-NULL, this is meant to be merged together with the data
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index e023bc4b01..bbf373ad21 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1067,7 +1067,7 @@ int qcow2_alloc_cluster_link_l2(BlockDriverState *bs,
QCowL2Meta *m)
set_l2_entry(s, l2_slice, l2_index + i, offset | QCOW_OFLAG_COPIED);
/* Update bitmap with the subclusters that were just written */
- if (has_subclusters(s)) {
+ if (has_subclusters(s) && !m->prealloc) {
uint64_t l2_bitmap = get_l2_bitmap(s, l2_slice, l2_index + i);
unsigned written_from = m->cow_start.offset;
unsigned written_to = m->cow_end.offset + m->cow_end.nb_bytes ?:
diff --git a/block/qcow2.c b/block/qcow2.c
index f443a68935..04572f39e1 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -2086,6 +2086,7 @@ static coroutine_fn int
qcow2_handle_l2meta(BlockDriverState *bs,
QCowL2Meta *next;
if (link_l2) {
+ assert(!l2meta->prealloc);
ret = qcow2_alloc_cluster_link_l2(bs, l2meta);
if (ret) {
goto out;
@@ -3131,6 +3132,7 @@ static int coroutine_fn preallocate_co(BlockDriverState
*bs, uint64_t offset,
while (meta) {
QCowL2Meta *next = meta->next;
+ meta->prealloc = true;
ret = qcow2_alloc_cluster_link_l2(bs, meta);
if (ret < 0) {
@@ -4224,6 +4226,7 @@ static int coroutine_fn
qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
int64_t clusters_allocated;
int64_t old_file_size, last_cluster, new_file_size;
uint64_t nb_new_data_clusters, nb_new_l2_tables;
+ bool subclusters_need_allocation = false;
/* With a data file, preallocation means just allocating the metadata
* and forwarding the truncate request to the data file */
@@ -4305,6 +4308,8 @@ static int coroutine_fn
qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
BDRV_REQ_ZERO_WRITE, NULL);
if (ret >= 0) {
flags &= ~BDRV_REQ_ZERO_WRITE;
+ /* Ensure that we read zeroes and not backing file data */
+ subclusters_need_allocation = true;
}
} else {
ret = -1;
@@ -4343,6 +4348,7 @@ static int coroutine_fn
qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
.offset = nb_clusters << s->cluster_bits,
.nb_bytes = 0,
},
+ .prealloc = !subclusters_need_allocation,
};
qemu_co_queue_init(&allocation.dependent_requests);
--
2.20.1
- [PATCH v10 19/34] qcow2: Handle QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC, (continued)
- [PATCH v10 19/34] qcow2: Handle QCOW2_SUBCLUSTER_UNALLOCATED_ALLOC, Alberto Garcia, 2020/07/03
- [PATCH v10 20/34] qcow2: Add subcluster support to calculate_l2_meta(), Alberto Garcia, 2020/07/03
- [PATCH v10 23/34] qcow2: Add subcluster support to discard_in_l2_slice(), Alberto Garcia, 2020/07/03
- [PATCH v10 26/34] qcow2: Clear the L2 bitmap when allocating a compressed cluster, Alberto Garcia, 2020/07/03
- [PATCH v10 22/34] qcow2: Add subcluster support to zero_in_l2_slice(), Alberto Garcia, 2020/07/03
- [PATCH v10 13/34] qcow2: Update get/set_l2_entry() and add get/set_l2_bitmap(), Alberto Garcia, 2020/07/03
- [PATCH v10 24/34] qcow2: Add subcluster support to check_refcounts_l2(), Alberto Garcia, 2020/07/03
- [PATCH v10 17/34] qcow2: Add cluster type parameter to qcow2_get_host_offset(), Alberto Garcia, 2020/07/03
- [PATCH v10 27/34] qcow2: Add subcluster support to handle_alloc_space(), Alberto Garcia, 2020/07/03
- [PATCH v10 29/34] qcow2: Add subcluster support to qcow2_measure(), Alberto Garcia, 2020/07/03
- [PATCH v10 30/34] qcow2: Add prealloc field to QCowL2Meta,
Alberto Garcia <=
- [PATCH v10 32/34] qcow2: Allow preallocation and backing files if extended_l2 is set, Alberto Garcia, 2020/07/03
- [PATCH v10 34/34] iotests: Add tests for qcow2 images with extended L2 entries, Alberto Garcia, 2020/07/03
- [PATCH v10 31/34] qcow2: Add the 'extended_l2' option and the QCOW2_INCOMPAT_EXTL2 bit, Alberto Garcia, 2020/07/03