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qcow2: Fix preallocation on images with unaligned sizes

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When resizing an image with qcow2_co_truncate() using the falloc or
full preallocation modes the code assumes that both the old and new
sizes are cluster-aligned.

There are two problems with this:

  1) The calculation of how many clusters are involved does not always
     get the right result.

     Example: creating a 60KB image and resizing it (with
     preallocation=full) to 80KB won't allocate the second cluster.

  2) No copy-on-write is performed, so in the previous example if
     there is a backing file then the first 60KB of the first cluster
     won't be filled with data from the backing file.

This patch fixes both issues.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-Id: <20200617140036.20311-1-berto@igalia.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Alberto Garcia 2020-06-17 16:00:36 +02:00 committed by Max Reitz
parent e8de7ba9ea
commit a5675f3901
3 changed files with 47 additions and 3 deletions
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17
block/qcow2.c
View File

@ -4239,8 +4239,8 @@ static int coroutine_fn qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
old_file_size = ROUND_UP(old_file_size, s->cluster_size);
}
nb_new_data_clusters = DIV_ROUND_UP(offset - old_length,
s->cluster_size);
nb_new_data_clusters = (ROUND_UP(offset, s->cluster_size) -
start_of_cluster(s, old_length)) >> s->cluster_bits;
/* This is an overestimation; we will not actually allocate space for
* these in the file but just make sure the new refcount structures are
@ -4317,10 +4317,21 @@ static int coroutine_fn qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
int64_t nb_clusters = MIN(
nb_new_data_clusters,
s->l2_slice_size - offset_to_l2_slice_index(s, guest_offset));
QCowL2Meta allocation = {
unsigned cow_start_length = offset_into_cluster(s, guest_offset);
QCowL2Meta allocation;
guest_offset = start_of_cluster(s, guest_offset);
allocation = (QCowL2Meta) {
.offset = guest_offset,
.alloc_offset = host_offset,
.nb_clusters = nb_clusters,
.cow_start = {
.offset = 0,
.nb_bytes = cow_start_length,
},
.cow_end = {
.offset = nb_clusters << s->cluster_bits,
.nb_bytes = 0,
},
};
qemu_co_queue_init(&allocation.dependent_requests);

24
tests/qemu-iotests/125
View File

@ -164,6 +164,30 @@ for GROWTH_SIZE in 16 48 80; do
done
done
# Test image resizing using preallocation and unaligned offsets
$QEMU_IMG create -f raw "$TEST_IMG.base" 128k | _filter_img_create
$QEMU_IO -c 'write -q -P 1 0 128k' -f raw "$TEST_IMG.base"
for orig_size in 31k 33k; do
echo "--- Resizing image from $orig_size to 96k ---"
_make_test_img -F raw -b "$TEST_IMG.base" -o cluster_size=64k "$orig_size"
$QEMU_IMG resize -f "$IMGFMT" --preallocation=full "$TEST_IMG" 96k
# The first part of the image should contain data from the backing file
$QEMU_IO -c "read -q -P 1 0 ${orig_size}" "$TEST_IMG"
# The resized part of the image should contain zeroes
$QEMU_IO -c "read -q -P 0 ${orig_size} 63k" "$TEST_IMG"
# If the image does not have an external data file we can also verify its
# actual size. The resized image should have 7 clusters:
# header, L1 table, L2 table, refcount table, refcount block, 2 data clusters
if ! _get_data_file "$TEST_IMG" > /dev/null; then
expected_file_length=$((65536 * 7))
file_length=$(stat -c '%s' "$TEST_IMG_FILE")
if [ "$file_length" != "$expected_file_length" ]; then
echo "ERROR: file length $file_length (expected $expected_file_length)"
fi
fi
echo
done
# success, all done
echo '*** done'
rm -f $seq.full

9
tests/qemu-iotests/125.out
View File

@ -767,4 +767,13 @@ wrote 2048000/2048000 bytes at offset 0
wrote 81920/81920 bytes at offset 2048000
80 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
Formatting 'TEST_DIR/t.IMGFMT.base', fmt=raw size=131072
--- Resizing image from 31k to 96k ---
Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=31744 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=raw
Image resized.
--- Resizing image from 33k to 96k ---
Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=33792 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=raw
Image resized.
*** done