block/qcow2.c | 17 ++++++++++++++--- tests/qemu-iotests/125 | 21 +++++++++++++++++++++ tests/qemu-iotests/125.out | 9 +++++++++ 3 files changed, 44 insertions(+), 3 deletions(-)
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>
---
block/qcow2.c | 17 ++++++++++++++---
tests/qemu-iotests/125 | 21 +++++++++++++++++++++
tests/qemu-iotests/125.out | 9 +++++++++
3 files changed, 44 insertions(+), 3 deletions(-)
diff --git a/block/qcow2.c b/block/qcow2.c
index 0cd2e6757e..e20590c3b7 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -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);
diff --git a/tests/qemu-iotests/125 b/tests/qemu-iotests/125
index d510984045..5c249b4b23 100755
--- a/tests/qemu-iotests/125
+++ b/tests/qemu-iotests/125
@@ -164,6 +164,27 @@ 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"
+ # The resized image should have 7 clusters:
+ # header, L1 table, L2 table, refcount table, refcount block, 2 data clusters
+ 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
+ echo
+done
+
# success, all done
echo '*** done'
rm -f $seq.full
diff --git a/tests/qemu-iotests/125.out b/tests/qemu-iotests/125.out
index 596905f533..7f76f7af20 100644
--- a/tests/qemu-iotests/125.out
+++ b/tests/qemu-iotests/125.out
@@ -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
--
2.20.1
On 6/10/20 4:46 AM, Alberto Garcia wrote: > 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> > --- > block/qcow2.c | 17 ++++++++++++++--- > tests/qemu-iotests/125 | 21 +++++++++++++++++++++ > tests/qemu-iotests/125.out | 9 +++++++++ > 3 files changed, 44 insertions(+), 3 deletions(-) > Reviewed-by: Eric Blake <eblake@redhat.com> -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org
On 10.06.20 11:46, Alberto Garcia wrote:
> 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>
> ---
> block/qcow2.c | 17 ++++++++++++++---
> tests/qemu-iotests/125 | 21 +++++++++++++++++++++
> tests/qemu-iotests/125.out | 9 +++++++++
> 3 files changed, 44 insertions(+), 3 deletions(-)
>
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 0cd2e6757e..e20590c3b7 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
[...]
> @@ -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,
> + },
(I don’t think we need to set .cow_end, but well, it doesn’t hurt either.)
Anyway, overall, the code change looks good to me, thanks!
> };
> qemu_co_queue_init(&allocation.dependent_requests);
>
> diff --git a/tests/qemu-iotests/125 b/tests/qemu-iotests/125
> index d510984045..5c249b4b23 100755
> --- a/tests/qemu-iotests/125
> +++ b/tests/qemu-iotests/125
> @@ -164,6 +164,27 @@ 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"
> + # The resized image should have 7 clusters:
> + # header, L1 table, L2 table, refcount table, refcount block, 2 data clusters
> + 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
Just one thing: Can we skip this check if $IMGOPTS has a data_file?
(i.e. if _get_data_file "$TEST_IMG" returns true)
Because if it has, the data clusters will be in that file and this is
bound to fail.
Max
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