qcow2: Make preallocate_co() resize the image to the correct size

This function preallocates metadata structures and then extends the
image to its new size, but that new size calculation is wrong because
it doesn't take into account that the host_offset variable is always
cluster-aligned.

This problem can be reproduced with preallocation=metadata when the
original size is not cluster-aligned but the new size is. In this case
the final image size will be shorter than expected.

   qemu-img create -f qcow2 img.qcow2 31k
   qemu-img resize --preallocation=metadata img.qcow2 128k

Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-Id: <adeb8b059917b141d5f5b3bd2a016262d3052c79.1599833007.git.berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
[mreitz: Mark compat=0.10 unsupported for iotest 125]
Signed-off-by: Max Reitz <mreitz@redhat.com>

1 files changed, 26 insertions, 18 deletions

diff --git a/tests/qemu-iotests/125 b/tests/qemu-iotests/125
index 7cb1c19..5720e86 100755
--- a/tests/qemu-iotests/125
+++ b/tests/qemu-iotests/125
@@ -43,6 +43,10 @@ get_image_size_on_host()
 
 _supported_fmt qcow2
 _supported_proto file
+# Growing a file with a backing file (without preallocation=full or
+# =falloc) requires zeroing the newly added area, which is impossible
+# to do quickly for v2 images, and hence is unsupported.
+_unsupported_imgopts 'compat=0.10'
 
 if [ -z "$TEST_IMG_FILE" ]; then
     TEST_IMG_FILE=$TEST_IMG
@@ -168,24 +172,28 @@ done
 $QEMU_IMG create -f raw "$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
+    for dst_size in 96k 128k; do
+        for prealloc in metadata full; do
+            echo "--- Resizing image from $orig_size to $dst_size (preallocation=$prealloc) ---"
+            _make_test_img -F raw -b "$TEST_IMG.base" -o cluster_size=64k "$orig_size"
+            $QEMU_IMG resize -f "$IMGFMT" --preallocation="$prealloc" "$TEST_IMG" "$dst_size"
+            # 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
+    done
 done
 
 # success, all done