iotests: Test downgrading an image using a small L2 slice size

expand_zero_clusters_in_l1() is used when downgrading qcow2 images
from v3 to v2 (compat=0.10). This is one of the functions that needed
more changes to support L2 slices, so this patch extends iotest 061 to
test downgrading a qcow2 image using a smaller slice size.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 3e5662dce5e4926c8fabbad4c0b9142b2a506dd4.1517840877.git.berto@igalia.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

tests/qemu-iotests/061

@@ -53,6 +53,22 @@ $PYTHON qcow2.py "$TEST_IMG" dump-header
 $QEMU_IO -c "read -P 0 0 128k" "$TEST_IMG" | _filter_qemu_io
 _check_test_img
 
+echo
+echo "=== Testing version downgrade with zero expansion and 4K cache entries ==="
+echo
+IMGOPTS="compat=1.1,lazy_refcounts=on" _make_test_img 64M
+$QEMU_IO -c "write -z 0 128k" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IO -c "write -z 32M 128k" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IO -c map "$TEST_IMG" | _filter_qemu_io
+$PYTHON qcow2.py "$TEST_IMG" dump-header
+$QEMU_IMG amend -o "compat=0.10" --image-opts \
+          driver=qcow2,file.filename=$TEST_IMG,l2-cache-entry-size=4096
+$PYTHON qcow2.py "$TEST_IMG" dump-header
+$QEMU_IO -c "read -P 0 0 128k" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IO -c "read -P 0 32M 128k" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IO -c map "$TEST_IMG" | _filter_qemu_io
+_check_test_img
+
 echo
 echo "=== Testing dirty version downgrade ==="
 echo

tests/qemu-iotests/061.out

@@ -52,6 +52,67 @@ read 131072/131072 bytes at offset 0
 128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 No errors were found on the image.
 
+=== Testing version downgrade with zero expansion and 4K cache entries ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864
+wrote 131072/131072 bytes at offset 0
+128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+wrote 131072/131072 bytes at offset 33554432
+128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+128 KiB (0x20000) bytes     allocated at offset 0 bytes (0x0)
+31.875 MiB (0x1fe0000) bytes not allocated at offset 128 KiB (0x20000)
+128 KiB (0x20000) bytes     allocated at offset 32 MiB (0x2000000)
+31.875 MiB (0x1fe0000) bytes not allocated at offset 32.125 MiB (0x2020000)
+magic                     0x514649fb
+version                   3
+backing_file_offset       0x0
+backing_file_size         0x0
+cluster_bits              16
+size                      67108864
+crypt_method              0
+l1_size                   1
+l1_table_offset           0x30000
+refcount_table_offset     0x10000
+refcount_table_clusters   1
+nb_snapshots              0
+snapshot_offset           0x0
+incompatible_features     0x0
+compatible_features       0x1
+autoclear_features        0x0
+refcount_order            4
+header_length             104
+
+Header extension:
+magic                     0x6803f857
+length                    144
+data                      <binary>
+
+magic                     0x514649fb
+version                   2
+backing_file_offset       0x0
+backing_file_size         0x0
+cluster_bits              16
+size                      67108864
+crypt_method              0
+l1_size                   1
+l1_table_offset           0x30000
+refcount_table_offset     0x10000
+refcount_table_clusters   1
+nb_snapshots              0
+snapshot_offset           0x0
+incompatible_features     0x0
+compatible_features       0x0
+autoclear_features        0x0
+refcount_order            4
+header_length             72
+
+read 131072/131072 bytes at offset 0
+128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+read 131072/131072 bytes at offset 33554432
+128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+64 MiB (0x4000000) bytes not allocated at offset 0 bytes (0x0)
+No errors were found on the image.
+
 === Testing dirty version downgrade ===
 
 Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864