iotests: qcow2 COW with minimal L2 cache size

This adds a test case to test 103 for performing a COW operation in a
qcow2 image using an L2 cache with minimal size (which should be at
least two clusters so the COW can access both source and destination
simultaneously).

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/103

@@ -93,6 +93,16 @@ $QEMU_IO -c "open -o l2-cache-size=1M,refcount-cache-size=0.25M $TEST_IMG" \
          -c 'read -P 42 0 64k' \
     | _filter_qemu_io
 
+echo
+echo '=== Testing minimal L2 cache and COW ==='
+echo
+
+$QEMU_IMG snapshot -c foo "$TEST_IMG"
+# This requires a COW operation, which accesses two L2 tables simultaneously
+# (COW source and destination), so there must be enough space in the cache to
+# place both tables there (and qemu should not crash)
+$QEMU_IO -c "open -o cache-size=0 $TEST_IMG" -c 'write 0 64k' | _filter_qemu_io
+
 # success, all done
 echo '*** done'
 rm -f $seq.full

tests/qemu-iotests/103.out

@@ -26,4 +26,9 @@ read 65536/65536 bytes at offset 0
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 read 65536/65536 bytes at offset 0
 64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+=== Testing minimal L2 cache and COW ===
+
+wrote 65536/65536 bytes at offset 0
+64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 *** done