qemu-iotests: 024: add rebasing test case for overlay_size > backing_size

Before previous commit, rebase was getting infitely stuck in case of
rebasing within the same backing chain and when overlay_size > backing_size.
Let's add this case to the rebasing test 024 to make sure it doesn't
break again.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Hanna Czenczek <hreitz@redhat.com>
Message-ID: <20230919165804.439110-3-andrey.drobyshev@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/024

@@ -199,6 +199,63 @@ echo
 # $BASE_OLD and $BASE_NEW)
 $QEMU_IMG map "$OVERLAY" | _filter_qemu_img_map
 
+# Check that rebase within the chain is working when
+# overlay_size > old_backing_size
+#
+# base_new <-- base_old <-- overlay
+#
+# Backing (new): 11 11 11 11 11
+# Backing (old): 22 22 22 22
+# Overlay:       -- -- -- -- --
+#
+# As a result, overlay should contain data identical to base_old, with the
+# last cluster remaining unallocated.
+
+echo
+echo "=== Test rebase within one backing chain ==="
+echo
+
+echo "Creating backing chain"
+echo
+
+TEST_IMG=$BASE_NEW _make_test_img $(( CLUSTER_SIZE * 5 ))
+TEST_IMG=$BASE_OLD _make_test_img -b "$BASE_NEW" -F $IMGFMT \
+    $(( CLUSTER_SIZE * 4 ))
+TEST_IMG=$OVERLAY _make_test_img -b "$BASE_OLD" -F $IMGFMT \
+    $(( CLUSTER_SIZE * 5 ))
+
+echo
+echo "Fill backing files with data"
+echo
+
+$QEMU_IO "$BASE_NEW" -c "write -P 0x11 0 $(( CLUSTER_SIZE * 5 ))" \
+    | _filter_qemu_io
+$QEMU_IO "$BASE_OLD" -c "write -P 0x22 0 $(( CLUSTER_SIZE * 4 ))" \
+    | _filter_qemu_io
+
+echo
+echo "Check the last cluster is zeroed in overlay before the rebase"
+echo
+$QEMU_IO "$OVERLAY" -c "read -P 0x00 $(( CLUSTER_SIZE * 4 )) $CLUSTER_SIZE" \
+    | _filter_qemu_io
+
+echo
+echo "Rebase onto another image in the same chain"
+echo
+
+$QEMU_IMG rebase -b "$BASE_NEW" -F $IMGFMT "$OVERLAY"
+
+echo "Verify that data is read the same before and after rebase"
+echo
+
+# Verify the first 4 clusters are still read the same as in the old base
+$QEMU_IO "$OVERLAY" -c "read -P 0x22 0 $(( CLUSTER_SIZE * 4 ))" \
+    | _filter_qemu_io
+# Verify the last cluster still reads as zeroes
+$QEMU_IO "$OVERLAY" -c "read -P 0x00 $(( CLUSTER_SIZE * 4 )) $CLUSTER_SIZE" \
+    | _filter_qemu_io
+
+echo
 
 # success, all done
 echo "*** done"

tests/qemu-iotests/024.out

@@ -171,4 +171,34 @@ read 65536/65536 bytes at offset 196608
 Offset          Length          File
 0               0x30000         TEST_DIR/subdir/t.IMGFMT
 0x30000         0x10000         TEST_DIR/subdir/t.IMGFMT.base_new
+
+=== Test rebase within one backing chain ===
+
+Creating backing chain
+
+Formatting 'TEST_DIR/subdir/t.IMGFMT.base_new', fmt=IMGFMT size=327680
+Formatting 'TEST_DIR/subdir/t.IMGFMT.base_old', fmt=IMGFMT size=262144 backing_file=TEST_DIR/subdir/t.IMGFMT.base_new backing_fmt=IMGFMT
+Formatting 'TEST_DIR/subdir/t.IMGFMT', fmt=IMGFMT size=327680 backing_file=TEST_DIR/subdir/t.IMGFMT.base_old backing_fmt=IMGFMT
+
+Fill backing files with data
+
+wrote 327680/327680 bytes at offset 0
+320 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+wrote 262144/262144 bytes at offset 0
+256 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+Check the last cluster is zeroed in overlay before the rebase
+
+read 65536/65536 bytes at offset 262144
+64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+Rebase onto another image in the same chain
+
+Verify that data is read the same before and after rebase
+
+read 262144/262144 bytes at offset 0
+256 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+read 65536/65536 bytes at offset 262144
+64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
 *** done