iotests: Test corruption during COW request

Extend test file 060 by a test case for corruption occuring concurrently
to a COW request. QEMU should not crash but rather return an appropriate
error message.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

tests/qemu-iotests/060

@@ -138,6 +138,32 @@ $QEMU_IMG snapshot -a foo "$TEST_IMG"
 _check_test_img
 $QEMU_IO -c "$OPEN_RO" -c "read -P 1 0 512" | _filter_qemu_io
 
+echo
+echo "=== Testing overlap while COW is in flight ==="
+echo
+# compat=0.10 is required in order to make the following discard actually
+# unallocate the sector rather than make it a zero sector - we want COW, after
+# all.
+IMGOPTS='compat=0.10' _make_test_img 1G
+# Write two clusters, the second one enforces creation of an L2 table after
+# the first data cluster.
+$QEMU_IO -c 'write 0k 64k' -c 'write 512M 64k' "$TEST_IMG" | _filter_qemu_io
+# Discard the first cluster. This cluster will soon enough be reallocated and
+# used for COW.
+$QEMU_IO -c 'discard 0k 64k' "$TEST_IMG" | _filter_qemu_io
+# Now, corrupt the image by marking the second L2 table cluster as free.
+poke_file "$TEST_IMG" '131084' "\x00\x00" # 0x2000c
+# Start a write operation requiring COW on the image stopping it right before
+# doing the read; then, trigger the corruption prevention by writing anything to
+# any unallocated cluster, leading to an attempt to overwrite the second L2
+# table. Finally, resume the COW write and see it fail (but not crash).
+echo "open -o file.driver=blkdebug $TEST_IMG
+break cow_read 0
+aio_write 0k 1k
+wait_break 0
+write 64k 64k
+resume 0" | $QEMU_IO | _filter_qemu_io
+
 # success, all done
 echo "*** done"
 rm -f $seq.full

tests/qemu-iotests/060.out

@@ -78,4 +78,19 @@ read 512/512 bytes at offset 0
 No errors were found on the image.
 read 512/512 bytes at offset 0
 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+=== Testing overlap while COW is in flight ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1073741824 
+wrote 65536/65536 bytes at offset 0
+64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+wrote 65536/65536 bytes at offset 536870912
+64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+discard 65536/65536 bytes at offset 0
+64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+qcow2: Preventing invalid write on metadata (overlaps with active L2 table); image marked as corrupt.
+blkdebug: Suspended request '0'
+write failed: Input/output error
+blkdebug: Resuming request '0'
+aio_write failed: No medium found
 *** done