qemu-iotests: Test qcow2 not leaking clusters on write error

This adds a test for a temporary write failure, which simulates the
situation after werror=stop/enospc has stopped the VM. We shouldn't
leave leaked clusters behind in such cases.

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

tests/qemu-iotests/026

@@ -200,6 +200,23 @@ done
 done
 done
 
+echo
+echo === Avoid cluster leaks after temporary failure ===
+echo
+
+cat > "$TEST_DIR/blkdebug.conf" <<EOF
+[inject-error]
+event = "write_aio"
+errno = "5"
+once = "on"
+EOF
+
+# After the failed first write, do a second write so that the updated refcount
+# block is actually written back
+_make_test_img 64M
+$QEMU_IO -c "write 0 1M" -c "write 0 1M" "$BLKDBG_TEST_IMG" | _filter_qemu_io
+_check_test_img
+
 # success, all done
 echo "*** done"
 rm -f $seq.full

tests/qemu-iotests/026.out

@@ -675,4 +675,12 @@ write failed: No space left on device
 
 96 leaked clusters were found on the image.
 This means waste of disk space, but no harm to data.
+
+=== Avoid cluster leaks after temporary failure ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864
+write failed: Input/output error
+wrote 1048576/1048576 bytes at offset 0
+1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+No errors were found on the image.
 *** done

tests/qemu-iotests/026.out.nocache

@@ -683,4 +683,12 @@ write failed: No space left on device
 
 96 leaked clusters were found on the image.
 This means waste of disk space, but no harm to data.
+
+=== Avoid cluster leaks after temporary failure ===
+
+Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864
+write failed: Input/output error
+wrote 1048576/1048576 bytes at offset 0
+1 MiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+No errors were found on the image.
 *** done