qcow2: Don't strand clusters near 2G intervals during commit

The qcow2_make_empty() function is reached during 'qemu-img commit',
in order to clear out ALL clusters of an image.  However, if the
image cannot use the fast code path (true if the image is format
0.10, or if the image contains a snapshot), the cluster size is
larger than 512, and the image is larger than 2G in size, then our
choice of sector_step causes problems.  Since it is not cluster
aligned, but qcow2_discard_clusters() silently ignores an unaligned
head or tail, we are leaving clusters allocated.

Enhance the testsuite to expose the flaw, and patch the problem by
ensuring our step size is aligned.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 25 insertions, 16 deletions

diff --git a/tests/qemu-iotests/097 b/tests/qemu-iotests/097
index 01d8dd0331..4c33e8038a 100755
--- a/tests/qemu-iotests/097
+++ b/tests/qemu-iotests/097
@@ -46,7 +46,7 @@ _supported_proto file
 _supported_os Linux
 
 
-# Four passes:
+# Four main passes:
 #  0: Two-layer backing chain, commit to upper backing file (implicitly)
 #     (in this case, the top image will be emptied)
 #  1: Two-layer backing chain, commit to upper backing file (explicitly)
@@ -56,22 +56,30 @@ _supported_os Linux
 #  3: Two-layer backing chain, commit to lower backing file
 #     (in this case, the top image will implicitly stay unchanged)
 #
+# Each pass is run twice, since qcow2 has different code paths for cleaning
+# an image depending on whether it has a snapshot.
+#
 # 020 already tests committing, so this only tests whether image chains are
 # working properly and that all images above the base are emptied; therefore,
-# no complicated patterns are necessary
+# no complicated patterns are necessary.  Check near the 2G mark, as qcow2
+# has been buggy at that boundary in the past.
 for i in 0 1 2 3; do
+for j in 0 1; do
 
 echo
-echo "=== Test pass $i ==="
+echo "=== Test pass $i.$j ==="
 echo
 
-TEST_IMG="$TEST_IMG.base" _make_test_img 64M
-TEST_IMG="$TEST_IMG.itmd" _make_test_img -b "$TEST_IMG.base" 64M
-_make_test_img -b "$TEST_IMG.itmd" 64M
+TEST_IMG="$TEST_IMG.base" _make_test_img 2100M
+TEST_IMG="$TEST_IMG.itmd" _make_test_img -b "$TEST_IMG.base" 2100M
+_make_test_img -b "$TEST_IMG.itmd" 2100M
+if [ $j -eq 0 ]; then
+    $QEMU_IMG snapshot -c snap "$TEST_IMG"
+fi
 
-$QEMU_IO -c 'write -P 1 0 192k' "$TEST_IMG.base" | _filter_qemu_io
-$QEMU_IO -c 'write -P 2 64k 128k' "$TEST_IMG.itmd" | _filter_qemu_io
-$QEMU_IO -c 'write -P 3 128k 64k' "$TEST_IMG" | _filter_qemu_io
+$QEMU_IO -c 'write -P 1 0x7ffd0000 192k' "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c 'write -P 2 0x7ffe0000 128k' "$TEST_IMG.itmd" | _filter_qemu_io
+$QEMU_IO -c 'write -P 3 0x7fff0000 64k' "$TEST_IMG" | _filter_qemu_io
 
 if [ $i -lt 3 ]; then
     if [ $i == 0 ]; then
@@ -88,12 +96,12 @@ if [ $i -lt 3 ]; then
     fi
 
     # Bottom should be unchanged
-    $QEMU_IO -c 'read -P 1 0 192k' "$TEST_IMG.base" | _filter_qemu_io
+    $QEMU_IO -c 'read -P 1 0x7ffd0000 192k' "$TEST_IMG.base" | _filter_qemu_io
 
     # Intermediate should contain changes from top
-    $QEMU_IO -c 'read -P 1 0 64k' "$TEST_IMG.itmd" | _filter_qemu_io
-    $QEMU_IO -c 'read -P 2 64k 64k' "$TEST_IMG.itmd" | _filter_qemu_io
-    $QEMU_IO -c 'read -P 3 128k 64k' "$TEST_IMG.itmd" | _filter_qemu_io
+    $QEMU_IO -c 'read -P 1 0x7ffd0000 64k' "$TEST_IMG.itmd" | _filter_qemu_io
+    $QEMU_IO -c 'read -P 2 0x7ffe0000 64k' "$TEST_IMG.itmd" | _filter_qemu_io
+    $QEMU_IO -c 'read -P 3 0x7fff0000 64k' "$TEST_IMG.itmd" | _filter_qemu_io
 
     # And in pass 0, the top image should be empty, whereas in both other passes
     # it should be unchanged (which is both checked by qemu-img map)
@@ -101,9 +109,9 @@ else
     $QEMU_IMG commit -b "$TEST_IMG.base" "$TEST_IMG"
 
     # Bottom should contain all changes
-    $QEMU_IO -c 'read -P 1 0 64k' "$TEST_IMG.base" | _filter_qemu_io
-    $QEMU_IO -c 'read -P 2 64k 64k' "$TEST_IMG.base" | _filter_qemu_io
-    $QEMU_IO -c 'read -P 3 128k 64k' "$TEST_IMG.base" | _filter_qemu_io
+    $QEMU_IO -c 'read -P 1 0x7ffd0000 64k' "$TEST_IMG.base" | _filter_qemu_io
+    $QEMU_IO -c 'read -P 2 0x7ffe0000 64k' "$TEST_IMG.base" | _filter_qemu_io
+    $QEMU_IO -c 'read -P 3 0x7fff0000 64k' "$TEST_IMG.base" | _filter_qemu_io
 
     # Both top and intermediate should be unchanged
 fi
@@ -113,6 +121,7 @@ $QEMU_IMG map "$TEST_IMG.itmd" | _filter_qemu_img_map
 $QEMU_IMG map "$TEST_IMG" | _filter_qemu_img_map
 
 done
+done
 
 
 # success, all done