@@ -4779,14 +4779,19 @@ static int img_bitmap(int argc, char **argv)
filename = argv[optind];
bitmap = argv[optind + 1];
- blk = img_open(image_opts, filename, fmt, BDRV_O_RDWR, false, false,
- false);
+ /*
+ * No need to open backing chains; we will be manipulating bitmaps
+ * directly in this image without reference to image contents.
+ */
+ blk = img_open(image_opts, filename, fmt, BDRV_O_RDWR | BDRV_O_NO_BACKING,
+ false, false, false);
if (!blk) {
goto out;
}
bs = blk_bs(blk);
if (src_filename) {
- src = img_open(false, src_filename, src_fmt, 0, false, false, false);
+ src = img_open(false, src_filename, src_fmt, BDRV_O_NO_BACKING,
+ false, false, false);
if (!src) {
goto out;
}
@@ -91,6 +91,15 @@ $QEMU_IMG bitmap --remove --image-opts \
driver=$IMGFMT,file.driver=file,file.filename="$TEST_IMG" tmp
_img_info --format-specific
+echo
+echo "=== Merge from top layer into backing image ==="
+echo
+
+$QEMU_IMG rebase -u -F qcow2 -b "$TEST_IMG.base" "$TEST_IMG"
+$QEMU_IMG bitmap --add --merge b2 -b "$TEST_IMG" -F $IMGFMT \
+ -f $IMGFMT "$TEST_IMG.base" b3
+_img_info --format-specific --backing-chain
+
echo
echo "=== Check bitmap contents ==="
echo
@@ -107,6 +116,9 @@ $QEMU_IMG map --output=json --image-opts \
nbd_server_start_unix_socket -r -f qcow2 -B b2 "$TEST_IMG"
$QEMU_IMG map --output=json --image-opts \
"$IMG,x-dirty-bitmap=qemu:dirty-bitmap:b2" | _filter_qemu_img_map
+nbd_server_start_unix_socket -r -f qcow2 -B b3 "$TEST_IMG"
+$QEMU_IMG map --output=json --image-opts \
+ "$IMG,x-dirty-bitmap=qemu:dirty-bitmap:b3" | _filter_qemu_img_map
# success, all done
echo '*** done'
@@ -68,6 +68,59 @@ Format specific information:
corrupt: false
extended l2: false
+=== Merge from top layer into backing image ===
+
+image: TEST_DIR/t.IMGFMT
+file format: IMGFMT
+virtual size: 10 MiB (10485760 bytes)
+cluster_size: 65536
+backing file: TEST_DIR/t.IMGFMT.base
+backing file format: IMGFMT
+Format specific information:
+ compat: 1.1
+ compression type: zlib
+ lazy refcounts: false
+ bitmaps:
+ [0]:
+ flags:
+ name: b1
+ granularity: 524288
+ [1]:
+ flags:
+ [0]: auto
+ name: b2
+ granularity: 65536
+ [2]:
+ flags:
+ name: b0
+ granularity: 65536
+ refcount bits: 16
+ corrupt: false
+ extended l2: false
+
+image: TEST_DIR/t.IMGFMT.base
+file format: IMGFMT
+virtual size: 10 MiB (10485760 bytes)
+cluster_size: 65536
+Format specific information:
+ compat: 1.1
+ compression type: zlib
+ lazy refcounts: false
+ bitmaps:
+ [0]:
+ flags:
+ [0]: auto
+ name: b0
+ granularity: 65536
+ [1]:
+ flags:
+ [0]: auto
+ name: b3
+ granularity: 65536
+ refcount bits: 16
+ corrupt: false
+ extended l2: false
+
=== Check bitmap contents ===
[{ "start": 0, "length": 3145728, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
@@ -79,4 +132,7 @@ Format specific information:
[{ "start": 0, "length": 2097152, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
{ "start": 2097152, "length": 1048576, "depth": 0, "zero": false, "data": false},
{ "start": 3145728, "length": 7340032, "depth": 0, "zero": false, "data": true, "offset": OFFSET}]
+[{ "start": 0, "length": 2097152, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
+{ "start": 2097152, "length": 1048576, "depth": 0, "zero": false, "data": false},
+{ "start": 3145728, "length": 7340032, "depth": 0, "zero": false, "data": true, "offset": OFFSET}]
*** done
If you have the chain 'base.qcow2 <- top.qcow2' and want to merge a bitmap from top into base, qemu-img was failing with: qemu-img: Could not open 'top.qcow2': Could not open backing file: Failed to get shared "write" lock Is another process using the image [base.qcow2]? The easiest fix is to not open the entire backing chain of either image (source or destination); after all, the point of 'qemu-img bitmap' is solely to manipulate bitmaps directly within a single qcow2 image, and this is made more precise if we don't pay attention to other images in the chain that may happen to have a bitmap by the same name. However, note that on a case-by-case analysis, there _are_ times where we treat it as a feature that we can access a bitmap from a backing layer in association with an overlay BDS. A demonstration of this is using NBD to expose both an overlay BDS (for constant contents) and a bitmap (for learning which blocks are interesting) during an incremental backup: Base <- Active <- Temporary \--block job ->/ where Temporary is being fed by a backup 'sync=none' job. When exposing Temporary over NBD, referring to a bitmap that lives only in Active is less effort than having to copy a bitmap into Temporary [1]. So the testsuite additions in this patch check both where bitmaps get allocated (the qemu-img info output), and that qemu-nbd is indeed able to access a bitmap inherited from the backing chain since it is a different use case than 'qemu-img bitmap'. [1] Full disclosure: prior to the recent commit 374eedd1c4 and friends, we were NOT able to see bitmaps through filters, which meant that we actually did not have nice clean semantics for uniformly being able to pick up bitmaps from anywhere in the backing chain (seen as a change in behavior between qemu 4.1 and 4.2 at commit 00e30f05de, when block-copy swapped from a one-off to a filter). Which means libvirt was already coded to copy bitmaps around for the sake of older qemu, even though modern qemu no longer needs it. Oh well. Fixes: http://bugzilla.redhat.com/1877209 Reported-by: Eyal Shenitzky <eshenitz@redhat.com> Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20200914191009.644842-1-eblake@redhat.com> [eblake: more commit message tweaks, per Max Reitz review] Reviewed-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> --- qemu-img.c | 11 ++++++-- tests/qemu-iotests/291 | 12 ++++++++ tests/qemu-iotests/291.out | 56 ++++++++++++++++++++++++++++++++++++++ 3 files changed, 76 insertions(+), 3 deletions(-)