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qemu-kvm/kvm-qemu-img-Support-bitmap-merge-into-backing-image.patch
Danilo C. L. de Paula a318bb58b7 * Mon Sep 28 2020 Danilo Cesar Lemes de Paula <ddepaula@redhat.com> - 5.1.0-10.el8 
- kvm-qemu-img-Support-bitmap-merge-into-backing-image.patch [bz#1877209]
- Resolves: bz#1877209
  ('qemu-img bitmaps --merge' failed when trying to merge top volume bitmap to base volume bitmap)
2020-09-28 10:55:54 -04:00

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From a768aa960a2e9e3b8dd72dfc7135a7e7d0814d3f Mon Sep 17 00:00:00 2001
From: Eric Blake <eblake@redhat.com>
Date: Wed, 23 Sep 2020 17:49:40 -0400
Subject: [PATCH] qemu-img: Support bitmap --merge into backing image
RH-Author: Eric Blake <eblake@redhat.com>
Message-id: <20200923174940.704681-2-eblake@redhat.com>
Patchwork-id: 98487
O-Subject: [RHEL-AV-8.3.0 qemu-kvm PATCH 1/1] qemu-img: Support bitmap --merge into backing image
Bugzilla: 1877209
RH-Acked-by: Sergio Lopez Pascual <slp@redhat.com>
RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>
RH-Acked-by: Max Reitz <mreitz@redhat.com>
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>
(cherry picked from commit 14f16bf9474c860ecc127a66a86961942319f7af)
Tweak 291.out since extended L2 is not backported.
Signed-off-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
---
qemu-img.c | 11 +++++---
tests/qemu-iotests/291 | 12 +++++++++
tests/qemu-iotests/291.out | 54 ++++++++++++++++++++++++++++++++++++++
3 files changed, 74 insertions(+), 3 deletions(-)
diff --git a/qemu-img.c b/qemu-img.c
index 5308773811f..b0ca321a6be 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -4747,14 +4747,19 @@ 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;
}
diff --git a/tests/qemu-iotests/291 b/tests/qemu-iotests/291
index 1e0bb76959b..4f837b20565 100755
--- a/tests/qemu-iotests/291
+++ b/tests/qemu-iotests/291
@@ -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'
diff --git a/tests/qemu-iotests/291.out b/tests/qemu-iotests/291.out
index 9f661515b41..332584f67a8 100644
--- a/tests/qemu-iotests/291.out
+++ b/tests/qemu-iotests/291.out
@@ -66,6 +66,57 @@ Format specific information:
refcount bits: 16
corrupt: 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
+
+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
+
=== Check bitmap contents ===
[{ "start": 0, "length": 3145728, "depth": 0, "zero": false, "data": true, "offset": OFFSET},
@@ -77,4 +128,7 @@ 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
--
2.27.0
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