block: rename backup-top to copy-before-write

We are going to convert backup_top to full featured public filter,
which can be used in separate of backup job. Start from renaming from
"how it used" to "what it does".

While updating comments in 283 iotest, drop and rephrase also things
about ".active", as this field is now dropped, and filter doesn't have
"inactive" mode.

Note that this change may be considered as incompatible interface
change, as backup-top filter format name was visible through
query-block and query-named-block-nodes.

Still, consider the following reasoning:

1. backup-top was never documented, so if someone depends on format
   name (for driver that can't be used other than it is automatically
   inserted on backup job start), it's a kind of "undocumented feature
   use". So I think we are free to change it.

2. There is a hope, that there is no such users: it's a lot more native
   to give a good node-name to backup-top filter if need to operate
   with it somehow, and don't touch format name.

3. Another "incompatible" change in further commit would be moving
   copy-before-write filter from using backing child to file child. And
   this is even more reasonable than renaming: for now all public
   filters are file-child based.

So, it's a risky change, but risk seems small and good interface worth
it.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20210824083856.17408-6-vsementsov@virtuozzo.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>

2 files changed, 17 insertions, 22 deletions

diff --git a/tests/qemu-iotests/283 b/tests/qemu-iotests/283
index 010c22f..a09e018 100755
--- a/tests/qemu-iotests/283
+++ b/tests/qemu-iotests/283
@@ -1,7 +1,7 @@
 #!/usr/bin/env python3
 # group: auto quick
 #
-# Test for backup-top filter permission activation failure
+# Test for copy-before-write filter permission conflict
 #
 # Copyright (c) 2019 Virtuozzo International GmbH.
 #
@@ -31,13 +31,13 @@ size = 1024 * 1024
 """ Test description
 
 When performing a backup, all writes on the source subtree must go through the
-backup-top filter so it can copy all data to the target before it is changed.
-backup-top filter is appended above source node, to achieve this thing, so all
-parents of source node are handled. A configuration with side parents of source
-sub-tree with write permission is unsupported (we'd have append several
-backup-top filter like nodes to handle such parents). The test create an
-example of such configuration and checks that a backup is then not allowed
-(blockdev-backup command should fail).
+copy-before-write filter so it can copy all data to the target before it is
+changed.  copy-before-write filter is appended above source node, to achieve
+this thing, so all parents of source node are handled. A configuration with
+side parents of source sub-tree with write permission is unsupported (we'd have
+append several copy-before-write filter like nodes to handle such parents). The
+test create an example of such configuration and checks that a backup is then
+not allowed (blockdev-backup command should fail).
 
 The configuration:
 
@@ -57,11 +57,10 @@ The configuration:
                         │    base     │ ◀──────────── │ other │
                         └─────────────┘               └───────┘
 
-On activation (see .active field of backup-top state in block/backup-top.c),
-backup-top is going to unshare write permission on its source child. Write
-unsharing will be propagated to the "source->base" link and will conflict with
-other node write permission. So permission update will fail and backup job will
-not be started.
+copy-before-write filter wants to unshare write permission on its source child.
+Write unsharing will be propagated to the "source->base" link and will conflict
+with other node write permission. So permission update will fail and backup job
+will not be started.
 
 Note, that the only thing which prevents backup of running on such
 configuration is default permission propagation scheme. It may be altered by
@@ -99,13 +98,9 @@ vm.qmp_log('blockdev-backup', sync='full', device='source', target='target')
 vm.shutdown()
 
 
-print('\n=== backup-top should be gone after job-finalize ===\n')
+print('\n=== copy-before-write filter should be gone after job-finalize ===\n')
 
-# Check that the backup-top node is gone after job-finalize.
-#
-# During finalization, the node becomes inactive and can no longer
-# function.  If it is still present, new parents might be attached, and
-# there would be no meaningful way to handle their I/O requests.
+# Check that the copy-before-write node is gone after job-finalize.
 
 vm = iotests.VM()
 vm.launch()
@@ -131,7 +126,7 @@ vm.qmp_log('blockdev-backup',
 
 vm.event_wait('BLOCK_JOB_PENDING', 5.0)
 
-# The backup-top filter should still be present prior to finalization
+# The copy-before-write filter should still be present prior to finalization
 assert vm.node_info('backup-filter') is not None
 
 vm.qmp_log('job-finalize', id='backup')
diff --git a/tests/qemu-iotests/283.out b/tests/qemu-iotests/283.out
index c6e12b1..f2b7219 100644
--- a/tests/qemu-iotests/283.out
+++ b/tests/qemu-iotests/283.out
@@ -5,9 +5,9 @@
 {"execute": "blockdev-add", "arguments": {"driver": "blkdebug", "image": "base", "node-name": "other", "take-child-perms": ["write"]}}
 {"return": {}}
 {"execute": "blockdev-backup", "arguments": {"device": "source", "sync": "full", "target": "target"}}
-{"error": {"class": "GenericError", "desc": "Cannot append backup-top filter: Permission conflict on node 'base': permissions 'write' are both required by node 'other' (uses node 'base' as 'image' child) and unshared by node 'source' (uses node 'base' as 'image' child)."}}
+{"error": {"class": "GenericError", "desc": "Cannot append copy-before-write filter: Permission conflict on node 'base': permissions 'write' are both required by node 'other' (uses node 'base' as 'image' child) and unshared by node 'source' (uses node 'base' as 'image' child)."}}
 
-=== backup-top should be gone after job-finalize ===
+=== copy-before-write filter should be gone after job-finalize ===
 
 {"execute": "blockdev-add", "arguments": {"driver": "null-co", "node-name": "source"}}
 {"return": {}}