[PATCH v4 0/3] qapi & doc: deprecate drive-backup

[PATCH v4 0/3] qapi & doc: deprecate drive-backup

[Markus Armbruster]

See 03 commit message for details. 01-02 are preparation docs update.

v4: deprecate drive-backup transaction by squashing
	[PATCH v4 5/5] block: Deprecate transaction type drive-backup
	Message-Id: <20211025042405.3762351-6-armbru@redhat.com>
    into PATCH 3

v3: wording fix-ups and improvements suggested by Kashyap
v2: add a lot of documentation changes
v1 was "[PATCH] qapi: deprecate drive-backup"

Vladimir Sementsov-Ogievskiy (3):
  docs/block-replication: use blockdev-backup
  docs/interop/bitmaps: use blockdev-backup
  qapi: deprecate drive-backup

 docs/about/deprecated.rst              |  11 +
 docs/block-replication.txt             |   4 +-
 docs/interop/bitmaps.rst               | 285 +++++++++++++++++++------
 docs/interop/live-block-operations.rst |  47 ++--
 qapi/block-core.json                   |   5 +-
 qapi/transaction.json                  |   6 +-
 6 files changed, 268 insertions(+), 90 deletions(-)

-- 
2.31.1

[PATCH v4 1/3] docs/block-replication: use blockdev-backup

[Markus Armbruster]

From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

We are going to deprecate drive-backup, so don't mention it here.
Moreover, blockdev-backup seems more correct in the context.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 docs/block-replication.txt | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/docs/block-replication.txt b/docs/block-replication.txt
index 108e9166a8..59eb2b33b3 100644
--- a/docs/block-replication.txt
+++ b/docs/block-replication.txt
@@ -79,7 +79,7 @@ Primary |                 ||  Secondary disk <--------- hidden-disk 5 <---------
                           ||        |                         |
                           ||        |                         |
                           ||        '-------------------------'
-                          ||           drive-backup sync=none 6
+                          ||         blockdev-backup sync=none 6
 
 1) The disk on the primary is represented by a block device with two
 children, providing replication between a primary disk and the host that
@@ -101,7 +101,7 @@ should support bdrv_make_empty() and backing file.
 that is modified by the primary VM. It should also start as an empty disk,
 and the driver supports bdrv_make_empty() and backing file.
 
-6) The drive-backup job (sync=none) is run to allow hidden-disk to buffer
+6) The blockdev-backup job (sync=none) is run to allow hidden-disk to buffer
 any state that would otherwise be lost by the speculative write-through
 of the NBD server into the secondary disk. So before block replication,
 the primary disk and secondary disk should contain the same data.
-- 
2.31.1

[PATCH v4 2/3] docs/interop/bitmaps: use blockdev-backup

[Markus Armbruster]

From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

We are going to deprecate drive-backup, so use modern interface here.
In examples where target image creation is shown, show blockdev-add as
well. If target creation omitted, omit blockdev-add as well.

Reviewed-by: Kashyap Chamarthy <kchamart@redhat.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 docs/interop/bitmaps.rst | 285 +++++++++++++++++++++++++++++----------
 1 file changed, 215 insertions(+), 70 deletions(-)

diff --git a/docs/interop/bitmaps.rst b/docs/interop/bitmaps.rst
index 059ad67929..1de46febdc 100644
--- a/docs/interop/bitmaps.rst
+++ b/docs/interop/bitmaps.rst
@@ -539,12 +539,11 @@ other partial disk images on top of a base image to reconstruct a full backup
 from the point in time at which the incremental backup was issued.
 
 The "Push Model" here references the fact that QEMU is "pushing" the modified
-blocks out to a destination. We will be using the `drive-backup
-<qemu-qmp-ref.html#index-drive_002dbackup>`_ and `blockdev-backup
-<qemu-qmp-ref.html#index-blockdev_002dbackup>`_ QMP commands to create both
+blocks out to a destination. We will be using the  `blockdev-backup
+<qemu-qmp-ref.html#index-blockdev_002dbackup>`_ QMP command to create both
 full and incremental backups.
 
-Both of these commands are jobs, which have their own QMP API for querying and
+The command is a background job, which has its own QMP API for querying and
 management documented in `Background jobs
 <qemu-qmp-ref.html#Background-jobs>`_.
 
@@ -557,6 +556,10 @@ create a new incremental backup chain attached to a drive.
 This example creates a new, full backup of "drive0" and accompanies it with a
 new, empty bitmap that records writes from this point in time forward.
 
+The target can be created with the help of `blockdev-add
+<qemu-qmp-ref.html#index-blockdev_002dadd>`_ or `blockdev-create
+<qemu-qmp-ref.html#index-blockdev_002dcreate>`_ command.
+
 .. note:: Any new writes that happen after this command is issued, even while
           the backup job runs, will be written locally and not to the backup
           destination. These writes will be recorded in the bitmap
@@ -576,12 +579,11 @@ new, empty bitmap that records writes from this point in time forward.
              }
            },
            {
-             "type": "drive-backup",
+             "type": "blockdev-backup",
              "data": {
                "device": "drive0",
-               "target": "/path/to/drive0.full.qcow2",
-               "sync": "full",
-               "format": "qcow2"
+               "target": "target0",
+               "sync": "full"
              }
            }
          ]
@@ -664,12 +666,11 @@ use a transaction to reset the bitmap while making a new full backup:
            }
          },
          {
-           "type": "drive-backup",
+           "type": "blockdev-backup",
            "data": {
              "device": "drive0",
-             "target": "/path/to/drive0.new_full.qcow2",
-             "sync": "full",
-             "format": "qcow2"
+             "target": "target0",
+             "sync": "full"
            }
          }
        ]
@@ -728,19 +729,35 @@ Example: First Incremental Backup
        $ qemu-img create -f qcow2 drive0.inc0.qcow2 \
          -b drive0.full.qcow2 -F qcow2
 
+#. Add target block node:
+
+   .. code-block:: QMP
+
+    -> {
+         "execute": "blockdev-add",
+         "arguments": {
+           "node-name": "target0",
+           "driver": "qcow2",
+           "file": {
+             "driver": "file",
+             "filename": "drive0.inc0.qcow2"
+           }
+         }
+       }
+
+    <- { "return": {} }
+
 #. Issue an incremental backup command:
 
    .. code-block:: QMP
 
     -> {
-         "execute": "drive-backup",
+         "execute": "blockdev-backup",
          "arguments": {
            "device": "drive0",
            "bitmap": "bitmap0",
-           "target": "drive0.inc0.qcow2",
-           "format": "qcow2",
-           "sync": "incremental",
-           "mode": "existing"
+           "target": "target0",
+           "sync": "incremental"
          }
        }
 
@@ -785,20 +802,36 @@ Example: Second Incremental Backup
        $ qemu-img create -f qcow2 drive0.inc1.qcow2 \
          -b drive0.inc0.qcow2 -F qcow2
 
+#. Add target block node:
+
+   .. code-block:: QMP
+
+    -> {
+         "execute": "blockdev-add",
+         "arguments": {
+           "node-name": "target0",
+           "driver": "qcow2",
+           "file": {
+             "driver": "file",
+             "filename": "drive0.inc1.qcow2"
+           }
+         }
+       }
+
+    <- { "return": {} }
+
 #. Issue a new incremental backup command. The only difference here is that we
    have changed the target image below.
 
    .. code-block:: QMP
 
     -> {
-         "execute": "drive-backup",
+         "execute": "blockdev-backup",
          "arguments": {
            "device": "drive0",
            "bitmap": "bitmap0",
-           "target": "drive0.inc1.qcow2",
-           "format": "qcow2",
-           "sync": "incremental",
-           "mode": "existing"
+           "target": "target0",
+           "sync": "incremental"
          }
        }
 
@@ -866,20 +899,36 @@ image:
              file for you, but you lose control over format options like
              compatibility and preallocation presets.
 
+#. Add target block node:
+
+   .. code-block:: QMP
+
+    -> {
+         "execute": "blockdev-add",
+         "arguments": {
+           "node-name": "target0",
+           "driver": "qcow2",
+           "file": {
+             "driver": "file",
+             "filename": "drive0.inc2.qcow2"
+           }
+         }
+       }
+
+    <- { "return": {} }
+
 #. Issue a new incremental backup command. Apart from the new destination
    image, there is no difference from the last two examples.
 
    .. code-block:: QMP
 
     -> {
-         "execute": "drive-backup",
+         "execute": "blockdev-backup",
          "arguments": {
            "device": "drive0",
            "bitmap": "bitmap0",
-           "target": "drive0.inc2.qcow2",
-           "format": "qcow2",
-           "sync": "incremental",
-           "mode": "existing"
+           "target": "target0",
+           "sync": "incremental"
          }
        }
 
@@ -930,6 +979,38 @@ point in time.
     $ qemu-img create -f qcow2 drive0.full.qcow2 64G
     $ qemu-img create -f qcow2 drive1.full.qcow2 64G
 
+#. Add target block nodes:
+
+   .. code-block:: QMP
+
+    -> {
+         "execute": "blockdev-add",
+         "arguments": {
+           "node-name": "target0",
+           "driver": "qcow2",
+           "file": {
+             "driver": "file",
+             "filename": "drive0.full.qcow2"
+           }
+         }
+       }
+
+    <- { "return": {} }
+
+    -> {
+         "execute": "blockdev-add",
+         "arguments": {
+           "node-name": "target1",
+           "driver": "qcow2",
+           "file": {
+             "driver": "file",
+             "filename": "drive1.full.qcow2"
+           }
+         }
+       }
+
+    <- { "return": {} }
+
 #. Create a full (anchor) backup for each drive, with accompanying bitmaps:
 
    .. code-block:: QMP
@@ -953,21 +1034,19 @@ point in time.
                }
              },
              {
-               "type": "drive-backup",
+               "type": "blockdev-backup",
                "data": {
                  "device": "drive0",
-                 "target": "/path/to/drive0.full.qcow2",
-                 "sync": "full",
-                 "format": "qcow2"
+                 "target": "target0",
+                 "sync": "full"
                }
              },
              {
-               "type": "drive-backup",
+               "type": "blockdev-backup",
                "data": {
                  "device": "drive1",
-                 "target": "/path/to/drive1.full.qcow2",
-                 "sync": "full",
-                 "format": "qcow2"
+                 "target": "target1",
+                 "sync": "full"
                }
              }
            ]
@@ -1016,6 +1095,38 @@ point in time.
      $ qemu-img create -f qcow2 drive1.inc0.qcow2 \
        -b drive1.full.qcow2 -F qcow2
 
+#. Add target block nodes:
+
+   .. code-block:: QMP
+
+    -> {
+         "execute": "blockdev-add",
+         "arguments": {
+           "node-name": "target0",
+           "driver": "qcow2",
+           "file": {
+             "driver": "file",
+             "filename": "drive0.inc0.qcow2"
+           }
+         }
+       }
+
+    <- { "return": {} }
+
+    -> {
+         "execute": "blockdev-add",
+         "arguments": {
+           "node-name": "target1",
+           "driver": "qcow2",
+           "file": {
+             "driver": "file",
+             "filename": "drive1.inc0.qcow2"
+           }
+         }
+       }
+
+    <- { "return": {} }
+
 #. Issue a multi-drive incremental push backup transaction:
 
    .. code-block:: QMP
@@ -1025,25 +1136,21 @@ point in time.
          "arguments": {
            "actions": [
              {
-               "type": "drive-backup",
+               "type": "blockev-backup",
                "data": {
                  "device": "drive0",
                  "bitmap": "bitmap0",
-                 "format": "qcow2",
-                 "mode": "existing",
                  "sync": "incremental",
-                 "target": "drive0.inc0.qcow2"
+                 "target": "target0"
                }
              },
              {
-               "type": "drive-backup",
+               "type": "blockdev-backup",
                "data": {
                  "device": "drive1",
                  "bitmap": "bitmap0",
-                 "format": "qcow2",
-                 "mode": "existing",
                  "sync": "incremental",
-                 "target": "drive1.inc0.qcow2"
+                 "target": "target1"
                }
              },
            ]
@@ -1119,19 +1226,35 @@ described above. This example demonstrates the single-job failure case:
        $ qemu-img create -f qcow2 drive0.inc0.qcow2 \
          -b drive0.full.qcow2 -F qcow2
 
+#. Add target block node:
+
+   .. code-block:: QMP
+
+    -> {
+         "execute": "blockdev-add",
+         "arguments": {
+           "node-name": "target0",
+           "driver": "qcow2",
+           "file": {
+             "driver": "file",
+             "filename": "drive0.inc0.qcow2"
+           }
+         }
+       }
+
+    <- { "return": {} }
+
 #. Attempt to create an incremental backup via QMP:
 
    .. code-block:: QMP
 
     -> {
-         "execute": "drive-backup",
+         "execute": "blockdev-backup",
          "arguments": {
            "device": "drive0",
            "bitmap": "bitmap0",
-           "target": "drive0.inc0.qcow2",
-           "format": "qcow2",
-           "sync": "incremental",
-           "mode": "existing"
+           "target": "target0",
+           "sync": "incremental"
          }
        }
 
@@ -1164,6 +1287,19 @@ described above. This example demonstrates the single-job failure case:
          "event": "BLOCK_JOB_COMPLETED"
        }
 
+#. Remove target node:
+
+   .. code-block:: QMP
+
+    -> {
+         "execute": "blockdev-del",
+         "arguments": {
+           "node-name": "target0",
+         }
+       }
+
+    <- { "return": {} }
+
 #. Delete the failed image, and re-create it.
 
    .. code:: bash
@@ -1172,20 +1308,36 @@ described above. This example demonstrates the single-job failure case:
        $ qemu-img create -f qcow2 drive0.inc0.qcow2 \
          -b drive0.full.qcow2 -F qcow2
 
+#. Add target block node:
+
+   .. code-block:: QMP
+
+    -> {
+         "execute": "blockdev-add",
+         "arguments": {
+           "node-name": "target0",
+           "driver": "qcow2",
+           "file": {
+             "driver": "file",
+             "filename": "drive0.inc0.qcow2"
+           }
+         }
+       }
+
+    <- { "return": {} }
+
 #. Retry the command after fixing the underlying problem, such as
    freeing up space on the backup volume:
 
    .. code-block:: QMP
 
     -> {
-         "execute": "drive-backup",
+         "execute": "blockdev-backup",
          "arguments": {
            "device": "drive0",
            "bitmap": "bitmap0",
-           "target": "drive0.inc0.qcow2",
-           "format": "qcow2",
-           "sync": "incremental",
-           "mode": "existing"
+           "target": "target0",
+           "sync": "incremental"
          }
        }
 
@@ -1210,7 +1362,8 @@ described above. This example demonstrates the single-job failure case:
 Example: Partial Transactional Failures
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-QMP commands like `drive-backup <qemu-qmp-ref.html#index-drive_002dbackup>`_
+QMP commands like `blockdev-backup
+<qemu-qmp-ref.html#index-blockdev_002dbackup>`_
 conceptually only start a job, and so transactions containing these commands
 may succeed even if the job it created later fails. This might have surprising
 interactions with notions of how a "transaction" ought to behave.
@@ -1240,25 +1393,21 @@ and one succeeds:
          "arguments": {
            "actions": [
            {
-             "type": "drive-backup",
+             "type": "blockdev-backup",
              "data": {
                "device": "drive0",
                "bitmap": "bitmap0",
-               "format": "qcow2",
-               "mode": "existing",
                "sync": "incremental",
-               "target": "drive0.inc0.qcow2"
+               "target": "target0"
              }
            },
            {
-             "type": "drive-backup",
+             "type": "blockdev-backup",
              "data": {
                "device": "drive1",
                "bitmap": "bitmap0",
-               "format": "qcow2",
-               "mode": "existing",
                "sync": "incremental",
-               "target": "drive1.inc0.qcow2"
+               "target": "target1"
              }
            }]
          }
@@ -1375,25 +1524,21 @@ applied:
            },
            "actions": [
            {
-             "type": "drive-backup",
+             "type": "blockdev-backup",
              "data": {
                "device": "drive0",
                "bitmap": "bitmap0",
-               "format": "qcow2",
-               "mode": "existing",
                "sync": "incremental",
-               "target": "drive0.inc0.qcow2"
+               "target": "target0"
              }
            },
            {
-             "type": "drive-backup",
+             "type": "blockdev-backup",
              "data": {
                "device": "drive1",
                "bitmap": "bitmap0",
-               "format": "qcow2",
-               "mode": "existing",
                "sync": "incremental",
-               "target": "drive1.inc0.qcow2"
+               "target": "target1"
              }
            }]
          }
-- 
2.31.1

[PATCH v4 3/3] qapi: deprecate drive-backup

[Markus Armbruster]

From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

Modern way is using blockdev-add + blockdev-backup, which provides a
lot more control on how target is opened.

As example of drive-backup problems consider the following:

User of drive-backup expects that target will be opened in the same
cache and aio mode as source. Corresponding logic is in
drive_backup_prepare(), where we take bs->open_flags of source.

It works rather bad if source was added by blockdev-add. Assume source
is qcow2 image. On blockdev-add we should specify aio and cache options
for file child of qcow2 node. What happens next:

drive_backup_prepare() looks at bs->open_flags of qcow2 source node.
But there no BDRV_O_NOCAHE neither BDRV_O_NATIVE_AIO: BDRV_O_NOCAHE is
places in bs->file->bs->open_flags, and BDRV_O_NATIVE_AIO is nowhere,
as file-posix parse options and simply set s->use_linux_aio.

The documentation is updated in a minimal way, so that drive-backup is
noted only as a deprecated command, and blockdev-backup used in most of
places.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Kashyap Chamarthy <kchamart@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 docs/about/deprecated.rst              | 11 ++++++
 docs/interop/live-block-operations.rst | 47 +++++++++++++++++---------
 qapi/block-core.json                   |  5 ++-
 qapi/transaction.json                  |  6 +++-
 4 files changed, 51 insertions(+), 18 deletions(-)

diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
index 56f9ad15ab..e3bdb89c65 100644
--- a/docs/about/deprecated.rst
+++ b/docs/about/deprecated.rst
@@ -239,6 +239,17 @@ single ``bitmap``, the new ``block-export-add`` uses a list of ``bitmaps``.
 Member ``values`` in return value elements with meta-type ``enum`` is
 deprecated.  Use ``members`` instead.
 
+``drive-backup`` (since 6.2)
+''''''''''''''''''''''''''''
+
+Use ``blockdev-backup`` in combination with ``blockdev-add`` instead.
+This change primarily separates the creation/opening process of the backup
+target with explicit, separate steps. ``blockdev-backup`` uses mostly the
+same arguments as ``drive-backup``, except the ``format`` and ``mode``
+options are removed in favor of using explicit ``blockdev-create`` and
+``blockdev-add`` calls. See :doc:`/interop/live-block-operations` for
+details.
+
 System accelerators
 -------------------
 
diff --git a/docs/interop/live-block-operations.rst b/docs/interop/live-block-operations.rst
index 9e3635b233..d403d96f58 100644
--- a/docs/interop/live-block-operations.rst
+++ b/docs/interop/live-block-operations.rst
@@ -116,8 +116,8 @@ QEMU block layer supports.
 (3) ``drive-mirror`` (and ``blockdev-mirror``): Synchronize a running
     disk to another image.
 
-(4) ``drive-backup`` (and ``blockdev-backup``): Point-in-time (live) copy
-    of a block device to a destination.
+(4) ``blockdev-backup`` (and the deprecated ``drive-backup``):
+    Point-in-time (live) copy of a block device to a destination.
 
 
 .. _`Interacting with a QEMU instance`:
@@ -555,13 +555,14 @@ Currently, there are four different kinds:
 
 (3) ``none`` -- Synchronize only the new writes from this point on.
 
-    .. note:: In the case of ``drive-backup`` (or ``blockdev-backup``),
-              the behavior of ``none`` synchronization mode is different.
-              Normally, a ``backup`` job consists of two parts: Anything
-              that is overwritten by the guest is first copied out to
-              the backup, and in the background the whole image is
-              copied from start to end. With ``sync=none``, it's only
-              the first part.
+    .. note:: In the case of ``blockdev-backup`` (or deprecated
+              ``drive-backup``), the behavior of ``none``
+              synchronization mode is different.  Normally, a
+              ``backup`` job consists of two parts: Anything that is
+              overwritten by the guest is first copied out to the
+              backup, and in the background the whole image is copied
+              from start to end. With ``sync=none``, it's only the
+              first part.
 
 (4) ``incremental`` -- Synchronize content that is described by the
     dirty bitmap
@@ -928,19 +929,22 @@ Shutdown the guest, by issuing the ``quit`` QMP command::
     }
 
 
-Live disk backup --- ``drive-backup`` and ``blockdev-backup``
--------------------------------------------------------------
+Live disk backup --- ``blockdev-backup`` and the deprecated``drive-backup``
+---------------------------------------------------------------------------
 
-The ``drive-backup`` (and its newer equivalent ``blockdev-backup``) allows
+The ``blockdev-backup`` (and the deprecated ``drive-backup``) allows
 you to create a point-in-time snapshot.
 
-In this case, the point-in-time is when you *start* the ``drive-backup``
-(or its newer equivalent ``blockdev-backup``) command.
+In this case, the point-in-time is when you *start* the
+``blockdev-backup`` (or deprecated ``drive-backup``) command.
 
 
 QMP invocation for ``drive-backup``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
+Note that ``drive-backup`` command is deprecated since QEMU 6.1 and
+will be removed in future.
+
 Yet again, starting afresh with our example disk image chain::
 
     [A] <-- [B] <-- [C] <-- [D]
@@ -965,11 +969,22 @@ will be issued, indicating the live block device job operation has
 completed, and no further action is required.
 
 
+Moving from the deprecated ``drive-backup`` to newer ``blockdev-backup``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+``blockdev-backup`` differs from ``drive-backup`` in how you specify
+the backup target. With ``blockdev-backup`` you can't specify filename
+as a target.  Instead you use ``node-name`` of existing block node,
+which you may add by ``blockdev-add`` or ``blockdev-create`` commands.
+Correspondingly, ``blockdev-backup`` doesn't have ``mode`` and
+``format`` arguments which don't apply to an existing block node. See
+following sections for details and examples.
+
+
 Notes on ``blockdev-backup``
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-The ``blockdev-backup`` command is equivalent in functionality to
-``drive-backup``, except that it operates at node-level in a Block Driver
+The ``blockdev-backup`` command operates at node-level in a Block Driver
 State (BDS) graph.
 
 E.g. the sequence of actions to create a point-in-time backup
diff --git a/qapi/block-core.json b/qapi/block-core.json
index b290782bf2..f4968d6404 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1709,6 +1709,9 @@
 # The operation can be stopped before it has completed using the
 # block-job-cancel command.
 #
+# Features:
+# @deprecated: This command is deprecated. Use @blockdev-backup instead.
+#
 # Returns: - nothing on success
 #          - If @device is not a valid block device, GenericError
 #
@@ -1724,7 +1727,7 @@
 #
 ##
 { 'command': 'drive-backup', 'boxed': true,
-  'data': 'DriveBackup' }
+  'data': 'DriveBackup', 'features': ['deprecated'] }
 
 ##
 # @blockdev-backup:
diff --git a/qapi/transaction.json b/qapi/transaction.json
index d175b5f863..381a2df782 100644
--- a/qapi/transaction.json
+++ b/qapi/transaction.json
@@ -54,6 +54,10 @@
 # @blockdev-snapshot-sync: since 1.1
 # @drive-backup: Since 1.6
 #
+# Features:
+# @deprecated: Member @drive-backup is deprecated.  Use member
+#              @blockdev-backup instead.
+#
 # Since: 1.1
 ##
 { 'enum': 'TransactionActionKind',
@@ -62,7 +66,7 @@
             'block-dirty-bitmap-disable', 'block-dirty-bitmap-merge',
             'blockdev-backup', 'blockdev-snapshot',
             'blockdev-snapshot-internal-sync', 'blockdev-snapshot-sync',
-            'drive-backup' ] }
+            { 'name': 'drive-backup', 'features': [ 'deprecated' ] } ] }
 
 ##
 # @AbortWrapper:
-- 
2.31.1

Re: [PATCH v4 3/3] qapi: deprecate drive-backup

[Eric Blake]

On Thu, Nov 04, 2021 at 09:58:11AM +0100, Markus Armbruster wrote:
> From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> 
> Modern way is using blockdev-add + blockdev-backup, which provides a
> lot more control on how target is opened.
> 
> As example of drive-backup problems consider the following:
> 
> User of drive-backup expects that target will be opened in the same
> cache and aio mode as source. Corresponding logic is in
> drive_backup_prepare(), where we take bs->open_flags of source.
> 
> It works rather bad if source was added by blockdev-add. Assume source
> is qcow2 image. On blockdev-add we should specify aio and cache options
> for file child of qcow2 node. What happens next:
> 
> drive_backup_prepare() looks at bs->open_flags of qcow2 source node.
> But there no BDRV_O_NOCAHE neither BDRV_O_NATIVE_AIO: BDRV_O_NOCAHE is
> places in bs->file->bs->open_flags, and BDRV_O_NATIVE_AIO is nowhere,
> as file-posix parse options and simply set s->use_linux_aio.
> 
> The documentation is updated in a minimal way, so that drive-backup is
> noted only as a deprecated command, and blockdev-backup used in most of
> places.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> Reviewed-by: Kashyap Chamarthy <kchamart@redhat.com>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---

Reviewed-by: Eric Blake <eblake@redhat.com>

I think this is appropriate for inclusion in 6.2, even if it did not
quite make soft freeze, so that we aren't delaying the deprecation for
an entire cycle.

>  docs/about/deprecated.rst              | 11 ++++++
>  docs/interop/live-block-operations.rst | 47 +++++++++++++++++---------
>  qapi/block-core.json                   |  5 ++-
>  qapi/transaction.json                  |  6 +++-
>  4 files changed, 51 insertions(+), 18 deletions(-)
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org