8:29 a.m.
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(a)virtuozzo.com>
Reviewed-by: Kashyap Chamarthy <kchamart(a)redhat.com>
---
docs/about/deprecated.rst | 11 ++++++
docs/interop/live-block-operations.rst | 47 +++++++++++++++++---------
qapi/block-core.json | 5 ++-
3 files changed, 46 insertions(+), 17 deletions(-)
diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
index 25b7ec8d92..4a4910143f 100644
--- a/docs/about/deprecated.rst
+++ b/docs/about/deprecated.rst
@@ -234,6 +234,17 @@ 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:
--
2.31.1