block: Deprecate "backing": ""

We have a clear replacement, so let's deprecate it.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-Id: <20180224154033.29559-8-mreitz@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
This commit is contained in:
Max Reitz 2018-02-24 16:40:33 +01:00 committed by Eric Blake
parent e59a0cf17b
commit 4f7be2806e
4 changed files with 15 additions and 4 deletions

View File

@ -2649,6 +2649,10 @@ static BlockDriverState *bdrv_open_inherit(const char *filename,
if (qobject_to(QNull, qdict_get(options, "backing")) != NULL ||
(backing && *backing == '\0'))
{
if (backing) {
warn_report("Use of \"backing\": \"\" is deprecated; "
"use \"backing\": null instead");
}
flags |= BDRV_O_NO_BACKING;
qdict_del(options, "backing");
}

View File

@ -1174,7 +1174,7 @@
# @overlay: reference to the existing block device that will become
# the overlay of @node, as part of creating the snapshot.
# It must not have a current backing file (this can be
# achieved by passing "backing": "" to blockdev-add).
# achieved by passing "backing": null to blockdev-add).
#
# Since: 2.5
##
@ -1347,7 +1347,7 @@
# "node-name": "node1534",
# "file": { "driver": "file",
# "filename": "hd1.qcow2" },
# "backing": "" } }
# "backing": null } }
#
# <- { "return": {} }
#

View File

@ -2789,6 +2789,13 @@ support page sizes < 4096 any longer.
The ``xlnx-ep108'' machine has been replaced by the ``xlnx-zcu102'' machine.
The ``xlnx-zcu102'' machine has the same features and capabilites in QEMU.
@section Block device options
@subsection "backing": "" (since 2.12.0)
In order to prevent QEMU from automatically opening an image's backing
chain, use ``"backing": null'' instead.
@node License
@appendix License

View File

@ -743,8 +743,8 @@ Reference to or definition of the data source block driver node
@item backing
Reference to or definition of the backing file block device (default is taken
from the image file). It is allowed to pass an empty string here in order to
disable the default backing file.
from the image file). It is allowed to pass @code{null} here in order to disable
the default backing file.
@item lazy-refcounts
Whether to enable the lazy refcounts feature (on/off; default is taken from the