We have a clear replacement, so let's deprecate it.
Signed-off-by: Max Reitz <mre...@redhat.com>
Reviewed-by: Eric Blake <ebl...@redhat.com>
Reviewed-by: Alberto Garcia <be...@igalia.com>
---
qapi/block-core.json | 4 ++--
block.c | 4 ++++
qemu-doc.texi | 7 +++++++
qemu-options.hx | 4 ++--
4 files changed, 15 insertions(+), 4 deletions(-)
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 5c5921bfb7..6cf695dfc5 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1090,7 +1090,7 @@
# @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
##
@@ -1238,7 +1238,7 @@
# "node-name": "node1534",
# "file": { "driver": "file",
# "filename": "hd1.qcow2" },
-# "backing": "" } }
+# "backing": null } }
#
# <- { "return": {} }
#
diff --git a/block.c b/block.c
index b86614d8ad..797706199d 100644
--- a/block.c
+++ b/block.c
@@ -2603,6 +2603,10 @@ static BlockDriverState *bdrv_open_inherit(const char
*filename,
if (qobject_to(qdict_get(options, "backing"), QNull) != 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");
}
diff --git a/qemu-doc.texi b/qemu-doc.texi
index 8e3556976b..1b537f3e00 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -2792,6 +2792,13 @@ 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The ``xlnx-ep108'' machine has been replaced by the ``xlnx-zcu102'' machine.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
diff --git a/qemu-options.hx b/qemu-options.hx
index 8ccd5dcaa6..ff84563206 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -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
--
2.14.3
