[Qemu-block] [PATCH 4/4] file-posix: Add dynamic-auto-read-only QAPI feature

[Kevin Wolf]

In commit 23dece19da4 ('file-posix: Make auto-read-only dynamic') ,
auto-read-only=on changed its behaviour in file-posix for the 4.0
release. This change cannot be detected through the usual mechanisms
like schema introspection. Add a new feature flag to the schema to
allow libvirt to detect the presence of the new behaviour.

Signed-off-by: Kevin Wolf <address@hidden>
---
 qapi/block-core.json | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 7ccbfff9d0..4f96d5846b 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -2843,6 +2843,13 @@
 #                         file is large, do not use in production.
 #                         (default: off) (since: 3.0)
 #
+# If the feature 'dynamic-auto-read-only' is present, enabled auto-read-only
+# means that the driver will open the image read-only at first, dynamically
+# reopen the image file read-write when the first writer is attached to the
+# node and reopen read-only when the last writer is detached. This allows to
+# give QEMU write permissions only on demand when an operation actually needs
+# write access.
+#
 # Since: 2.9
 ##
 { 'struct': 'BlockdevOptionsFile',
@@ -2852,7 +2859,9 @@
             '*aio': 'BlockdevAioOptions',
            '*drop-cache': {'type': 'bool',
                            'if': 'defined(CONFIG_LINUX)'},
-            '*x-check-cache-dropped': 'bool' } }
+            '*x-check-cache-dropped': 'bool' },
+  'features': [ { 'name': 'dynamic-auto-read-only',
+                  'if': 'defined(CONFIG_POSIX)' } ] }
 
 ##
 # @BlockdevOptionsNull:
-- 
2.20.1