docs: binderfs: add section about feature files

Document how binder feature files can be used to determine whether a
feature is supported by the binder driver. "oneway_spam_detection" is
used as an example as it is the first available feature file.

Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Link: https://lore.kernel.org/r/20210715031805.1725878-2-cmllamas@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/admin-guide/binderfs.rst b/Documentation/admin-guide/binderfs.rst
index 199d843..41a4db0 100644 (file)
--- a/Documentation/admin-guide/binderfs.rst
+++ b/Documentation/admin-guide/binderfs.rst
@@ -72,3 +72,16 @@ that the `rm() <rm_>`_ tool can be used to delete them. Note that the
 ``binder-control`` device cannot be deleted since this would make the binderfs
 instance unusable.  The ``binder-control`` device will be deleted when the
 binderfs instance is unmounted and all references to it have been dropped.
+
+Binder features
+---------------
+
+Assuming an instance of binderfs has been mounted at ``/dev/binderfs``, the
+features supported by the binder driver can be located under
+``/dev/binderfs/features/``. The presence of individual files can be tested
+to determine whether a particular feature is supported by the driver.
+
+Example::
+
+        cat /dev/binderfs/features/oneway_spam_detection
+        1