fs: Add a driver to access U-Boot environment variables

Add a driver working on top of ubootvar device and exposing U-Boot
environment variable data as files.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Cory Tusar <cory.tusar@zii.aero>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 28 insertions, 0 deletions

diff --git a/Documentation/filesystems/ubootvarfs.rst b/Documentation/filesystems/ubootvarfs.rst
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+.. index:: ubootvarfs (filesystem)
+
+.. _filesystems_ubootvarfs:
+
+U-Boot environment filesystem
+=============================
+
+barebox supports accessing U-Boot environment contents as a regular
+filesystems in both read and write modes.  U-Boot environment data
+(ubootvar) device supports automount, so no explicit mount command
+should be necessary and accessing the environment should be as easy
+as:
+
+.. code-block:: console
+
+  barebox:/ ls -l /mnt/ubootvar0
+
+However the filesystem can be explicitly mounted with the following
+command:
+
+.. code-block:: console
+
+  barebox:/ mount -t ubootvarfs /dev/device /mnt/path
+
+**NOTE** Current implementation of the filesystem driver uses lazy
+synchronization, any changes made to the environment will not be
+written to the medium until the filesystem is unmounted (will happen
+automatically on Barebox shutdown)