1 files changed, 47 insertions, 3 deletions

diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index bd55038b56f5..81e5be6e6e35 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -151,7 +151,7 @@ The get_sb() method has the following arguments:
   const char *dev_name: the device name we are mounting.
 
   void *data: arbitrary mount options, usually comes as an ASCII
-        string
+        string (see "Mount Options" section)
 
   struct vfsmount *mnt: a vfs-internal representation of a mount point
 
@@ -182,7 +182,7 @@ A fill_super() method implementation has the following arguments:
         must initialize this properly.
 
   void *data: arbitrary mount options, usually comes as an ASCII
-        string
+        string (see "Mount Options" section)
 
   int silent: whether or not to be silent on error
 
@@ -291,7 +291,8 @@ or bottom half).
 
   umount_begin: called when the VFS is unmounting a filesystem.
 
-  show_options: called by the VFS to show mount options for /proc/<pid>/mounts.
+  show_options: called by the VFS to show mount options for
+        /proc/<pid>/mounts.  (see "Mount Options" section)
 
   quota_read: called by the VFS to read from filesystem quota file.
 
@@ -969,6 +970,49 @@ manipulate dentries:
 For further information on dentry locking, please refer to the document
 Documentation/filesystems/dentry-locking.txt.
 
+Mount Options
+=============
+
+Parsing options
+---------------
+
+On mount and remount the filesystem is passed a string containing a
+comma separated list of mount options.  The options can have either of
+these forms:
+
+  option
+  option=value
+
+The <linux/parser.h> header defines an API that helps parse these
+options.  There are plenty of examples on how to use it in existing
+filesystems.
+
+Showing options
+---------------
+
+If a filesystem accepts mount options, it must define show_options()
+to show all the currently active options.  The rules are:
+
+  - options MUST be shown which are not default or their values differ
+    from the default
+
+  - options MAY be shown which are enabled by default or have their
+    default value
+
+Options used only internally between a mount helper and the kernel
+(such as file descriptors), or which only have an effect during the
+mounting (such as ones controlling the creation of a journal) are exempt
+from the above rules.
+
+The underlying reason for the above rules is to make sure, that a
+mount can be accurately replicated (e.g. umounting and mounting again)
+based on the information found in /proc/mounts.
+
+A simple method of saving options at mount/remount time and showing
+them is provided with the save_mount_options() and
+generic_show_options() helper functions.  Please note, that using
+these may have drawbacks.  For more info see header comments for these
+functions in fs/namespace.c.
 
 Resources
 =========