docs: fs: convert docs without extension to ReST

There are 3 remaining files without an extension inside the fs docs
dir.

Manually convert them to ReST.

In the case of the nfs/exporting.rst file, as the nfs docs
aren't ported yet, I opted to convert and add a :orphan: there,
with should be removed when it gets added into a nfs-specific
part of the fs documentation.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/filesystems/directory-locking → Documentation/filesystems/directory-locking.rst

@@ -1,12 +1,17 @@
-	Locking scheme used for directory operations is based on two
+=================
+Directory Locking
+=================
+
+
+Locking scheme used for directory operations is based on two
 kinds of locks - per-inode (->i_rwsem) and per-filesystem
 (->s_vfs_rename_mutex).
 
-	When taking the i_rwsem on multiple non-directory objects, we
+When taking the i_rwsem on multiple non-directory objects, we
 always acquire the locks in order by increasing address.  We'll call
 that "inode pointer" order in the following.
 
-	For our purposes all operations fall in 5 classes:
+For our purposes all operations fall in 5 classes:
 
 1) read access.  Locking rules: caller locks directory we are accessing.
 The lock is taken shared.
@@ -27,25 +32,29 @@ NB: we might get away with locking the the source (and target in exchange
 case) shared.
 
 5) link creation.  Locking rules:
+
 	* lock parent
 	* check that source is not a directory
 	* lock source
 	* call the method.
+
 All locks are exclusive.
 
 6) cross-directory rename.  The trickiest in the whole bunch.  Locking
 rules:
+
 	* lock the filesystem
 	* lock parents in "ancestors first" order.
 	* find source and target.
 	* if old parent is equal to or is a descendent of target
-		fail with -ENOTEMPTY
+	  fail with -ENOTEMPTY
 	* if new parent is equal to or is a descendent of source
-		fail with -ELOOP
+	  fail with -ELOOP
 	* If it's an exchange, lock both the source and the target.
 	* If the target exists, lock it.  If the source is a non-directory,
 	  lock it.  If we need to lock both, do so in inode pointer order.
 	* call the method.
+
 All ->i_rwsem are taken exclusive.  Again, we might get away with locking
 the the source (and target in exchange case) shared.
 
@@ -54,10 +63,11 @@ read, modified or removed by method will be locked by caller.
 
 
 If no directory is its own ancestor, the scheme above is deadlock-free.
+
 Proof:
 
 	First of all, at any moment we have a partial ordering of the
-objects - A < B iff A is an ancestor of B.
+	objects - A < B iff A is an ancestor of B.
 
 	That ordering can change.  However, the following is true:
 
@@ -77,32 +87,32 @@ objects - A < B iff A is an ancestor of B.
     non-directory object, except renames, which take locks on source and
     target in inode pointer order in the case they are not directories.)
 
-	Now consider the minimal deadlock.  Each process is blocked on
+Now consider the minimal deadlock.  Each process is blocked on
 attempt to acquire some lock and already holds at least one lock.  Let's
 consider the set of contended locks.  First of all, filesystem lock is
 not contended, since any process blocked on it is not holding any locks.
 Thus all processes are blocked on ->i_rwsem.
 
-	By (3), any process holding a non-directory lock can only be
+By (3), any process holding a non-directory lock can only be
 waiting on another non-directory lock with a larger address.  Therefore
 the process holding the "largest" such lock can always make progress, and
 non-directory objects are not included in the set of contended locks.
 
-	Thus link creation can't be a part of deadlock - it can't be
+Thus link creation can't be a part of deadlock - it can't be
 blocked on source and it means that it doesn't hold any locks.
 
-	Any contended object is either held by cross-directory rename or
+Any contended object is either held by cross-directory rename or
 has a child that is also contended.  Indeed, suppose that it is held by
 operation other than cross-directory rename.  Then the lock this operation
 is blocked on belongs to child of that object due to (1).
 
-	It means that one of the operations is cross-directory rename.
+It means that one of the operations is cross-directory rename.
 Otherwise the set of contended objects would be infinite - each of them
 would have a contended child and we had assumed that no object is its
 own descendent.  Moreover, there is exactly one cross-directory rename
 (see above).
 
-	Consider the object blocking the cross-directory rename.  One
+Consider the object blocking the cross-directory rename.  One
 of its descendents is locked by cross-directory rename (otherwise we
 would again have an infinite set of contended objects).  But that
 means that cross-directory rename is taking locks out of order.  Due
@@ -112,7 +122,7 @@ try to acquire lock on descendent before the lock on ancestor.
 Contradiction.  I.e.  deadlock is impossible.  Q.E.D.
 
 
-	These operations are guaranteed to avoid loop creation.  Indeed,
+These operations are guaranteed to avoid loop creation.  Indeed,
 the only operation that could introduce loops is cross-directory rename.
 Since the only new (parent, child) pair added by rename() is (new parent,
 source), such loop would have to contain these objects and the rest of it
@@ -123,13 +133,13 @@ new parent had been equal to or a descendent of source since the moment when
 we had acquired filesystem lock and rename() would fail with -ELOOP in that
 case.
 
-	While this locking scheme works for arbitrary DAGs, it relies on
+While this locking scheme works for arbitrary DAGs, it relies on
 ability to check that directory is a descendent of another object.  Current
 implementation assumes that directory graph is a tree.  This assumption is
 also preserved by all operations (cross-directory rename on a tree that would
 not introduce a cycle will leave it a tree and link() fails for directories).
 
-	Notice that "directory" in the above == "anything that might have
+Notice that "directory" in the above == "anything that might have
 children", so if we are going to introduce hybrid objects we will need
 either to make sure that link(2) doesn't work for them or to make changes
 in is_subdir() that would make it work even in presence of such beasts.

Documentation/filesystems/index.rst

@@ -20,6 +20,8 @@ algorithms work.
    path-lookup
    api-summary
    splice
+   locking
+   directory-locking
 
 Filesystem support layers
 =========================