linux-kernel - [PATCH 03/73] VFS: Comment mount following code [ver #2]

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Message-ID: <20120221175744.25235.42690.stgit@warthog.procyon.org.uk>
Date:	Tue, 21 Feb 2012 17:57:44 +0000
From:	David Howells <dhowells@...hat.com>
To:	linux-fsdevel@...r.kernel.org, viro@...IV.linux.org.uk,
	valerie.aurora@...il.com
Cc:	linux-kernel@...r.kernel.org,
	Valerie Aurora <vaurora@...hat.com> (Original author),
	David Howells <dhowells@...hat.com>
Subject: [PATCH 03/73] VFS: Comment mount following code [ver #2]

Add comments describing what the directions "up" and "down" mean and ref count
handling to the VFS mount following family of functions.

Signed-off-by: Valerie Aurora <vaurora@...hat.com> (Original author)
Signed-off-by: David Howells <dhowells@...hat.com>
---

 fs/namei.c     |   10 ++++++++++
 fs/namespace.c |   16 ++++++++++++++--
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index a780ea5..4dc0e1d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -688,6 +688,16 @@ static int follow_up_rcu(struct path *path)
 	return 1;
 }
 
+/*
+ * follow_up - Find the mountpoint of path's vfsmount
+ *
+ * Given a path, find the mountpoint of its source file system.
+ * Replace @path with the path of the mountpoint in the parent mount.
+ * Up is towards /.
+ *
+ * Return 1 if we went up a level and 0 if we were already at the
+ * root.
+ */
 int follow_up(struct path *path)
 {
 	struct mount *mnt = real_mount(path->mnt);
diff --git a/fs/namespace.c b/fs/namespace.c
index baedd0b..35c3b80 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -515,8 +515,20 @@ struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry,
 }
 
 /*
- * lookup_mnt increments the ref count before returning
- * the vfsmount struct.
+ * lookup_mnt - Return the first child mount mounted at path
+ *
+ * "First" means first mounted chronologically.  If you create the
+ * following mounts:
+ *
+ * mount /dev/sda1 /mnt
+ * mount /dev/sda2 /mnt
+ * mount /dev/sda3 /mnt
+ *
+ * Then lookup_mnt() on the base /mnt dentry in the root mount will
+ * return successively the root dentry and vfsmount of /dev/sda1, then
+ * /dev/sda2, then /dev/sda3, then NULL.
+ *
+ * lookup_mnt takes a reference to the found vfsmount.
  */
 struct vfsmount *lookup_mnt(struct path *path)
 {

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