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    Subject[PATCH 01/39] VFS: Comment follow_mount() and friends
    Date
    Add comments describing what the directions "up" and "down" mean and
    ref count handling to the VFS follow_mount() family of functions.

    Signed-off-by: Valerie Aurora <vaurora@redhat.com>
    Cc: Alexander Viro <viro@zeniv.linux.org.uk>
    ---
    fs/namei.c | 43 +++++++++++++++++++++++++++++++++++++++----
    fs/namespace.c | 16 ++++++++++++++--
    2 files changed, 53 insertions(+), 6 deletions(-)

    diff --git a/fs/namei.c b/fs/namei.c
    index a7dce91..dda6b7e 100644
    --- a/fs/namei.c
    +++ b/fs/namei.c
    @@ -596,6 +596,17 @@ loop:
    return err;
    }

    +/*
    + * 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 vfsmount *parent;
    @@ -616,8 +627,22 @@ int follow_up(struct path *path)
    return 1;
    }

    -/* no need for dcache_lock, as serialization is taken care in
    - * namespace.c
    +/*
    + * __follow_mount - Return the most recent mount at this mountpoint
    + *
    + * Given a mountpoint, find the most recently mounted file system at
    + * this mountpoint and return the path to its root dentry. This is
    + * the file system that is visible, and it is in the direction of VFS
    + * "down" - away from the root of the mount tree. See comments to
    + * lookup_mnt() for an example of "down."
    + *
    + * Does not decrement the refcount on the given mount even if it
    + * follows it to another mount and returns that path instead.
    + *
    + * Returns 0 if path was unchanged, 1 if we followed it to another mount.
    + *
    + * No need for dcache_lock, as serialization is taken care in
    + * namespace.c.
    */
    static int __follow_mount(struct path *path)
    {
    @@ -636,6 +661,12 @@ static int __follow_mount(struct path *path)
    return res;
    }

    +/*
    + * Like __follow_mount, but no return value and drops references to
    + * both mnt and dentry of the given path if it follows to another
    + * mount.
    + */
    +
    static void follow_mount(struct path *path)
    {
    while (d_mountpoint(path->dentry)) {
    @@ -649,8 +680,12 @@ static void follow_mount(struct path *path)
    }
    }

    -/* no need for dcache_lock, as serialization is taken care in
    - * namespace.c
    +/*
    + * Like follow_mount(), but traverses only one layer instead of
    + * continuing until it runs out.
    + *
    + * No need for dcache_lock, as serialization is taken care in
    + * namespace.c.
    */
    int follow_down(struct path *path)
    {
    diff --git a/fs/namespace.c b/fs/namespace.c
    index 8174c8a..1cd59a0 100644
    --- a/fs/namespace.c
    +++ b/fs/namespace.c
    @@ -433,8 +433,20 @@ struct vfsmount *__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)
    {
    --
    1.6.3.3


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