autofs4: add miscellaneous device for ioctls

Add a miscellaneous device to the autofs4 module for routing ioctls.  This
provides the ability to obtain an ioctl file handle for an autofs mount
point that is possibly covered by another mount.

The actual problem with autofs is that it can't reconnect to existing
mounts.  Immediately one things of just adding the ability to remount
autofs file systems would solve it, but alas, that can't work.  This is
because autofs direct mounts and the implementation of "on demand mount
and expire" of nested mount trees have the file system mounted on top of
the mount trigger dentry.

To resolve this a miscellaneous device node for routing ioctl commands to
these mount points has been implemented in the autofs4 kernel module and a
library added to autofs.  This provides the ability to open a file
descriptor for these over mounted autofs mount points.

Please refer to Documentation/filesystems/autofs4-mount-control.txt for a
discussion of the problem, implementation alternatives considered and a
description of the interface.

[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: build fix]
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 8 deletions

diff --git a/fs/autofs4/expire.c b/fs/autofs4/expire.c
index e79dd09e12a1..cde2f8e8935a 100644
--- a/fs/autofs4/expire.c
+++ b/fs/autofs4/expire.c
@@ -244,10 +244,10 @@ cont:
 }
 
 /* Check if we can expire a direct mount (possibly a tree) */
-static struct dentry *autofs4_expire_direct(struct super_block *sb,
-                                            struct vfsmount *mnt,
-                                            struct autofs_sb_info *sbi,
-                                            int how)
+struct dentry *autofs4_expire_direct(struct super_block *sb,
+                                     struct vfsmount *mnt,
+                                     struct autofs_sb_info *sbi,
+                                     int how)
 {
         unsigned long timeout;
         struct dentry *root = dget(sb->s_root);
@@ -283,10 +283,10 @@ static struct dentry *autofs4_expire_direct(struct super_block *sb,
  *  - it is unused by any user process
  *  - it has been unused for exp_timeout time
  */
-static struct dentry *autofs4_expire_indirect(struct super_block *sb,
-                                              struct vfsmount *mnt,
-                                              struct autofs_sb_info *sbi,
-                                              int how)
+struct dentry *autofs4_expire_indirect(struct super_block *sb,
+                                       struct vfsmount *mnt,
+                                       struct autofs_sb_info *sbi,
+                                       int how)
 {
         unsigned long timeout;
         struct dentry *root = sb->s_root;