vfs: add i_op->dentry_open()

Add a new inode operation i_op->dentry_open().  This is for stacked filesystems
that want to return a struct file from a different filesystem.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

2 files changed, 9 insertions, 0 deletions

diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 94d93b1f8b53..b30753cbf431 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -67,6 +67,7 @@ prototypes:
                                 struct file *, unsigned open_flag,
                                 umode_t create_mode, int *opened);
         int (*tmpfile) (struct inode *, struct dentry *, umode_t);
+        int (*dentry_open)(struct dentry *, struct file *, const struct cred *);
 
 locking rules:
         all may block
@@ -96,6 +97,7 @@ fiemap:		no
 update_time:    no
 atomic_open:    yes
 tmpfile:        no
+dentry_open:    no
 
         Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_mutex on
 victim.
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index fceff7c00a3c..20bf204426ca 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -364,6 +364,7 @@ struct inode_operations {
         int (*atomic_open)(struct inode *, struct dentry *, struct file *,
                         unsigned open_flag, umode_t create_mode, int *opened);
         int (*tmpfile) (struct inode *, struct dentry *, umode_t);
+        int (*dentry_open)(struct dentry *, struct file *, const struct cred *);
 };
 
 Again, all methods are called without any locks being held, unless
@@ -696,6 +697,12 @@ struct address_space_operations {
         but instead uses bmap to find out where the blocks in the file
         are and uses those addresses directly.
 
+  dentry_open: *WARNING: probably going away soon, do not use!* This is an
+        alternative to f_op->open(), the difference is that this method may open
+        a file not necessarily originating from the same filesystem as the one
+        i_op->open() was called on.  It may be useful for stacking filesystems
+        which want to allow native I/O directly on underlying files.
+
 
   invalidatepage: If a page has PagePrivate set, then invalidatepage
         will be called when part or all of the page is to be removed