[RFC PATCH 34/35] vfs: simplify d_op->d_real()

[Miklos Szeredi <mszeredi@redhat.com>]

The only remaining user of d_real() is file_dentry().

Simplify code related to ->d_real() by:

 - remove dead code from overlayfs implementation
 - remove the open_flags argument
 - expand d_real() helper into file_dentry()
 - remove d_real() helper, since there are no callers and makes no sense to
   add new ones

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 Documentation/filesystems/Locking |  3 +--
 Documentation/filesystems/vfs.txt | 22 +++-------------
 fs/overlayfs/super.c              | 55 +++++++--------------------------------
 include/linux/dcache.h            | 24 +----------------
 include/linux/fs.h                |  7 ++++-
 5 files changed, 21 insertions(+), 90 deletions(-)

diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index a4afe96f0112..e1d7e43d302c 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -21,8 +21,7 @@ prototypes:
 	char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
 	struct vfsmount *(*d_automount)(struct path *path);
 	int (*d_manage)(const struct path *, bool);
-	struct dentry *(*d_real)(struct dentry *, const struct inode *,
-				 unsigned int);
+	struct dentry *(*d_real)(struct dentry *, const struct inode *);
 
 locking rules:
 		rename_lock	->d_lock	may block	rcu-walk
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index af54d3651ff8..632d5c58fde9 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -990,8 +990,7 @@ struct dentry_operations {
 	char *(*d_dname)(struct dentry *, char *, int);
 	struct vfsmount *(*d_automount)(struct path *);
 	int (*d_manage)(const struct path *, bool);
-	struct dentry *(*d_real)(struct dentry *, const struct inode *,
-				 unsigned int);
+	struct dentry *(*d_real)(struct dentry *, const struct inode *);
 };
 
   d_revalidate: called when the VFS needs to revalidate a dentry. This
@@ -1124,23 +1123,8 @@ struct dentry_operations {
 	This function is only used if DCACHE_MANAGE_TRANSIT is set on the
 	dentry being transited from.
 
-  d_real: overlay/union type filesystems implement this method to return one of
-	the underlying dentries hidden by the overlay.  It is used in three
-	different modes:
-
-	Called from open it may need to copy-up the file depending on the
-	supplied open flags.  This mode is selected with a non-zero flags
-	argument.  In this mode the d_real method can return an error.
-
-	Called from file_dentry() it returns the real dentry matching the inode
-	argument.  The real dentry may be from a lower layer already copied up,
-	but still referenced from the file.  This mode is selected with a
-	non-NULL inode argument.  This will always succeed.
-
-	With NULL inode and zero flags the topmost real underlying dentry is
-	returned.  This will always succeed.
-
-	This method is never called with both non-NULL inode and non-zero flags.
+  d_real: This is called from file_dentry().  It returns the real dentry
+	matching the inode argument.
 
 Each dentry has a pointer to its parent dentry, as well as a hash list
 of child dentries. Child dentries are basically like files in a
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index f2a83fabe2eb..ab1642fcece3 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -80,64 +80,29 @@ static void ovl_dentry_release(struct dentry *dentry)
 	}
 }
 
-static int ovl_check_append_only(struct inode *inode, int flag)
-{
-	/*
-	 * This test was moot in vfs may_open() because overlay inode does
-	 * not have the S_APPEND flag, so re-check on real upper inode
-	 */
-	if (IS_APPEND(inode)) {
-		if  ((flag & O_ACCMODE) != O_RDONLY && !(flag & O_APPEND))
-			return -EPERM;
-		if (flag & O_TRUNC)
-			return -EPERM;
-	}
-
-	return 0;
-}
-
 static struct dentry *ovl_d_real(struct dentry *dentry,
-				 const struct inode *inode,
-				 unsigned int open_flags)
+				 const struct inode *inode)
 {
 	struct dentry *real;
-	int err;
+
+	if (WARN_ON(!inode))
+		return dentry;
 
 	/* It's an overlay file */
-	if (inode && d_inode(dentry) == inode)
+	if (d_inode(dentry) == inode)
 		return dentry;
 
-	if (!d_is_reg(dentry)) {
-		if (!inode || inode == d_inode(dentry))
-			return dentry;
+	if (!d_is_reg(dentry))
 		goto bug;
-	}
 
-	if (open_flags) {
-		err = ovl_open_maybe_copy_up(dentry, open_flags);
-		if (err)
-			return ERR_PTR(err);
-	}
-
-	real = ovl_dentry_upper(dentry);
-	if (real && (!inode || inode == d_inode(real))) {
-		if (!inode) {
-			err = ovl_check_append_only(d_inode(real), open_flags);
-			if (err)
-				return ERR_PTR(err);
-		}
+	real = ovl_dentry_real(dentry);
+	if (inode == d_inode(real))
 		return real;
-	}
-
-	real = ovl_dentry_lower(dentry);
-	if (!real)
-		goto bug;
 
 	/* Handle recursion */
-	real = d_real(real, inode, open_flags);
+	if (unlikely(real->d_flags & DCACHE_OP_REAL))
+		return real->d_op->d_real(real, inode);
 
-	if (!inode || inode == d_inode(real))
-		return real;
 bug:
 	WARN(1, "ovl_d_real(%pd4, %s:%lu): real dentry not found\n", dentry,
 	     inode ? inode->i_sb->s_id : "NULL", inode ? inode->i_ino : 0);
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 129ef05759a9..712cc21c2e6d 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -147,8 +147,7 @@ struct dentry_operations {
 	char *(*d_dname)(struct dentry *, char *, int);
 	struct vfsmount *(*d_automount)(struct path *);
 	int (*d_manage)(const struct path *, bool);
-	struct dentry *(*d_real)(struct dentry *, const struct inode *,
-				 unsigned int);
+	struct dentry *(*d_real)(struct dentry *, const struct inode *);
 } ____cacheline_aligned;
 
 /*
@@ -565,27 +564,6 @@ static inline struct dentry *d_backing_dentry(struct dentry *upper)
 	return upper;
 }
 
-/**
- * d_real - Return the real dentry
- * @dentry: the dentry to query
- * @inode: inode to select the dentry from multiple layers (can be NULL)
- * @flags: open flags to control copy-up behavior
- *
- * If dentry is on a union/overlay, then return the underlying, real dentry.
- * Otherwise return the dentry itself.
- *
- * See also: Documentation/filesystems/vfs.txt
- */
-static inline struct dentry *d_real(struct dentry *dentry,
-				    const struct inode *inode,
-				    unsigned int flags)
-{
-	if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
-		return dentry->d_op->d_real(dentry, inode, flags);
-	else
-		return dentry;
-}
-
 struct name_snapshot {
 	const unsigned char *name;
 	unsigned char inline_name[DNAME_INLINE_LEN];
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 6db6e83004d6..77403c19dc69 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1234,7 +1234,12 @@ static inline struct inode *file_inode(const struct file *f)
 
 static inline struct dentry *file_dentry(const struct file *file)
 {
-	return d_real(file->f_path.dentry, file_inode(file), 0);
+	struct dentry *dentry = file->f_path.dentry;
+
+	if (unlikely(dentry->d_flags & DCACHE_OP_REAL))
+		return dentry->d_op->d_real(dentry, file_inode(file));
+	else
+		return dentry;
 }
 
 static inline int locks_lock_file_wait(struct file *filp, struct file_lock *fl)
-- 
2.14.3