vfs: merge .d_select_inode() into .d_real()

The two methods essentially do the same: find the real dentry/inode
belonging to an overlay dentry.  The difference is in the usage:

vfs_open() uses ->d_select_inode() and expects the function to perform
copy-up if necessary based on the open flags argument.

file_dentry() uses ->d_real() passing in the overlay dentry as well as the
underlying inode.

vfs_rename() uses ->d_select_inode() but passes zero flags.  ->d_real()
with a zero inode would have worked just as well here.

This patch merges the functionality of ->d_select_inode() into ->d_real()
by adding an 'open_flags' argument to the latter.

[Al Viro] Make the signature of d_real() match that of ->d_real() again.
And constify the inode argument, while we are at it.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/dcache.c

@@ -1729,7 +1729,6 @@ void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
 				DCACHE_OP_REVALIDATE	|
 				DCACHE_OP_WEAK_REVALIDATE	|
 				DCACHE_OP_DELETE	|
-				DCACHE_OP_SELECT_INODE	|
 				DCACHE_OP_REAL));
 	dentry->d_op = op;
 	if (!op)
@@ -1746,8 +1745,6 @@ void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
 		dentry->d_flags |= DCACHE_OP_DELETE;
 	if (op->d_prune)
 		dentry->d_flags |= DCACHE_OP_PRUNE;
-	if (op->d_select_inode)
-		dentry->d_flags |= DCACHE_OP_SELECT_INODE;
 	if (op->d_real)
 		dentry->d_flags |= DCACHE_OP_REAL;
 

fs/namei.c

@@ -4328,7 +4328,7 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 	 * Check source == target.
 	 * On overlayfs need to look at underlying inodes.
 	 */
-	if (vfs_select_inode(old_dentry, 0) == vfs_select_inode(new_dentry, 0))
+	if (d_real_inode(old_dentry) == d_real_inode(new_dentry))
 		return 0;
 
 	error = may_delete(old_dir, old_dentry, is_dir);

fs/open.c

@@ -840,13 +840,13 @@ EXPORT_SYMBOL(file_path);
 int vfs_open(const struct path *path, struct file *file,
 	     const struct cred *cred)
 {
-	struct inode *inode = vfs_select_inode(path->dentry, file->f_flags);
+	struct dentry *dentry = d_real(path->dentry, NULL, file->f_flags);
 
-	if (IS_ERR(inode))
-		return PTR_ERR(inode);
+	if (IS_ERR(dentry))
+		return PTR_ERR(dentry);
 
 	file->f_path = *path;
-	return do_dentry_open(file, inode, NULL, cred);
+	return do_dentry_open(file, d_backing_inode(dentry), NULL, cred);
 }
 
 struct file *dentry_open(const struct path *path, int flags,

fs/overlayfs/inode.c

@@ -325,36 +325,25 @@ static bool ovl_open_need_copy_up(int flags, enum ovl_path_type type,
 	return true;
 }
 
-struct inode *ovl_d_select_inode(struct dentry *dentry, unsigned file_flags)
+int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags)
 {
-	int err;
+	int err = 0;
 	struct path realpath;
 	enum ovl_path_type type;
 
-	if (d_is_dir(dentry))
-		return d_backing_inode(dentry);
-
 	type = ovl_path_real(dentry, &realpath);
 	if (ovl_open_need_copy_up(file_flags, type, realpath.dentry)) {
 		err = ovl_want_write(dentry);
-		if (err)
-			return ERR_PTR(err);
-
-		if (file_flags & O_TRUNC)
-			err = ovl_copy_up_truncate(dentry);
-		else
-			err = ovl_copy_up(dentry);
-		ovl_drop_write(dentry);
-		if (err)
-			return ERR_PTR(err);
-
-		ovl_path_upper(dentry, &realpath);
+		if (!err) {
+			if (file_flags & O_TRUNC)
+				err = ovl_copy_up_truncate(dentry);
+			else
+				err = ovl_copy_up(dentry);
+			ovl_drop_write(dentry);
+		}
 	}
 
-	if (realpath.dentry->d_flags & DCACHE_OP_SELECT_INODE)
-		return realpath.dentry->d_op->d_select_inode(realpath.dentry, file_flags);
-
-	return d_backing_inode(realpath.dentry);
+	return err;
 }
 
 static const struct inode_operations ovl_file_inode_operations = {

fs/overlayfs/overlayfs.h

@@ -179,7 +179,7 @@ ssize_t ovl_getxattr(struct dentry *dentry, struct inode *inode,
 		     const char *name, void *value, size_t size);
 ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size);
 int ovl_removexattr(struct dentry *dentry, const char *name);
-struct inode *ovl_d_select_inode(struct dentry *dentry, unsigned file_flags);
+int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags);
 
 struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,
 			    struct ovl_entry *oe);

fs/overlayfs/super.c

@@ -304,7 +304,9 @@ static void ovl_dentry_release(struct dentry *dentry)
 	}
 }
 
-static struct dentry *ovl_d_real(struct dentry *dentry, struct inode *inode)
+static struct dentry *ovl_d_real(struct dentry *dentry,
+				 const struct inode *inode,
+				 unsigned int open_flags)
 {
 	struct dentry *real;
 
@@ -314,6 +316,16 @@ static struct dentry *ovl_d_real(struct dentry *dentry, struct inode *inode)
 		goto bug;
 	}
 
+	if (d_is_negative(dentry))
+		return dentry;
+
+	if (open_flags) {
+		int 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)))
 		return real;
@@ -326,9 +338,7 @@ static struct dentry *ovl_d_real(struct dentry *dentry, struct inode *inode)
 		return real;
 
 	/* Handle recursion */
-	if (real->d_flags & DCACHE_OP_REAL)
-		return real->d_op->d_real(real, inode);
-
+	return d_real(real, inode, open_flags);
 bug:
 	WARN(1, "ovl_d_real(%pd4, %s:%lu\n): real dentry not found\n", dentry,
 	     inode ? inode->i_sb->s_id : "NULL", inode ? inode->i_ino : 0);
@@ -378,13 +388,11 @@ static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
 
 static const struct dentry_operations ovl_dentry_operations = {
 	.d_release = ovl_dentry_release,
-	.d_select_inode = ovl_d_select_inode,
 	.d_real = ovl_d_real,
 };
 
 static const struct dentry_operations ovl_reval_dentry_operations = {
 	.d_release = ovl_dentry_release,
-	.d_select_inode = ovl_d_select_inode,
 	.d_real = ovl_d_real,
 	.d_revalidate = ovl_dentry_revalidate,
 	.d_weak_revalidate = ovl_dentry_weak_revalidate,

include/linux/dcache.h

@@ -139,8 +139,7 @@ struct dentry_operations {
 	char *(*d_dname)(struct dentry *, char *, int);
 	struct vfsmount *(*d_automount)(struct path *);
 	int (*d_manage)(struct dentry *, bool);
-	struct inode *(*d_select_inode)(struct dentry *, unsigned);
-	struct dentry *(*d_real)(struct dentry *, struct inode *);
+	struct dentry *(*d_real)(struct dentry *, const struct inode *, unsigned int);
 } ____cacheline_aligned;
 
 /*
@@ -206,10 +205,8 @@ struct dentry_operations {
 
 #define DCACHE_MAY_FREE			0x00800000
 #define DCACHE_FALLTHRU			0x01000000 /* Fall through to lower layer */
-#define DCACHE_OP_SELECT_INODE		0x02000000 /* Unioned entry: dcache op selects inode */
-
-#define DCACHE_ENCRYPTED_WITH_KEY	0x04000000 /* dir is encrypted with a valid key */
-#define DCACHE_OP_REAL			0x08000000
+#define DCACHE_ENCRYPTED_WITH_KEY	0x02000000 /* dir is encrypted with a valid key */
+#define DCACHE_OP_REAL			0x04000000
 
 #define DCACHE_PAR_LOOKUP		0x10000000 /* being looked up (with parent locked shared) */
 #define DCACHE_DENTRY_CURSOR		0x20000000
@@ -557,25 +554,16 @@ static inline struct dentry *d_backing_dentry(struct dentry *upper)
 	return upper;
 }
 
-static inline struct dentry *d_real(struct dentry *dentry)
+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, NULL);
+		return dentry->d_op->d_real(dentry, inode, flags);
 	else
 		return dentry;
 }
 
-static inline struct inode *vfs_select_inode(struct dentry *dentry,
-					     unsigned open_flags)
-{
-	struct inode *inode = d_inode(dentry);
-
-	if (inode && unlikely(dentry->d_flags & DCACHE_OP_SELECT_INODE))
-		inode = dentry->d_op->d_select_inode(dentry, open_flags);
-
-	return inode;
-}
-
 /**
  * d_real_inode - Return the real inode
  * @dentry: The dentry to query
@@ -585,7 +573,7 @@ static inline struct inode *vfs_select_inode(struct dentry *dentry,
  */
 static inline struct inode *d_real_inode(struct dentry *dentry)
 {
-	return d_backing_inode(d_real(dentry));
+	return d_backing_inode(d_real(dentry, NULL, 0));
 }
 
 

include/linux/fs.h

@@ -1272,12 +1272,7 @@ static inline struct inode *file_inode(const struct file *f)
 
 static inline struct dentry *file_dentry(const struct file *file)
 {
-	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;
+	return d_real(file->f_path.dentry, file_inode(file), 0);
 }
 
 static inline int locks_lock_file_wait(struct file *filp, struct file_lock *fl)