vfs: add vfs_select_inode() helper

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org> # v4.2+

fs/open.c

@@ -840,16 +840,12 @@ EXPORT_SYMBOL(file_path);
 int vfs_open(const struct path *path, struct file *file,
 	     const struct cred *cred)
 {
-	struct dentry *dentry = path->dentry;
-	struct inode *inode = dentry->d_inode;
+	struct inode *inode = vfs_select_inode(path->dentry, file->f_flags);
 
-	file->f_path = *path;
-	if (dentry->d_flags & DCACHE_OP_SELECT_INODE) {
-		inode = dentry->d_op->d_select_inode(dentry, file->f_flags);
 	if (IS_ERR(inode))
 		return PTR_ERR(inode);
-	}
 
+	file->f_path = *path;
 	return do_dentry_open(file, inode, NULL, cred);
 }
 

include/linux/dcache.h

@@ -565,4 +565,16 @@ static inline struct dentry *d_real(struct dentry *dentry)
 		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;
+}
+
+
 #endif	/* __LINUX_DCACHE_H */