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, 27 insertions, 5 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 43927d14db67..75306b3c9526 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3064,9 +3064,12 @@ finish_open_created:
         error = may_open(&nd->path, acc_mode, open_flag);
         if (error)
                 goto out;
-        file->f_path.mnt = nd->path.mnt;
-        error = finish_open(file, nd->path.dentry, NULL, opened);
-        if (error) {
+
+        BUG_ON(*opened & FILE_OPENED); /* once it's opened, it's opened */
+        error = vfs_open(&nd->path, file, current_cred());
+        if (!error) {
+                *opened |= FILE_OPENED;
+        } else {
                 if (error == -EOPENSTALE)
                         goto stale_open;
                 goto out;
diff --git a/fs/open.c b/fs/open.c
index d6fd3acde134..de92c13b58be 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -823,8 +823,7 @@ struct file *dentry_open(const struct path *path, int flags,
         f = get_empty_filp();
         if (!IS_ERR(f)) {
                 f->f_flags = flags;
-                f->f_path = *path;
-                error = do_dentry_open(f, NULL, cred);
+                error = vfs_open(path, f, cred);
                 if (!error) {
                         /* from now on we need fput() to dispose of f */
                         error = open_check_o_direct(f);
@@ -841,6 +840,26 @@ struct file *dentry_open(const struct path *path, int flags,
 }
 EXPORT_SYMBOL(dentry_open);
 
+/**
+ * vfs_open - open the file at the given path
+ * @path: path to open
+ * @filp: newly allocated file with f_flag initialized
+ * @cred: credentials to use
+ */
+int vfs_open(const struct path *path, struct file *filp,
+             const struct cred *cred)
+{
+        struct inode *inode = path->dentry->d_inode;
+
+        if (inode->i_op->dentry_open)
+                return inode->i_op->dentry_open(path->dentry, filp, cred);
+        else {
+                filp->f_path = *path;
+                return do_dentry_open(filp, NULL, cred);
+        }
+}
+EXPORT_SYMBOL(vfs_open);
+
 static inline int build_open_flags(int flags, umode_t mode, struct open_flags *op)
 {
         int lookup_flags = 0;