[RFC][PATCH 36/42] new helper: alloc_file_clone()

[Al Viro <viro@ZenIV.linux.org.uk>]

From: Al Viro <viro@zeniv.linux.org.uk>

alloc_file_clone(old_file, mode, ops): create a new struct file with
->f_path equal to that of old_file.  pipe converted.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/file_table.c      | 11 +++++++++++
 fs/pipe.c            |  4 +---
 include/linux/file.h |  2 ++
 3 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index 23bc46ea5f4b..9097a6fb5a2f 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -209,6 +209,17 @@ struct file *alloc_file_pseudo(struct inode *inode, struct vfsmount *mnt,
 }
 EXPORT_SYMBOL(alloc_file_pseudo);
 
+struct file *alloc_file_clone(struct file *base, fmode_t mode,
+				const struct file_operations *fops)
+{
+	struct file *f = alloc_file(&base->f_path, mode, fops);
+	if (!IS_ERR(f)) {
+		path_get(&f->f_path);
+		f->f_mapping = base->f_mapping;
+	}
+	return f;
+}
+
 /* the real guts of fput() - releasing the last reference to file
  */
 static void __fput(struct file *file)
diff --git a/fs/pipe.c b/fs/pipe.c
index c8c4265bf87b..94323a1d7c92 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -760,14 +760,12 @@ int create_pipe_files(struct file **res, int flags)
 	f->f_flags = O_WRONLY | (flags & (O_NONBLOCK | O_DIRECT));
 	f->private_data = inode->i_pipe;
 
-	res[0] = alloc_file(&f->f_path, FMODE_READ, &pipefifo_fops);
+	res[0] = alloc_file_clone(f, FMODE_READ, &pipefifo_fops);
 	if (IS_ERR(res[0])) {
 		put_pipe_info(inode, inode->i_pipe);
 		fput(f);
 		return PTR_ERR(res[0]);
 	}
-
-	path_get(&f->f_path);
 	res[0]->private_data = inode->i_pipe;
 	res[0]->f_flags = O_RDONLY | (flags & O_NONBLOCK);
 	res[1] = f;
diff --git a/include/linux/file.h b/include/linux/file.h
index 0a4ef2315f75..22becbfd4cec 100644
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -23,6 +23,8 @@ extern struct file *alloc_file(const struct path *, fmode_t mode,
 	const struct file_operations *fop);
 extern struct file *alloc_file_pseudo(struct inode *, struct vfsmount *,
 	const char *, fmode_t, const struct file_operations *);
+extern struct file *alloc_file_clone(struct file *, fmode_t,
+	const struct file_operations *);
 
 static inline void fput_light(struct file *file, int fput_needed)
 {
-- 
2.11.0