fs: add f_pipe

Only regular files with FMODE_ATOMIC_POS and directories need
f_pos_lock. Place a new f_pipe member in a union with f_pos_lock
that they can use and make them stop abusing f_version in follow-up
patches.

Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

1 files changed, 7 insertions, 0 deletions

diff --git a/fs/file_table.c b/fs/file_table.c
index 3ef558f27a1c..7ce4d5dac080 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -156,6 +156,13 @@ static int init_file(struct file *f, int flags, const struct cred *cred)
 	}
 
 	spin_lock_init(&f->f_lock);
+	/*
+	 * Note that f_pos_lock is only used for files raising
+	 * FMODE_ATOMIC_POS and directories. Other files such as pipes
+	 * don't need it and since f_pos_lock is in a union may reuse
+	 * the space for other purposes. They are expected to initialize
+	 * the respective member when opening the file.
+	 */
 	mutex_init(&f->f_pos_lock);
 	f->f_flags = flags;
 	f->f_mode = OPEN_FMODE(flags);