TTY: devpts, do not set driver_data

The goal is to stop setting and using tty->driver_data in devpts code.
It should be used solely by the driver's code, pty in this case.

Now driver_data are managed only in the pty driver. devpts_pty_new is
switched to accept what we used to dig out of tty_struct, i.e. device
node number and index.

This also removes a note about driver_data being set outside of the
driver.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/pty.c

@@ -4,9 +4,6 @@
  *  Added support for a Unix98-style ptmx device.
  *    -- C. Scott Ananian <cananian@alumni.princeton.edu>, 14-Jan-1998
  *
- *  When reading this code see also fs/devpts. In particular note that the
- *  driver_data field is used by the devpts side as a binding to the devpts
- *  inode.
  */
 
 #include <linux/module.h>
@@ -59,7 +56,7 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 #ifdef CONFIG_UNIX98_PTYS
 		if (tty->driver == ptm_driver) {
 		        mutex_lock(&devpts_mutex);
-			devpts_pty_kill(tty->link);
+			devpts_pty_kill(tty->link->driver_data);
 		        mutex_unlock(&devpts_mutex);
 		}
 #endif
@@ -651,7 +648,9 @@ static int ptmx_open(struct inode *inode, struct file *filp)
 
 	tty_add_file(tty, filp);
 
-	slave_inode = devpts_pty_new(inode, tty->link);
+	slave_inode = devpts_pty_new(inode,
+			MKDEV(UNIX98_PTY_SLAVE_MAJOR, index), index,
+			tty->link);
 	if (IS_ERR(slave_inode)) {
 		retval = PTR_ERR(slave_inode);
 		goto err_release;
@@ -662,6 +661,7 @@ static int ptmx_open(struct inode *inode, struct file *filp)
 		goto err_release;
 
 	tty_unlock(tty);
+	tty->link->driver_data = slave_inode;
 	return 0;
 err_release:
 	tty_unlock(tty);

fs/devpts/inode.c

@@ -545,12 +545,9 @@ void devpts_kill_index(struct inode *ptmx_inode, int idx)
 	mutex_unlock(&allocated_ptys_lock);
 }
 
-struct inode *devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty)
+struct inode *devpts_pty_new(struct inode *ptmx_inode, dev_t device, int index,
+		void *priv)
 {
-	/* tty layer puts index from devpts_new_index() in here */
-	int number = tty->index;
-	struct tty_driver *driver = tty->driver;
-	dev_t device = MKDEV(driver->major, driver->minor_start+number);
 	struct dentry *dentry;
 	struct super_block *sb = pts_sb_from_inode(ptmx_inode);
 	struct inode *inode;
@@ -559,23 +556,18 @@ struct inode *devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty)
 	struct pts_mount_opts *opts = &fsi->mount_opts;
 	char s[12];
 
-	/* We're supposed to be given the slave end of a pty */
-	BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY);
-	BUG_ON(driver->subtype != PTY_TYPE_SLAVE);
-
 	inode = new_inode(sb);
 	if (!inode)
 		return ERR_PTR(-ENOMEM);
 
-	inode->i_ino = number + 3;
+	inode->i_ino = index + 3;
 	inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
 	inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 	init_special_inode(inode, S_IFCHR|opts->mode, device);
-	inode->i_private = tty;
+	inode->i_private = priv;
-	tty->driver_data = inode;
 
-	sprintf(s, "%d", number);
+	sprintf(s, "%d", index);
 
 	mutex_lock(&root->d_inode->i_mutex);
 
@@ -613,9 +605,8 @@ void *devpts_get_priv(struct inode *pts_inode)
 	return priv;
 }
 
-void devpts_pty_kill(struct tty_struct *tty)
+void devpts_pty_kill(struct inode *inode)
 {
-	struct inode *inode = tty->driver_data;
 	struct super_block *sb = pts_sb_from_inode(inode);
 	struct dentry *root = sb->s_root;
 	struct dentry *dentry;

include/linux/devpts_fs.h

@@ -20,11 +20,12 @@
 int devpts_new_index(struct inode *ptmx_inode);
 void devpts_kill_index(struct inode *ptmx_inode, int idx);
 /* mknod in devpts */
-struct inode *devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty);
+struct inode *devpts_pty_new(struct inode *ptmx_inode, dev_t device, int index,
+		void *priv);
 /* get private structure */
 void *devpts_get_priv(struct inode *pts_inode);
 /* unlink */
-void devpts_pty_kill(struct tty_struct *tty);
+void devpts_pty_kill(struct inode *inode);
 
 #else
 
@@ -32,7 +33,7 @@ void devpts_pty_kill(struct tty_struct *tty);
 static inline int devpts_new_index(struct inode *ptmx_inode) { return -EINVAL; }
 static inline void devpts_kill_index(struct inode *ptmx_inode, int idx) { }
 static inline struct inode *devpts_pty_new(struct inode *ptmx_inode,
-		struct tty_struct *tty)
+		dev_t device, int index, void *priv)
 {
 	return ERR_PTR(-EINVAL);
 }
@@ -40,7 +41,7 @@ static inline void *devpts_get_priv(struct inode *pts_inode)
 {
 	return NULL;
 }
-static inline void devpts_pty_kill(struct tty_struct *tty) { }
+static inline void devpts_pty_kill(struct inode *inode) { }
 
 #endif