Merge branch 'ptmx-cleanup'

Merge the ptmx internal interface cleanup branch.

This doesn't change semantics, but it should be a sane basis for
eventually getting the multi-instance devpts code into some sane shape
where we can get rid of the kernel config option.  Which we can
hopefully get done next merge window..

* ptmx-cleanup:
  devpts: clean up interface to pty drivers

drivers/tty/pty.c

@@ -663,14 +663,14 @@ static int pty_unix98_install(struct tty_driver *driver, struct tty_struct *tty)
 /* this is called once with whichever end is closed last */
 static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty)
 {
-	struct inode *ptmx_inode;
+	struct pts_fs_info *fsi;
 
 	if (tty->driver->subtype == PTY_TYPE_MASTER)
-		ptmx_inode = tty->driver_data;
+		fsi = tty->driver_data;
 	else
-		ptmx_inode = tty->link->driver_data;
-	devpts_kill_index(ptmx_inode, tty->index);
-	devpts_del_ref(ptmx_inode);
+		fsi = tty->link->driver_data;
+	devpts_kill_index(fsi, tty->index);
+	devpts_put_ref(fsi);
 }
 
 static const struct tty_operations ptm_unix98_ops = {
@@ -720,6 +720,7 @@ static const struct tty_operations pty_unix98_ops = {
 
 static int ptmx_open(struct inode *inode, struct file *filp)
 {
+	struct pts_fs_info *fsi;
 	struct tty_struct *tty;
 	struct inode *slave_inode;
 	int retval;
@@ -734,47 +735,41 @@ static int ptmx_open(struct inode *inode, struct file *filp)
 	if (retval)
 		return retval;
 
+	fsi = devpts_get_ref(inode, filp);
+	retval = -ENODEV;
+	if (!fsi)
+		goto out_free_file;
+
 	/* find a device that is not in use. */
 	mutex_lock(&devpts_mutex);
-	index = devpts_new_index(inode);
-	if (index < 0) {
-		retval = index;
-		mutex_unlock(&devpts_mutex);
-		goto err_file;
-	}
-
+	index = devpts_new_index(fsi);
 	mutex_unlock(&devpts_mutex);
 
-	mutex_lock(&tty_mutex);
-	tty = tty_init_dev(ptm_driver, index);
+	retval = index;
+	if (index < 0)
+		goto out_put_ref;
 
-	if (IS_ERR(tty)) {
-		retval = PTR_ERR(tty);
-		goto out;
-	}
 
+	mutex_lock(&tty_mutex);
+	tty = tty_init_dev(ptm_driver, index);
 	/* The tty returned here is locked so we can safely
 	   drop the mutex */
 	mutex_unlock(&tty_mutex);
 
-	set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
-	tty->driver_data = inode;
+	retval = PTR_ERR(tty);
+	if (IS_ERR(tty))
+		goto out;
 
 	/*
-	 * In the case where all references to ptmx inode are dropped and we
-	 * still have /dev/tty opened pointing to the master/slave pair (ptmx
-	 * is closed/released before /dev/tty), we must make sure that the inode
-	 * is still valid when we call the final pty_unix98_shutdown, thus we
-	 * hold an additional reference to the ptmx inode. For the same /dev/tty
-	 * last close case, we also need to make sure the super_block isn't
-	 * destroyed (devpts instance unmounted), before /dev/tty is closed and
-	 * on its release devpts_kill_index is called.
+	 * From here on out, the tty is "live", and the index and
+	 * fsi will be killed/put by the tty_release()
 	 */
-	devpts_add_ref(inode);
+	set_bit(TTY_PTY_LOCK, &tty->flags); /* LOCK THE SLAVE */
+	tty->driver_data = fsi;
 
 	tty_add_file(tty, filp);
 
-	slave_inode = devpts_pty_new(inode,
+	slave_inode = devpts_pty_new(fsi,
 			MKDEV(UNIX98_PTY_SLAVE_MAJOR, index), index,
 			tty->link);
 	if (IS_ERR(slave_inode)) {
@@ -793,12 +788,14 @@ static int ptmx_open(struct inode *inode, struct file *filp)
 	return 0;
 err_release:
 	tty_unlock(tty);
+	// This will also put-ref the fsi
 	tty_release(inode, filp);
 	return retval;
 out:
-	mutex_unlock(&tty_mutex);
-	devpts_kill_index(inode, index);
-err_file:
+	devpts_kill_index(fsi, index);
+out_put_ref:
+	devpts_put_ref(fsi);
+out_free_file:
 	tty_free_file(filp);
 	return retval;
 }

fs/devpts/inode.c

@@ -128,6 +128,7 @@ static const match_table_t tokens = {
 struct pts_fs_info {
 	struct ida allocated_ptys;
 	struct pts_mount_opts mount_opts;
+	struct super_block *sb;
 	struct dentry *ptmx_dentry;
 };
 
@@ -358,7 +359,7 @@ static const struct super_operations devpts_sops = {
 	.show_options	= devpts_show_options,
 };
 
-static void *new_pts_fs_info(void)
+static void *new_pts_fs_info(struct super_block *sb)
 {
 	struct pts_fs_info *fsi;
 
@@ -369,6 +370,7 @@ static void *new_pts_fs_info(void)
 	ida_init(&fsi->allocated_ptys);
 	fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
 	fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
+	fsi->sb = sb;
 
 	return fsi;
 }
@@ -384,7 +386,7 @@ devpts_fill_super(struct super_block *s, void *data, int silent)
 	s->s_op = &devpts_sops;
 	s->s_time_gran = 1;
 
-	s->s_fs_info = new_pts_fs_info();
+	s->s_fs_info = new_pts_fs_info(s);
 	if (!s->s_fs_info)
 		goto fail;
 
@@ -524,17 +526,14 @@ static struct file_system_type devpts_fs_type = {
  * to the System V naming convention
  */
 
-int devpts_new_index(struct inode *ptmx_inode)
+int devpts_new_index(struct pts_fs_info *fsi)
 {
-	struct super_block *sb = pts_sb_from_inode(ptmx_inode);
-	struct pts_fs_info *fsi;
 	int index;
 	int ida_ret;
 
-	if (!sb)
+	if (!fsi)
 		return -ENODEV;
 
-	fsi = DEVPTS_SB(sb);
 retry:
 	if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
 		return -ENOMEM;
@@ -564,11 +563,8 @@ retry:
 	return index;
 }
 
-void devpts_kill_index(struct inode *ptmx_inode, int idx)
+void devpts_kill_index(struct pts_fs_info *fsi, int idx)
 {
-	struct super_block *sb = pts_sb_from_inode(ptmx_inode);
-	struct pts_fs_info *fsi = DEVPTS_SB(sb);
-
 	mutex_lock(&allocated_ptys_lock);
 	ida_remove(&fsi->allocated_ptys, idx);
 	pty_count--;
@@ -578,21 +574,25 @@ void devpts_kill_index(struct inode *ptmx_inode, int idx)
 /*
  * pty code needs to hold extra references in case of last /dev/tty close
  */
-
-void devpts_add_ref(struct inode *ptmx_inode)
+struct pts_fs_info *devpts_get_ref(struct inode *ptmx_inode, struct file *file)
 {
-	struct super_block *sb = pts_sb_from_inode(ptmx_inode);
+	struct super_block *sb;
+	struct pts_fs_info *fsi;
+
+	sb = pts_sb_from_inode(ptmx_inode);
+	if (!sb)
+		return NULL;
+	fsi = DEVPTS_SB(sb);
+	if (!fsi)
+		return NULL;
 
 	atomic_inc(&sb->s_active);
-	ihold(ptmx_inode);
+	return fsi;
 }
 
-void devpts_del_ref(struct inode *ptmx_inode)
+void devpts_put_ref(struct pts_fs_info *fsi)
 {
-	struct super_block *sb = pts_sb_from_inode(ptmx_inode);
-
-	iput(ptmx_inode);
-	deactivate_super(sb);
+	deactivate_super(fsi->sb);
 }
 
 /**
@@ -604,22 +604,21 @@ void devpts_del_ref(struct inode *ptmx_inode)
  *
  * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
  */
-struct inode *devpts_pty_new(struct inode *ptmx_inode, dev_t device, int index,
+struct inode *devpts_pty_new(struct pts_fs_info *fsi, dev_t device, int index,
 		void *priv)
 {
 	struct dentry *dentry;
-	struct super_block *sb = pts_sb_from_inode(ptmx_inode);
+	struct super_block *sb;
 	struct inode *inode;
 	struct dentry *root;
-	struct pts_fs_info *fsi;
 	struct pts_mount_opts *opts;
 	char s[12];
 
-	if (!sb)
+	if (!fsi)
 		return ERR_PTR(-ENODEV);
 
+	sb = fsi->sb;
 	root = sb->s_root;
-	fsi = DEVPTS_SB(sb);
 	opts = &fsi->mount_opts;
 
 	inode = new_inode(sb);

include/linux/devpts_fs.h

@@ -15,38 +15,24 @@
 
 #include <linux/errno.h>
 
+struct pts_fs_info;
+
 #ifdef CONFIG_UNIX98_PTYS
 
-int devpts_new_index(struct inode *ptmx_inode);
-void devpts_kill_index(struct inode *ptmx_inode, int idx);
-void devpts_add_ref(struct inode *ptmx_inode);
-void devpts_del_ref(struct inode *ptmx_inode);
+/* Look up a pts fs info and get a ref to it */
+struct pts_fs_info *devpts_get_ref(struct inode *, struct file *);
+void devpts_put_ref(struct pts_fs_info *);
+
+int devpts_new_index(struct pts_fs_info *);
+void devpts_kill_index(struct pts_fs_info *, int);
+
 /* mknod in devpts */
-struct inode *devpts_pty_new(struct inode *ptmx_inode, dev_t device, int index,
-		void *priv);
+struct inode *devpts_pty_new(struct pts_fs_info *, dev_t, int, void *);
 /* get private structure */
 void *devpts_get_priv(struct inode *pts_inode);
 /* unlink */
 void devpts_pty_kill(struct inode *inode);
 
-#else
-
-/* Dummy stubs in the no-pty case */
-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 void devpts_add_ref(struct inode *ptmx_inode) { }
-static inline void devpts_del_ref(struct inode *ptmx_inode) { }
-static inline struct inode *devpts_pty_new(struct inode *ptmx_inode,
-		dev_t device, int index, void *priv)
-{
-	return ERR_PTR(-EINVAL);
-}
-static inline void *devpts_get_priv(struct inode *pts_inode)
-{
-	return NULL;
-}
-static inline void devpts_pty_kill(struct inode *inode) { }
-
 #endif