devpts: more pty driver interface cleanups

This is more prep-work for the upcoming pty changes.  Still just code
cleanup with no actual semantic changes.

This removes a bunch pointless complexity by just having the slave pty
side remember the dentry associated with the devpts slave rather than
the inode.  That allows us to remove all the "look up the dentry" code
for when we want to remove it again.

Together with moving the tty pointer from "inode->i_private" to
"dentry->d_fsdata" and getting rid of pointless inode locking, this
removes about 30 lines of code.  Not only is the end result smaller,
it's simpler and easier to understand.

The old code, for example, depended on the d_find_alias() to not just
find the dentry, but also to check that it is still hashed, which in
turn validated the tty pointer in the inode.

That is a _very_ roundabout way to say "invalidate the cached tty
pointer when the dentry is removed".

The new code just does

	dentry->d_fsdata = NULL;

in devpts_pty_kill() instead, invalidating the tty pointer rather more
directly and obviously.  Don't do something complex and subtle when the
obvious straightforward approach will do.

The rest of the patch (ie apart from code deletion and the above tty
pointer clearing) is just switching the calling convention to pass the
dentry or file pointer around instead of the inode.

Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Peter Anvin <hpa@zytor.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Serge Hallyn <serge.hallyn@ubuntu.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Aurelien Jarno <aurelien@aurel32.net>
Cc: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Cc: Jann Horn <jann@thejh.net>
Cc: Greg KH <greg@kroah.com>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Florian Weimer <fw@deneb.enyo.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 41 deletions

diff --git a/fs/devpts/inode.c b/fs/devpts/inode.c
index 0af8e7d70d27..0b2954d7172d 100644
--- a/fs/devpts/inode.c
+++ b/fs/devpts/inode.c
@@ -604,8 +604,7 @@ void devpts_put_ref(struct pts_fs_info *fsi)
  *
  * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
  */
-struct inode *devpts_pty_new(struct pts_fs_info *fsi, dev_t device, int index,
-		void *priv)
+struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
 {
 	struct dentry *dentry;
 	struct super_block *sb;
@@ -629,25 +628,21 @@ struct inode *devpts_pty_new(struct pts_fs_info *fsi, dev_t device, int index,
 	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 = priv;
+	init_special_inode(inode, S_IFCHR|opts->mode, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));
 
 	sprintf(s, "%d", index);
 
-	inode_lock(d_inode(root));
-
 	dentry = d_alloc_name(root, s);
 	if (dentry) {
+		dentry->d_fsdata = priv;
 		d_add(dentry, inode);
 		fsnotify_create(d_inode(root), dentry);
 	} else {
 		iput(inode);
-		inode = ERR_PTR(-ENOMEM);
+		dentry = ERR_PTR(-ENOMEM);
 	}
 
-	inode_unlock(d_inode(root));
-
-	return inode;
+	return dentry;
 }
 
 /**
@@ -656,24 +651,10 @@ struct inode *devpts_pty_new(struct pts_fs_info *fsi, dev_t device, int index,
  *
  * Returns whatever was passed as priv in devpts_pty_new for a given inode.
  */
-void *devpts_get_priv(struct inode *pts_inode)
+void *devpts_get_priv(struct dentry *dentry)
 {
-	struct dentry *dentry;
-	void *priv = NULL;
-
-	BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
-
-	/* Ensure dentry has not been deleted by devpts_pty_kill() */
-	dentry = d_find_alias(pts_inode);
-	if (!dentry)
-		return NULL;
-
-	if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
-		priv = pts_inode->i_private;
-
-	dput(dentry);
-
-	return priv;
+	WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
+	return dentry->d_fsdata;
 }
 
 /**
@@ -682,24 +663,14 @@ void *devpts_get_priv(struct inode *pts_inode)
  *
  * This is an inverse operation of devpts_pty_new.
  */
-void devpts_pty_kill(struct inode *inode)
+void devpts_pty_kill(struct dentry *dentry)
 {
-	struct super_block *sb = pts_sb_from_inode(inode);
-	struct dentry *root = sb->s_root;
-	struct dentry *dentry;
+	WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);
 
-	BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
-
-	inode_lock(d_inode(root));
-
-	dentry = d_find_alias(inode);
-
-	drop_nlink(inode);
+	dentry->d_fsdata = NULL;
+	drop_nlink(dentry->d_inode);
 	d_delete(dentry);
 	dput(dentry);	/* d_alloc_name() in devpts_pty_new() */
-	dput(dentry);		/* d_find_alias above */
-
-	inode_unlock(d_inode(root));
 }
 
 static int __init init_devpts_fs(void)