[PATCH 3/4]: Move devpts globals into init_pts_ns

[sukadev@us.ibm.com]

Matt, Serge, please sign-off on this version.
---
From: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Subject: [PATCH 3/4]: Move devpts globals into init_pts_ns

Move devpts global variables 'allocated_ptys' and 'devpts_mnt' into a new
'pts_namespace' and remove the 'devpts_root'.

Changelog: 
	- Split these relatively simpler changes off from the patch that
	  supports remounting devpts.

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
---
 fs/devpts/inode.c         |   84 ++++++++++++++++++++++++++++++++--------------
 include/linux/devpts_fs.h |   10 +++++
 2 files changed, 70 insertions(+), 24 deletions(-)

Index: 2.6.25-rc8-mm1/fs/devpts/inode.c
===================================================================
--- 2.6.25-rc8-mm1.orig/fs/devpts/inode.c	2008-04-11 10:12:09.000000000 -0700
+++ 2.6.25-rc8-mm1/fs/devpts/inode.c	2008-04-12 10:10:33.000000000 -0700
@@ -28,12 +28,8 @@
 #define DEVPTS_DEFAULT_MODE 0600
 
 extern int pty_limit;			/* Config limit on Unix98 ptys */
-static DEFINE_IDR(allocated_ptys);
 static DECLARE_MUTEX(allocated_ptys_lock);
 
-static struct vfsmount *devpts_mnt;
-static struct dentry *devpts_root;
-
 static struct {
 	int setuid;
 	int setgid;
@@ -54,6 +50,14 @@ static match_table_t tokens = {
 	{Opt_err, NULL}
 };
 
+struct pts_namespace init_pts_ns = {
+	.kref = {
+		.refcount = ATOMIC_INIT(2),
+	},
+	.allocated_ptys = IDR_INIT(init_pts_ns.allocated_ptys),
+	.mnt = NULL,
+};
+
 static int devpts_remount(struct super_block *sb, int *flags, char *data)
 {
 	char *p;
@@ -140,7 +144,7 @@ devpts_fill_super(struct super_block *s,
 	inode->i_fop = &simple_dir_operations;
 	inode->i_nlink = 2;
 
-	devpts_root = s->s_root = d_alloc_root(inode);
+	s->s_root = d_alloc_root(inode);
 	if (s->s_root)
 		return 0;
 	
@@ -168,10 +172,9 @@ static struct file_system_type devpts_fs
  * to the System V naming convention
  */
 
-static struct dentry *get_node(int num)
+static struct dentry *get_node(struct dentry *root, int num)
 {
 	char s[12];
-	struct dentry *root = devpts_root;
 	mutex_lock(&root->d_inode->i_mutex);
 	return lookup_one_len(s, root, sprintf(s, "%d", num));
 }
@@ -180,14 +183,17 @@ int devpts_new_index(void)
 {
 	int index;
 	int idr_ret;
+	struct pts_namespace *pts_ns;
+
+	pts_ns = &init_pts_ns;
 
 retry:
-	if (!idr_pre_get(&allocated_ptys, GFP_KERNEL)) {
+	if (!idr_pre_get(&pts_ns->allocated_ptys, GFP_KERNEL)) {
 		return -ENOMEM;
 	}
 
 	down(&allocated_ptys_lock);
-	idr_ret = idr_get_new(&allocated_ptys, NULL, &index);
+	idr_ret = idr_get_new(&pts_ns->allocated_ptys, NULL, &index);
 	if (idr_ret < 0) {
 		up(&allocated_ptys_lock);
 		if (idr_ret == -EAGAIN)
@@ -196,7 +202,7 @@ retry:
 	}
 
 	if (index >= pty_limit) {
-		idr_remove(&allocated_ptys, index);
+		idr_remove(&pts_ns->allocated_ptys, index);
 		up(&allocated_ptys_lock);
 		return -EIO;
 	}
@@ -206,8 +212,10 @@ retry:
 
 void devpts_kill_index(int idx)
 {
+	struct pts_namespace *pts_ns = &init_pts_ns;
+
 	down(&allocated_ptys_lock);
-	idr_remove(&allocated_ptys, idx);
+	idr_remove(&pts_ns->allocated_ptys, idx);
 	up(&allocated_ptys_lock);
 }
 
@@ -217,12 +225,26 @@ int devpts_pty_new(struct tty_struct *tt
 	struct tty_driver *driver = tty->driver;
 	dev_t device = MKDEV(driver->major, driver->minor_start+number);
 	struct dentry *dentry;
-	struct inode *inode = new_inode(devpts_mnt->mnt_sb);
+	struct dentry *root;
+	struct inode *inode;
+	struct pts_namespace *pts_ns;
 
 	/* 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);
 
+	pts_ns = &init_pts_ns;
+	root = pts_ns->mnt->mnt_root;
+
+	mutex_lock(&root->d_inode->i_mutex);
+	inode = idr_find(&pts_ns->allocated_ptys, number);
+	mutex_unlock(&root->d_inode->i_mutex);
+
+	if (inode && !IS_ERR(inode))
+		return -EEXIST;
+
+	inode = new_inode(pts_ns->mnt->mnt_sb);
+
 	if (!inode)
 		return -ENOMEM;
 
@@ -232,23 +254,28 @@ int devpts_pty_new(struct tty_struct *tt
 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 	init_special_inode(inode, S_IFCHR|config.mode, device);
 	inode->i_private = tty;
+	idr_replace(&pts_ns->allocated_ptys, inode, number);
 
-	dentry = get_node(number);
+	dentry = get_node(root, number);
 	if (!IS_ERR(dentry) && !dentry->d_inode) {
 		d_instantiate(dentry, inode);
-		fsnotify_create(devpts_root->d_inode, dentry);
+		fsnotify_create(root->d_inode, dentry);
 	}
 
-	mutex_unlock(&devpts_root->d_inode->i_mutex);
+	mutex_unlock(&root->d_inode->i_mutex);
 
 	return 0;
 }
 
 struct tty_struct *devpts_get_tty(int number)
 {
-	struct dentry *dentry = get_node(number);
+	struct dentry *root;
+	struct dentry *dentry;
 	struct tty_struct *tty;
 
+	root = init_pts_ns.mnt->mnt_root;
+	dentry = get_node(root, number);
+
 	tty = NULL;
 	if (!IS_ERR(dentry)) {
 		if (dentry->d_inode)
@@ -256,14 +283,18 @@ struct tty_struct *devpts_get_tty(int nu
 		dput(dentry);
 	}
 
-	mutex_unlock(&devpts_root->d_inode->i_mutex);
+	mutex_unlock(&root->d_inode->i_mutex);
 
 	return tty;
 }
 
 void devpts_pty_kill(int number)
 {
-	struct dentry *dentry = get_node(number);
+	struct dentry *root;
+	struct dentry *dentry;
+
+	root = init_pts_ns.mnt->mnt_root;
+	dentry = get_node(root, number);
 
 	if (!IS_ERR(dentry)) {
 		struct inode *inode = dentry->d_inode;
@@ -274,16 +305,21 @@ void devpts_pty_kill(int number)
 		}
 		dput(dentry);
 	}
-	mutex_unlock(&devpts_root->d_inode->i_mutex);
+	mutex_unlock(&root->d_inode->i_mutex);
 }
 
 static int __init init_devpts_fs(void)
 {
-	int err = register_filesystem(&devpts_fs_type);
+	struct vfsmount *mnt;
+	int err;
+
+	err = register_filesystem(&devpts_fs_type);
 	if (!err) {
-		devpts_mnt = kern_mount(&devpts_fs_type);
-		if (IS_ERR(devpts_mnt))
-			err = PTR_ERR(devpts_mnt);
+		mnt = kern_mount(&devpts_fs_type);
+		if (IS_ERR(mnt))
+			err = PTR_ERR(mnt);
+		else
+			init_pts_ns.mnt = mnt;
 	}
 	return err;
 }
@@ -291,7 +327,7 @@ static int __init init_devpts_fs(void)
 static void __exit exit_devpts_fs(void)
 {
 	unregister_filesystem(&devpts_fs_type);
-	mntput(devpts_mnt);
+	mntput(init_pts_ns.mnt);
 }
 
 module_init(init_devpts_fs)
Index: 2.6.25-rc8-mm1/include/linux/devpts_fs.h
===================================================================
--- 2.6.25-rc8-mm1.orig/include/linux/devpts_fs.h	2008-04-11 10:34:16.000000000 -0700
+++ 2.6.25-rc8-mm1/include/linux/devpts_fs.h	2008-04-12 08:52:57.000000000 -0700
@@ -14,6 +14,16 @@
 #define _LINUX_DEVPTS_FS_H
 
 #include <linux/errno.h>
+#include <linux/kref.h>
+#include <linux/idr.h>
+
+struct pts_namespace {
+	struct kref kref;
+	struct idr allocated_ptys;
+	struct vfsmount *mnt;
+};
+
+extern struct pts_namespace init_pts_ns;
 
 #ifdef CONFIG_UNIX98_PTYS