fs/devpts/inode.c - kernel/msm-4.9 - Gitiles

 /* -*- linux-c -*- --------------------------------------------------------- *
  *
  * linux/fs/devpts/inode.c
  *
  *  Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
  *
  * This file is part of the Linux kernel and is made available under
  * the terms of the GNU General Public License, version 2, or at your
  * option, any later version, incorporated herein by reference.
  *
  * ------------------------------------------------------------------------- */

 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/fs.h>
 #include <linux/sched.h>
 #include <linux/namei.h>
 #include <linux/slab.h>
 #include <linux/mount.h>
 #include <linux/tty.h>
 #include <linux/mutex.h>
 #include <linux/magic.h>
 #include <linux/idr.h>
 #include <linux/devpts_fs.h>
 #include <linux/parser.h>
 #include <linux/fsnotify.h>
 #include <linux/seq_file.h>

 #define DEVPTS_DEFAULT_MODE 0600
 /*
  * ptmx is a new node in /dev/pts and will be unused in legacy (single-
  * instance) mode. To prevent surprises in user space, set permissions of
  * ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
  * permissions.
  */
 #define DEVPTS_DEFAULT_PTMX_MODE 0000
 #define PTMX_MINOR	2

 extern int pty_limit;			/* Config limit on Unix98 ptys */
 static DEFINE_MUTEX(allocated_ptys_lock);

 static struct vfsmount *devpts_mnt;

 struct pts_mount_opts {
 	int setuid;
 	int setgid;
 	uid_t   uid;
 	gid_t   gid;
 	umode_t mode;
 	umode_t ptmxmode;
 	int newinstance;
 };

 enum {
 	Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,
 	Opt_err
 };

 static const match_table_t tokens = {
 	{Opt_uid, "uid=%u"},
 	{Opt_gid, "gid=%u"},
 	{Opt_mode, "mode=%o"},
 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 	{Opt_ptmxmode, "ptmxmode=%o"},
 	{Opt_newinstance, "newinstance"},
 #endif
 	{Opt_err, NULL}
 };

 struct pts_fs_info {
 	struct ida allocated_ptys;
 	struct pts_mount_opts mount_opts;
 	struct dentry *ptmx_dentry;
 };

 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
 {
 	return sb->s_fs_info;
 }

 static inline struct super_block *pts_sb_from_inode(struct inode *inode)
 {
 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 	if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
 		return inode->i_sb;
 #endif
 	return devpts_mnt->mnt_sb;
 }

 #define PARSE_MOUNT	0
 #define PARSE_REMOUNT	1

 /*
  * parse_mount_options():
  * 	Set @opts to mount options specified in @data. If an option is not
  * 	specified in @data, set it to its default value. The exception is
  * 	'newinstance' option which can only be set/cleared on a mount (i.e.
  * 	cannot be changed during remount).
  *
  * Note: @data may be NULL (in which case all options are set to default).
  */
 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
 {
 	char *p;

 	opts->setuid  = 0;
 	opts->setgid  = 0;
 	opts->uid     = 0;
 	opts->gid     = 0;
 	opts->mode    = DEVPTS_DEFAULT_MODE;
 	opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;

 	/* newinstance makes sense only on initial mount */
 	if (op == PARSE_MOUNT)
 		opts->newinstance = 0;

 	while ((p = strsep(&data, ",")) != NULL) {
 		substring_t args[MAX_OPT_ARGS];
 		int token;
 		int option;

 		if (!*p)
 			continue;

 		token = match_token(p, tokens, args);
 		switch (token) {
 		case Opt_uid:
 			if (match_int(&args[0], &option))
 				return -EINVAL;
 			opts->uid = option;
 			opts->setuid = 1;
 			break;
 		case Opt_gid:
 			if (match_int(&args[0], &option))
 				return -EINVAL;
 			opts->gid = option;
 			opts->setgid = 1;
 			break;
 		case Opt_mode:
 			if (match_octal(&args[0], &option))
 				return -EINVAL;
 			opts->mode = option & S_IALLUGO;
 			break;
 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 		case Opt_ptmxmode:
 			if (match_octal(&args[0], &option))
 				return -EINVAL;
 			opts->ptmxmode = option & S_IALLUGO;
 			break;
 		case Opt_newinstance:
 			/* newinstance makes sense only on initial mount */
 			if (op == PARSE_MOUNT)
 				opts->newinstance = 1;
 			break;
 #endif
 		default:
 			printk(KERN_ERR "devpts: called with bogus options\n");
 			return -EINVAL;
 		}
 	}

 	return 0;
 }

 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 static int mknod_ptmx(struct super_block *sb)
 {
 	int mode;
 	int rc = -ENOMEM;
 	struct dentry *dentry;
 	struct inode *inode;
 	struct dentry *root = sb->s_root;
 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
 	struct pts_mount_opts *opts = &fsi->mount_opts;

 	mutex_lock(&root->d_inode->i_mutex);

 	/* If we have already created ptmx node, return */
 	if (fsi->ptmx_dentry) {
 		rc = 0;
 		goto out;
 	}

 	dentry = d_alloc_name(root, "ptmx");
 	if (!dentry) {
 		printk(KERN_NOTICE "Unable to alloc dentry for ptmx node\n");
 		goto out;
 	}

 	/*
 	 * Create a new 'ptmx' node in this mount of devpts.
 	 */
 	inode = new_inode(sb);
 	if (!inode) {
 		printk(KERN_ERR "Unable to alloc inode for ptmx node\n");
 		dput(dentry);
 		goto out;
 	}

 	inode->i_ino = 2;
 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;

 	mode = S_IFCHR|opts->ptmxmode;
 	init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));

 	d_add(dentry, inode);

 	fsi->ptmx_dentry = dentry;
 	rc = 0;
 out:
 	mutex_unlock(&root->d_inode->i_mutex);
 	return rc;
 }

 static void update_ptmx_mode(struct pts_fs_info *fsi)
 {
 	struct inode *inode;
 	if (fsi->ptmx_dentry) {
 		inode = fsi->ptmx_dentry->d_inode;
 		inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
 	}
 }
 #else
 static inline void update_ptmx_mode(struct pts_fs_info *fsi)
 {
        return;
 }
 #endif

 static int devpts_remount(struct super_block *sb, int *flags, char *data)
 {
 	int err;
 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
 	struct pts_mount_opts *opts = &fsi->mount_opts;

 	err = parse_mount_options(data, PARSE_REMOUNT, opts);

 	/*
 	 * parse_mount_options() restores options to default values
 	 * before parsing and may have changed ptmxmode. So, update the
 	 * mode in the inode too. Bogus options don't fail the remount,
 	 * so do this even on error return.
 	 */
 	update_ptmx_mode(fsi);

 	return err;
 }

 static int devpts_show_options(struct seq_file *seq, struct vfsmount *vfs)
 {
 	struct pts_fs_info *fsi = DEVPTS_SB(vfs->mnt_sb);
 	struct pts_mount_opts *opts = &fsi->mount_opts;

 	if (opts->setuid)
 		seq_printf(seq, ",uid=%u", opts->uid);
 	if (opts->setgid)
 		seq_printf(seq, ",gid=%u", opts->gid);
 	seq_printf(seq, ",mode=%03o", opts->mode);
 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 	seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
 #endif

 	return 0;
 }

 static const struct super_operations devpts_sops = {
 	.statfs		= simple_statfs,
 	.remount_fs	= devpts_remount,
 	.show_options	= devpts_show_options,
 };

 static void *new_pts_fs_info(void)
 {
 	struct pts_fs_info *fsi;

 	fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
 	if (!fsi)
 		return NULL;

 	ida_init(&fsi->allocated_ptys);
 	fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
 	fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;

 	return fsi;
 }

 static int
 devpts_fill_super(struct super_block *s, void *data, int silent)
 {
 	struct inode *inode;

 	s->s_blocksize = 1024;
 	s->s_blocksize_bits = 10;
 	s->s_magic = DEVPTS_SUPER_MAGIC;
 	s->s_op = &devpts_sops;
 	s->s_time_gran = 1;

 	s->s_fs_info = new_pts_fs_info();
 	if (!s->s_fs_info)
 		goto fail;

 	inode = new_inode(s);
 	if (!inode)
 		goto free_fsi;
 	inode->i_ino = 1;
 	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
 	inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
 	inode->i_op = &simple_dir_inode_operations;
 	inode->i_fop = &simple_dir_operations;
 	inode->i_nlink = 2;

 	s->s_root = d_alloc_root(inode);
 	if (s->s_root)
 		return 0;

 	printk(KERN_ERR "devpts: get root dentry failed\n");
 	iput(inode);

 free_fsi:
 	kfree(s->s_fs_info);
 fail:
 	return -ENOMEM;
 }

 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
 static int compare_init_pts_sb(struct super_block *s, void *p)
 {
 	if (devpts_mnt)
 		return devpts_mnt->mnt_sb == s;
 	return 0;
 }

 /*
  * devpts_mount()
  *
  *     If the '-o newinstance' mount option was specified, mount a new
  *     (private) instance of devpts.  PTYs created in this instance are
  *     independent of the PTYs in other devpts instances.
  *
  *     If the '-o newinstance' option was not specified, mount/remount the
  *     initial kernel mount of devpts.  This type of mount gives the
  *     legacy, single-instance semantics.
  *
  *     The 'newinstance' option is needed to support multiple namespace
  *     semantics in devpts while preserving backward compatibility of the
  *     current 'single-namespace' semantics. i.e all mounts of devpts
  *     without the 'newinstance' mount option should bind to the initial
  *     kernel mount, like mount_single().
  *
  *     Mounts with 'newinstance' option create a new, private namespace.
  *
  *     NOTE:
  *
  *     For single-mount semantics, devpts cannot use mount_single(),
  *     because mount_single()/sget() find and use the super-block from
  *     the most recent mount of devpts. But that recent mount may be a
  *     'newinstance' mount and mount_single() would pick the newinstance
  *     super-block instead of the initial super-block.
  */
 static struct dentry *devpts_mount(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data)
 {
 	int error;
 	struct pts_mount_opts opts;
 	struct super_block *s;

 	error = parse_mount_options(data, PARSE_MOUNT, &opts);
 	if (error)
 		return ERR_PTR(error);

 	if (opts.newinstance)
 		s = sget(fs_type, NULL, set_anon_super, NULL);
 	else
 		s = sget(fs_type, compare_init_pts_sb, set_anon_super, NULL);

 	if (IS_ERR(s))
 		return ERR_CAST(s);

 	if (!s->s_root) {
 		s->s_flags = flags;
 		error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
 		if (error)
 			goto out_undo_sget;
 		s->s_flags |= MS_ACTIVE;
 	}

 	memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));

 	error = mknod_ptmx(s);
 	if (error)
 		goto out_undo_sget;

 	return dget(s->s_root);

 out_undo_sget:
 	deactivate_locked_super(s);
 	return ERR_PTR(error);
 }

 #else
 /*
  * This supports only the legacy single-instance semantics (no
  * multiple-instance semantics)
  */
 static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags,
 		const char *dev_name, void *data)
 {
 	return mount_single(fs_type, flags, data, devpts_fill_super);
 }
 #endif

 static void devpts_kill_sb(struct super_block *sb)
 {
 	struct pts_fs_info *fsi = DEVPTS_SB(sb);

 	kfree(fsi);
 	kill_litter_super(sb);
 }

 static struct file_system_type devpts_fs_type = {
 	.name		= "devpts",
 	.mount		= devpts_mount,
 	.kill_sb	= devpts_kill_sb,
 };

 /*
  * The normal naming convention is simply /dev/pts/<number>; this conforms
  * to the System V naming convention
  */

 int devpts_new_index(struct inode *ptmx_inode)
 {
 	struct super_block *sb = pts_sb_from_inode(ptmx_inode);
 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
 	int index;
 	int ida_ret;

 retry:
 	if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
 		return -ENOMEM;

 	mutex_lock(&allocated_ptys_lock);
 	ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
 	if (ida_ret < 0) {
 		mutex_unlock(&allocated_ptys_lock);
 		if (ida_ret == -EAGAIN)
 			goto retry;
 		return -EIO;
 	}

 	if (index >= pty_limit) {
 		ida_remove(&fsi->allocated_ptys, index);
 		mutex_unlock(&allocated_ptys_lock);
 		return -EIO;
 	}
 	mutex_unlock(&allocated_ptys_lock);
 	return index;
 }

 void devpts_kill_index(struct inode *ptmx_inode, 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);
 	mutex_unlock(&allocated_ptys_lock);
 }

 int devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty)
 {
 	/* 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 = new_inode(sb);
 	struct dentry *root = sb->s_root;
 	struct pts_fs_info *fsi = DEVPTS_SB(sb);
 	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);

 	if (!inode)
 		return -ENOMEM;

 	inode->i_ino = number + 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;
 	tty->driver_data = inode;

 	sprintf(s, "%d", number);

 	mutex_lock(&root->d_inode->i_mutex);

 	dentry = d_alloc_name(root, s);
 	if (!IS_ERR(dentry)) {
 		d_add(dentry, inode);
 		fsnotify_create(root->d_inode, dentry);
 	}

 	mutex_unlock(&root->d_inode->i_mutex);

 	return 0;
 }

 struct tty_struct *devpts_get_tty(struct inode *pts_inode, int number)
 {
 	struct dentry *dentry;
 	struct tty_struct *tty;

 	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;

 	tty = NULL;
 	if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
 		tty = (struct tty_struct *)pts_inode->i_private;

 	dput(dentry);

 	return tty;
 }

 void devpts_pty_kill(struct tty_struct *tty)
 {
 	struct inode *inode = tty->driver_data;
 	struct super_block *sb = pts_sb_from_inode(inode);
 	struct dentry *root = sb->s_root;
 	struct dentry *dentry;

 	BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));

 	mutex_lock(&root->d_inode->i_mutex);

 	dentry = d_find_alias(inode);
 	if (IS_ERR(dentry))
 		goto out;

 	if (dentry) {
 		inode->i_nlink--;
 		d_delete(dentry);
 		dput(dentry);	/* d_alloc_name() in devpts_pty_new() */
 	}

 	dput(dentry);		/* d_find_alias above */
 out:
 	mutex_unlock(&root->d_inode->i_mutex);
 }

 static int __init init_devpts_fs(void)
 {
 	int 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);
 			unregister_filesystem(&devpts_fs_type);
 		}
 	}
 	return err;
 }
 module_init(init_devpts_fs)
	/* -- linux-c -- --------------------------------------------------------- *
	*
	* linux/fs/devpts/inode.c
	*
	* Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
	*
	* This file is part of the Linux kernel and is made available under
	* the terms of the GNU General Public License, version 2, or at your
	* option, any later version, incorporated herein by reference.
	*
	* ------------------------------------------------------------------------- */

	#include <linux/module.h>
	#include <linux/init.h>
	#include <linux/fs.h>
	#include <linux/sched.h>
	#include <linux/namei.h>
	#include <linux/slab.h>
	#include <linux/mount.h>
	#include <linux/tty.h>
	#include <linux/mutex.h>
	#include <linux/magic.h>
	#include <linux/idr.h>
	#include <linux/devpts_fs.h>
	#include <linux/parser.h>
	#include <linux/fsnotify.h>
	#include <linux/seq_file.h>

	#define DEVPTS_DEFAULT_MODE 0600
	/*
	* ptmx is a new node in /dev/pts and will be unused in legacy (single-
	* instance) mode. To prevent surprises in user space, set permissions of
	* ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
	* permissions.
	*/
	#define DEVPTS_DEFAULT_PTMX_MODE 0000
	#define PTMX_MINOR 2

	extern int pty_limit; /* Config limit on Unix98 ptys */
	static DEFINE_MUTEX(allocated_ptys_lock);

	static struct vfsmount *devpts_mnt;

	struct pts_mount_opts {
	int setuid;
	int setgid;
	uid_t uid;
	gid_t gid;
	umode_t mode;
	umode_t ptmxmode;
	int newinstance;
	};

	enum {
	Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,
	Opt_err
	};

	static const match_table_t tokens = {
	{Opt_uid, "uid=%u"},
	{Opt_gid, "gid=%u"},
	{Opt_mode, "mode=%o"},
	#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
	{Opt_ptmxmode, "ptmxmode=%o"},
	{Opt_newinstance, "newinstance"},
	#endif
	{Opt_err, NULL}
	};

	struct pts_fs_info {
	struct ida allocated_ptys;
	struct pts_mount_opts mount_opts;
	struct dentry *ptmx_dentry;
	};

	static inline struct pts_fs_info DEVPTS_SB(struct super_block sb)
	{
	return sb->s_fs_info;
	}

	static inline struct super_block pts_sb_from_inode(struct inode inode)
	{
	#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
	if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
	return inode->i_sb;
	#endif
	return devpts_mnt->mnt_sb;
	}

	#define PARSE_MOUNT 0
	#define PARSE_REMOUNT 1

	/*
	* parse_mount_options():
	* Set @opts to mount options specified in @data. If an option is not
	* specified in @data, set it to its default value. The exception is
	* 'newinstance' option which can only be set/cleared on a mount (i.e.
	* cannot be changed during remount).
	*
	* Note: @data may be NULL (in which case all options are set to default).
	*/
	static int parse_mount_options(char data, int op, struct pts_mount_opts opts)
	{
	char *p;

	opts->setuid = 0;
	opts->setgid = 0;
	opts->uid = 0;
	opts->gid = 0;
	opts->mode = DEVPTS_DEFAULT_MODE;
	opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;

	/* newinstance makes sense only on initial mount */
	if (op == PARSE_MOUNT)
	opts->newinstance = 0;

	while ((p = strsep(&data, ",")) != NULL) {
	substring_t args[MAX_OPT_ARGS];
	int token;
	int option;

	if (!*p)
	continue;

	token = match_token(p, tokens, args);
	switch (token) {
	case Opt_uid:
	if (match_int(&args[0], &option))
	return -EINVAL;
	opts->uid = option;
	opts->setuid = 1;
	break;
	case Opt_gid:
	if (match_int(&args[0], &option))
	return -EINVAL;
	opts->gid = option;
	opts->setgid = 1;
	break;
	case Opt_mode:
	if (match_octal(&args[0], &option))
	return -EINVAL;
	opts->mode = option & S_IALLUGO;
	break;
	#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
	case Opt_ptmxmode:
	if (match_octal(&args[0], &option))
	return -EINVAL;
	opts->ptmxmode = option & S_IALLUGO;
	break;
	case Opt_newinstance:
	/* newinstance makes sense only on initial mount */
	if (op == PARSE_MOUNT)
	opts->newinstance = 1;
	break;
	#endif
	default:
	printk(KERN_ERR "devpts: called with bogus options\n");
	return -EINVAL;
	}
	}

	return 0;
	}

	#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
	static int mknod_ptmx(struct super_block *sb)
	{
	int mode;
	int rc = -ENOMEM;
	struct dentry *dentry;
	struct inode *inode;
	struct dentry *root = sb->s_root;
	struct pts_fs_info *fsi = DEVPTS_SB(sb);
	struct pts_mount_opts *opts = &fsi->mount_opts;

	mutex_lock(&root->d_inode->i_mutex);

	/* If we have already created ptmx node, return */
	if (fsi->ptmx_dentry) {
	rc = 0;
	goto out;
	}

	dentry = d_alloc_name(root, "ptmx");
	if (!dentry) {
	printk(KERN_NOTICE "Unable to alloc dentry for ptmx node\n");
	goto out;
	}

	/*
	* Create a new 'ptmx' node in this mount of devpts.
	*/
	inode = new_inode(sb);
	if (!inode) {
	printk(KERN_ERR "Unable to alloc inode for ptmx node\n");
	dput(dentry);
	goto out;
	}

	inode->i_ino = 2;
	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;

	mode = S_IFCHR\|opts->ptmxmode;
	init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));

	d_add(dentry, inode);

	fsi->ptmx_dentry = dentry;
	rc = 0;
	out:
	mutex_unlock(&root->d_inode->i_mutex);
	return rc;
	}

	static void update_ptmx_mode(struct pts_fs_info *fsi)
	{
	struct inode *inode;
	if (fsi->ptmx_dentry) {
	inode = fsi->ptmx_dentry->d_inode;
	inode->i_mode = S_IFCHR\|fsi->mount_opts.ptmxmode;
	}
	}
	#else
	static inline void update_ptmx_mode(struct pts_fs_info *fsi)
	{
	return;
	}
	#endif

	static int devpts_remount(struct super_block sb, int flags, char *data)
	{
	int err;
	struct pts_fs_info *fsi = DEVPTS_SB(sb);
	struct pts_mount_opts *opts = &fsi->mount_opts;

	err = parse_mount_options(data, PARSE_REMOUNT, opts);

	/*
	* parse_mount_options() restores options to default values
	* before parsing and may have changed ptmxmode. So, update the
	* mode in the inode too. Bogus options don't fail the remount,
	* so do this even on error return.
	*/
	update_ptmx_mode(fsi);

	return err;
	}

	static int devpts_show_options(struct seq_file seq, struct vfsmount vfs)
	{
	struct pts_fs_info *fsi = DEVPTS_SB(vfs->mnt_sb);
	struct pts_mount_opts *opts = &fsi->mount_opts;

	if (opts->setuid)
	seq_printf(seq, ",uid=%u", opts->uid);
	if (opts->setgid)
	seq_printf(seq, ",gid=%u", opts->gid);
	seq_printf(seq, ",mode=%03o", opts->mode);
	#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
	seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
	#endif

	return 0;
	}

	static const struct super_operations devpts_sops = {
	.statfs = simple_statfs,
	.remount_fs = devpts_remount,
	.show_options = devpts_show_options,
	};

	static void *new_pts_fs_info(void)
	{
	struct pts_fs_info *fsi;

	fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
	if (!fsi)
	return NULL;

	ida_init(&fsi->allocated_ptys);
	fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
	fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;

	return fsi;
	}

	static int
	devpts_fill_super(struct super_block s, void data, int silent)
	{
	struct inode *inode;

	s->s_blocksize = 1024;
	s->s_blocksize_bits = 10;
	s->s_magic = DEVPTS_SUPER_MAGIC;
	s->s_op = &devpts_sops;
	s->s_time_gran = 1;

	s->s_fs_info = new_pts_fs_info();
	if (!s->s_fs_info)
	goto fail;

	inode = new_inode(s);
	if (!inode)
	goto free_fsi;
	inode->i_ino = 1;
	inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
	inode->i_mode = S_IFDIR \| S_IRUGO \| S_IXUGO \| S_IWUSR;
	inode->i_op = &simple_dir_inode_operations;
	inode->i_fop = &simple_dir_operations;
	inode->i_nlink = 2;

	s->s_root = d_alloc_root(inode);
	if (s->s_root)
	return 0;

	printk(KERN_ERR "devpts: get root dentry failed\n");
	iput(inode);

	free_fsi:
	kfree(s->s_fs_info);
	fail:
	return -ENOMEM;
	}

	#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
	static int compare_init_pts_sb(struct super_block s, void p)
	{
	if (devpts_mnt)
	return devpts_mnt->mnt_sb == s;
	return 0;
	}

	/*
	* devpts_mount()
	*
	* If the '-o newinstance' mount option was specified, mount a new
	* (private) instance of devpts. PTYs created in this instance are
	* independent of the PTYs in other devpts instances.
	*
	* If the '-o newinstance' option was not specified, mount/remount the
	* initial kernel mount of devpts. This type of mount gives the
	* legacy, single-instance semantics.
	*
	* The 'newinstance' option is needed to support multiple namespace
	* semantics in devpts while preserving backward compatibility of the
	* current 'single-namespace' semantics. i.e all mounts of devpts
	* without the 'newinstance' mount option should bind to the initial
	* kernel mount, like mount_single().
	*
	* Mounts with 'newinstance' option create a new, private namespace.
	*
	* NOTE:
	*
	* For single-mount semantics, devpts cannot use mount_single(),
	* because mount_single()/sget() find and use the super-block from
	* the most recent mount of devpts. But that recent mount may be a
	* 'newinstance' mount and mount_single() would pick the newinstance
	* super-block instead of the initial super-block.
	*/
	static struct dentry devpts_mount(struct file_system_type fs_type,
	int flags, const char dev_name, void data)
	{
	int error;
	struct pts_mount_opts opts;
	struct super_block *s;

	error = parse_mount_options(data, PARSE_MOUNT, &opts);
	if (error)
	return ERR_PTR(error);

	if (opts.newinstance)
	s = sget(fs_type, NULL, set_anon_super, NULL);
	else
	s = sget(fs_type, compare_init_pts_sb, set_anon_super, NULL);

	if (IS_ERR(s))
	return ERR_CAST(s);

	if (!s->s_root) {
	s->s_flags = flags;
	error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
	if (error)
	goto out_undo_sget;
	s->s_flags \|= MS_ACTIVE;
	}

	memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));

	error = mknod_ptmx(s);
	if (error)
	goto out_undo_sget;

	return dget(s->s_root);

	out_undo_sget:
	deactivate_locked_super(s);
	return ERR_PTR(error);
	}

	#else
	/*
	* This supports only the legacy single-instance semantics (no
	* multiple-instance semantics)
	*/
	static struct dentry devpts_mount(struct file_system_type fs_type, int flags,
	const char dev_name, void data)
	{
	return mount_single(fs_type, flags, data, devpts_fill_super);
	}
	#endif

	static void devpts_kill_sb(struct super_block *sb)
	{
	struct pts_fs_info *fsi = DEVPTS_SB(sb);

	kfree(fsi);
	kill_litter_super(sb);
	}

	static struct file_system_type devpts_fs_type = {
	.name = "devpts",
	.mount = devpts_mount,
	.kill_sb = devpts_kill_sb,
	};

	/*
	* The normal naming convention is simply /dev/pts/<number>; this conforms
	* to the System V naming convention
	*/

	int devpts_new_index(struct inode *ptmx_inode)
	{
	struct super_block *sb = pts_sb_from_inode(ptmx_inode);
	struct pts_fs_info *fsi = DEVPTS_SB(sb);
	int index;
	int ida_ret;

	retry:
	if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
	return -ENOMEM;

	mutex_lock(&allocated_ptys_lock);
	ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
	if (ida_ret < 0) {
	mutex_unlock(&allocated_ptys_lock);
	if (ida_ret == -EAGAIN)
	goto retry;
	return -EIO;
	}

	if (index >= pty_limit) {
	ida_remove(&fsi->allocated_ptys, index);
	mutex_unlock(&allocated_ptys_lock);
	return -EIO;
	}
	mutex_unlock(&allocated_ptys_lock);
	return index;
	}

	void devpts_kill_index(struct inode *ptmx_inode, 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);
	mutex_unlock(&allocated_ptys_lock);
	}

	int devpts_pty_new(struct inode ptmx_inode, struct tty_struct tty)
	{
	/* 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 = new_inode(sb);
	struct dentry *root = sb->s_root;
	struct pts_fs_info *fsi = DEVPTS_SB(sb);
	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);

	if (!inode)
	return -ENOMEM;

	inode->i_ino = number + 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;
	tty->driver_data = inode;

	sprintf(s, "%d", number);

	mutex_lock(&root->d_inode->i_mutex);

	dentry = d_alloc_name(root, s);
	if (!IS_ERR(dentry)) {
	d_add(dentry, inode);
	fsnotify_create(root->d_inode, dentry);
	}

	mutex_unlock(&root->d_inode->i_mutex);

	return 0;
	}

	struct tty_struct devpts_get_tty(struct inode pts_inode, int number)
	{
	struct dentry *dentry;
	struct tty_struct *tty;

	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;

	tty = NULL;
	if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
	tty = (struct tty_struct *)pts_inode->i_private;

	dput(dentry);

	return tty;
	}

	void devpts_pty_kill(struct tty_struct *tty)
	{
	struct inode *inode = tty->driver_data;
	struct super_block *sb = pts_sb_from_inode(inode);
	struct dentry *root = sb->s_root;
	struct dentry *dentry;

	BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));

	mutex_lock(&root->d_inode->i_mutex);

	dentry = d_find_alias(inode);
	if (IS_ERR(dentry))
	goto out;

	if (dentry) {
	inode->i_nlink--;
	d_delete(dentry);
	dput(dentry); /* d_alloc_name() in devpts_pty_new() */
	}

	dput(dentry); /* d_find_alias above */
	out:
	mutex_unlock(&root->d_inode->i_mutex);
	}

	static int __init init_devpts_fs(void)
	{
	int 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);
	unregister_filesystem(&devpts_fs_type);
	}
	}
	return err;
	}
	module_init(init_devpts_fs)