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.
  *
  * ------------------------------------------------------------------------- */

 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

 #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

 /*
  * sysctl support for setting limits on the number of Unix98 ptys allocated.
  * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
  */
 static int pty_limit = NR_UNIX98_PTY_DEFAULT;
 static int pty_reserve = NR_UNIX98_PTY_RESERVE;
 static int pty_limit_min;
 static int pty_limit_max = INT_MAX;
 static int pty_count;

 static struct ctl_table pty_table[] = {
 	{
 		.procname	= "max",
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.data		= &pty_limit,
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &pty_limit_min,
 		.extra2		= &pty_limit_max,
 	}, {
 		.procname	= "reserve",
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.data		= &pty_reserve,
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &pty_limit_min,
 		.extra2		= &pty_limit_max,
 	}, {
 		.procname	= "nr",
 		.maxlen		= sizeof(int),
 		.mode		= 0444,
 		.data		= &pty_count,
 		.proc_handler	= proc_dointvec,
 	},
 	{}
 };

 static struct ctl_table pty_kern_table[] = {
 	{
 		.procname	= "pty",
 		.mode		= 0555,
 		.child		= pty_table,
 	},
 	{}
 };

 static struct ctl_table pty_root_table[] = {
 	{
 		.procname	= "kernel",
 		.mode		= 0555,
 		.child		= pty_kern_table,
 	},
 	{}
 };

 static DEFINE_MUTEX(allocated_ptys_lock);

 struct pts_mount_opts {
 	int setuid;
 	int setgid;
 	kuid_t   uid;
 	kgid_t   gid;
 	umode_t mode;
 	umode_t ptmxmode;
 	int reserve;
 	int max;
 };

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

 static const match_table_t tokens = {
 	{Opt_uid, "uid=%u"},
 	{Opt_gid, "gid=%u"},
 	{Opt_mode, "mode=%o"},
 	{Opt_ptmxmode, "ptmxmode=%o"},
 	{Opt_newinstance, "newinstance"},
 	{Opt_max, "max=%d"},
 	{Opt_err, NULL}
 };

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

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

 struct pts_fs_info *devpts_acquire(struct file *filp)
 {
 	struct pts_fs_info *result;
 	struct path path;
 	struct super_block *sb;
 	int err;

 	path = filp->f_path;
 	path_get(&path);

 	/* Has the devpts filesystem already been found? */
 	sb = path.mnt->mnt_sb;
 	if (sb->s_magic != DEVPTS_SUPER_MAGIC) {
 		/* Is a devpts filesystem at "pts" in the same directory? */
 		err = path_pts(&path);
 		if (err) {
 			result = ERR_PTR(err);
 			goto out;
 		}

 		/* Is the path the root of a devpts filesystem? */
 		result = ERR_PTR(-ENODEV);
 		sb = path.mnt->mnt_sb;
 		if ((sb->s_magic != DEVPTS_SUPER_MAGIC) ||
 		    (path.mnt->mnt_root != sb->s_root))
 			goto out;
 	}

 	/*
 	 * pty code needs to hold extra references in case of last /dev/tty close
 	 */
 	atomic_inc(&sb->s_active);
 	result = DEVPTS_SB(sb);

 out:
 	path_put(&path);
 	return result;
 }

 void devpts_release(struct pts_fs_info *fsi)
 {
 	deactivate_super(fsi->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.
  *
  * 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;
 	kuid_t uid;
 	kgid_t gid;

 	opts->setuid  = 0;
 	opts->setgid  = 0;
 	opts->uid     = GLOBAL_ROOT_UID;
 	opts->gid     = GLOBAL_ROOT_GID;
 	opts->mode    = DEVPTS_DEFAULT_MODE;
 	opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
 	opts->max     = NR_UNIX98_PTY_MAX;

 	/* Only allow instances mounted from the initial mount
 	 * namespace to tap the reserve pool of ptys.
 	 */
 	if (op == PARSE_MOUNT)
 		opts->reserve =
 			(current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);

 	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;
 			uid = make_kuid(current_user_ns(), option);
 			if (!uid_valid(uid))
 				return -EINVAL;
 			opts->uid = uid;
 			opts->setuid = 1;
 			break;
 		case Opt_gid:
 			if (match_int(&args[0], &option))
 				return -EINVAL;
 			gid = make_kgid(current_user_ns(), option);
 			if (!gid_valid(gid))
 				return -EINVAL;
 			opts->gid = gid;
 			opts->setgid = 1;
 			break;
 		case Opt_mode:
 			if (match_octal(&args[0], &option))
 				return -EINVAL;
 			opts->mode = option & S_IALLUGO;
 			break;
 		case Opt_ptmxmode:
 			if (match_octal(&args[0], &option))
 				return -EINVAL;
 			opts->ptmxmode = option & S_IALLUGO;
 			break;
 		case Opt_newinstance:
 			break;
 		case Opt_max:
 			if (match_int(&args[0], &option) ||
 			    option < 0 || option > NR_UNIX98_PTY_MAX)
 				return -EINVAL;
 			opts->max = option;
 			break;
 		default:
 			pr_err("called with bogus options\n");
 			return -EINVAL;
 		}
 	}

 	return 0;
 }

 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;
 	kuid_t ptmx_uid = current_fsuid();
 	kgid_t ptmx_gid = current_fsgid();

 	inode_lock(d_inode(root));

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

 	dentry = d_alloc_name(root, "ptmx");
 	if (!dentry) {
 		pr_err("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) {
 		pr_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));
 	inode->i_uid = ptmx_uid;
 	inode->i_gid = ptmx_gid;

 	d_add(dentry, inode);

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

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

 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 dentry *root)
 {
 	struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
 	struct pts_mount_opts *opts = &fsi->mount_opts;

 	if (opts->setuid)
 		seq_printf(seq, ",uid=%u",
 			   from_kuid_munged(&init_user_ns, opts->uid));
 	if (opts->setgid)
 		seq_printf(seq, ",gid=%u",
 			   from_kgid_munged(&init_user_ns, opts->gid));
 	seq_printf(seq, ",mode=%03o", opts->mode);
 	seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
 	if (opts->max < NR_UNIX98_PTY_MAX)
 		seq_printf(seq, ",max=%d", opts->max);

 	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(struct super_block *sb)
 {
 	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;
 	fsi->sb = sb;

 	return fsi;
 }

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

 	s->s_iflags &= ~SB_I_NODEV;
 	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;

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

 	error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
 	if (error)
 		goto fail;

 	error = -ENOMEM;
 	inode = new_inode(s);
 	if (!inode)
 		goto fail;
 	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;
 	set_nlink(inode, 2);

 	s->s_root = d_make_root(inode);
 	if (!s->s_root) {
 		pr_err("get root dentry failed\n");
 		goto fail;
 	}

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

 	return 0;
 fail_dput:
 	dput(s->s_root);
 	s->s_root = NULL;
 fail:
 	return error;
 }

 /*
  * devpts_mount()
  *
  *     Mount a new (private) instance of devpts.  PTYs created in this
  *     instance are independent of the PTYs in other devpts instances.
  */
 static struct dentry *devpts_mount(struct file_system_type *fs_type,
 	int flags, const char *dev_name, void *data)
 {
 	return mount_nodev(fs_type, flags, data, devpts_fill_super);
 }

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

 	if (fsi)
 		ida_destroy(&fsi->allocated_ptys);
 	kfree(fsi);
 	kill_litter_super(sb);
 }

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

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

 int devpts_new_index(struct pts_fs_info *fsi)
 {
 	int index;
 	int ida_ret;

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

 	mutex_lock(&allocated_ptys_lock);
 	if (pty_count >= (pty_limit -
 			  (fsi->mount_opts.reserve ? 0 : pty_reserve))) {
 		mutex_unlock(&allocated_ptys_lock);
 		return -ENOSPC;
 	}

 	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 >= fsi->mount_opts.max) {
 		ida_remove(&fsi->allocated_ptys, index);
 		mutex_unlock(&allocated_ptys_lock);
 		return -ENOSPC;
 	}
 	pty_count++;
 	mutex_unlock(&allocated_ptys_lock);
 	return index;
 }

 void devpts_kill_index(struct pts_fs_info *fsi, int idx)
 {
 	mutex_lock(&allocated_ptys_lock);
 	ida_remove(&fsi->allocated_ptys, idx);
 	pty_count--;
 	mutex_unlock(&allocated_ptys_lock);
 }

 /**
  * devpts_pty_new -- create a new inode in /dev/pts/
  * @ptmx_inode: inode of the master
  * @device: major+minor of the node to be created
  * @index: used as a name of the node
  * @priv: what's given back by devpts_get_priv
  *
  * The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
  */
 struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
 {
 	struct dentry *dentry;
 	struct super_block *sb = fsi->sb;
 	struct inode *inode;
 	struct dentry *root;
 	struct pts_mount_opts *opts;
 	char s[12];

 	root = sb->s_root;
 	opts = &fsi->mount_opts;

 	inode = new_inode(sb);
 	if (!inode)
 		return ERR_PTR(-ENOMEM);

 	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, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));

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

 	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);
 		dentry = ERR_PTR(-ENOMEM);
 	}

 	return dentry;
 }

 /**
  * devpts_get_priv -- get private data for a slave
  * @pts_inode: inode of the slave
  *
  * Returns whatever was passed as priv in devpts_pty_new for a given inode.
  */
 void *devpts_get_priv(struct dentry *dentry)
 {
 	if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
 		return NULL;
 	return dentry->d_fsdata;
 }

 /**
  * devpts_pty_kill -- remove inode form /dev/pts/
  * @inode: inode of the slave to be removed
  *
  * This is an inverse operation of devpts_pty_new.
  */
 void devpts_pty_kill(struct dentry *dentry)
 {
 	WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);

 	dentry->d_fsdata = NULL;
 	drop_nlink(dentry->d_inode);
 	d_delete(dentry);
 	dput(dentry);	/* d_alloc_name() in devpts_pty_new() */
 }

 static int __init init_devpts_fs(void)
 {
 	int err = register_filesystem(&devpts_fs_type);
 	if (!err) {
 		register_sysctl_table(pty_root_table);
 	}
 	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.
	*
	* ------------------------------------------------------------------------- */

	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

	#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

	/*
	* sysctl support for setting limits on the number of Unix98 ptys allocated.
	* Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
	*/
	static int pty_limit = NR_UNIX98_PTY_DEFAULT;
	static int pty_reserve = NR_UNIX98_PTY_RESERVE;
	static int pty_limit_min;
	static int pty_limit_max = INT_MAX;
	static int pty_count;

	static struct ctl_table pty_table[] = {
	{
	.procname = "max",
	.maxlen = sizeof(int),
	.mode = 0644,
	.data = &pty_limit,
	.proc_handler = proc_dointvec_minmax,
	.extra1 = &pty_limit_min,
	.extra2 = &pty_limit_max,
	}, {
	.procname = "reserve",
	.maxlen = sizeof(int),
	.mode = 0644,
	.data = &pty_reserve,
	.proc_handler = proc_dointvec_minmax,
	.extra1 = &pty_limit_min,
	.extra2 = &pty_limit_max,
	}, {
	.procname = "nr",
	.maxlen = sizeof(int),
	.mode = 0444,
	.data = &pty_count,
	.proc_handler = proc_dointvec,
	},
	{}
	};

	static struct ctl_table pty_kern_table[] = {
	{
	.procname = "pty",
	.mode = 0555,
	.child = pty_table,
	},
	{}
	};

	static struct ctl_table pty_root_table[] = {
	{
	.procname = "kernel",
	.mode = 0555,
	.child = pty_kern_table,
	},
	{}
	};

	static DEFINE_MUTEX(allocated_ptys_lock);

	struct pts_mount_opts {
	int setuid;
	int setgid;
	kuid_t uid;
	kgid_t gid;
	umode_t mode;
	umode_t ptmxmode;
	int reserve;
	int max;
	};

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

	static const match_table_t tokens = {
	{Opt_uid, "uid=%u"},
	{Opt_gid, "gid=%u"},
	{Opt_mode, "mode=%o"},
	{Opt_ptmxmode, "ptmxmode=%o"},
	{Opt_newinstance, "newinstance"},
	{Opt_max, "max=%d"},
	{Opt_err, NULL}
	};

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

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

	struct pts_fs_info devpts_acquire(struct file filp)
	{
	struct pts_fs_info *result;
	struct path path;
	struct super_block *sb;
	int err;

	path = filp->f_path;
	path_get(&path);

	/* Has the devpts filesystem already been found? */
	sb = path.mnt->mnt_sb;
	if (sb->s_magic != DEVPTS_SUPER_MAGIC) {
	/* Is a devpts filesystem at "pts" in the same directory? */
	err = path_pts(&path);
	if (err) {
	result = ERR_PTR(err);
	goto out;
	}

	/* Is the path the root of a devpts filesystem? */
	result = ERR_PTR(-ENODEV);
	sb = path.mnt->mnt_sb;
	if ((sb->s_magic != DEVPTS_SUPER_MAGIC) \|\|
	(path.mnt->mnt_root != sb->s_root))
	goto out;
	}

	/*
	* pty code needs to hold extra references in case of last /dev/tty close
	*/
	atomic_inc(&sb->s_active);
	result = DEVPTS_SB(sb);

	out:
	path_put(&path);
	return result;
	}

	void devpts_release(struct pts_fs_info *fsi)
	{
	deactivate_super(fsi->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.
	*
	* 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;
	kuid_t uid;
	kgid_t gid;

	opts->setuid = 0;
	opts->setgid = 0;
	opts->uid = GLOBAL_ROOT_UID;
	opts->gid = GLOBAL_ROOT_GID;
	opts->mode = DEVPTS_DEFAULT_MODE;
	opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
	opts->max = NR_UNIX98_PTY_MAX;

	/* Only allow instances mounted from the initial mount
	* namespace to tap the reserve pool of ptys.
	*/
	if (op == PARSE_MOUNT)
	opts->reserve =
	(current->nsproxy->mnt_ns == init_task.nsproxy->mnt_ns);

	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;
	uid = make_kuid(current_user_ns(), option);
	if (!uid_valid(uid))
	return -EINVAL;
	opts->uid = uid;
	opts->setuid = 1;
	break;
	case Opt_gid:
	if (match_int(&args[0], &option))
	return -EINVAL;
	gid = make_kgid(current_user_ns(), option);
	if (!gid_valid(gid))
	return -EINVAL;
	opts->gid = gid;
	opts->setgid = 1;
	break;
	case Opt_mode:
	if (match_octal(&args[0], &option))
	return -EINVAL;
	opts->mode = option & S_IALLUGO;
	break;
	case Opt_ptmxmode:
	if (match_octal(&args[0], &option))
	return -EINVAL;
	opts->ptmxmode = option & S_IALLUGO;
	break;
	case Opt_newinstance:
	break;
	case Opt_max:
	if (match_int(&args[0], &option) \|\|
	option < 0 \|\| option > NR_UNIX98_PTY_MAX)
	return -EINVAL;
	opts->max = option;
	break;
	default:
	pr_err("called with bogus options\n");
	return -EINVAL;
	}
	}

	return 0;
	}

	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;
	kuid_t ptmx_uid = current_fsuid();
	kgid_t ptmx_gid = current_fsgid();

	inode_lock(d_inode(root));

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

	dentry = d_alloc_name(root, "ptmx");
	if (!dentry) {
	pr_err("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) {
	pr_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));
	inode->i_uid = ptmx_uid;
	inode->i_gid = ptmx_gid;

	d_add(dentry, inode);

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

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

	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 dentry root)
	{
	struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
	struct pts_mount_opts *opts = &fsi->mount_opts;

	if (opts->setuid)
	seq_printf(seq, ",uid=%u",
	from_kuid_munged(&init_user_ns, opts->uid));
	if (opts->setgid)
	seq_printf(seq, ",gid=%u",
	from_kgid_munged(&init_user_ns, opts->gid));
	seq_printf(seq, ",mode=%03o", opts->mode);
	seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
	if (opts->max < NR_UNIX98_PTY_MAX)
	seq_printf(seq, ",max=%d", opts->max);

	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(struct super_block sb)
	{
	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;
	fsi->sb = sb;

	return fsi;
	}

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

	s->s_iflags &= ~SB_I_NODEV;
	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;

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

	error = parse_mount_options(data, PARSE_MOUNT, &DEVPTS_SB(s)->mount_opts);
	if (error)
	goto fail;

	error = -ENOMEM;
	inode = new_inode(s);
	if (!inode)
	goto fail;
	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;
	set_nlink(inode, 2);

	s->s_root = d_make_root(inode);
	if (!s->s_root) {
	pr_err("get root dentry failed\n");
	goto fail;
	}

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

	return 0;
	fail_dput:
	dput(s->s_root);
	s->s_root = NULL;
	fail:
	return error;
	}

	/*
	* devpts_mount()
	*
	* Mount a new (private) instance of devpts. PTYs created in this
	* instance are independent of the PTYs in other devpts instances.
	*/
	static struct dentry devpts_mount(struct file_system_type fs_type,
	int flags, const char dev_name, void data)
	{
	return mount_nodev(fs_type, flags, data, devpts_fill_super);
	}

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

	if (fsi)
	ida_destroy(&fsi->allocated_ptys);
	kfree(fsi);
	kill_litter_super(sb);
	}

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

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

	int devpts_new_index(struct pts_fs_info *fsi)
	{
	int index;
	int ida_ret;

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

	mutex_lock(&allocated_ptys_lock);
	if (pty_count >= (pty_limit -
	(fsi->mount_opts.reserve ? 0 : pty_reserve))) {
	mutex_unlock(&allocated_ptys_lock);
	return -ENOSPC;
	}

	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 >= fsi->mount_opts.max) {
	ida_remove(&fsi->allocated_ptys, index);
	mutex_unlock(&allocated_ptys_lock);
	return -ENOSPC;
	}
	pty_count++;
	mutex_unlock(&allocated_ptys_lock);
	return index;
	}

	void devpts_kill_index(struct pts_fs_info *fsi, int idx)
	{
	mutex_lock(&allocated_ptys_lock);
	ida_remove(&fsi->allocated_ptys, idx);
	pty_count--;
	mutex_unlock(&allocated_ptys_lock);
	}

	/**
	* devpts_pty_new -- create a new inode in /dev/pts/
	* @ptmx_inode: inode of the master
	* @device: major+minor of the node to be created
	* @index: used as a name of the node
	* @priv: what's given back by devpts_get_priv
	*
	* The created inode is returned. Remove it from /dev/pts/ by devpts_pty_kill.
	*/
	struct dentry devpts_pty_new(struct pts_fs_info fsi, int index, void *priv)
	{
	struct dentry *dentry;
	struct super_block *sb = fsi->sb;
	struct inode *inode;
	struct dentry *root;
	struct pts_mount_opts *opts;
	char s[12];

	root = sb->s_root;
	opts = &fsi->mount_opts;

	inode = new_inode(sb);
	if (!inode)
	return ERR_PTR(-ENOMEM);

	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, MKDEV(UNIX98_PTY_SLAVE_MAJOR, index));

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

	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);
	dentry = ERR_PTR(-ENOMEM);
	}

	return dentry;
	}

	/**
	* devpts_get_priv -- get private data for a slave
	* @pts_inode: inode of the slave
	*
	* Returns whatever was passed as priv in devpts_pty_new for a given inode.
	*/
	void devpts_get_priv(struct dentry dentry)
	{
	if (dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC)
	return NULL;
	return dentry->d_fsdata;
	}

	/**
	* devpts_pty_kill -- remove inode form /dev/pts/
	* @inode: inode of the slave to be removed
	*
	* This is an inverse operation of devpts_pty_new.
	*/
	void devpts_pty_kill(struct dentry *dentry)
	{
	WARN_ON_ONCE(dentry->d_sb->s_magic != DEVPTS_SUPER_MAGIC);

	dentry->d_fsdata = NULL;
	drop_nlink(dentry->d_inode);
	d_delete(dentry);
	dput(dentry); /* d_alloc_name() in devpts_pty_new() */
	}

	static int __init init_devpts_fs(void)
	{
	int err = register_filesystem(&devpts_fs_type);
	if (!err) {
	register_sysctl_table(pty_root_table);
	}
	return err;
	}
	module_init(init_devpts_fs)