1 /* -*- linux-c -*- --------------------------------------------------------- *
3 * linux/fs/devpts/inode.c
5 * Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
7 * This file is part of the Linux kernel and is made available under
8 * the terms of the GNU General Public License, version 2, or at your
9 * option, any later version, incorporated herein by reference.
11 * ------------------------------------------------------------------------- */
13 #include <linux/module.h>
14 #include <linux/init.h>
16 #include <linux/sched.h>
17 #include <linux/namei.h>
18 #include <linux/slab.h>
19 #include <linux/mount.h>
20 #include <linux/tty.h>
21 #include <linux/mutex.h>
22 #include <linux/magic.h>
23 #include <linux/idr.h>
24 #include <linux/devpts_fs.h>
25 #include <linux/parser.h>
26 #include <linux/fsnotify.h>
27 #include <linux/seq_file.h>
29 #define DEVPTS_DEFAULT_MODE 0600
31 * ptmx is a new node in /dev/pts and will be unused in legacy (single-
32 * instance) mode. To prevent surprises in user space, set permissions of
33 * ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
36 #define DEVPTS_DEFAULT_PTMX_MODE 0000
40 * sysctl support for setting limits on the number of Unix98 ptys allocated.
41 * Otherwise one can eat up all kernel memory by opening /dev/ptmx repeatedly.
43 static int pty_limit = NR_UNIX98_PTY_DEFAULT;
44 static int pty_reserve = NR_UNIX98_PTY_RESERVE;
45 static int pty_limit_min;
46 static int pty_limit_max = INT_MAX;
49 static struct ctl_table pty_table[] = {
52 .maxlen = sizeof(int),
55 .proc_handler = proc_dointvec_minmax,
56 .extra1 = &pty_limit_min,
57 .extra2 = &pty_limit_max,
59 .procname = "reserve",
60 .maxlen = sizeof(int),
63 .proc_handler = proc_dointvec_minmax,
64 .extra1 = &pty_limit_min,
65 .extra2 = &pty_limit_max,
68 .maxlen = sizeof(int),
71 .proc_handler = proc_dointvec,
76 static struct ctl_table pty_kern_table[] = {
85 static struct ctl_table pty_root_table[] = {
89 .child = pty_kern_table,
94 static DEFINE_MUTEX(allocated_ptys_lock);
96 static struct vfsmount *devpts_mnt;
98 struct pts_mount_opts {
110 Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance, Opt_max,
114 static const match_table_t tokens = {
117 {Opt_mode, "mode=%o"},
118 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
119 {Opt_ptmxmode, "ptmxmode=%o"},
120 {Opt_newinstance, "newinstance"},
127 struct ida allocated_ptys;
128 struct pts_mount_opts mount_opts;
129 struct dentry *ptmx_dentry;
132 static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
134 return sb->s_fs_info;
137 static inline struct super_block *pts_sb_from_inode(struct inode *inode)
139 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
140 if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
143 return devpts_mnt->mnt_sb;
146 #define PARSE_MOUNT 0
147 #define PARSE_REMOUNT 1
150 * parse_mount_options():
151 * Set @opts to mount options specified in @data. If an option is not
152 * specified in @data, set it to its default value. The exception is
153 * 'newinstance' option which can only be set/cleared on a mount (i.e.
154 * cannot be changed during remount).
156 * Note: @data may be NULL (in which case all options are set to default).
158 static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
166 opts->mode = DEVPTS_DEFAULT_MODE;
167 opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
168 opts->max = NR_UNIX98_PTY_MAX;
170 /* newinstance makes sense only on initial mount */
171 if (op == PARSE_MOUNT)
172 opts->newinstance = 0;
174 while ((p = strsep(&data, ",")) != NULL) {
175 substring_t args[MAX_OPT_ARGS];
182 token = match_token(p, tokens, args);
185 if (match_int(&args[0], &option))
191 if (match_int(&args[0], &option))
197 if (match_octal(&args[0], &option))
199 opts->mode = option & S_IALLUGO;
201 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
203 if (match_octal(&args[0], &option))
205 opts->ptmxmode = option & S_IALLUGO;
207 case Opt_newinstance:
208 /* newinstance makes sense only on initial mount */
209 if (op == PARSE_MOUNT)
210 opts->newinstance = 1;
213 if (match_int(&args[0], &option) ||
214 option < 0 || option > NR_UNIX98_PTY_MAX)
220 printk(KERN_ERR "devpts: called with bogus options\n");
228 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
229 static int mknod_ptmx(struct super_block *sb)
233 struct dentry *dentry;
235 struct dentry *root = sb->s_root;
236 struct pts_fs_info *fsi = DEVPTS_SB(sb);
237 struct pts_mount_opts *opts = &fsi->mount_opts;
239 mutex_lock(&root->d_inode->i_mutex);
241 /* If we have already created ptmx node, return */
242 if (fsi->ptmx_dentry) {
247 dentry = d_alloc_name(root, "ptmx");
249 printk(KERN_NOTICE "Unable to alloc dentry for ptmx node\n");
254 * Create a new 'ptmx' node in this mount of devpts.
256 inode = new_inode(sb);
258 printk(KERN_ERR "Unable to alloc inode for ptmx node\n");
264 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
266 mode = S_IFCHR|opts->ptmxmode;
267 init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
269 d_add(dentry, inode);
271 fsi->ptmx_dentry = dentry;
274 mutex_unlock(&root->d_inode->i_mutex);
278 static void update_ptmx_mode(struct pts_fs_info *fsi)
281 if (fsi->ptmx_dentry) {
282 inode = fsi->ptmx_dentry->d_inode;
283 inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
287 static inline void update_ptmx_mode(struct pts_fs_info *fsi)
293 static int devpts_remount(struct super_block *sb, int *flags, char *data)
296 struct pts_fs_info *fsi = DEVPTS_SB(sb);
297 struct pts_mount_opts *opts = &fsi->mount_opts;
299 err = parse_mount_options(data, PARSE_REMOUNT, opts);
302 * parse_mount_options() restores options to default values
303 * before parsing and may have changed ptmxmode. So, update the
304 * mode in the inode too. Bogus options don't fail the remount,
305 * so do this even on error return.
307 update_ptmx_mode(fsi);
312 static int devpts_show_options(struct seq_file *seq, struct dentry *root)
314 struct pts_fs_info *fsi = DEVPTS_SB(root->d_sb);
315 struct pts_mount_opts *opts = &fsi->mount_opts;
318 seq_printf(seq, ",uid=%u", opts->uid);
320 seq_printf(seq, ",gid=%u", opts->gid);
321 seq_printf(seq, ",mode=%03o", opts->mode);
322 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
323 seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
324 if (opts->max < NR_UNIX98_PTY_MAX)
325 seq_printf(seq, ",max=%d", opts->max);
331 static const struct super_operations devpts_sops = {
332 .statfs = simple_statfs,
333 .remount_fs = devpts_remount,
334 .show_options = devpts_show_options,
337 static void *new_pts_fs_info(void)
339 struct pts_fs_info *fsi;
341 fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
345 ida_init(&fsi->allocated_ptys);
346 fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
347 fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
353 devpts_fill_super(struct super_block *s, void *data, int silent)
357 s->s_blocksize = 1024;
358 s->s_blocksize_bits = 10;
359 s->s_magic = DEVPTS_SUPER_MAGIC;
360 s->s_op = &devpts_sops;
363 s->s_fs_info = new_pts_fs_info();
367 inode = new_inode(s);
371 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
372 inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
373 inode->i_op = &simple_dir_inode_operations;
374 inode->i_fop = &simple_dir_operations;
377 s->s_root = d_alloc_root(inode);
381 printk(KERN_ERR "devpts: get root dentry failed\n");
388 #ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
389 static int compare_init_pts_sb(struct super_block *s, void *p)
392 return devpts_mnt->mnt_sb == s;
399 * If the '-o newinstance' mount option was specified, mount a new
400 * (private) instance of devpts. PTYs created in this instance are
401 * independent of the PTYs in other devpts instances.
403 * If the '-o newinstance' option was not specified, mount/remount the
404 * initial kernel mount of devpts. This type of mount gives the
405 * legacy, single-instance semantics.
407 * The 'newinstance' option is needed to support multiple namespace
408 * semantics in devpts while preserving backward compatibility of the
409 * current 'single-namespace' semantics. i.e all mounts of devpts
410 * without the 'newinstance' mount option should bind to the initial
411 * kernel mount, like mount_single().
413 * Mounts with 'newinstance' option create a new, private namespace.
417 * For single-mount semantics, devpts cannot use mount_single(),
418 * because mount_single()/sget() find and use the super-block from
419 * the most recent mount of devpts. But that recent mount may be a
420 * 'newinstance' mount and mount_single() would pick the newinstance
421 * super-block instead of the initial super-block.
423 static struct dentry *devpts_mount(struct file_system_type *fs_type,
424 int flags, const char *dev_name, void *data)
427 struct pts_mount_opts opts;
428 struct super_block *s;
430 error = parse_mount_options(data, PARSE_MOUNT, &opts);
432 return ERR_PTR(error);
434 if (opts.newinstance)
435 s = sget(fs_type, NULL, set_anon_super, NULL);
437 s = sget(fs_type, compare_init_pts_sb, set_anon_super, NULL);
444 error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
447 s->s_flags |= MS_ACTIVE;
450 memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));
452 error = mknod_ptmx(s);
456 return dget(s->s_root);
459 deactivate_locked_super(s);
460 return ERR_PTR(error);
465 * This supports only the legacy single-instance semantics (no
466 * multiple-instance semantics)
468 static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags,
469 const char *dev_name, void *data)
471 return mount_single(fs_type, flags, data, devpts_fill_super);
475 static void devpts_kill_sb(struct super_block *sb)
477 struct pts_fs_info *fsi = DEVPTS_SB(sb);
480 kill_litter_super(sb);
483 static struct file_system_type devpts_fs_type = {
485 .mount = devpts_mount,
486 .kill_sb = devpts_kill_sb,
490 * The normal naming convention is simply /dev/pts/<number>; this conforms
491 * to the System V naming convention
494 int devpts_new_index(struct inode *ptmx_inode)
496 struct super_block *sb = pts_sb_from_inode(ptmx_inode);
497 struct pts_fs_info *fsi = DEVPTS_SB(sb);
502 if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
505 mutex_lock(&allocated_ptys_lock);
506 if (pty_count >= pty_limit -
507 (fsi->mount_opts.newinstance ? pty_reserve : 0)) {
508 mutex_unlock(&allocated_ptys_lock);
512 ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
514 mutex_unlock(&allocated_ptys_lock);
515 if (ida_ret == -EAGAIN)
520 if (index >= fsi->mount_opts.max) {
521 ida_remove(&fsi->allocated_ptys, index);
522 mutex_unlock(&allocated_ptys_lock);
526 mutex_unlock(&allocated_ptys_lock);
530 void devpts_kill_index(struct inode *ptmx_inode, int idx)
532 struct super_block *sb = pts_sb_from_inode(ptmx_inode);
533 struct pts_fs_info *fsi = DEVPTS_SB(sb);
535 mutex_lock(&allocated_ptys_lock);
536 ida_remove(&fsi->allocated_ptys, idx);
538 mutex_unlock(&allocated_ptys_lock);
541 int devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty)
543 /* tty layer puts index from devpts_new_index() in here */
544 int number = tty->index;
545 struct tty_driver *driver = tty->driver;
546 dev_t device = MKDEV(driver->major, driver->minor_start+number);
547 struct dentry *dentry;
548 struct super_block *sb = pts_sb_from_inode(ptmx_inode);
549 struct inode *inode = new_inode(sb);
550 struct dentry *root = sb->s_root;
551 struct pts_fs_info *fsi = DEVPTS_SB(sb);
552 struct pts_mount_opts *opts = &fsi->mount_opts;
556 /* We're supposed to be given the slave end of a pty */
557 BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY);
558 BUG_ON(driver->subtype != PTY_TYPE_SLAVE);
563 inode->i_ino = number + 3;
564 inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
565 inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
566 inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
567 init_special_inode(inode, S_IFCHR|opts->mode, device);
568 inode->i_private = tty;
569 tty->driver_data = inode;
571 sprintf(s, "%d", number);
573 mutex_lock(&root->d_inode->i_mutex);
575 dentry = d_alloc_name(root, s);
577 d_add(dentry, inode);
578 fsnotify_create(root->d_inode, dentry);
584 mutex_unlock(&root->d_inode->i_mutex);
589 struct tty_struct *devpts_get_tty(struct inode *pts_inode, int number)
591 struct dentry *dentry;
592 struct tty_struct *tty;
594 BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
596 /* Ensure dentry has not been deleted by devpts_pty_kill() */
597 dentry = d_find_alias(pts_inode);
602 if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
603 tty = (struct tty_struct *)pts_inode->i_private;
610 void devpts_pty_kill(struct tty_struct *tty)
612 struct inode *inode = tty->driver_data;
613 struct super_block *sb = pts_sb_from_inode(inode);
614 struct dentry *root = sb->s_root;
615 struct dentry *dentry;
617 BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
619 mutex_lock(&root->d_inode->i_mutex);
621 dentry = d_find_alias(inode);
625 dput(dentry); /* d_alloc_name() in devpts_pty_new() */
626 dput(dentry); /* d_find_alias above */
628 mutex_unlock(&root->d_inode->i_mutex);
631 static int __init init_devpts_fs(void)
633 int err = register_filesystem(&devpts_fs_type);
634 struct ctl_table_header *table;
637 table = register_sysctl_table(pty_root_table);
638 devpts_mnt = kern_mount(&devpts_fs_type);
639 if (IS_ERR(devpts_mnt)) {
640 err = PTR_ERR(devpts_mnt);
641 unregister_filesystem(&devpts_fs_type);
642 unregister_sysctl_table(table);
647 module_init(init_devpts_fs)