linux/fs/devpts/inode.c

// SPDX-License-Identifier: GPL-2.0-or-later
/* -*- linux-c -*- --------------------------------------------------------- *
 *
 * linux/fs/devpts/inode.c
 *
 *  Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
 *
 * ------------------------------------------------------------------------- */

#define pr_fmt(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 …
/*
 * 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 …
#define PTMX_MINOR …

/*
 * 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 = …;
static int pty_reserve = …;
static int pty_limit_min;
static int pty_limit_max = …;
static atomic_t pty_count = …;

static struct ctl_table pty_table[] = …;

struct pts_mount_opts { … };

enum { … };

static const match_table_t tokens = …;

struct pts_fs_info { … };

static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
{ … }

static int devpts_ptmx_path(struct path *path)
{ … }

/*
 * Try to find a suitable devpts filesystem. We support the following
 * scenarios:
 * - The ptmx device node is located in the same directory as the devpts
 *   mount where the pts device nodes are located.
 *   This is e.g. the case when calling open on the /dev/pts/ptmx device
 *   node when the devpts filesystem is mounted at /dev/pts.
 * - The ptmx device node is located outside the devpts filesystem mount
 *   where the pts device nodes are located. For example, the ptmx device
 *   is a symlink, separate device node, or bind-mount.
 *   A supported scenario is bind-mounting /dev/pts/ptmx to /dev/ptmx and
 *   then calling open on /dev/ptmx. In this case a suitable pts
 *   subdirectory can be found in the common parent directory /dev of the
 *   devpts mount and the ptmx bind-mount, after resolving the /dev/ptmx
 *   bind-mount.
 *   If no suitable pts subdirectory can be found this function will fail.
 *   This is e.g. the case when bind-mounting /dev/pts/ptmx to /ptmx.
 */
struct vfsmount *devpts_mntget(struct file *filp, struct pts_fs_info *fsi)
{ … }

struct pts_fs_info *devpts_acquire(struct file *filp)
{ … }

void devpts_release(struct pts_fs_info *fsi)
{ … }

#define PARSE_MOUNT …
#define PARSE_REMOUNT …

/*
 * 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)
{ … }

static int mknod_ptmx(struct super_block *sb)
{ … }

static void update_ptmx_mode(struct pts_fs_info *fsi)
{ … }

static int devpts_remount(struct super_block *sb, int *flags, char *data)
{ … }

static int devpts_show_options(struct seq_file *seq, struct dentry *root)
{ … }

static const struct super_operations devpts_sops = …;

static void *new_pts_fs_info(struct super_block *sb)
{ … }

static int
devpts_fill_super(struct super_block *s, void *data, int silent)
{ … }

/*
 * 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)
{ … }

static void devpts_kill_sb(struct super_block *sb)
{ … }

static struct file_system_type devpts_fs_type = …;

/*
 * 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)
{ … }

void devpts_kill_index(struct pts_fs_info *fsi, int idx)
{ … }

/**
 * devpts_pty_new -- create a new inode in /dev/pts/
 * @fsi: Filesystem info for this instance.
 * @index: used as a name of the node
 * @priv: what's given back by devpts_get_priv
 *
 * The dentry for the created inode is returned.
 * Remove it from /dev/pts/ with devpts_pty_kill().
 */
struct dentry *devpts_pty_new(struct pts_fs_info *fsi, int index, void *priv)
{ … }

/**
 * devpts_get_priv -- get private data for a slave
 * @dentry: dentry of the slave
 *
 * Returns whatever was passed as priv in devpts_pty_new for a given inode.
 */
void *devpts_get_priv(struct dentry *dentry)
{ … }

/**
 * devpts_pty_kill -- remove inode form /dev/pts/
 * @dentry: dentry of the slave to be removed
 *
 * This is an inverse operation of devpts_pty_new.
 */
void devpts_pty_kill(struct dentry *dentry)
{ … }

static int __init init_devpts_fs(void)
{ … }
module_init(…) …