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/* -*- linux-c -*- --------------------------------------------------------- *
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* linux/fs/devpts/inode.c
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* Copyright 1998-2004 H. Peter Anvin -- All Rights Reserved
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* This file is part of the Linux kernel and is made available under
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* the terms of the GNU General Public License, version 2, or at your
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* option, any later version, incorporated herein by reference.
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* ------------------------------------------------------------------------- */
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/sched.h>
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#include <linux/namei.h>
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#include <linux/slab.h>
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#include <linux/mount.h>
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#include <linux/tty.h>
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#include <linux/mutex.h>
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#include <linux/magic.h>
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#include <linux/idr.h>
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#include <linux/devpts_fs.h>
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#include <linux/parser.h>
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#include <linux/fsnotify.h>
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#include <linux/seq_file.h>
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#define DEVPTS_DEFAULT_MODE 0600
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* ptmx is a new node in /dev/pts and will be unused in legacy (single-
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* instance) mode. To prevent surprises in user space, set permissions of
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* ptmx to 0. Use 'chmod' or remount with '-o ptmxmode' to set meaningful
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#define DEVPTS_DEFAULT_PTMX_MODE 0000
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extern int pty_limit; /* Config limit on Unix98 ptys */
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static DEFINE_MUTEX(allocated_ptys_lock);
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static struct vfsmount *devpts_mnt;
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struct pts_mount_opts {
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Opt_uid, Opt_gid, Opt_mode, Opt_ptmxmode, Opt_newinstance,
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static const match_table_t tokens = {
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{Opt_mode, "mode=%o"},
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#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
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{Opt_ptmxmode, "ptmxmode=%o"},
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{Opt_newinstance, "newinstance"},
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struct ida allocated_ptys;
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struct pts_mount_opts mount_opts;
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struct dentry *ptmx_dentry;
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static inline struct pts_fs_info *DEVPTS_SB(struct super_block *sb)
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static inline struct super_block *pts_sb_from_inode(struct inode *inode)
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#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
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if (inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
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return devpts_mnt->mnt_sb;
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#define PARSE_REMOUNT 1
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* parse_mount_options():
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* Set @opts to mount options specified in @data. If an option is not
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* specified in @data, set it to its default value. The exception is
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* 'newinstance' option which can only be set/cleared on a mount (i.e.
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* cannot be changed during remount).
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* Note: @data may be NULL (in which case all options are set to default).
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static int parse_mount_options(char *data, int op, struct pts_mount_opts *opts)
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opts->mode = DEVPTS_DEFAULT_MODE;
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opts->ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
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/* newinstance makes sense only on initial mount */
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if (op == PARSE_MOUNT)
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opts->newinstance = 0;
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while ((p = strsep(&data, ",")) != NULL) {
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substring_t args[MAX_OPT_ARGS];
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token = match_token(p, tokens, args);
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if (match_int(&args[0], &option))
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if (match_int(&args[0], &option))
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if (match_octal(&args[0], &option))
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opts->mode = option & S_IALLUGO;
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#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
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if (match_octal(&args[0], &option))
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opts->ptmxmode = option & S_IALLUGO;
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case Opt_newinstance:
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/* newinstance makes sense only on initial mount */
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if (op == PARSE_MOUNT)
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opts->newinstance = 1;
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printk(KERN_ERR "devpts: called with bogus options\n");
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#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
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static int mknod_ptmx(struct super_block *sb)
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struct dentry *dentry;
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struct dentry *root = sb->s_root;
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struct pts_fs_info *fsi = DEVPTS_SB(sb);
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struct pts_mount_opts *opts = &fsi->mount_opts;
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mutex_lock(&root->d_inode->i_mutex);
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/* If we have already created ptmx node, return */
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if (fsi->ptmx_dentry) {
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dentry = d_alloc_name(root, "ptmx");
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printk(KERN_NOTICE "Unable to alloc dentry for ptmx node\n");
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* Create a new 'ptmx' node in this mount of devpts.
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inode = new_inode(sb);
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printk(KERN_ERR "Unable to alloc inode for ptmx node\n");
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inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
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mode = S_IFCHR|opts->ptmxmode;
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init_special_inode(inode, mode, MKDEV(TTYAUX_MAJOR, 2));
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d_add(dentry, inode);
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fsi->ptmx_dentry = dentry;
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mutex_unlock(&root->d_inode->i_mutex);
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static void update_ptmx_mode(struct pts_fs_info *fsi)
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if (fsi->ptmx_dentry) {
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inode = fsi->ptmx_dentry->d_inode;
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inode->i_mode = S_IFCHR|fsi->mount_opts.ptmxmode;
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static inline void update_ptmx_mode(struct pts_fs_info *fsi)
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static int devpts_remount(struct super_block *sb, int *flags, char *data)
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struct pts_fs_info *fsi = DEVPTS_SB(sb);
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struct pts_mount_opts *opts = &fsi->mount_opts;
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err = parse_mount_options(data, PARSE_REMOUNT, opts);
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* parse_mount_options() restores options to default values
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* before parsing and may have changed ptmxmode. So, update the
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* mode in the inode too. Bogus options don't fail the remount,
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* so do this even on error return.
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update_ptmx_mode(fsi);
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static int devpts_show_options(struct seq_file *seq, struct vfsmount *vfs)
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struct pts_fs_info *fsi = DEVPTS_SB(vfs->mnt_sb);
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struct pts_mount_opts *opts = &fsi->mount_opts;
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seq_printf(seq, ",uid=%u", opts->uid);
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seq_printf(seq, ",gid=%u", opts->gid);
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seq_printf(seq, ",mode=%03o", opts->mode);
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#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
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seq_printf(seq, ",ptmxmode=%03o", opts->ptmxmode);
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static const struct super_operations devpts_sops = {
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.statfs = simple_statfs,
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.remount_fs = devpts_remount,
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.show_options = devpts_show_options,
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static void *new_pts_fs_info(void)
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struct pts_fs_info *fsi;
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fsi = kzalloc(sizeof(struct pts_fs_info), GFP_KERNEL);
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ida_init(&fsi->allocated_ptys);
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fsi->mount_opts.mode = DEVPTS_DEFAULT_MODE;
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fsi->mount_opts.ptmxmode = DEVPTS_DEFAULT_PTMX_MODE;
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devpts_fill_super(struct super_block *s, void *data, int silent)
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s->s_blocksize = 1024;
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s->s_blocksize_bits = 10;
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s->s_magic = DEVPTS_SUPER_MAGIC;
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s->s_op = &devpts_sops;
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s->s_fs_info = new_pts_fs_info();
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inode = new_inode(s);
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inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
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inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR;
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inode->i_op = &simple_dir_inode_operations;
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inode->i_fop = &simple_dir_operations;
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s->s_root = d_alloc_root(inode);
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printk(KERN_ERR "devpts: get root dentry failed\n");
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#ifdef CONFIG_DEVPTS_MULTIPLE_INSTANCES
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static int compare_init_pts_sb(struct super_block *s, void *p)
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return devpts_mnt->mnt_sb == s;
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* If the '-o newinstance' mount option was specified, mount a new
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* (private) instance of devpts. PTYs created in this instance are
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* independent of the PTYs in other devpts instances.
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* If the '-o newinstance' option was not specified, mount/remount the
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* initial kernel mount of devpts. This type of mount gives the
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* legacy, single-instance semantics.
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* The 'newinstance' option is needed to support multiple namespace
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* semantics in devpts while preserving backward compatibility of the
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* current 'single-namespace' semantics. i.e all mounts of devpts
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* without the 'newinstance' mount option should bind to the initial
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* kernel mount, like mount_single().
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* Mounts with 'newinstance' option create a new, private namespace.
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* For single-mount semantics, devpts cannot use mount_single(),
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* because mount_single()/sget() find and use the super-block from
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* the most recent mount of devpts. But that recent mount may be a
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* 'newinstance' mount and mount_single() would pick the newinstance
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* super-block instead of the initial super-block.
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static struct dentry *devpts_mount(struct file_system_type *fs_type,
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int flags, const char *dev_name, void *data)
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struct pts_mount_opts opts;
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struct super_block *s;
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error = parse_mount_options(data, PARSE_MOUNT, &opts);
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return ERR_PTR(error);
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if (opts.newinstance)
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s = sget(fs_type, NULL, set_anon_super, NULL);
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s = sget(fs_type, compare_init_pts_sb, set_anon_super, NULL);
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error = devpts_fill_super(s, data, flags & MS_SILENT ? 1 : 0);
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s->s_flags |= MS_ACTIVE;
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memcpy(&(DEVPTS_SB(s))->mount_opts, &opts, sizeof(opts));
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error = mknod_ptmx(s);
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return dget(s->s_root);
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deactivate_locked_super(s);
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return ERR_PTR(error);
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* This supports only the legacy single-instance semantics (no
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* multiple-instance semantics)
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static struct dentry *devpts_mount(struct file_system_type *fs_type, int flags,
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const char *dev_name, void *data)
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return mount_single(fs_type, flags, data, devpts_fill_super);
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static void devpts_kill_sb(struct super_block *sb)
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struct pts_fs_info *fsi = DEVPTS_SB(sb);
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kill_litter_super(sb);
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static struct file_system_type devpts_fs_type = {
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.mount = devpts_mount,
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.kill_sb = devpts_kill_sb,
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* The normal naming convention is simply /dev/pts/<number>; this conforms
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* to the System V naming convention
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int devpts_new_index(struct inode *ptmx_inode)
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struct super_block *sb = pts_sb_from_inode(ptmx_inode);
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struct pts_fs_info *fsi = DEVPTS_SB(sb);
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if (!ida_pre_get(&fsi->allocated_ptys, GFP_KERNEL))
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mutex_lock(&allocated_ptys_lock);
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ida_ret = ida_get_new(&fsi->allocated_ptys, &index);
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mutex_unlock(&allocated_ptys_lock);
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if (ida_ret == -EAGAIN)
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if (index >= pty_limit) {
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ida_remove(&fsi->allocated_ptys, index);
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mutex_unlock(&allocated_ptys_lock);
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mutex_unlock(&allocated_ptys_lock);
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void devpts_kill_index(struct inode *ptmx_inode, int idx)
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struct super_block *sb = pts_sb_from_inode(ptmx_inode);
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struct pts_fs_info *fsi = DEVPTS_SB(sb);
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mutex_lock(&allocated_ptys_lock);
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ida_remove(&fsi->allocated_ptys, idx);
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mutex_unlock(&allocated_ptys_lock);
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int devpts_pty_new(struct inode *ptmx_inode, struct tty_struct *tty)
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/* tty layer puts index from devpts_new_index() in here */
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int number = tty->index;
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struct tty_driver *driver = tty->driver;
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dev_t device = MKDEV(driver->major, driver->minor_start+number);
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struct dentry *dentry;
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struct super_block *sb = pts_sb_from_inode(ptmx_inode);
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struct inode *inode = new_inode(sb);
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struct dentry *root = sb->s_root;
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struct pts_fs_info *fsi = DEVPTS_SB(sb);
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struct pts_mount_opts *opts = &fsi->mount_opts;
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/* We're supposed to be given the slave end of a pty */
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BUG_ON(driver->type != TTY_DRIVER_TYPE_PTY);
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BUG_ON(driver->subtype != PTY_TYPE_SLAVE);
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inode->i_ino = number + 3;
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inode->i_uid = opts->setuid ? opts->uid : current_fsuid();
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inode->i_gid = opts->setgid ? opts->gid : current_fsgid();
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inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
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init_special_inode(inode, S_IFCHR|opts->mode, device);
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inode->i_private = tty;
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tty->driver_data = inode;
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sprintf(s, "%d", number);
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mutex_lock(&root->d_inode->i_mutex);
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dentry = d_alloc_name(root, s);
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d_add(dentry, inode);
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fsnotify_create(root->d_inode, dentry);
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mutex_unlock(&root->d_inode->i_mutex);
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struct tty_struct *devpts_get_tty(struct inode *pts_inode, int number)
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struct dentry *dentry;
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struct tty_struct *tty;
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BUG_ON(pts_inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
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/* Ensure dentry has not been deleted by devpts_pty_kill() */
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dentry = d_find_alias(pts_inode);
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if (pts_inode->i_sb->s_magic == DEVPTS_SUPER_MAGIC)
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tty = (struct tty_struct *)pts_inode->i_private;
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void devpts_pty_kill(struct tty_struct *tty)
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struct inode *inode = tty->driver_data;
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struct super_block *sb = pts_sb_from_inode(inode);
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struct dentry *root = sb->s_root;
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struct dentry *dentry;
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BUG_ON(inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR));
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mutex_lock(&root->d_inode->i_mutex);
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dentry = d_find_alias(inode);
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dput(dentry); /* d_alloc_name() in devpts_pty_new() */
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dput(dentry); /* d_find_alias above */
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mutex_unlock(&root->d_inode->i_mutex);
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static int __init init_devpts_fs(void)
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int err = register_filesystem(&devpts_fs_type);
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devpts_mnt = kern_mount(&devpts_fs_type);
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if (IS_ERR(devpts_mnt)) {
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err = PTR_ERR(devpts_mnt);
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unregister_filesystem(&devpts_fs_type);
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module_init(init_devpts_fs)