C++ DEVPTS_SB函数代码示例

/*
 * 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 path path;
	int err = 0;

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

	/* Walk upward while the start point is a bind mount of
	 * a single file.
	 */
	while (path.mnt->mnt_root == path.dentry)
		if (follow_up(&path) == 0)
			break;

	/* devpts_ptmx_path() finds a devpts fs or returns an error. */
	if ((path.mnt->mnt_sb->s_magic != DEVPTS_SUPER_MAGIC) ||
	    (DEVPTS_SB(path.mnt->mnt_sb) != fsi))
		err = devpts_ptmx_path(&path);
	dput(path.dentry);
	if (!err) {
		if (DEVPTS_SB(path.mnt->mnt_sb) == fsi)
			return path.mnt;

		err = -ENODEV;
	}

	mntput(path.mnt);
	return ERR_PTR(err);
}

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;
}

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

	kfree(fsi);
	kill_litter_super(sb);
}

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 root_uid;
	kgid_t root_gid;

	root_uid = make_kuid(current_user_ns(), 0);
	root_gid = make_kgid(current_user_ns(), 0);
	if (!uid_valid(root_uid) || !gid_valid(root_gid))
		return -EINVAL;

	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));
	inode->i_uid = root_uid;
	inode->i_gid = root_gid;

	d_add(dentry, inode);

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

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);
}

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(inode);

	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 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);
	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;
}

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;
}

/*
 * 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);

	/* Require newinstance for all user namespace mounts to ensure
	 * the mount options are not changed.
	 */
	if ((current_user_ns() != &init_user_ns) && !opts.newinstance)
		return ERR_PTR(-EINVAL);

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

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

	if (!s->s_root) {
		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);
}

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 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;
}

/*
 * devpts_get_sb()
 *
 *     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 get_sb_single().
 *
 *     Mounts with 'newinstance' option create a new, private namespace.
 *
 *     NOTE:
 *
 *     For single-mount semantics, devpts cannot use get_sb_single(),
 *     because get_sb_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 get_sb_single() would pick the newinstance
 *     super-block instead of the initial super-block.
 */
static int devpts_get_sb(struct file_system_type *fs_type,
	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
{
	int error;
	struct pts_mount_opts opts;
	struct super_block *s;

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

	simple_set_mnt(mnt, s);

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

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

	return 0;

out_dput:
	dput(s->s_root); /* undo dget() in simple_set_mnt() */

out_undo_sget:
	deactivate_locked_super(s);
	return error;
}

/**
 * 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 inode *devpts_pty_new(struct inode *ptmx_inode, dev_t device, int index,
		void *priv)
{
	struct dentry *dentry;
	struct super_block *sb = pts_sb_from_inode(ptmx_inode);
	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;
	char s[12];

	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, device);
	inode->i_private = priv;

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

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

	dentry = d_alloc_name(root, s);
	if (dentry) {
		d_add(dentry, inode);
		fsnotify_create(root->d_inode, dentry);
	} else {
		iput(inode);
		inode = ERR_PTR(-ENOMEM);
	}

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

	return inode;
}