drivers/base/devtmpfs.c - kernel/common - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * devtmpfs - kernel-maintained tmpfs-based /dev
  *
  * Copyright (C) 2009, Kay Sievers <[email protected]>
  *
  * During bootup, before any driver core device is registered,
  * devtmpfs, a tmpfs-based filesystem is created. Every driver-core
  * device which requests a device node, will add a node in this
  * filesystem.
  * By default, all devices are named after the name of the device,
  * owned by root and have a default mode of 0600. Subsystems can
  * overwrite the default setting if needed.
  */

 #include <linux/kernel.h>
 #include <linux/syscalls.h>
 #include <linux/mount.h>
 #include <linux/device.h>
 #include <linux/genhd.h>
 #include <linux/namei.h>
 #include <linux/fs.h>
 #include <linux/shmem_fs.h>
 #include <linux/ramfs.h>
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/kthread.h>
 #include <linux/init_syscalls.h>
 #include <uapi/linux/mount.h>
 #include "base.h"

 static struct task_struct *thread;

 static int __initdata mount_dev = IS_ENABLED(CONFIG_DEVTMPFS_MOUNT);

 static DEFINE_SPINLOCK(req_lock);

 static struct req {
 	struct req *next;
 	struct completion done;
 	int err;
 	const char *name;
 	umode_t mode;	/* 0 => delete */
 	kuid_t uid;
 	kgid_t gid;
 	struct device *dev;
 } *requests;

 static int __init mount_param(char *str)
 {
 	mount_dev = simple_strtoul(str, NULL, 0);
 	return 1;
 }
 __setup("devtmpfs.mount=", mount_param);

 static struct vfsmount *mnt;

 static struct dentry *public_dev_mount(struct file_system_type *fs_type, int flags,
 		      const char *dev_name, void *data)
 {
 	struct super_block *s = mnt->mnt_sb;
 	int err;

 	atomic_inc(&s->s_active);
 	down_write(&s->s_umount);
 	err = reconfigure_single(s, flags, data);
 	if (err < 0) {
 		deactivate_locked_super(s);
 		return ERR_PTR(err);
 	}
 	return dget(s->s_root);
 }

 static struct file_system_type internal_fs_type = {
 	.name = "devtmpfs",
 #ifdef CONFIG_TMPFS
 	.init_fs_context = shmem_init_fs_context,
 	.parameters	= shmem_fs_parameters,
 #else
 	.init_fs_context = ramfs_init_fs_context,
 	.parameters	= ramfs_fs_parameters,
 #endif
 	.kill_sb = kill_litter_super,
 };

 static struct file_system_type dev_fs_type = {
 	.name = "devtmpfs",
 	.mount = public_dev_mount,
 };

 #ifdef CONFIG_BLOCK
 static inline int is_blockdev(struct device *dev)
 {
 	return dev->class == &block_class;
 }
 #else
 static inline int is_blockdev(struct device *dev) { return 0; }
 #endif

 static int devtmpfs_submit_req(struct req *req, const char *tmp)
 {
 	init_completion(&req->done);

 	spin_lock(&req_lock);
 	req->next = requests;
 	requests = req;
 	spin_unlock(&req_lock);

 	wake_up_process(thread);
 	wait_for_completion(&req->done);

 	kfree(tmp);

 	return req->err;
 }

 int devtmpfs_create_node(struct device *dev)
 {
 	const char *tmp = NULL;
 	struct req req;

 	if (!thread)
 		return 0;

 	req.mode = 0;
 	req.uid = GLOBAL_ROOT_UID;
 	req.gid = GLOBAL_ROOT_GID;
 	req.name = device_get_devnode(dev, &req.mode, &req.uid, &req.gid, &tmp);
 	if (!req.name)
 		return -ENOMEM;

 	if (req.mode == 0)
 		req.mode = 0600;
 	if (is_blockdev(dev))
 		req.mode |= S_IFBLK;
 	else
 		req.mode |= S_IFCHR;

 	req.dev = dev;

 	return devtmpfs_submit_req(&req, tmp);
 }

 int devtmpfs_delete_node(struct device *dev)
 {
 	const char *tmp = NULL;
 	struct req req;

 	if (!thread)
 		return 0;

 	req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
 	if (!req.name)
 		return -ENOMEM;

 	req.mode = 0;
 	req.dev = dev;

 	return devtmpfs_submit_req(&req, tmp);
 }

 static int dev_mkdir(const char *name, umode_t mode)
 {
 	struct dentry *dentry;
 	struct path path;
 	int err;

 	dentry = kern_path_create(AT_FDCWD, name, &path, LOOKUP_DIRECTORY);
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);

 	err = vfs_mkdir(&init_user_ns, d_inode(path.dentry), dentry, mode);
 	if (!err)
 		/* mark as kernel-created inode */
 		d_inode(dentry)->i_private = &thread;
 	done_path_create(&path, dentry);
 	return err;
 }

 static int create_path(const char *nodepath)
 {
 	char *path;
 	char *s;
 	int err = 0;

 	/* parent directories do not exist, create them */
 	path = kstrdup(nodepath, GFP_KERNEL);
 	if (!path)
 		return -ENOMEM;

 	s = path;
 	for (;;) {
 		s = strchr(s, '/');
 		if (!s)
 			break;
 		s[0] = '\0';
 		err = dev_mkdir(path, 0755);
 		if (err && err != -EEXIST)
 			break;
 		s[0] = '/';
 		s++;
 	}
 	kfree(path);
 	return err;
 }

 static int handle_create(const char *nodename, umode_t mode, kuid_t uid,
 			 kgid_t gid, struct device *dev)
 {
 	struct dentry *dentry;
 	struct path path;
 	int err;

 	dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
 	if (dentry == ERR_PTR(-ENOENT)) {
 		create_path(nodename);
 		dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
 	}
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);

 	err = vfs_mknod(&init_user_ns, d_inode(path.dentry), dentry, mode,
 			dev->devt);
 	if (!err) {
 		struct iattr newattrs;

 		newattrs.ia_mode = mode;
 		newattrs.ia_uid = uid;
 		newattrs.ia_gid = gid;
 		newattrs.ia_valid = ATTR_MODE|ATTR_UID|ATTR_GID;
 		inode_lock(d_inode(dentry));
 		notify_change(&init_user_ns, dentry, &newattrs, NULL);
 		inode_unlock(d_inode(dentry));

 		/* mark as kernel-created inode */
 		d_inode(dentry)->i_private = &thread;
 	}
 	done_path_create(&path, dentry);
 	return err;
 }

 static int dev_rmdir(const char *name)
 {
 	struct path parent;
 	struct dentry *dentry;
 	int err;

 	dentry = kern_path_locked(name, &parent);
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);
 	if (d_really_is_positive(dentry)) {
 		if (d_inode(dentry)->i_private == &thread)
 			err = vfs_rmdir(&init_user_ns, d_inode(parent.dentry),
 					dentry);
 		else
 			err = -EPERM;
 	} else {
 		err = -ENOENT;
 	}
 	dput(dentry);
 	inode_unlock(d_inode(parent.dentry));
 	path_put(&parent);
 	return err;
 }

 static int delete_path(const char *nodepath)
 {
 	char *path;
 	int err = 0;

 	path = kstrdup(nodepath, GFP_KERNEL);
 	if (!path)
 		return -ENOMEM;

 	for (;;) {
 		char *base;

 		base = strrchr(path, '/');
 		if (!base)
 			break;
 		base[0] = '\0';
 		err = dev_rmdir(path);
 		if (err)
 			break;
 	}

 	kfree(path);
 	return err;
 }

 static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
 {
 	/* did we create it */
 	if (inode->i_private != &thread)
 		return 0;

 	/* does the dev_t match */
 	if (is_blockdev(dev)) {
 		if (!S_ISBLK(stat->mode))
 			return 0;
 	} else {
 		if (!S_ISCHR(stat->mode))
 			return 0;
 	}
 	if (stat->rdev != dev->devt)
 		return 0;

 	/* ours */
 	return 1;
 }

 static int handle_remove(const char *nodename, struct device *dev)
 {
 	struct path parent;
 	struct dentry *dentry;
 	int deleted = 0;
 	int err;

 	dentry = kern_path_locked(nodename, &parent);
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);

 	if (d_really_is_positive(dentry)) {
 		struct kstat stat;
 		struct path p = {.mnt = parent.mnt, .dentry = dentry};
 		err = vfs_getattr(&p, &stat, STATX_TYPE | STATX_MODE,
 				  AT_STATX_SYNC_AS_STAT);
 		if (!err && dev_mynode(dev, d_inode(dentry), &stat)) {
 			struct iattr newattrs;
 			/*
 			 * before unlinking this node, reset permissions
 			 * of possible references like hardlinks
 			 */
 			newattrs.ia_uid = GLOBAL_ROOT_UID;
 			newattrs.ia_gid = GLOBAL_ROOT_GID;
 			newattrs.ia_mode = stat.mode & ~0777;
 			newattrs.ia_valid =
 				ATTR_UID|ATTR_GID|ATTR_MODE;
 			inode_lock(d_inode(dentry));
 			notify_change(&init_user_ns, dentry, &newattrs, NULL);
 			inode_unlock(d_inode(dentry));
 			err = vfs_unlink(&init_user_ns, d_inode(parent.dentry),
 					 dentry, NULL);
 			if (!err || err == -ENOENT)
 				deleted = 1;
 		}
 	} else {
 		err = -ENOENT;
 	}
 	dput(dentry);
 	inode_unlock(d_inode(parent.dentry));

 	path_put(&parent);
 	if (deleted && strchr(nodename, '/'))
 		delete_path(nodename);
 	return err;
 }

 /*
  * If configured, or requested by the commandline, devtmpfs will be
  * auto-mounted after the kernel mounted the root filesystem.
  */
 int __init devtmpfs_mount(void)
 {
 	int err;

 	if (!mount_dev)
 		return 0;

 	if (!thread)
 		return 0;

 	err = init_mount("devtmpfs", "dev", "devtmpfs", MS_SILENT, NULL);
 	if (err)
 		printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
 	else
 		printk(KERN_INFO "devtmpfs: mounted\n");
 	return err;
 }

 static __initdata DECLARE_COMPLETION(setup_done);

 static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
 		  struct device *dev)
 {
 	if (mode)
 		return handle_create(name, mode, uid, gid, dev);
 	else
 		return handle_remove(name, dev);
 }

 static void __noreturn devtmpfs_work_loop(void)
 {
 	while (1) {
 		spin_lock(&req_lock);
 		while (requests) {
 			struct req *req = requests;
 			requests = NULL;
 			spin_unlock(&req_lock);
 			while (req) {
 				struct req *next = req->next;
 				req->err = handle(req->name, req->mode,
 						  req->uid, req->gid, req->dev);
 				complete(&req->done);
 				req = next;
 			}
 			spin_lock(&req_lock);
 		}
 		__set_current_state(TASK_INTERRUPTIBLE);
 		spin_unlock(&req_lock);
 		schedule();
 	}
 }

 static noinline int __init devtmpfs_setup(void *p)
 {
 	int err;

 	err = ksys_unshare(CLONE_NEWNS);
 	if (err)
 		goto out;
 	err = init_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, NULL);
 	if (err)
 		goto out;
 	init_chdir("/.."); /* will traverse into overmounted root */
 	init_chroot(".");
 out:
 	*(int *)p = err;
 	return err;
 }

 /*
  * The __ref is because devtmpfs_setup needs to be __init for the routines it
  * calls.  That call is done while devtmpfs_init, which is marked __init,
  * synchronously waits for it to complete.
  */
 static int __ref devtmpfsd(void *p)
 {
 	int err = devtmpfs_setup(p);

 	complete(&setup_done);
 	if (err)
 		return err;
 	devtmpfs_work_loop();
 	return 0;
 }

 /*
  * Create devtmpfs instance, driver-core devices will add their device
  * nodes here.
  */
 int __init devtmpfs_init(void)
 {
 	char opts[] = "mode=0755";
 	int err;

 	mnt = vfs_kern_mount(&internal_fs_type, 0, "devtmpfs", opts);
 	if (IS_ERR(mnt)) {
 		printk(KERN_ERR "devtmpfs: unable to create devtmpfs %ld\n",
 				PTR_ERR(mnt));
 		return PTR_ERR(mnt);
 	}
 	err = register_filesystem(&dev_fs_type);
 	if (err) {
 		printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
 		       "type %i\n", err);
 		return err;
 	}

 	thread = kthread_run(devtmpfsd, &err, "kdevtmpfs");
 	if (!IS_ERR(thread)) {
 		wait_for_completion(&setup_done);
 	} else {
 		err = PTR_ERR(thread);
 		thread = NULL;
 	}

 	if (err) {
 		printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
 		unregister_filesystem(&dev_fs_type);
 		return err;
 	}

 	printk(KERN_INFO "devtmpfs: initialized\n");
 	return 0;
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* devtmpfs - kernel-maintained tmpfs-based /dev
	*
	* Copyright (C) 2009, Kay Sievers <[email protected]>
	*
	* During bootup, before any driver core device is registered,
	* devtmpfs, a tmpfs-based filesystem is created. Every driver-core
	* device which requests a device node, will add a node in this
	* filesystem.
	* By default, all devices are named after the name of the device,
	* owned by root and have a default mode of 0600. Subsystems can
	* overwrite the default setting if needed.
	*/

	#include <linux/kernel.h>
	#include <linux/syscalls.h>
	#include <linux/mount.h>
	#include <linux/device.h>
	#include <linux/genhd.h>
	#include <linux/namei.h>
	#include <linux/fs.h>
	#include <linux/shmem_fs.h>
	#include <linux/ramfs.h>
	#include <linux/sched.h>
	#include <linux/slab.h>
	#include <linux/kthread.h>
	#include <linux/init_syscalls.h>
	#include <uapi/linux/mount.h>
	#include "base.h"

	static struct task_struct *thread;

	static int __initdata mount_dev = IS_ENABLED(CONFIG_DEVTMPFS_MOUNT);

	static DEFINE_SPINLOCK(req_lock);

	static struct req {
	struct req *next;
	struct completion done;
	int err;
	const char *name;
	umode_t mode; /* 0 => delete */
	kuid_t uid;
	kgid_t gid;
	struct device *dev;
	} *requests;

	static int __init mount_param(char *str)
	{
	mount_dev = simple_strtoul(str, NULL, 0);
	return 1;
	}
	__setup("devtmpfs.mount=", mount_param);

	static struct vfsmount *mnt;

	static struct dentry public_dev_mount(struct file_system_type fs_type, int flags,
	const char dev_name, void data)
	{
	struct super_block *s = mnt->mnt_sb;
	int err;

	atomic_inc(&s->s_active);
	down_write(&s->s_umount);
	err = reconfigure_single(s, flags, data);
	if (err < 0) {
	deactivate_locked_super(s);
	return ERR_PTR(err);
	}
	return dget(s->s_root);
	}

	static struct file_system_type internal_fs_type = {
	.name = "devtmpfs",
	#ifdef CONFIG_TMPFS
	.init_fs_context = shmem_init_fs_context,
	.parameters = shmem_fs_parameters,
	#else
	.init_fs_context = ramfs_init_fs_context,
	.parameters = ramfs_fs_parameters,
	#endif
	.kill_sb = kill_litter_super,
	};

	static struct file_system_type dev_fs_type = {
	.name = "devtmpfs",
	.mount = public_dev_mount,
	};

	#ifdef CONFIG_BLOCK
	static inline int is_blockdev(struct device *dev)
	{
	return dev->class == &block_class;
	}
	#else
	static inline int is_blockdev(struct device *dev) { return 0; }
	#endif

	static int devtmpfs_submit_req(struct req req, const char tmp)
	{
	init_completion(&req->done);

	spin_lock(&req_lock);
	req->next = requests;
	requests = req;
	spin_unlock(&req_lock);

	wake_up_process(thread);
	wait_for_completion(&req->done);

	kfree(tmp);

	return req->err;
	}

	int devtmpfs_create_node(struct device *dev)
	{
	const char *tmp = NULL;
	struct req req;

	if (!thread)
	return 0;

	req.mode = 0;
	req.uid = GLOBAL_ROOT_UID;
	req.gid = GLOBAL_ROOT_GID;
	req.name = device_get_devnode(dev, &req.mode, &req.uid, &req.gid, &tmp);
	if (!req.name)
	return -ENOMEM;

	if (req.mode == 0)
	req.mode = 0600;
	if (is_blockdev(dev))
	req.mode \|= S_IFBLK;
	else
	req.mode \|= S_IFCHR;

	req.dev = dev;

	return devtmpfs_submit_req(&req, tmp);
	}

	int devtmpfs_delete_node(struct device *dev)
	{
	const char *tmp = NULL;
	struct req req;

	if (!thread)
	return 0;

	req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
	if (!req.name)
	return -ENOMEM;

	req.mode = 0;
	req.dev = dev;

	return devtmpfs_submit_req(&req, tmp);
	}

	static int dev_mkdir(const char *name, umode_t mode)
	{
	struct dentry *dentry;
	struct path path;
	int err;

	dentry = kern_path_create(AT_FDCWD, name, &path, LOOKUP_DIRECTORY);
	if (IS_ERR(dentry))
	return PTR_ERR(dentry);

	err = vfs_mkdir(&init_user_ns, d_inode(path.dentry), dentry, mode);
	if (!err)
	/* mark as kernel-created inode */
	d_inode(dentry)->i_private = &thread;
	done_path_create(&path, dentry);
	return err;
	}

	static int create_path(const char *nodepath)
	{
	char *path;
	char *s;
	int err = 0;

	/* parent directories do not exist, create them */
	path = kstrdup(nodepath, GFP_KERNEL);
	if (!path)
	return -ENOMEM;

	s = path;
	for (;;) {
	s = strchr(s, '/');
	if (!s)
	break;
	s[0] = '\0';
	err = dev_mkdir(path, 0755);
	if (err && err != -EEXIST)
	break;
	s[0] = '/';
	s++;
	}
	kfree(path);
	return err;
	}

	static int handle_create(const char *nodename, umode_t mode, kuid_t uid,
	kgid_t gid, struct device *dev)
	{
	struct dentry *dentry;
	struct path path;
	int err;

	dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
	if (dentry == ERR_PTR(-ENOENT)) {
	create_path(nodename);
	dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
	}
	if (IS_ERR(dentry))
	return PTR_ERR(dentry);

	err = vfs_mknod(&init_user_ns, d_inode(path.dentry), dentry, mode,
	dev->devt);
	if (!err) {
	struct iattr newattrs;

	newattrs.ia_mode = mode;
	newattrs.ia_uid = uid;
	newattrs.ia_gid = gid;
	newattrs.ia_valid = ATTR_MODE\|ATTR_UID\|ATTR_GID;
	inode_lock(d_inode(dentry));
	notify_change(&init_user_ns, dentry, &newattrs, NULL);
	inode_unlock(d_inode(dentry));

	/* mark as kernel-created inode */
	d_inode(dentry)->i_private = &thread;
	}
	done_path_create(&path, dentry);
	return err;
	}

	static int dev_rmdir(const char *name)
	{
	struct path parent;
	struct dentry *dentry;
	int err;

	dentry = kern_path_locked(name, &parent);
	if (IS_ERR(dentry))
	return PTR_ERR(dentry);
	if (d_really_is_positive(dentry)) {
	if (d_inode(dentry)->i_private == &thread)
	err = vfs_rmdir(&init_user_ns, d_inode(parent.dentry),
	dentry);
	else
	err = -EPERM;
	} else {
	err = -ENOENT;
	}
	dput(dentry);
	inode_unlock(d_inode(parent.dentry));
	path_put(&parent);
	return err;
	}

	static int delete_path(const char *nodepath)
	{
	char *path;
	int err = 0;

	path = kstrdup(nodepath, GFP_KERNEL);
	if (!path)
	return -ENOMEM;

	for (;;) {
	char *base;

	base = strrchr(path, '/');
	if (!base)
	break;
	base[0] = '\0';
	err = dev_rmdir(path);
	if (err)
	break;
	}

	kfree(path);
	return err;
	}

	static int dev_mynode(struct device dev, struct inode inode, struct kstat *stat)
	{
	/* did we create it */
	if (inode->i_private != &thread)
	return 0;

	/* does the dev_t match */
	if (is_blockdev(dev)) {
	if (!S_ISBLK(stat->mode))
	return 0;
	} else {
	if (!S_ISCHR(stat->mode))
	return 0;
	}
	if (stat->rdev != dev->devt)
	return 0;

	/* ours */
	return 1;
	}

	static int handle_remove(const char nodename, struct device dev)
	{
	struct path parent;
	struct dentry *dentry;
	int deleted = 0;
	int err;

	dentry = kern_path_locked(nodename, &parent);
	if (IS_ERR(dentry))
	return PTR_ERR(dentry);

	if (d_really_is_positive(dentry)) {
	struct kstat stat;
	struct path p = {.mnt = parent.mnt, .dentry = dentry};
	err = vfs_getattr(&p, &stat, STATX_TYPE \| STATX_MODE,
	AT_STATX_SYNC_AS_STAT);
	if (!err && dev_mynode(dev, d_inode(dentry), &stat)) {
	struct iattr newattrs;
	/*
	* before unlinking this node, reset permissions
	* of possible references like hardlinks
	*/
	newattrs.ia_uid = GLOBAL_ROOT_UID;
	newattrs.ia_gid = GLOBAL_ROOT_GID;
	newattrs.ia_mode = stat.mode & ~0777;
	newattrs.ia_valid =
	ATTR_UID\|ATTR_GID\|ATTR_MODE;
	inode_lock(d_inode(dentry));
	notify_change(&init_user_ns, dentry, &newattrs, NULL);
	inode_unlock(d_inode(dentry));
	err = vfs_unlink(&init_user_ns, d_inode(parent.dentry),
	dentry, NULL);
	if (!err \|\| err == -ENOENT)
	deleted = 1;
	}
	} else {
	err = -ENOENT;
	}
	dput(dentry);
	inode_unlock(d_inode(parent.dentry));

	path_put(&parent);
	if (deleted && strchr(nodename, '/'))
	delete_path(nodename);
	return err;
	}

	/*
	* If configured, or requested by the commandline, devtmpfs will be
	* auto-mounted after the kernel mounted the root filesystem.
	*/
	int __init devtmpfs_mount(void)
	{
	int err;

	if (!mount_dev)
	return 0;

	if (!thread)
	return 0;

	err = init_mount("devtmpfs", "dev", "devtmpfs", MS_SILENT, NULL);
	if (err)
	printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
	else
	printk(KERN_INFO "devtmpfs: mounted\n");
	return err;
	}

	static __initdata DECLARE_COMPLETION(setup_done);

	static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
	struct device *dev)
	{
	if (mode)
	return handle_create(name, mode, uid, gid, dev);
	else
	return handle_remove(name, dev);
	}

	static void __noreturn devtmpfs_work_loop(void)
	{
	while (1) {
	spin_lock(&req_lock);
	while (requests) {
	struct req *req = requests;
	requests = NULL;
	spin_unlock(&req_lock);
	while (req) {
	struct req *next = req->next;
	req->err = handle(req->name, req->mode,
	req->uid, req->gid, req->dev);
	complete(&req->done);
	req = next;
	}
	spin_lock(&req_lock);
	}
	__set_current_state(TASK_INTERRUPTIBLE);
	spin_unlock(&req_lock);
	schedule();
	}
	}

	static noinline int __init devtmpfs_setup(void *p)
	{
	int err;

	err = ksys_unshare(CLONE_NEWNS);
	if (err)
	goto out;
	err = init_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, NULL);
	if (err)
	goto out;
	init_chdir("/.."); /* will traverse into overmounted root */
	init_chroot(".");
	out:
	(int )p = err;
	return err;
	}

	/*
	* The __ref is because devtmpfs_setup needs to be __init for the routines it
	* calls. That call is done while devtmpfs_init, which is marked __init,
	* synchronously waits for it to complete.
	*/
	static int __ref devtmpfsd(void *p)
	{
	int err = devtmpfs_setup(p);

	complete(&setup_done);
	if (err)
	return err;
	devtmpfs_work_loop();
	return 0;
	}

	/*
	* Create devtmpfs instance, driver-core devices will add their device
	* nodes here.
	*/
	int __init devtmpfs_init(void)
	{
	char opts[] = "mode=0755";
	int err;

	mnt = vfs_kern_mount(&internal_fs_type, 0, "devtmpfs", opts);
	if (IS_ERR(mnt)) {
	printk(KERN_ERR "devtmpfs: unable to create devtmpfs %ld\n",
	PTR_ERR(mnt));
	return PTR_ERR(mnt);
	}
	err = register_filesystem(&dev_fs_type);
	if (err) {
	printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
	"type %i\n", err);
	return err;
	}

	thread = kthread_run(devtmpfsd, &err, "kdevtmpfs");
	if (!IS_ERR(thread)) {
	wait_for_completion(&setup_done);
	} else {
	err = PTR_ERR(thread);
	thread = NULL;
	}

	if (err) {
	printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
	unregister_filesystem(&dev_fs_type);
	return err;
	}

	printk(KERN_INFO "devtmpfs: initialized\n");
	return 0;
	}