/*
   * devtmpfs - kernel-maintained tmpfs-based /dev
   *
   * Copyright (C) 2009, Kay Sievers <kay.sievers@vrfy.org>
   *
   * 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 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>

  static struct task_struct *thread;

  
  #if defined CONFIG_DEVTMPFS_MOUNT

  static int mount_dev = 1;

  #else

  static int mount_dev;

  #endif

  static DEFINE_SPINLOCK(req_lock);
  
  static struct req {
  	struct req *next;
  	struct completion done;
  	int err;
  	const char *name;

  	umode_t mode;	/* 0 => delete */

  	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 dentry *dev_mount(struct file_system_type *fs_type, int flags,
  		      const char *dev_name, void *data)

  {

  #ifdef CONFIG_TMPFS

  	return mount_single(fs_type, flags, data, shmem_fill_super);

  #else

  	return mount_single(fs_type, flags, data, ramfs_fill_super);

  #endif

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

  	.mount = dev_mount,

  	.kill_sb = kill_litter_super,
  };
  
  #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

  int devtmpfs_create_node(struct device *dev)
  {
  	const char *tmp = NULL;
  	struct req req;
  
  	if (!thread)
  		return 0;
  
  	req.mode = 0;
  	req.name = device_get_devnode(dev, &req.mode, &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;
  
  	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_delete_node(struct device *dev)
  {
  	const char *tmp = NULL;
  	struct req req;
  
  	if (!thread)
  		return 0;
  
  	req.name = device_get_devnode(dev, NULL, &tmp);
  	if (!req.name)
  		return -ENOMEM;
  
  	req.mode = 0;
  	req.dev = dev;
  
  	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;
  }

  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, 1);
  	if (IS_ERR(dentry))
  		return PTR_ERR(dentry);
  
  	err = vfs_mkdir(path.dentry->d_inode, dentry, mode);
  	if (!err)
  		/* mark as kernel-created inode */
  		dentry->d_inode->i_private = &thread;
  	dput(dentry);
  	mutex_unlock(&path.dentry->d_inode->i_mutex);
  	path_put(&path);

  	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, 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(path.dentry->d_inode,
  			dentry, mode, dev->devt);
  	if (!err) {
  		struct iattr newattrs;
  
  		/* fixup possibly umasked mode */
  		newattrs.ia_mode = mode;
  		newattrs.ia_valid = ATTR_MODE;
  		mutex_lock(&dentry->d_inode->i_mutex);
  		notify_change(dentry, &newattrs);
  		mutex_unlock(&dentry->d_inode->i_mutex);
  
  		/* mark as kernel-created inode */
  		dentry->d_inode->i_private = &thread;

  	}

  	dput(dentry);

  	mutex_unlock(&path.dentry->d_inode->i_mutex);
  	path_put(&path);

  	return err;
  }
  
  static int dev_rmdir(const char *name)
  {
  	struct nameidata nd;
  	struct dentry *dentry;
  	int err;

  	err = kern_path_parent(name, &nd);

  	if (err)
  		return err;
  
  	mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
  	dentry = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
  	if (!IS_ERR(dentry)) {

  		if (dentry->d_inode) {

  			if (dentry->d_inode->i_private == &thread)

  				err = vfs_rmdir(nd.path.dentry->d_inode,
  						dentry);
  			else
  				err = -EPERM;
  		} else {

  			err = -ENOENT;

  		}

  		dput(dentry);
  	} else {
  		err = PTR_ERR(dentry);
  	}

  	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);

  	path_put(&nd.path);
  	return err;
  }
  
  static int delete_path(const char *nodepath)
  {
  	const 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 nameidata nd;
  	struct dentry *dentry;
  	struct kstat stat;
  	int deleted = 1;
  	int err;

  	err = kern_path_parent(nodename, &nd);

  	if (err)

  		return err;

  
  	mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
  	dentry = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
  	if (!IS_ERR(dentry)) {
  		if (dentry->d_inode) {
  			err = vfs_getattr(nd.path.mnt, dentry, &stat);
  			if (!err && dev_mynode(dev, dentry->d_inode, &stat)) {

  				struct iattr newattrs;
  				/*
  				 * before unlinking this node, reset permissions
  				 * of possible references like hardlinks
  				 */
  				newattrs.ia_uid = 0;
  				newattrs.ia_gid = 0;
  				newattrs.ia_mode = stat.mode & ~0777;
  				newattrs.ia_valid =
  					ATTR_UID|ATTR_GID|ATTR_MODE;
  				mutex_lock(&dentry->d_inode->i_mutex);
  				notify_change(dentry, &newattrs);
  				mutex_unlock(&dentry->d_inode->i_mutex);

  				err = vfs_unlink(nd.path.dentry->d_inode,
  						 dentry);
  				if (!err || err == -ENOENT)
  					deleted = 1;
  			}
  		} else {
  			err = -ENOENT;
  		}
  		dput(dentry);
  	} else {
  		err = PTR_ERR(dentry);
  	}
  	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
  
  	path_put(&nd.path);
  	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 devtmpfs_mount(const char *mntdir)

  {

  	int err;

  	if (!mount_dev)

  		return 0;

  	if (!thread)

  		return 0;

  	err = sys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT, NULL);

  	if (err)
  		printk(KERN_INFO "devtmpfs: error mounting %i
  ", err);
  	else
  		printk(KERN_INFO "devtmpfs: mounted
  ");

  	return err;
  }

  static DECLARE_COMPLETION(setup_done);

  static int handle(const char *name, umode_t mode, struct device *dev)

  {
  	if (mode)
  		return handle_create(name, mode, dev);
  	else
  		return handle_remove(name, dev);
  }
  
  static int devtmpfsd(void *p)
  {
  	char options[] = "mode=0755";
  	int *err = p;
  	*err = sys_unshare(CLONE_NEWNS);
  	if (*err)
  		goto out;
  	*err = sys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, options);
  	if (*err)
  		goto out;
  	sys_chdir("/.."); /* will traverse into overmounted root */
  	sys_chroot(".");
  	complete(&setup_done);
  	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->dev);
  				complete(&req->done);

  				req = next;

  			}
  			spin_lock(&req_lock);
  		}

  		__set_current_state(TASK_INTERRUPTIBLE);

  		spin_unlock(&req_lock);
  		schedule();

  	}
  	return 0;
  out:
  	complete(&setup_done);
  	return *err;
  }

  /*
   * Create devtmpfs instance, driver-core devices will add their device
   * nodes here.
   */
  int __init devtmpfs_init(void)
  {

  	int err = register_filesystem(&dev_fs_type);

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

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