/*
   *  inode.c - part of tracefs, a pseudo file system for activating tracing
   *
   * Based on debugfs by: Greg Kroah-Hartman <greg@kroah.com>
   *
   *  Copyright (C) 2014 Red Hat Inc, author: Steven Rostedt <srostedt@redhat.com>
   *
   *	This program is free software; you can redistribute it and/or
   *	modify it under the terms of the GNU General Public License version
   *	2 as published by the Free Software Foundation.
   *
   * tracefs is the file system that is used by the tracing infrastructure.
   *
   */
  
  #include <linux/module.h>
  #include <linux/fs.h>
  #include <linux/mount.h>

  #include <linux/kobject.h>

  #include <linux/namei.h>
  #include <linux/tracefs.h>
  #include <linux/fsnotify.h>
  #include <linux/seq_file.h>
  #include <linux/parser.h>
  #include <linux/magic.h>
  #include <linux/slab.h>
  
  #define TRACEFS_DEFAULT_MODE	0700
  
  static struct vfsmount *tracefs_mount;
  static int tracefs_mount_count;
  static bool tracefs_registered;
  
  static ssize_t default_read_file(struct file *file, char __user *buf,
  				 size_t count, loff_t *ppos)
  {
  	return 0;
  }
  
  static ssize_t default_write_file(struct file *file, const char __user *buf,
  				   size_t count, loff_t *ppos)
  {
  	return count;
  }
  
  static const struct file_operations tracefs_file_operations = {
  	.read =		default_read_file,
  	.write =	default_write_file,
  	.open =		simple_open,
  	.llseek =	noop_llseek,
  };

  static struct tracefs_dir_ops {
  	int (*mkdir)(const char *name);
  	int (*rmdir)(const char *name);
  } tracefs_ops;
  
  static char *get_dname(struct dentry *dentry)
  {
  	const char *dname;
  	char *name;
  	int len = dentry->d_name.len;
  
  	dname = dentry->d_name.name;
  	name = kmalloc(len + 1, GFP_KERNEL);
  	if (!name)
  		return NULL;
  	memcpy(name, dname, len);
  	name[len] = 0;
  	return name;
  }
  
  static int tracefs_syscall_mkdir(struct inode *inode, struct dentry *dentry, umode_t mode)
  {
  	char *name;
  	int ret;
  
  	name = get_dname(dentry);
  	if (!name)
  		return -ENOMEM;
  
  	/*
  	 * The mkdir call can call the generic functions that create
  	 * the files within the tracefs system. It is up to the individual
  	 * mkdir routine to handle races.
  	 */

  	inode_unlock(inode);

  	ret = tracefs_ops.mkdir(name);

  	inode_lock(inode);

  
  	kfree(name);
  
  	return ret;
  }
  
  static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
  {
  	char *name;
  	int ret;
  
  	name = get_dname(dentry);
  	if (!name)
  		return -ENOMEM;
  
  	/*
  	 * The rmdir call can call the generic functions that create
  	 * the files within the tracefs system. It is up to the individual
  	 * rmdir routine to handle races.
  	 * This time we need to unlock not only the parent (inode) but
  	 * also the directory that is being deleted.
  	 */

  	inode_unlock(inode);
  	inode_unlock(dentry->d_inode);

  
  	ret = tracefs_ops.rmdir(name);

  	inode_lock_nested(inode, I_MUTEX_PARENT);
  	inode_lock(dentry->d_inode);

  
  	kfree(name);
  
  	return ret;
  }
  
  static const struct inode_operations tracefs_dir_inode_operations = {
  	.lookup		= simple_lookup,
  	.mkdir		= tracefs_syscall_mkdir,
  	.rmdir		= tracefs_syscall_rmdir,
  };

  static struct inode *tracefs_get_inode(struct super_block *sb)
  {
  	struct inode *inode = new_inode(sb);
  	if (inode) {
  		inode->i_ino = get_next_ino();

  		inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);

  	}
  	return inode;
  }
  
  struct tracefs_mount_opts {
  	kuid_t uid;
  	kgid_t gid;
  	umode_t mode;
  };
  
  enum {
  	Opt_uid,
  	Opt_gid,
  	Opt_mode,
  	Opt_err
  };
  
  static const match_table_t tokens = {
  	{Opt_uid, "uid=%u"},
  	{Opt_gid, "gid=%u"},
  	{Opt_mode, "mode=%o"},
  	{Opt_err, NULL}
  };
  
  struct tracefs_fs_info {
  	struct tracefs_mount_opts mount_opts;
  };
  
  static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
  {
  	substring_t args[MAX_OPT_ARGS];
  	int option;
  	int token;
  	kuid_t uid;
  	kgid_t gid;
  	char *p;
  
  	opts->mode = TRACEFS_DEFAULT_MODE;
  
  	while ((p = strsep(&data, ",")) != NULL) {
  		if (!*p)
  			continue;
  
  		token = match_token(p, tokens, args);
  		switch (token) {
  		case Opt_uid:
  			if (match_int(&args[0], &option))
  				return -EINVAL;
  			uid = make_kuid(current_user_ns(), option);
  			if (!uid_valid(uid))
  				return -EINVAL;
  			opts->uid = uid;
  			break;
  		case Opt_gid:
  			if (match_int(&args[0], &option))
  				return -EINVAL;
  			gid = make_kgid(current_user_ns(), option);
  			if (!gid_valid(gid))
  				return -EINVAL;
  			opts->gid = gid;
  			break;
  		case Opt_mode:
  			if (match_octal(&args[0], &option))
  				return -EINVAL;
  			opts->mode = option & S_IALLUGO;
  			break;
  		/*
  		 * We might like to report bad mount options here;
  		 * but traditionally tracefs has ignored all mount options
  		 */
  		}
  	}
  
  	return 0;
  }
  
  static int tracefs_apply_options(struct super_block *sb)
  {
  	struct tracefs_fs_info *fsi = sb->s_fs_info;
  	struct inode *inode = sb->s_root->d_inode;
  	struct tracefs_mount_opts *opts = &fsi->mount_opts;
  
  	inode->i_mode &= ~S_IALLUGO;
  	inode->i_mode |= opts->mode;
  
  	inode->i_uid = opts->uid;
  	inode->i_gid = opts->gid;
  
  	return 0;
  }
  
  static int tracefs_remount(struct super_block *sb, int *flags, char *data)
  {
  	int err;
  	struct tracefs_fs_info *fsi = sb->s_fs_info;
  
  	sync_filesystem(sb);
  	err = tracefs_parse_options(data, &fsi->mount_opts);
  	if (err)
  		goto fail;
  
  	tracefs_apply_options(sb);
  
  fail:
  	return err;
  }
  
  static int tracefs_show_options(struct seq_file *m, struct dentry *root)
  {
  	struct tracefs_fs_info *fsi = root->d_sb->s_fs_info;
  	struct tracefs_mount_opts *opts = &fsi->mount_opts;
  
  	if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
  		seq_printf(m, ",uid=%u",
  			   from_kuid_munged(&init_user_ns, opts->uid));
  	if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
  		seq_printf(m, ",gid=%u",
  			   from_kgid_munged(&init_user_ns, opts->gid));
  	if (opts->mode != TRACEFS_DEFAULT_MODE)
  		seq_printf(m, ",mode=%o", opts->mode);
  
  	return 0;
  }
  
  static const struct super_operations tracefs_super_operations = {
  	.statfs		= simple_statfs,
  	.remount_fs	= tracefs_remount,
  	.show_options	= tracefs_show_options,
  };
  
  static int trace_fill_super(struct super_block *sb, void *data, int silent)
  {
  	static struct tree_descr trace_files[] = {{""}};
  	struct tracefs_fs_info *fsi;
  	int err;
  
  	save_mount_options(sb, data);
  
  	fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
  	sb->s_fs_info = fsi;
  	if (!fsi) {
  		err = -ENOMEM;
  		goto fail;
  	}
  
  	err = tracefs_parse_options(data, &fsi->mount_opts);
  	if (err)
  		goto fail;
  
  	err  =  simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
  	if (err)
  		goto fail;
  
  	sb->s_op = &tracefs_super_operations;
  
  	tracefs_apply_options(sb);
  
  	return 0;
  
  fail:
  	kfree(fsi);
  	sb->s_fs_info = NULL;
  	return err;
  }
  
  static struct dentry *trace_mount(struct file_system_type *fs_type,
  			int flags, const char *dev_name,
  			void *data)
  {
  	return mount_single(fs_type, flags, data, trace_fill_super);
  }
  
  static struct file_system_type trace_fs_type = {
  	.owner =	THIS_MODULE,
  	.name =		"tracefs",
  	.mount =	trace_mount,
  	.kill_sb =	kill_litter_super,
  };
  MODULE_ALIAS_FS("tracefs");
  
  static struct dentry *start_creating(const char *name, struct dentry *parent)
  {
  	struct dentry *dentry;
  	int error;
  
  	pr_debug("tracefs: creating file '%s'
  ",name);
  
  	error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
  			      &tracefs_mount_count);
  	if (error)
  		return ERR_PTR(error);
  
  	/* If the parent is not specified, we create it in the root.
  	 * We need the root dentry to do this, which is in the super
  	 * block. A pointer to that is in the struct vfsmount that we
  	 * have around.
  	 */
  	if (!parent)
  		parent = tracefs_mount->mnt_root;

  	inode_lock(parent->d_inode);

  	dentry = lookup_one_len(name, parent, strlen(name));
  	if (!IS_ERR(dentry) && dentry->d_inode) {
  		dput(dentry);
  		dentry = ERR_PTR(-EEXIST);
  	}

  
  	if (IS_ERR(dentry)) {

  		inode_unlock(parent->d_inode);

  		simple_release_fs(&tracefs_mount, &tracefs_mount_count);
  	}

  	return dentry;
  }
  
  static struct dentry *failed_creating(struct dentry *dentry)
  {

  	inode_unlock(dentry->d_parent->d_inode);

  	dput(dentry);
  	simple_release_fs(&tracefs_mount, &tracefs_mount_count);
  	return NULL;
  }
  
  static struct dentry *end_creating(struct dentry *dentry)
  {

  	inode_unlock(dentry->d_parent->d_inode);

  	return dentry;
  }
  
  /**
   * tracefs_create_file - create a file in the tracefs filesystem
   * @name: a pointer to a string containing the name of the file to create.
   * @mode: the permission that the file should have.
   * @parent: a pointer to the parent dentry for this file.  This should be a
   *          directory dentry if set.  If this parameter is NULL, then the
   *          file will be created in the root of the tracefs filesystem.
   * @data: a pointer to something that the caller will want to get to later
   *        on.  The inode.i_private pointer will point to this value on
   *        the open() call.
   * @fops: a pointer to a struct file_operations that should be used for
   *        this file.
   *
   * This is the basic "create a file" function for tracefs.  It allows for a
   * wide range of flexibility in creating a file, or a directory (if you want
   * to create a directory, the tracefs_create_dir() function is
   * recommended to be used instead.)
   *
   * This function will return a pointer to a dentry if it succeeds.  This
   * pointer must be passed to the tracefs_remove() function when the file is
   * to be removed (no automatic cleanup happens if your module is unloaded,
   * you are responsible here.)  If an error occurs, %NULL will be returned.
   *
   * If tracefs is not enabled in the kernel, the value -%ENODEV will be
   * returned.
   */
  struct dentry *tracefs_create_file(const char *name, umode_t mode,
  				   struct dentry *parent, void *data,
  				   const struct file_operations *fops)
  {
  	struct dentry *dentry;
  	struct inode *inode;
  
  	if (!(mode & S_IFMT))
  		mode |= S_IFREG;
  	BUG_ON(!S_ISREG(mode));
  	dentry = start_creating(name, parent);
  
  	if (IS_ERR(dentry))
  		return NULL;
  
  	inode = tracefs_get_inode(dentry->d_sb);
  	if (unlikely(!inode))
  		return failed_creating(dentry);
  
  	inode->i_mode = mode;
  	inode->i_fop = fops ? fops : &tracefs_file_operations;
  	inode->i_private = data;
  	d_instantiate(dentry, inode);
  	fsnotify_create(dentry->d_parent->d_inode, dentry);
  	return end_creating(dentry);
  }

  static struct dentry *__create_dir(const char *name, struct dentry *parent,
  				   const struct inode_operations *ops)
  {
  	struct dentry *dentry = start_creating(name, parent);
  	struct inode *inode;
  
  	if (IS_ERR(dentry))
  		return NULL;
  
  	inode = tracefs_get_inode(dentry->d_sb);
  	if (unlikely(!inode))
  		return failed_creating(dentry);
  
  	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
  	inode->i_op = ops;
  	inode->i_fop = &simple_dir_operations;
  
  	/* directory inodes start off with i_nlink == 2 (for "." entry) */
  	inc_nlink(inode);
  	d_instantiate(dentry, inode);
  	inc_nlink(dentry->d_parent->d_inode);
  	fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
  	return end_creating(dentry);
  }

  /**
   * tracefs_create_dir - create a directory in the tracefs filesystem
   * @name: a pointer to a string containing the name of the directory to
   *        create.
   * @parent: a pointer to the parent dentry for this file.  This should be a
   *          directory dentry if set.  If this parameter is NULL, then the
   *          directory will be created in the root of the tracefs filesystem.
   *
   * This function creates a directory in tracefs with the given name.
   *
   * This function will return a pointer to a dentry if it succeeds.  This
   * pointer must be passed to the tracefs_remove() function when the file is
   * to be removed. If an error occurs, %NULL will be returned.
   *
   * If tracing is not enabled in the kernel, the value -%ENODEV will be
   * returned.
   */
  struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
  {

  	return __create_dir(name, parent, &simple_dir_inode_operations);
  }

  /**
   * tracefs_create_instance_dir - create the tracing instances directory
   * @name: The name of the instances directory to create
   * @parent: The parent directory that the instances directory will exist
   * @mkdir: The function to call when a mkdir is performed.
   * @rmdir: The function to call when a rmdir is performed.
   *
   * Only one instances directory is allowed.
   *
   * The instances directory is special as it allows for mkdir and rmdir to
   * to be done by userspace. When a mkdir or rmdir is performed, the inode
   * locks are released and the methhods passed in (@mkdir and @rmdir) are
   * called without locks and with the name of the directory being created
   * within the instances directory.
   *
   * Returns the dentry of the instances directory.
   */
  struct dentry *tracefs_create_instance_dir(const char *name, struct dentry *parent,
  					  int (*mkdir)(const char *name),
  					  int (*rmdir)(const char *name))
  {
  	struct dentry *dentry;
  
  	/* Only allow one instance of the instances directory. */
  	if (WARN_ON(tracefs_ops.mkdir || tracefs_ops.rmdir))

  		return NULL;

  	dentry = __create_dir(name, parent, &tracefs_dir_inode_operations);
  	if (!dentry)
  		return NULL;

  	tracefs_ops.mkdir = mkdir;
  	tracefs_ops.rmdir = rmdir;

  	return dentry;

  }

  static int __tracefs_remove(struct dentry *dentry, struct dentry *parent)
  {
  	int ret = 0;

  	if (simple_positive(dentry)) {

  		if (dentry->d_inode) {
  			dget(dentry);
  			switch (dentry->d_inode->i_mode & S_IFMT) {
  			case S_IFDIR:
  				ret = simple_rmdir(parent->d_inode, dentry);
  				break;
  			default:
  				simple_unlink(parent->d_inode, dentry);
  				break;
  			}
  			if (!ret)
  				d_delete(dentry);
  			dput(dentry);
  		}
  	}
  	return ret;
  }
  
  /**
   * tracefs_remove - removes a file or directory from the tracefs filesystem
   * @dentry: a pointer to a the dentry of the file or directory to be
   *          removed.
   *
   * This function removes a file or directory in tracefs that was previously
   * created with a call to another tracefs function (like
   * tracefs_create_file() or variants thereof.)
   */
  void tracefs_remove(struct dentry *dentry)
  {
  	struct dentry *parent;
  	int ret;
  
  	if (IS_ERR_OR_NULL(dentry))
  		return;
  
  	parent = dentry->d_parent;

  	inode_lock(parent->d_inode);

  	ret = __tracefs_remove(dentry, parent);

  	inode_unlock(parent->d_inode);

  	if (!ret)
  		simple_release_fs(&tracefs_mount, &tracefs_mount_count);
  }
  
  /**
   * tracefs_remove_recursive - recursively removes a directory
   * @dentry: a pointer to a the dentry of the directory to be removed.
   *
   * This function recursively removes a directory tree in tracefs that
   * was previously created with a call to another tracefs function
   * (like tracefs_create_file() or variants thereof.)
   */
  void tracefs_remove_recursive(struct dentry *dentry)
  {
  	struct dentry *child, *parent;
  
  	if (IS_ERR_OR_NULL(dentry))
  		return;

  	parent = dentry;
   down:

  	inode_lock(parent->d_inode);

   loop:
  	/*
  	 * The parent->d_subdirs is protected by the d_lock. Outside that
  	 * lock, the child can be unlinked and set to be freed which can
  	 * use the d_u.d_child as the rcu head and corrupt this list.
  	 */
  	spin_lock(&parent->d_lock);
  	list_for_each_entry(child, &parent->d_subdirs, d_child) {

  		if (!simple_positive(child))

  			continue;
  
  		/* perhaps simple_empty(child) makes more sense */
  		if (!list_empty(&child->d_subdirs)) {
  			spin_unlock(&parent->d_lock);

  			inode_unlock(parent->d_inode);

  			parent = child;
  			goto down;
  		}
  
  		spin_unlock(&parent->d_lock);
  
  		if (!__tracefs_remove(child, parent))
  			simple_release_fs(&tracefs_mount, &tracefs_mount_count);
  
  		/*
  		 * The parent->d_lock protects agaist child from unlinking
  		 * from d_subdirs. When releasing the parent->d_lock we can
  		 * no longer trust that the next pointer is valid.
  		 * Restart the loop. We'll skip this one with the

  		 * simple_positive() check.

  		 */
  		goto loop;
  	}
  	spin_unlock(&parent->d_lock);

  	inode_unlock(parent->d_inode);

  	child = parent;
  	parent = parent->d_parent;

  	inode_lock(parent->d_inode);

  
  	if (child != dentry)
  		/* go up */
  		goto loop;
  
  	if (!__tracefs_remove(child, parent))
  		simple_release_fs(&tracefs_mount, &tracefs_mount_count);

  	inode_unlock(parent->d_inode);

  }
  
  /**
   * tracefs_initialized - Tells whether tracefs has been registered
   */
  bool tracefs_initialized(void)
  {
  	return tracefs_registered;
  }
  
  static int __init tracefs_init(void)
  {
  	int retval;

  	retval = sysfs_create_mount_point(kernel_kobj, "tracing");
  	if (retval)

  		return -EINVAL;

  	retval = register_filesystem(&trace_fs_type);
  	if (!retval)
  		tracefs_registered = true;
  
  	return retval;
  }
  core_initcall(tracefs_init);