/* -*- mode: c; c-basic-offset: 8; -*-
   * vim: noexpandtab sw=8 ts=8 sts=0:
   *
   * file.c - operations for regular (text) files.
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public
   * License as published by the Free Software Foundation; either
   * version 2 of the License, or (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * General Public License for more details.
   *
   * You should have received a copy of the GNU General Public
   * License along with this program; if not, write to the
   * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   * Boston, MA 021110-1307, USA.
   *
   * Based on sysfs:
   * 	sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
   *
   * configfs Copyright (C) 2005 Oracle.  All rights reserved.
   */
  
  #include <linux/fs.h>
  #include <linux/module.h>
  #include <linux/slab.h>
  #include <linux/mutex.h>
  #include <asm/uaccess.h>
  
  #include <linux/configfs.h>
  #include "configfs_internal.h"
  
  /*
   * A simple attribute can only be 4096 characters.  Why 4k?  Because the
   * original code limited it to PAGE_SIZE.  That's a bad idea, though,
   * because an attribute of 16k on ia64 won't work on x86.  So we limit to
   * 4k, our minimum common page size.
   */
  #define SIMPLE_ATTR_SIZE 4096
  
  struct configfs_buffer {
  	size_t			count;
  	loff_t			pos;
  	char			* page;
  	struct configfs_item_operations	* ops;
  	struct mutex		mutex;
  	int			needs_read_fill;
  };
  
  
  /**
   *	fill_read_buffer - allocate and fill buffer from item.
   *	@dentry:	dentry pointer.
   *	@buffer:	data buffer for file.
   *
   *	Allocate @buffer->page, if it hasn't been already, then call the
   *	config_item's show() method to fill the buffer with this attribute's
   *	data.
   *	This is called only once, on the file's first read.
   */
  static int fill_read_buffer(struct dentry * dentry, struct configfs_buffer * buffer)
  {
  	struct configfs_attribute * attr = to_attr(dentry);
  	struct config_item * item = to_item(dentry->d_parent);
  	struct configfs_item_operations * ops = buffer->ops;
  	int ret = 0;
  	ssize_t count;
  
  	if (!buffer->page)
  		buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
  	if (!buffer->page)
  		return -ENOMEM;
  
  	count = ops->show_attribute(item,attr,buffer->page);
  	buffer->needs_read_fill = 0;
  	BUG_ON(count > (ssize_t)SIMPLE_ATTR_SIZE);
  	if (count >= 0)
  		buffer->count = count;
  	else
  		ret = count;
  	return ret;
  }
  
  /**
   *	configfs_read_file - read an attribute.
   *	@file:	file pointer.
   *	@buf:	buffer to fill.
   *	@count:	number of bytes to read.
   *	@ppos:	starting offset in file.
   *
   *	Userspace wants to read an attribute file. The attribute descriptor
   *	is in the file's ->d_fsdata. The target item is in the directory's
   *	->d_fsdata.
   *
   *	We call fill_read_buffer() to allocate and fill the buffer from the
   *	item's show() method exactly once (if the read is happening from
   *	the beginning of the file). That should fill the entire buffer with
   *	all the data the item has to offer for that attribute.
   *	We then call flush_read_buffer() to copy the buffer to userspace
   *	in the increments specified.
   */
  
  static ssize_t
  configfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
  {
  	struct configfs_buffer * buffer = file->private_data;
  	ssize_t retval = 0;
  
  	mutex_lock(&buffer->mutex);
  	if (buffer->needs_read_fill) {
  		if ((retval = fill_read_buffer(file->f_path.dentry,buffer)))
  			goto out;
  	}
  	pr_debug("%s: count = %zd, ppos = %lld, buf = %s
  ",
  		 __func__, count, *ppos, buffer->page);
  	retval = simple_read_from_buffer(buf, count, ppos, buffer->page,
  					 buffer->count);
  out:
  	mutex_unlock(&buffer->mutex);
  	return retval;
  }
  
  
  /**
   *	fill_write_buffer - copy buffer from userspace.
   *	@buffer:	data buffer for file.
   *	@buf:		data from user.
   *	@count:		number of bytes in @userbuf.
   *
   *	Allocate @buffer->page if it hasn't been already, then
   *	copy the user-supplied buffer into it.
   */
  
  static int
  fill_write_buffer(struct configfs_buffer * buffer, const char __user * buf, size_t count)
  {
  	int error;
  
  	if (!buffer->page)
  		buffer->page = (char *)__get_free_pages(GFP_KERNEL, 0);
  	if (!buffer->page)
  		return -ENOMEM;
  
  	if (count >= SIMPLE_ATTR_SIZE)
  		count = SIMPLE_ATTR_SIZE - 1;
  	error = copy_from_user(buffer->page,buf,count);
  	buffer->needs_read_fill = 1;
  	/* if buf is assumed to contain a string, terminate it by \0,
  	 * so e.g. sscanf() can scan the string easily */
  	buffer->page[count] = 0;
  	return error ? -EFAULT : count;
  }
  
  
  /**
   *	flush_write_buffer - push buffer to config_item.
   *	@dentry:	dentry to the attribute
   *	@buffer:	data buffer for file.
   *	@count:		number of bytes
   *
   *	Get the correct pointers for the config_item and the attribute we're
   *	dealing with, then call the store() method for the attribute,
   *	passing the buffer that we acquired in fill_write_buffer().
   */
  
  static int
  flush_write_buffer(struct dentry * dentry, struct configfs_buffer * buffer, size_t count)
  {
  	struct configfs_attribute * attr = to_attr(dentry);
  	struct config_item * item = to_item(dentry->d_parent);
  	struct configfs_item_operations * ops = buffer->ops;
  
  	return ops->store_attribute(item,attr,buffer->page,count);
  }
  
  
  /**
   *	configfs_write_file - write an attribute.
   *	@file:	file pointer
   *	@buf:	data to write
   *	@count:	number of bytes
   *	@ppos:	starting offset
   *
   *	Similar to configfs_read_file(), though working in the opposite direction.
   *	We allocate and fill the data from the user in fill_write_buffer(),
   *	then push it to the config_item in flush_write_buffer().
   *	There is no easy way for us to know if userspace is only doing a partial
   *	write, so we don't support them. We expect the entire buffer to come
   *	on the first write.
   *	Hint: if you're writing a value, first read the file, modify only the
   *	the value you're changing, then write entire buffer back.
   */
  
  static ssize_t
  configfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
  {
  	struct configfs_buffer * buffer = file->private_data;
  	ssize_t len;
  
  	mutex_lock(&buffer->mutex);
  	len = fill_write_buffer(buffer, buf, count);
  	if (len > 0)
  		len = flush_write_buffer(file->f_path.dentry, buffer, len);
  	if (len > 0)
  		*ppos += len;
  	mutex_unlock(&buffer->mutex);
  	return len;
  }
  
  static int check_perm(struct inode * inode, struct file * file)
  {
  	struct config_item *item = configfs_get_config_item(file->f_path.dentry->d_parent);
  	struct configfs_attribute * attr = to_attr(file->f_path.dentry);
  	struct configfs_buffer * buffer;
  	struct configfs_item_operations * ops = NULL;
  	int error = 0;
  
  	if (!item || !attr)
  		goto Einval;
  
  	/* Grab the module reference for this attribute if we have one */
  	if (!try_module_get(attr->ca_owner)) {
  		error = -ENODEV;
  		goto Done;
  	}
  
  	if (item->ci_type)
  		ops = item->ci_type->ct_item_ops;
  	else
  		goto Eaccess;
  
  	/* File needs write support.
  	 * The inode's perms must say it's ok,
  	 * and we must have a store method.
  	 */
  	if (file->f_mode & FMODE_WRITE) {
  
  		if (!(inode->i_mode & S_IWUGO) || !ops->store_attribute)
  			goto Eaccess;
  
  	}
  
  	/* File needs read support.
  	 * The inode's perms must say it's ok, and we there
  	 * must be a show method for it.
  	 */
  	if (file->f_mode & FMODE_READ) {
  		if (!(inode->i_mode & S_IRUGO) || !ops->show_attribute)
  			goto Eaccess;
  	}
  
  	/* No error? Great, allocate a buffer for the file, and store it
  	 * it in file->private_data for easy access.
  	 */
  	buffer = kzalloc(sizeof(struct configfs_buffer),GFP_KERNEL);
  	if (!buffer) {
  		error = -ENOMEM;
  		goto Enomem;
  	}
  	mutex_init(&buffer->mutex);
  	buffer->needs_read_fill = 1;
  	buffer->ops = ops;
  	file->private_data = buffer;
  	goto Done;
  
   Einval:
  	error = -EINVAL;
  	goto Done;
   Eaccess:
  	error = -EACCES;
   Enomem:
  	module_put(attr->ca_owner);
   Done:
  	if (error && item)
  		config_item_put(item);
  	return error;
  }
  
  static int configfs_open_file(struct inode * inode, struct file * filp)
  {
  	return check_perm(inode,filp);
  }
  
  static int configfs_release(struct inode * inode, struct file * filp)
  {
  	struct config_item * item = to_item(filp->f_path.dentry->d_parent);
  	struct configfs_attribute * attr = to_attr(filp->f_path.dentry);
  	struct module * owner = attr->ca_owner;
  	struct configfs_buffer * buffer = filp->private_data;
  
  	if (item)
  		config_item_put(item);
  	/* After this point, attr should not be accessed. */
  	module_put(owner);
  
  	if (buffer) {
  		if (buffer->page)
  			free_page((unsigned long)buffer->page);
  		mutex_destroy(&buffer->mutex);
  		kfree(buffer);
  	}
  	return 0;
  }
  
  const struct file_operations configfs_file_operations = {
  	.read		= configfs_read_file,
  	.write		= configfs_write_file,
  	.llseek		= generic_file_llseek,
  	.open		= configfs_open_file,
  	.release	= configfs_release,
  };
  
  
  int configfs_add_file(struct dentry * dir, const struct configfs_attribute * attr, int type)
  {
  	struct configfs_dirent * parent_sd = dir->d_fsdata;
  	umode_t mode = (attr->ca_mode & S_IALLUGO) | S_IFREG;
  	int error = 0;
  
  	mutex_lock_nested(&dir->d_inode->i_mutex, I_MUTEX_NORMAL);
  	error = configfs_make_dirent(parent_sd, NULL, (void *) attr, mode, type);
  	mutex_unlock(&dir->d_inode->i_mutex);
  
  	return error;
  }
  
  
  /**
   *	configfs_create_file - create an attribute file for an item.
   *	@item:	item we're creating for.
   *	@attr:	atrribute descriptor.
   */
  
  int configfs_create_file(struct config_item * item, const struct configfs_attribute * attr)
  {
  	BUG_ON(!item || !item->ci_dentry || !attr);
  
  	return configfs_add_file(item->ci_dentry, attr,
  				 CONFIGFS_ITEM_ATTR);
  }