/* -*- 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\n",
                 __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, count);
        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);
}