file.c

Go to the documentation of this file.

/* -*- 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;
};


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;
}

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;
}


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;
}


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);
}


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;
}


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);
}