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/*
* fs/sysfs/file.c - sysfs regular (text) file implementation
*
* Copyright (c) 2001-3 Patrick Mochel
* Copyright (c) 2007 SUSE Linux Products GmbH
* Copyright (c) 2007 Tejun Heo <teheo@suse.de>
*
* This file is released under the GPLv2.
*
* Please see Documentation/filesystems/sysfs.txt for more information.
*/
#include <linux/module.h>
#include <linux/kobject.h>
#include <linux/kallsyms.h>
#include <linux/slab.h>
#include <linux/fsnotify.h>
#include <linux/namei.h>
#include <linux/poll.h>
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/limits.h>
#include <asm/uaccess.h>
#include "sysfs.h"
/*
* There's one sysfs_buffer for each open file and one
* sysfs_open_dirent for each sysfs_dirent with one or more open
* files.
*
* filp->private_data points to sysfs_buffer and
* sysfs_dirent->s_attr.open points to sysfs_open_dirent. s_attr.open
* is protected by sysfs_open_dirent_lock.
*/
static DEFINE_SPINLOCK(sysfs_open_dirent_lock);
struct sysfs_open_dirent {
atomic_t refcnt;
atomic_t event;
wait_queue_head_t poll;
struct list_head buffers; /* goes through sysfs_buffer.list */
};
struct sysfs_buffer {
size_t count;
loff_t pos;
char * page;
const struct sysfs_ops * ops;
struct mutex mutex;
int needs_read_fill;
int event;
struct list_head list;
};
/**
* fill_read_buffer - allocate and fill buffer from object.
* @dentry: dentry pointer.
* @buffer: data buffer for file.
*
* Allocate @buffer->page, if it hasn't been already, then call the
* kobject's show() method to fill the buffer with this attribute's
* data.
* This is called only once, on the file's first read unless an error
* is returned.
*/
static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer)
{
struct sysfs_dirent *attr_sd = dentry->d_fsdata;
struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
const struct sysfs_ops * 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;
/* need attr_sd for attr and ops, its parent for kobj */
if (!sysfs_get_active(attr_sd))
return -ENODEV;
buffer->event = atomic_read(&attr_sd->s_attr.open->event);
count = ops->show(kobj, attr_sd->s_attr.attr, buffer->page);
sysfs_put_active(attr_sd);
/*
* The code works fine with PAGE_SIZE return but it's likely to
* indicate truncated result or overflow in normal use cases.
*/
if (count >= (ssize_t)PAGE_SIZE) {
print_symbol("fill_read_buffer: %s returned bad count\n",
(unsigned long)ops->show);
/* Try to struggle along */
count = PAGE_SIZE - 1;
}
if (count >= 0) {
buffer->needs_read_fill = 0;
buffer->count = count;
} else {
ret = count;
}
return ret;
}
/**
* sysfs_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 object is in the directory's
* ->d_fsdata.
*
* We call fill_read_buffer() to allocate and fill the buffer from the
* object'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 object 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
sysfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
struct sysfs_buffer * buffer = file->private_data;
ssize_t retval = 0;
mutex_lock(&buffer->mutex);
if (buffer->needs_read_fill || *ppos == 0) {
retval = fill_read_buffer(file->f_path.dentry,buffer);
if (retval)
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 sysfs_buffer * buffer, const char __user * buf, size_t count)
{
int error;
if (!buffer->page)
buffer->page = (char *)get_zeroed_page(GFP_KERNEL);
if (!buffer->page)
return -ENOMEM;
if (count >= PAGE_SIZE)
count = PAGE_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 kobject.
* @dentry: dentry to the attribute
* @buffer: data buffer for file.
* @count: number of bytes
*
* Get the correct pointers for the kobject 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 sysfs_buffer * buffer, size_t count)
{
struct sysfs_dirent *attr_sd = dentry->d_fsdata;
struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
const struct sysfs_ops * ops = buffer->ops;
int rc;
/* need attr_sd for attr and ops, its parent for kobj */
if (!sysfs_get_active(attr_sd))
return -ENODEV;
rc = ops->store(kobj, attr_sd->s_attr.attr, buffer->page, count);
sysfs_put_active(attr_sd);
return rc;
}
/**
* sysfs_write_file - write an attribute.
* @file: file pointer
* @buf: data to write
* @count: number of bytes
* @ppos: starting offset
*
* Similar to sysfs_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 kobject 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
sysfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
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