file.c 19.2 KB
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/*
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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.
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 */

#include <linux/module.h>
#include <linux/kobject.h>
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#include <linux/kallsyms.h>
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#include <linux/slab.h>
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#include <linux/fsnotify.h>
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#include <linux/namei.h>
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#include <linux/poll.h>
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#include <linux/list.h>
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#include <linux/mutex.h>
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#include <linux/limits.h>
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#include <linux/uaccess.h>
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#include "sysfs.h"

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/*
 * 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.
 */
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static DEFINE_SPINLOCK(sysfs_open_dirent_lock);
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struct sysfs_open_dirent {
	atomic_t		refcnt;
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	atomic_t		event;
	wait_queue_head_t	poll;
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	struct list_head	buffers; /* goes through sysfs_buffer.list */
};

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struct sysfs_buffer {
	size_t			count;
	loff_t			pos;
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	char			*page;
	const struct sysfs_ops	*ops;
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	struct mutex		mutex;
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	int			needs_read_fill;
	int			event;
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	struct list_head	list;
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};
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/**
 *	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
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 *	kobject's show() method to fill the buffer with this attribute's
 *	data.
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 *	This is called only once, on the file's first read unless an error
 *	is returned.
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 */
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static int fill_read_buffer(struct dentry *dentry, struct sysfs_buffer *buffer)
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{
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	struct sysfs_dirent *attr_sd = dentry->d_fsdata;
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	struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
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	const struct sysfs_ops *ops = buffer->ops;
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	int ret = 0;
	ssize_t count;

	if (!buffer->page)
		buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
	if (!buffer->page)
		return -ENOMEM;

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	/* need attr_sd for attr and ops, its parent for kobj */
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	if (!sysfs_get_active(attr_sd))
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		return -ENODEV;

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	buffer->event = atomic_read(&attr_sd->s_attr.open->event);
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	count = ops->show(kobj, attr_sd->s_attr.attr, buffer->page);
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	sysfs_put_active(attr_sd);
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	/*
	 * The code works fine with PAGE_SIZE return but it's likely to
	 * indicate truncated result or overflow in normal use cases.
	 */
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	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;
	}
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	if (count >= 0) {
		buffer->needs_read_fill = 0;
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		buffer->count = count;
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	} else {
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		ret = count;
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	}
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	return ret;
}

/**
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 *	sysfs_read_file - read an attribute.
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 *	@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)
{
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	struct sysfs_buffer *buffer = file->private_data;
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	ssize_t retval = 0;

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	mutex_lock(&buffer->mutex);
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	if (buffer->needs_read_fill || *ppos == 0) {
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		retval = fill_read_buffer(file->f_path.dentry, buffer);
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		if (retval)
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			goto out;
	}
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	pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n",
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		 __func__, count, *ppos, buffer->page);
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	retval = simple_read_from_buffer(buf, count, ppos, buffer->page,
					 buffer->count);
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out:
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	mutex_unlock(&buffer->mutex);
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	return retval;
}

/**
 *	fill_write_buffer - copy buffer from userspace.
 *	@buffer:	data buffer for file.
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 *	@buf:		data from user.
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 *	@count:		number of bytes in @userbuf.
 *
 *	Allocate @buffer->page if it hasn't been already, then
 *	copy the user-supplied buffer into it.
 */
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static int fill_write_buffer(struct sysfs_buffer *buffer,
			     const char __user *buf, size_t count)
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{
	int error;

	if (!buffer->page)
		buffer->page = (char *)get_zeroed_page(GFP_KERNEL);
	if (!buffer->page)
		return -ENOMEM;

	if (count >= PAGE_SIZE)
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		count = PAGE_SIZE - 1;
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	error = copy_from_user(buffer->page, buf, count);
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	buffer->needs_read_fill = 1;
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	/* 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;
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	return error ? -EFAULT : count;
}


/**
 *	flush_write_buffer - push buffer to kobject.
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 *	@dentry:	dentry to the attribute
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 *	@buffer:	data buffer for file.
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 *	@count:		number of bytes
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 *
 *	Get the correct pointers for the kobject and the attribute we're
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 *	dealing with, then call the store() method for the attribute,
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 *	passing the buffer that we acquired in fill_write_buffer().
 */
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static int flush_write_buffer(struct dentry *dentry,
			      struct sysfs_buffer *buffer, size_t count)
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{
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	struct sysfs_dirent *attr_sd = dentry->d_fsdata;
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	struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
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	const struct sysfs_ops *ops = buffer->ops;
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	int rc;

	/* need attr_sd for attr and ops, its parent for kobj */
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	if (!sysfs_get_active(attr_sd))
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		return -ENODEV;

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	rc = ops->store(kobj, attr_sd->s_attr.attr, buffer->page, count);
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	sysfs_put_active(attr_sd);
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	return rc;
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}


/**
 *	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
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 *	on the first write.
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 *	Hint: if you're writing a value, first read the file, modify only the
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 *	the value you're changing, then write entire buffer back.
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 */
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static ssize_t sysfs_write_file(struct file *file, const char __user *buf,
				size_t count, loff_t *ppos)
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{
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	struct sysfs_buffer *buffer = file->private_data;
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	ssize_t len;

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	mutex_lock(&buffer->mutex);
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	len = fill_write_buffer(buffer, buf, count);
	if (len > 0)
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		len = flush_write_buffer(file->f_path.dentry, buffer, len);
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	if (len > 0)
		*ppos += len;
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	mutex_unlock(&buffer->mutex);
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	return len;
}

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/**
 *	sysfs_get_open_dirent - get or create sysfs_open_dirent
 *	@sd: target sysfs_dirent
 *	@buffer: sysfs_buffer for this instance of open
 *
 *	If @sd->s_attr.open exists, increment its reference count;
 *	otherwise, create one.  @buffer is chained to the buffers
 *	list.
 *
 *	LOCKING:
 *	Kernel thread context (may sleep).
 *
 *	RETURNS:
 *	0 on success, -errno on failure.
 */
static int sysfs_get_open_dirent(struct sysfs_dirent *sd,
				 struct sysfs_buffer *buffer)
{
	struct sysfs_open_dirent *od, *new_od = NULL;

 retry:
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	spin_lock_irq(&sysfs_open_dirent_lock);
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	if (!sd->s_attr.open && new_od) {
		sd->s_attr.open = new_od;
		new_od = NULL;
	}

	od = sd->s_attr.open;
	if (od) {
		atomic_inc(&od->refcnt);
		list_add_tail(&buffer->list, &od->buffers);
	}

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	spin_unlock_irq(&sysfs_open_dirent_lock);
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	if (od) {
		kfree(new_od);
		return 0;
	}

	/* not there, initialize a new one and retry */
	new_od = kmalloc(sizeof(*new_od), GFP_KERNEL);
	if (!new_od)
		return -ENOMEM;

	atomic_set(&new_od->refcnt, 0);
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	atomic_set(&new_od->event, 1);
	init_waitqueue_head(&new_od->poll);
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	INIT_LIST_HEAD(&new_od->buffers);
	goto retry;
}

/**
 *	sysfs_put_open_dirent - put sysfs_open_dirent
 *	@sd: target sysfs_dirent
 *	@buffer: associated sysfs_buffer
 *
 *	Put @sd->s_attr.open and unlink @buffer from the buffers list.
 *	If reference count reaches zero, disassociate and free it.
 *
 *	LOCKING:
 *	None.
 */
static void sysfs_put_open_dirent(struct sysfs_dirent *sd,
				  struct sysfs_buffer *buffer)
{
	struct sysfs_open_dirent *od = sd->s_attr.open;
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	unsigned long flags;
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	spin_lock_irqsave(&sysfs_open_dirent_lock, flags);
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	list_del(&buffer->list);
	if (atomic_dec_and_test(&od->refcnt))
		sd->s_attr.open = NULL;
	else
		od = NULL;

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	spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags);
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	kfree(od);
}

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static int sysfs_open_file(struct inode *inode, struct file *file)
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{
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	struct sysfs_dirent *attr_sd = file->f_path.dentry->d_fsdata;
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	struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
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	struct sysfs_buffer *buffer;
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	const struct sysfs_ops *ops;
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	int error = -EACCES;
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	/* need attr_sd for attr and ops, its parent for kobj */
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	if (!sysfs_get_active(attr_sd))
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		return -ENODEV;
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	/* every kobject with an attribute needs a ktype assigned */
	if (kobj->ktype && kobj->ktype->sysfs_ops)
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		ops = kobj->ktype->sysfs_ops;
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	else {
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		WARN(1, KERN_ERR
		     "missing sysfs attribute operations for kobject: %s\n",
		     kobject_name(kobj));
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		goto err_out;
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	}
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	/* File needs write support.
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	 * The inode's perms must say it's ok,
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	 * and we must have a store method.
	 */
	if (file->f_mode & FMODE_WRITE) {
		if (!(inode->i_mode & S_IWUGO) || !ops->store)
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			goto err_out;
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	}

	/* 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)
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			goto err_out;
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	}

	/* No error? Great, allocate a buffer for the file, and store it
	 * it in file->private_data for easy access.
	 */
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	error = -ENOMEM;
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	buffer = kzalloc(sizeof(struct sysfs_buffer), GFP_KERNEL);
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	if (!buffer)
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		goto err_out;
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	mutex_init(&buffer->mutex);
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	buffer->needs_read_fill = 1;
	buffer->ops = ops;
	file->private_data = buffer;

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	/* make sure we have open dirent struct */
	error = sysfs_get_open_dirent(attr_sd, buffer);
	if (error)
		goto err_free;

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	/* open succeeded, put active references */
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	sysfs_put_active(attr_sd);
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	return 0;

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 err_free:
	kfree(buffer);
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 err_out:
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	sysfs_put_active(attr_sd);
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	return error;
}

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static int sysfs_release(struct inode *inode, struct file *filp)
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{
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	struct sysfs_dirent *sd = filp->f_path.dentry->d_fsdata;
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	struct sysfs_buffer *buffer = filp->private_data;
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	sysfs_put_open_dirent(sd, buffer);

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	if (buffer->page)
		free_page((unsigned long)buffer->page);
	kfree(buffer);

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	return 0;
}

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/* Sysfs attribute files are pollable.  The idea is that you read
 * the content and then you use 'poll' or 'select' to wait for
 * the content to change.  When the content changes (assuming the
 * manager for the kobject supports notification), poll will
 * return POLLERR|POLLPRI, and select will return the fd whether
 * it is waiting for read, write, or exceptions.
 * Once poll/select indicates that the value has changed, you
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 * need to close and re-open the file, or seek to 0 and read again.
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 * Reminder: this only works for attributes which actively support
 * it, and it is not possible to test an attribute from userspace
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 * to see if it supports poll (Neither 'poll' nor 'select' return
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 * an appropriate error code).  When in doubt, set a suitable timeout value.
 */
static unsigned int sysfs_poll(struct file *filp, poll_table *wait)
{
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	struct sysfs_buffer *buffer = filp->private_data;
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	struct sysfs_dirent *attr_sd = filp->f_path.dentry->d_fsdata;
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	struct sysfs_open_dirent *od = attr_sd->s_attr.open;
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	/* need parent for the kobj, grab both */
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	if (!sysfs_get_active(attr_sd))
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		goto trigger;
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	poll_wait(filp, &od->poll, wait);
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	sysfs_put_active(attr_sd);
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	if (buffer->event != atomic_read(&od->event))
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		goto trigger;
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	return DEFAULT_POLLMASK;
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 trigger:
	buffer->needs_read_fill = 1;
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	return DEFAULT_POLLMASK|POLLERR|POLLPRI;
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}

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void sysfs_notify_dirent(struct sysfs_dirent *sd)
{
	struct sysfs_open_dirent *od;
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	unsigned long flags;
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	spin_lock_irqsave(&sysfs_open_dirent_lock, flags);
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	if (!WARN_ON(sysfs_type(sd) != SYSFS_KOBJ_ATTR)) {
		od = sd->s_attr.open;
		if (od) {
			atomic_inc(&od->event);
			wake_up_interruptible(&od->poll);
		}
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	}

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	spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags);
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}
EXPORT_SYMBOL_GPL(sysfs_notify_dirent);

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void sysfs_notify(struct kobject *k, const char *dir, const char *attr)
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{
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	struct sysfs_dirent *sd = k->sd;
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	mutex_lock(&sysfs_mutex);

	if (sd && dir)
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		sd = sysfs_find_dirent(sd, NULL, dir);
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	if (sd && attr)
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		sd = sysfs_find_dirent(sd, NULL, attr);
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	if (sd)
		sysfs_notify_dirent(sd);
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	mutex_unlock(&sysfs_mutex);
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}
EXPORT_SYMBOL_GPL(sysfs_notify);

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const struct file_operations sysfs_file_operations = {
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	.read		= sysfs_read_file,
	.write		= sysfs_write_file,
	.llseek		= generic_file_llseek,
	.open		= sysfs_open_file,
	.release	= sysfs_release,
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	.poll		= sysfs_poll,
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};

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int sysfs_add_file_mode_ns(struct sysfs_dirent *dir_sd,
			   const struct attribute *attr, int type,
			   umode_t amode, const void *ns)
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{
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	umode_t mode = (amode & S_IALLUGO) | S_IFREG;
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	struct sysfs_addrm_cxt acxt;
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	struct sysfs_dirent *sd;
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	int rc;
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	sd = sysfs_new_dirent(attr->name, mode, type);
	if (!sd)
		return -ENOMEM;
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	sd->s_ns = ns;
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	sd->s_attr.attr = (void *)attr;
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	sysfs_dirent_init_lockdep(sd);
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	sysfs_addrm_start(&acxt, dir_sd);
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	rc = sysfs_add_one(&acxt, sd);
	sysfs_addrm_finish(&acxt);
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	if (rc)
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		sysfs_put(sd);
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	return rc;
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}


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int sysfs_add_file(struct sysfs_dirent *dir_sd, const struct attribute *attr,
		   int type)
{
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	return sysfs_add_file_mode_ns(dir_sd, attr, type, attr->mode, NULL);
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}

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/**
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 * sysfs_create_file_ns - create an attribute file for an object with custom ns
 * @kobj: object we're creating for
 * @attr: attribute descriptor
 * @ns: namespace the new file should belong to
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 */
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int sysfs_create_file_ns(struct kobject *kobj, const struct attribute *attr,
			 const void *ns)
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{
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	BUG_ON(!kobj || !kobj->sd || !attr);
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	return sysfs_add_file_mode_ns(kobj->sd, attr, SYSFS_KOBJ_ATTR,
				      attr->mode, ns);
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}
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EXPORT_SYMBOL_GPL(sysfs_create_file_ns);
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int sysfs_create_files(struct kobject *kobj, const struct attribute **ptr)
{
	int err = 0;
	int i;

	for (i = 0; ptr[i] && !err; i++)
		err = sysfs_create_file(kobj, ptr[i]);
	if (err)
		while (--i >= 0)
			sysfs_remove_file(kobj, ptr[i]);
	return err;
}
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EXPORT_SYMBOL_GPL(sysfs_create_files);
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/**
 * sysfs_add_file_to_group - add an attribute file to a pre-existing group.
 * @kobj: object we're acting for.
 * @attr: attribute descriptor.
 * @group: group name.
 */
int sysfs_add_file_to_group(struct kobject *kobj,
		const struct attribute *attr, const char *group)
{
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	struct sysfs_dirent *dir_sd;
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	int error;

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	if (group)
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		dir_sd = sysfs_get_dirent(kobj->sd, group);
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	else
		dir_sd = sysfs_get(kobj->sd);

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	if (!dir_sd)
		return -ENOENT;

	error = sysfs_add_file(dir_sd, attr, SYSFS_KOBJ_ATTR);
	sysfs_put(dir_sd);

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	return error;
}
EXPORT_SYMBOL_GPL(sysfs_add_file_to_group);

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/**
 * sysfs_chmod_file - update the modified mode value on an object attribute.
 * @kobj: object we're acting for.
 * @attr: attribute descriptor.
 * @mode: file permissions.
 *
 */
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int sysfs_chmod_file(struct kobject *kobj, const struct attribute *attr,
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		     umode_t mode)
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{
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	struct sysfs_dirent *sd;
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	struct iattr newattrs;
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	int rc;

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	mutex_lock(&sysfs_mutex);
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	rc = -ENOENT;
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	sd = sysfs_find_dirent(kobj->sd, NULL, attr->name);
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	if (!sd)
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		goto out;
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	newattrs.ia_mode = (mode & S_IALLUGO) | (sd->s_mode & ~S_IALLUGO);
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	newattrs.ia_valid = ATTR_MODE;
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	rc = sysfs_sd_setattr(sd, &newattrs);
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 out:
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	mutex_unlock(&sysfs_mutex);
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	return rc;
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}
EXPORT_SYMBOL_GPL(sysfs_chmod_file);

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/**
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 * sysfs_remove_file_ns - remove an object attribute with a custom ns tag
 * @kobj: object we're acting for
 * @attr: attribute descriptor
 * @ns: namespace tag of the file to remove
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 *
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 * Hash the attribute name and namespace tag and kill the victim.
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 */
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void sysfs_remove_file_ns(struct kobject *kobj, const struct attribute *attr,
			  const void *ns)
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{
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	struct sysfs_dirent *dir_sd = kobj->sd;
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	sysfs_hash_and_remove(dir_sd, ns, attr->name);
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}
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EXPORT_SYMBOL_GPL(sysfs_remove_file_ns);
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void sysfs_remove_files(struct kobject *kobj, const struct attribute **ptr)
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{
	int i;
	for (i = 0; ptr[i]; i++)
		sysfs_remove_file(kobj, ptr[i]);
}
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EXPORT_SYMBOL_GPL(sysfs_remove_files);
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/**
 * sysfs_remove_file_from_group - remove an attribute file from a group.
 * @kobj: object we're acting for.
 * @attr: attribute descriptor.
 * @group: group name.
 */
void sysfs_remove_file_from_group(struct kobject *kobj,
		const struct attribute *attr, const char *group)
{
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	struct sysfs_dirent *dir_sd;
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	if (group)
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		dir_sd = sysfs_get_dirent(kobj->sd, group);
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	else
		dir_sd = sysfs_get(kobj->sd);
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	if (dir_sd) {
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		sysfs_hash_and_remove(dir_sd, NULL, attr->name);
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		sysfs_put(dir_sd);
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	}
}
EXPORT_SYMBOL_GPL(sysfs_remove_file_from_group);

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struct sysfs_schedule_callback_struct {
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	struct list_head	workq_list;
	struct kobject		*kobj;
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	void			(*func)(void *);
	void			*data;
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	struct module		*owner;
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	struct work_struct	work;
};

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static struct workqueue_struct *sysfs_workqueue;
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static DEFINE_MUTEX(sysfs_workq_mutex);
static LIST_HEAD(sysfs_workq);
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static void sysfs_schedule_callback_work(struct work_struct *work)
{
	struct sysfs_schedule_callback_struct *ss = container_of(work,
			struct sysfs_schedule_callback_struct, work);

	(ss->func)(ss->data);
	kobject_put(ss->kobj);
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	module_put(ss->owner);
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	mutex_lock(&sysfs_workq_mutex);
	list_del(&ss->workq_list);
	mutex_unlock(&sysfs_workq_mutex);
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	kfree(ss);
}

/**
 * sysfs_schedule_callback - helper to schedule a callback for a kobject
 * @kobj: object we're acting for.
 * @func: callback function to invoke later.
 * @data: argument to pass to @func.
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 * @owner: module owning the callback code
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 *
 * sysfs attribute methods must not unregister themselves or their parent
 * kobject (which would amount to the same thing).  Attempts to do so will
 * deadlock, since unregistration is mutually exclusive with driver
 * callbacks.
 *
 * Instead methods can call this routine, which will attempt to allocate
 * and schedule a workqueue request to call back @func with @data as its
 * argument in the workqueue's process context.  @kobj will be pinned
 * until @func returns.
 *
 * Returns 0 if the request was submitted, -ENOMEM if storage could not
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 * be allocated, -ENODEV if a reference to @owner isn't available,
 * -EAGAIN if a callback has already been scheduled for @kobj.
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 */
int sysfs_schedule_callback(struct kobject *kobj, void (*func)(void *),
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		void *data, struct module *owner)
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{
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	struct sysfs_schedule_callback_struct *ss, *tmp;
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	if (!try_module_get(owner))
		return -ENODEV;
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	mutex_lock(&sysfs_workq_mutex);
	list_for_each_entry_safe(ss, tmp, &sysfs_workq, workq_list)
		if (ss->kobj == kobj) {
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			module_put(owner);
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			mutex_unlock(&sysfs_workq_mutex);
			return -EAGAIN;
		}
	mutex_unlock(&sysfs_workq_mutex);

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	if (sysfs_workqueue == NULL) {
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		sysfs_workqueue = create_singlethread_workqueue("sysfsd");
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		if (sysfs_workqueue == NULL) {
			module_put(owner);
			return -ENOMEM;
		}
	}

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	ss = kmalloc(sizeof(*ss), GFP_KERNEL);
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	if (!ss) {
		module_put(owner);
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		return -ENOMEM;
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	}
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	kobject_get(kobj);
	ss->kobj = kobj;
	ss->func = func;
	ss->data = data;
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	ss->owner = owner;
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	INIT_WORK(&ss->work, sysfs_schedule_callback_work);
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	INIT_LIST_HEAD(&ss->workq_list);
	mutex_lock(&sysfs_workq_mutex);
	list_add_tail(&ss->workq_list, &sysfs_workq);
	mutex_unlock(&sysfs_workq_mutex);
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	queue_work(sysfs_workqueue, &ss->work);
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	return 0;
}
EXPORT_SYMBOL_GPL(sysfs_schedule_callback);