fs/sysfs/file.c - maze/linux - Git at Google

 /*
  * file.c - operations for regular (text) files.
  */

 #include <linux/module.h>
 #include <linux/dnotify.h>
 #include <linux/kobject.h>
 #include <linux/namei.h>
 #include <asm/uaccess.h>
 #include <asm/semaphore.h>

 #include "sysfs.h"

 #define to_subsys(k) container_of(k,struct subsystem,kset.kobj)
 #define to_sattr(a) container_of(a,struct subsys_attribute,attr)

 /*
  * Subsystem file operations.
  * These operations allow subsystems to have files that can be
  * read/written.
  */
 static ssize_t
 subsys_attr_show(struct kobject * kobj, struct attribute * attr, char * page)
 {
 	struct subsystem * s = to_subsys(kobj);
 	struct subsys_attribute * sattr = to_sattr(attr);
 	ssize_t ret = -EIO;

 	if (sattr->show)
 		ret = sattr->show(s,page);
 	return ret;
 }

 static ssize_t
 subsys_attr_store(struct kobject * kobj, struct attribute * attr,
 		  const char * page, size_t count)
 {
 	struct subsystem * s = to_subsys(kobj);
 	struct subsys_attribute * sattr = to_sattr(attr);
 	ssize_t ret = -EIO;

 	if (sattr->store)
 		ret = sattr->store(s,page,count);
 	return ret;
 }

 static struct sysfs_ops subsys_sysfs_ops = {
 	.show	= subsys_attr_show,
 	.store	= subsys_attr_store,
 };


 struct sysfs_buffer {
 	size_t			count;
 	loff_t			pos;
 	char			* page;
 	struct sysfs_ops	* ops;
 	struct semaphore	sem;
 	int			needs_read_fill;
 };


 /**
  *	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.
  */
 static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer)
 {
 	struct attribute * attr = to_attr(dentry);
 	struct kobject * kobj = to_kobj(dentry->d_parent);
 	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;

 	count = ops->show(kobj,attr,buffer->page);
 	buffer->needs_read_fill = 0;
 	BUG_ON(count > (ssize_t)PAGE_SIZE);
 	if (count >= 0)
 		buffer->count = count;
 	else
 		ret = count;
 	return ret;
 }


 /**
  *	flush_read_buffer - push buffer to userspace.
  *	@buffer:	data buffer for file.
  *	@buf:		user-passed buffer.
  *	@count:		number of bytes requested.
  *	@ppos:		file position.
  *
  *	Copy the buffer we filled in fill_read_buffer() to userspace.
  *	This is done at the reader's leisure, copying and advancing
  *	the amount they specify each time.
  *	This may be called continuously until the buffer is empty.
  */
 static int flush_read_buffer(struct sysfs_buffer * buffer, char __user * buf,
 			     size_t count, loff_t * ppos)
 {
 	int error;

 	if (*ppos > buffer->count)
 		return 0;

 	if (count > (buffer->count - *ppos))
 		count = buffer->count - *ppos;

 	error = copy_to_user(buf,buffer->page + *ppos,count);
 	if (!error)
 		*ppos += count;
 	return error ? -EFAULT : count;
 }

 /**
  *	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;

 	down(&buffer->sem);
 	if (buffer->needs_read_fill) {
 		if ((retval = fill_read_buffer(file->f_dentry,buffer)))
 			goto out;
 	}
 	pr_debug("%s: count = %d, ppos = %lld, buf = %s\n",
 		 __FUNCTION__,count,*ppos,buffer->page);
 	retval = flush_read_buffer(buffer,buf,count,ppos);
 out:
 	up(&buffer->sem);
 	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;
 	error = copy_from_user(buffer->page,buf,count);
 	buffer->needs_read_fill = 1;
 	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 attribute * attr = to_attr(dentry);
 	struct kobject * kobj = to_kobj(dentry->d_parent);
 	struct sysfs_ops * ops = buffer->ops;

 	return ops->store(kobj,attr,buffer->page,count);
 }


 /**
  *	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)
 {
 	struct sysfs_buffer * buffer = file->private_data;
 	ssize_t len;

 	down(&buffer->sem);
 	len = fill_write_buffer(buffer, buf, count);
 	if (len > 0)
 		len = flush_write_buffer(file->f_dentry, buffer, len);
 	if (len > 0)
 		*ppos += len;
 	up(&buffer->sem);
 	return len;
 }

 static int check_perm(struct inode * inode, struct file * file)
 {
 	struct kobject *kobj = sysfs_get_kobject(file->f_dentry->d_parent);
 	struct attribute * attr = to_attr(file->f_dentry);
 	struct sysfs_buffer * buffer;
 	struct sysfs_ops * ops = NULL;
 	int error = 0;

 	if (!kobj || !attr)
 		goto Einval;

 	/* Grab the module reference for this attribute if we have one */
 	if (!try_module_get(attr->owner)) {
 		error = -ENODEV;
 		goto Done;
 	}

 	/* if the kobject has no ktype, then we assume that it is a subsystem
 	 * itself, and use ops for it.
 	 */
 	if (kobj->kset && kobj->kset->ktype)
 		ops = kobj->kset->ktype->sysfs_ops;
 	else if (kobj->ktype)
 		ops = kobj->ktype->sysfs_ops;
 	else
 		ops = &subsys_sysfs_ops;

 	/* No sysfs operations, either from having no subsystem,
 	 * or the subsystem have no operations.
 	 */
 	if (!ops)
 		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)
 			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)
 			goto Eaccess;
 	}

 	/* No error? Great, allocate a buffer for the file, and store it
 	 * it in file->private_data for easy access.
 	 */
 	buffer = kmalloc(sizeof(struct sysfs_buffer),GFP_KERNEL);
 	if (buffer) {
 		memset(buffer,0,sizeof(struct sysfs_buffer));
 		init_MUTEX(&buffer->sem);
 		buffer->needs_read_fill = 1;
 		buffer->ops = ops;
 		file->private_data = buffer;
 	} else
 		error = -ENOMEM;
 	goto Done;

  Einval:
 	error = -EINVAL;
 	goto Done;
  Eaccess:
 	error = -EACCES;
 	module_put(attr->owner);
  Done:
 	if (error && kobj)
 		kobject_put(kobj);
 	return error;
 }

 static int sysfs_open_file(struct inode * inode, struct file * filp)
 {
 	return check_perm(inode,filp);
 }

 static int sysfs_release(struct inode * inode, struct file * filp)
 {
 	struct kobject * kobj = to_kobj(filp->f_dentry->d_parent);
 	struct attribute * attr = to_attr(filp->f_dentry);
 	struct module * owner = attr->owner;
 	struct sysfs_buffer * buffer = filp->private_data;

 	if (kobj)
 		kobject_put(kobj);
 	/* After this point, attr should not be accessed. */
 	module_put(owner);

 	if (buffer) {
 		if (buffer->page)
 			free_page((unsigned long)buffer->page);
 		kfree(buffer);
 	}
 	return 0;
 }

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


 int sysfs_add_file(struct dentry * dir, const struct attribute * attr, int type)
 {
 	struct sysfs_dirent * parent_sd = dir->d_fsdata;
 	umode_t mode = (attr->mode & S_IALLUGO) | S_IFREG;
 	int error = 0;

 	down(&dir->d_inode->i_sem);
 	error = sysfs_make_dirent(parent_sd, NULL, (void *) attr, mode, type);
 	up(&dir->d_inode->i_sem);

 	return error;
 }


 /**
  *	sysfs_create_file - create an attribute file for an object.
  *	@kobj:	object we're creating for.
  *	@attr:	atrribute descriptor.
  */

 int sysfs_create_file(struct kobject * kobj, const struct attribute * attr)
 {
 	BUG_ON(!kobj || !kobj->dentry || !attr);

 	return sysfs_add_file(kobj->dentry, attr, SYSFS_KOBJ_ATTR);

 }


 /**
  * sysfs_update_file - update the modified timestamp on an object attribute.
  * @kobj: object we're acting for.
  * @attr: attribute descriptor.
  *
  * Also call dnotify for the dentry, which lots of userspace programs
  * use.
  */
 int sysfs_update_file(struct kobject * kobj, const struct attribute * attr)
 {
 	struct dentry * dir = kobj->dentry;
 	struct dentry * victim;
 	int res = -ENOENT;

 	down(&dir->d_inode->i_sem);
 	victim = lookup_one_len(attr->name, dir, strlen(attr->name));
 	if (!IS_ERR(victim)) {
 		/* make sure dentry is really there */
 		if (victim->d_inode &&
 		    (victim->d_parent->d_inode == dir->d_inode)) {
 			victim->d_inode->i_mtime = CURRENT_TIME;
 			dnotify_parent(victim, DN_MODIFY);

 			/**
 			 * Drop reference from initial sysfs_get_dentry().
 			 */
 			dput(victim);
 			res = 0;
 		} else
 			d_drop(victim);

 		/**
 		 * Drop the reference acquired from sysfs_get_dentry() above.
 		 */
 		dput(victim);
 	}
 	up(&dir->d_inode->i_sem);

 	return res;
 }


 /**
  * sysfs_chmod_file - update the modified mode value on an object attribute.
  * @kobj: object we're acting for.
  * @attr: attribute descriptor.
  * @mode: file permissions.
  *
  */
 int sysfs_chmod_file(struct kobject *kobj, struct attribute *attr, mode_t mode)
 {
 	struct dentry *dir = kobj->dentry;
 	struct dentry *victim;
 	struct sysfs_dirent *sd;
 	umode_t umode = (mode & S_IALLUGO) | S_IFREG;
 	int res = -ENOENT;

 	down(&dir->d_inode->i_sem);
 	victim = lookup_one_len(attr->name, dir, strlen(attr->name));
 	if (!IS_ERR(victim)) {
 		if (victim->d_inode &&
 		    (victim->d_parent->d_inode == dir->d_inode)) {
 			sd = victim->d_fsdata;
 			attr->mode = mode;
 			sd->s_mode = umode;
 			victim->d_inode->i_mode = umode;
 			dput(victim);
 			res = 0;
 		}
 	}
 	up(&dir->d_inode->i_sem);

 	return res;
 }
 EXPORT_SYMBOL_GPL(sysfs_chmod_file);


 /**
  *	sysfs_remove_file - remove an object attribute.
  *	@kobj:	object we're acting for.
  *	@attr:	attribute descriptor.
  *
  *	Hash the attribute name and kill the victim.
  */

 void sysfs_remove_file(struct kobject * kobj, const struct attribute * attr)
 {
 	sysfs_hash_and_remove(kobj->dentry,attr->name);
 }


 EXPORT_SYMBOL_GPL(sysfs_create_file);
 EXPORT_SYMBOL_GPL(sysfs_remove_file);
 EXPORT_SYMBOL_GPL(sysfs_update_file);
	/*
	* file.c - operations for regular (text) files.
	*/

	#include <linux/module.h>
	#include <linux/dnotify.h>
	#include <linux/kobject.h>
	#include <linux/namei.h>
	#include <asm/uaccess.h>
	#include <asm/semaphore.h>

	#include "sysfs.h"

	#define to_subsys(k) container_of(k,struct subsystem,kset.kobj)
	#define to_sattr(a) container_of(a,struct subsys_attribute,attr)

	/*
	* Subsystem file operations.
	* These operations allow subsystems to have files that can be
	* read/written.
	*/
	static ssize_t
	subsys_attr_show(struct kobject * kobj, struct attribute * attr, char * page)
	{
	struct subsystem * s = to_subsys(kobj);
	struct subsys_attribute * sattr = to_sattr(attr);
	ssize_t ret = -EIO;

	if (sattr->show)
	ret = sattr->show(s,page);
	return ret;
	}

	static ssize_t
	subsys_attr_store(struct kobject * kobj, struct attribute * attr,
	const char * page, size_t count)
	{
	struct subsystem * s = to_subsys(kobj);
	struct subsys_attribute * sattr = to_sattr(attr);
	ssize_t ret = -EIO;

	if (sattr->store)
	ret = sattr->store(s,page,count);
	return ret;
	}

	static struct sysfs_ops subsys_sysfs_ops = {
	.show = subsys_attr_show,
	.store = subsys_attr_store,
	};


	struct sysfs_buffer {
	size_t count;
	loff_t pos;
	char * page;
	struct sysfs_ops * ops;
	struct semaphore sem;
	int needs_read_fill;
	};


	/**
	* 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.
	*/
	static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer)
	{
	struct attribute * attr = to_attr(dentry);
	struct kobject * kobj = to_kobj(dentry->d_parent);
	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;

	count = ops->show(kobj,attr,buffer->page);
	buffer->needs_read_fill = 0;
	BUG_ON(count > (ssize_t)PAGE_SIZE);
	if (count >= 0)
	buffer->count = count;
	else
	ret = count;
	return ret;
	}


	/**
	* flush_read_buffer - push buffer to userspace.
	* @buffer: data buffer for file.
	* @buf: user-passed buffer.
	* @count: number of bytes requested.
	* @ppos: file position.
	*
	* Copy the buffer we filled in fill_read_buffer() to userspace.
	* This is done at the reader's leisure, copying and advancing
	* the amount they specify each time.
	* This may be called continuously until the buffer is empty.
	*/
	static int flush_read_buffer(struct sysfs_buffer * buffer, char __user * buf,
	size_t count, loff_t * ppos)
	{
	int error;

	if (*ppos > buffer->count)
	return 0;

	if (count > (buffer->count - *ppos))
	count = buffer->count - *ppos;

	error = copy_to_user(buf,buffer->page + *ppos,count);
	if (!error)
	*ppos += count;
	return error ? -EFAULT : count;
	}

	/**
	* 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;

	down(&buffer->sem);
	if (buffer->needs_read_fill) {
	if ((retval = fill_read_buffer(file->f_dentry,buffer)))
	goto out;
	}
	pr_debug("%s: count = %d, ppos = %lld, buf = %s\n",
	__FUNCTION__,count,*ppos,buffer->page);
	retval = flush_read_buffer(buffer,buf,count,ppos);
	out:
	up(&buffer->sem);
	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;
	error = copy_from_user(buffer->page,buf,count);
	buffer->needs_read_fill = 1;
	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 attribute * attr = to_attr(dentry);
	struct kobject * kobj = to_kobj(dentry->d_parent);
	struct sysfs_ops * ops = buffer->ops;

	return ops->store(kobj,attr,buffer->page,count);
	}


	/**
	* 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)
	{
	struct sysfs_buffer * buffer = file->private_data;
	ssize_t len;

	down(&buffer->sem);
	len = fill_write_buffer(buffer, buf, count);
	if (len > 0)
	len = flush_write_buffer(file->f_dentry, buffer, len);
	if (len > 0)
	*ppos += len;
	up(&buffer->sem);
	return len;
	}

	static int check_perm(struct inode * inode, struct file * file)
	{
	struct kobject *kobj = sysfs_get_kobject(file->f_dentry->d_parent);
	struct attribute * attr = to_attr(file->f_dentry);
	struct sysfs_buffer * buffer;
	struct sysfs_ops * ops = NULL;
	int error = 0;

	if (!kobj \|\| !attr)
	goto Einval;

	/* Grab the module reference for this attribute if we have one */
	if (!try_module_get(attr->owner)) {
	error = -ENODEV;
	goto Done;
	}

	/* if the kobject has no ktype, then we assume that it is a subsystem
	* itself, and use ops for it.
	*/
	if (kobj->kset && kobj->kset->ktype)
	ops = kobj->kset->ktype->sysfs_ops;
	else if (kobj->ktype)
	ops = kobj->ktype->sysfs_ops;
	else
	ops = &subsys_sysfs_ops;

	/* No sysfs operations, either from having no subsystem,
	* or the subsystem have no operations.
	*/
	if (!ops)
	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)
	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)
	goto Eaccess;
	}

	/* No error? Great, allocate a buffer for the file, and store it
	* it in file->private_data for easy access.
	*/
	buffer = kmalloc(sizeof(struct sysfs_buffer),GFP_KERNEL);
	if (buffer) {
	memset(buffer,0,sizeof(struct sysfs_buffer));
	init_MUTEX(&buffer->sem);
	buffer->needs_read_fill = 1;
	buffer->ops = ops;
	file->private_data = buffer;
	} else
	error = -ENOMEM;
	goto Done;

	Einval:
	error = -EINVAL;
	goto Done;
	Eaccess:
	error = -EACCES;
	module_put(attr->owner);
	Done:
	if (error && kobj)
	kobject_put(kobj);
	return error;
	}

	static int sysfs_open_file(struct inode * inode, struct file * filp)
	{
	return check_perm(inode,filp);
	}

	static int sysfs_release(struct inode * inode, struct file * filp)
	{
	struct kobject * kobj = to_kobj(filp->f_dentry->d_parent);
	struct attribute * attr = to_attr(filp->f_dentry);
	struct module * owner = attr->owner;
	struct sysfs_buffer * buffer = filp->private_data;

	if (kobj)
	kobject_put(kobj);
	/* After this point, attr should not be accessed. */
	module_put(owner);

	if (buffer) {
	if (buffer->page)
	free_page((unsigned long)buffer->page);
	kfree(buffer);
	}
	return 0;
	}

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


	int sysfs_add_file(struct dentry * dir, const struct attribute * attr, int type)
	{
	struct sysfs_dirent * parent_sd = dir->d_fsdata;
	umode_t mode = (attr->mode & S_IALLUGO) \| S_IFREG;
	int error = 0;

	down(&dir->d_inode->i_sem);
	error = sysfs_make_dirent(parent_sd, NULL, (void *) attr, mode, type);
	up(&dir->d_inode->i_sem);

	return error;
	}


	/**
	* sysfs_create_file - create an attribute file for an object.
	* @kobj: object we're creating for.
	* @attr: atrribute descriptor.
	*/

	int sysfs_create_file(struct kobject * kobj, const struct attribute * attr)
	{
	BUG_ON(!kobj \|\| !kobj->dentry \|\| !attr);

	return sysfs_add_file(kobj->dentry, attr, SYSFS_KOBJ_ATTR);

	}


	/**
	* sysfs_update_file - update the modified timestamp on an object attribute.
	* @kobj: object we're acting for.
	* @attr: attribute descriptor.
	*
	* Also call dnotify for the dentry, which lots of userspace programs
	* use.
	*/
	int sysfs_update_file(struct kobject * kobj, const struct attribute * attr)
	{
	struct dentry * dir = kobj->dentry;
	struct dentry * victim;
	int res = -ENOENT;

	down(&dir->d_inode->i_sem);
	victim = lookup_one_len(attr->name, dir, strlen(attr->name));
	if (!IS_ERR(victim)) {
	/* make sure dentry is really there */
	if (victim->d_inode &&
	(victim->d_parent->d_inode == dir->d_inode)) {
	victim->d_inode->i_mtime = CURRENT_TIME;
	dnotify_parent(victim, DN_MODIFY);

	/**
	* Drop reference from initial sysfs_get_dentry().
	*/
	dput(victim);
	res = 0;
	} else
	d_drop(victim);

	/**
	* Drop the reference acquired from sysfs_get_dentry() above.
	*/
	dput(victim);
	}
	up(&dir->d_inode->i_sem);

	return res;
	}


	/**
	* sysfs_chmod_file - update the modified mode value on an object attribute.
	* @kobj: object we're acting for.
	* @attr: attribute descriptor.
	* @mode: file permissions.
	*
	*/
	int sysfs_chmod_file(struct kobject kobj, struct attribute attr, mode_t mode)
	{
	struct dentry *dir = kobj->dentry;
	struct dentry *victim;
	struct sysfs_dirent *sd;
	umode_t umode = (mode & S_IALLUGO) \| S_IFREG;
	int res = -ENOENT;

	down(&dir->d_inode->i_sem);
	victim = lookup_one_len(attr->name, dir, strlen(attr->name));
	if (!IS_ERR(victim)) {
	if (victim->d_inode &&
	(victim->d_parent->d_inode == dir->d_inode)) {
	sd = victim->d_fsdata;
	attr->mode = mode;
	sd->s_mode = umode;
	victim->d_inode->i_mode = umode;
	dput(victim);
	res = 0;
	}
	}
	up(&dir->d_inode->i_sem);

	return res;
	}
	EXPORT_SYMBOL_GPL(sysfs_chmod_file);


	/**
	* sysfs_remove_file - remove an object attribute.
	* @kobj: object we're acting for.
	* @attr: attribute descriptor.
	*
	* Hash the attribute name and kill the victim.
	*/

	void sysfs_remove_file(struct kobject * kobj, const struct attribute * attr)
	{
	sysfs_hash_and_remove(kobj->dentry,attr->name);
	}


	EXPORT_SYMBOL_GPL(sysfs_create_file);
	EXPORT_SYMBOL_GPL(sysfs_remove_file);
	EXPORT_SYMBOL_GPL(sysfs_update_file);