path: root/fs/sysfs/file.c

/*
 * 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 <linux/uaccess.h>
#include <linux/seq_file.h>
#include <linux/mm.h>

#include "sysfs.h"

/*
 * There's one sysfs_open_file for each open file and one sysfs_open_dirent
 * for each sysfs_dirent with one or more open files.
 *
 * sysfs_dirent->s_attr.open points to sysfs_open_dirent.  s_attr.open is
 * protected by sysfs_open_dirent_lock.
 *
 * filp->private_data points to seq_file whose ->private points to
 * sysfs_open_file.  sysfs_open_files are chained at
 * sysfs_open_dirent->files, which is protected by sysfs_open_file_mutex.
 */
static DEFINE_SPINLOCK(sysfs_open_dirent_lock);
static DEFINE_MUTEX(sysfs_open_file_mutex);

struct sysfs_open_dirent {
	atomic_t		refcnt;
	atomic_t		event;
	wait_queue_head_t	poll;
	struct list_head	files; /* goes through sysfs_open_file.list */
};

struct sysfs_open_file {
	struct sysfs_dirent	*sd;
	struct file		*file;
	struct mutex		mutex;
	int			event;
	struct list_head	list;

	bool			mmapped;
	const struct vm_operations_struct *vm_ops;
};

static bool sysfs_is_bin(struct sysfs_dirent *sd)
{
	return sysfs_type(sd) == SYSFS_KOBJ_BIN_ATTR;
}

static struct sysfs_open_file *sysfs_of(struct file *file)
{
	return ((struct seq_file *)file->private_data)->private;
}

/*
 * Determine ktype->sysfs_ops for the given sysfs_dirent.  This function
 * must be called while holding an active reference.
 */
static const struct sysfs_ops *sysfs_file_ops(struct sysfs_dirent *sd)
{
	struct kobject *kobj = sd->s_parent->s_dir.kobj;

	if (!sysfs_ignore_lockdep(sd))
		lockdep_assert_held(sd);
	return kobj->ktype ? kobj->ktype->sysfs_ops : NULL;
}

/*
 * Reads on sysfs are handled through seq_file, which takes care of hairy
 * details like buffering and seeking.  The following function pipes
 * sysfs_ops->show() result through seq_file.
 */
static int sysfs_seq_show(struct seq_file *sf, void *v)
{
	struct sysfs_open_file *of = sf->private;
	struct kobject *kobj = of->sd->s_parent->s_dir.kobj;
	const struct sysfs_ops *ops;
	char *buf;
	ssize_t count;

	/* acquire buffer and ensure that it's >= PAGE_SIZE */
	count = seq_get_buf(sf, &buf);
	if (count < PAGE_SIZE) {
		seq_commit(sf, -1);
		return 0;
	}

	/*
	 * Need @of->sd for attr and ops, its parent for kobj.  @of->mutex
	 * nests outside active ref and is just to ensure that the ops
	 * aren't called concurrently for the same open file.
	 */
	mutex_lock(&of->mutex);
	if (!sysfs_get_active(of->sd)) {
		mutex_unlock(&of->mutex);
		return -ENODEV;
	}

	of->event = atomic_read(&of->sd->s_attr.open->event);

	/*
	 * Lookup @ops and invoke show().  Control may reach here via seq
	 * file lseek even if @ops->show() isn't implemented.
	 */
	ops = sysfs_file_ops(of->sd);
	if (ops->show)
		count = ops->show(kobj, of->sd->s_attr.attr, buf);
	else
		count = 0;

	sysfs_put_active(of->sd);
	mutex_unlock(&of->mutex);

	if (count < 0)
		return count;

	/*
	 * 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;
	}
	seq_commit(sf, count);
	return 0;
}