2 * fs/sysfs/file.c - sysfs regular (text) file implementation
4 * Copyright (c) 2001-3 Patrick Mochel
5 * Copyright (c) 2007 SUSE Linux Products GmbH
6 * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
8 * This file is released under the GPLv2.
10 * Please see Documentation/filesystems/sysfs.txt for more information.
13 #include <linux/module.h>
14 #include <linux/kobject.h>
15 #include <linux/kallsyms.h>
16 #include <linux/slab.h>
17 #include <linux/fsnotify.h>
18 #include <linux/namei.h>
19 #include <linux/poll.h>
20 #include <linux/list.h>
21 #include <linux/mutex.h>
22 #include <linux/limits.h>
23 #include <asm/uaccess.h>
28 * There's one sysfs_buffer for each open file and one
29 * sysfs_open_dirent for each sysfs_dirent with one or more open
32 * filp->private_data points to sysfs_buffer and
33 * sysfs_dirent->s_attr.open points to sysfs_open_dirent. s_attr.open
34 * is protected by sysfs_open_dirent_lock.
36 static DEFINE_SPINLOCK(sysfs_open_dirent_lock);
38 struct sysfs_open_dirent {
41 wait_queue_head_t poll;
42 struct list_head buffers; /* goes through sysfs_buffer.list */
49 const struct sysfs_ops *ops;
53 struct list_head list;
57 * fill_read_buffer - allocate and fill buffer from object.
58 * @dentry: dentry pointer.
59 * @buffer: data buffer for file.
61 * Allocate @buffer->page, if it hasn't been already, then call the
62 * kobject's show() method to fill the buffer with this attribute's
64 * This is called only once, on the file's first read unless an error
67 static int fill_read_buffer(struct dentry *dentry, struct sysfs_buffer *buffer)
69 struct sysfs_dirent *attr_sd = dentry->d_fsdata;
70 struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
71 const struct sysfs_ops *ops = buffer->ops;
76 buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
80 /* need attr_sd for attr and ops, its parent for kobj */
81 if (!sysfs_get_active(attr_sd))
84 buffer->event = atomic_read(&attr_sd->s_attr.open->event);
85 count = ops->show(kobj, attr_sd->s_attr.attr, buffer->page);
87 sysfs_put_active(attr_sd);
90 * The code works fine with PAGE_SIZE return but it's likely to
91 * indicate truncated result or overflow in normal use cases.
93 if (count >= (ssize_t)PAGE_SIZE) {
94 print_symbol("fill_read_buffer: %s returned bad count\n",
95 (unsigned long)ops->show);
96 /* Try to struggle along */
97 count = PAGE_SIZE - 1;
100 buffer->needs_read_fill = 0;
101 buffer->count = count;
109 * sysfs_read_file - read an attribute.
110 * @file: file pointer.
111 * @buf: buffer to fill.
112 * @count: number of bytes to read.
113 * @ppos: starting offset in file.
115 * Userspace wants to read an attribute file. The attribute descriptor
116 * is in the file's ->d_fsdata. The target object is in the directory's
119 * We call fill_read_buffer() to allocate and fill the buffer from the
120 * object's show() method exactly once (if the read is happening from
121 * the beginning of the file). That should fill the entire buffer with
122 * all the data the object has to offer for that attribute.
123 * We then call flush_read_buffer() to copy the buffer to userspace
124 * in the increments specified.
128 sysfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
130 struct sysfs_buffer *buffer = file->private_data;
133 mutex_lock(&buffer->mutex);
134 if (buffer->needs_read_fill || *ppos == 0) {
135 retval = fill_read_buffer(file->f_path.dentry, buffer);
139 pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n",
140 __func__, count, *ppos, buffer->page);
141 retval = simple_read_from_buffer(buf, count, ppos, buffer->page,
144 mutex_unlock(&buffer->mutex);
149 * fill_write_buffer - copy buffer from userspace.
150 * @buffer: data buffer for file.
151 * @buf: data from user.
152 * @count: number of bytes in @userbuf.
154 * Allocate @buffer->page if it hasn't been already, then
155 * copy the user-supplied buffer into it.
157 static int fill_write_buffer(struct sysfs_buffer *buffer,
158 const char __user *buf, size_t count)
163 buffer->page = (char *)get_zeroed_page(GFP_KERNEL);
167 if (count >= PAGE_SIZE)
168 count = PAGE_SIZE - 1;
169 error = copy_from_user(buffer->page, buf, count);
170 buffer->needs_read_fill = 1;
171 /* if buf is assumed to contain a string, terminate it by \0,
172 so e.g. sscanf() can scan the string easily */
173 buffer->page[count] = 0;
174 return error ? -EFAULT : count;
179 * flush_write_buffer - push buffer to kobject.
180 * @dentry: dentry to the attribute
181 * @buffer: data buffer for file.
182 * @count: number of bytes
184 * Get the correct pointers for the kobject and the attribute we're
185 * dealing with, then call the store() method for the attribute,
186 * passing the buffer that we acquired in fill_write_buffer().
189 flush_write_buffer(struct dentry *dentry, struct sysfs_buffer *buffer, size_t count)
191 struct sysfs_dirent *attr_sd = dentry->d_fsdata;
192 struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
193 const struct sysfs_ops *ops = buffer->ops;
196 /* need attr_sd for attr and ops, its parent for kobj */
197 if (!sysfs_get_active(attr_sd))
200 rc = ops->store(kobj, attr_sd->s_attr.attr, buffer->page, count);
202 sysfs_put_active(attr_sd);
209 * sysfs_write_file - write an attribute.
210 * @file: file pointer
211 * @buf: data to write
212 * @count: number of bytes
213 * @ppos: starting offset
215 * Similar to sysfs_read_file(), though working in the opposite direction.
216 * We allocate and fill the data from the user in fill_write_buffer(),
217 * then push it to the kobject in flush_write_buffer().
218 * There is no easy way for us to know if userspace is only doing a partial
219 * write, so we don't support them. We expect the entire buffer to come
220 * on the first write.
221 * Hint: if you're writing a value, first read the file, modify only the
222 * the value you're changing, then write entire buffer back.
226 sysfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
228 struct sysfs_buffer *buffer = file->private_data;
231 mutex_lock(&buffer->mutex);
232 len = fill_write_buffer(buffer, buf, count);
234 len = flush_write_buffer(file->f_path.dentry, buffer, len);
237 mutex_unlock(&buffer->mutex);
242 * sysfs_get_open_dirent - get or create sysfs_open_dirent
243 * @sd: target sysfs_dirent
244 * @buffer: sysfs_buffer for this instance of open
246 * If @sd->s_attr.open exists, increment its reference count;
247 * otherwise, create one. @buffer is chained to the buffers
251 * Kernel thread context (may sleep).
254 * 0 on success, -errno on failure.
256 static int sysfs_get_open_dirent(struct sysfs_dirent *sd,
257 struct sysfs_buffer *buffer)
259 struct sysfs_open_dirent *od, *new_od = NULL;
262 spin_lock_irq(&sysfs_open_dirent_lock);
264 if (!sd->s_attr.open && new_od) {
265 sd->s_attr.open = new_od;
269 od = sd->s_attr.open;
271 atomic_inc(&od->refcnt);
272 list_add_tail(&buffer->list, &od->buffers);
275 spin_unlock_irq(&sysfs_open_dirent_lock);
282 /* not there, initialize a new one and retry */
283 new_od = kmalloc(sizeof(*new_od), GFP_KERNEL);
287 atomic_set(&new_od->refcnt, 0);
288 atomic_set(&new_od->event, 1);
289 init_waitqueue_head(&new_od->poll);
290 INIT_LIST_HEAD(&new_od->buffers);
295 * sysfs_put_open_dirent - put sysfs_open_dirent
296 * @sd: target sysfs_dirent
297 * @buffer: associated sysfs_buffer
299 * Put @sd->s_attr.open and unlink @buffer from the buffers list.
300 * If reference count reaches zero, disassociate and free it.
305 static void sysfs_put_open_dirent(struct sysfs_dirent *sd,
306 struct sysfs_buffer *buffer)
308 struct sysfs_open_dirent *od = sd->s_attr.open;
311 spin_lock_irqsave(&sysfs_open_dirent_lock, flags);
313 list_del(&buffer->list);
314 if (atomic_dec_and_test(&od->refcnt))
315 sd->s_attr.open = NULL;
319 spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags);
324 static int sysfs_open_file(struct inode *inode, struct file *file)
326 struct sysfs_dirent *attr_sd = file->f_path.dentry->d_fsdata;
327 struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
328 struct sysfs_buffer *buffer;
329 const struct sysfs_ops *ops;
332 /* need attr_sd for attr and ops, its parent for kobj */
333 if (!sysfs_get_active(attr_sd))
336 /* every kobject with an attribute needs a ktype assigned */
337 if (kobj->ktype && kobj->ktype->sysfs_ops)
338 ops = kobj->ktype->sysfs_ops;
340 WARN(1, KERN_ERR "missing sysfs attribute operations for "
341 "kobject: %s\n", kobject_name(kobj));
345 /* File needs write support.
346 * The inode's perms must say it's ok,
347 * and we must have a store method.
349 if (file->f_mode & FMODE_WRITE) {
350 if (!(inode->i_mode & S_IWUGO) || !ops->store)
354 /* File needs read support.
355 * The inode's perms must say it's ok, and we there
356 * must be a show method for it.
358 if (file->f_mode & FMODE_READ) {
359 if (!(inode->i_mode & S_IRUGO) || !ops->show)
363 /* No error? Great, allocate a buffer for the file, and store it
364 * it in file->private_data for easy access.
367 buffer = kzalloc(sizeof(struct sysfs_buffer), GFP_KERNEL);
371 mutex_init(&buffer->mutex);
372 buffer->needs_read_fill = 1;
374 file->private_data = buffer;
376 /* make sure we have open dirent struct */
377 error = sysfs_get_open_dirent(attr_sd, buffer);
381 /* open succeeded, put active references */
382 sysfs_put_active(attr_sd);
388 sysfs_put_active(attr_sd);
392 static int sysfs_release(struct inode *inode, struct file *filp)
394 struct sysfs_dirent *sd = filp->f_path.dentry->d_fsdata;
395 struct sysfs_buffer *buffer = filp->private_data;
397 sysfs_put_open_dirent(sd, buffer);
400 free_page((unsigned long)buffer->page);
406 /* Sysfs attribute files are pollable. The idea is that you read
407 * the content and then you use 'poll' or 'select' to wait for
408 * the content to change. When the content changes (assuming the
409 * manager for the kobject supports notification), poll will
410 * return POLLERR|POLLPRI, and select will return the fd whether
411 * it is waiting for read, write, or exceptions.
412 * Once poll/select indicates that the value has changed, you
413 * need to close and re-open the file, or seek to 0 and read again.
414 * Reminder: this only works for attributes which actively support
415 * it, and it is not possible to test an attribute from userspace
416 * to see if it supports poll (Neither 'poll' nor 'select' return
417 * an appropriate error code). When in doubt, set a suitable timeout value.
419 static unsigned int sysfs_poll(struct file *filp, poll_table *wait)
421 struct sysfs_buffer *buffer = filp->private_data;
422 struct sysfs_dirent *attr_sd = filp->f_path.dentry->d_fsdata;
423 struct sysfs_open_dirent *od = attr_sd->s_attr.open;
425 /* need parent for the kobj, grab both */
426 if (!sysfs_get_active(attr_sd))
429 poll_wait(filp, &od->poll, wait);
431 sysfs_put_active(attr_sd);
433 if (buffer->event != atomic_read(&od->event))
436 return DEFAULT_POLLMASK;
439 buffer->needs_read_fill = 1;
440 return DEFAULT_POLLMASK|POLLERR|POLLPRI;
443 void sysfs_notify_dirent(struct sysfs_dirent *sd)
445 struct sysfs_open_dirent *od;
448 spin_lock_irqsave(&sysfs_open_dirent_lock, flags);
450 if (!WARN_ON(sysfs_type(sd) != SYSFS_KOBJ_ATTR)) {
451 od = sd->s_attr.open;
453 atomic_inc(&od->event);
454 wake_up_interruptible(&od->poll);
458 spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags);
460 EXPORT_SYMBOL_GPL(sysfs_notify_dirent);
462 void sysfs_notify(struct kobject *k, const char *dir, const char *attr)
464 struct sysfs_dirent *sd = k->sd;
466 mutex_lock(&sysfs_mutex);
469 sd = sysfs_find_dirent(sd, NULL, dir);
471 sd = sysfs_find_dirent(sd, NULL, attr);
473 sysfs_notify_dirent(sd);
475 mutex_unlock(&sysfs_mutex);
477 EXPORT_SYMBOL_GPL(sysfs_notify);
479 const struct file_operations sysfs_file_operations = {
480 .read = sysfs_read_file,
481 .write = sysfs_write_file,
482 .llseek = generic_file_llseek,
483 .open = sysfs_open_file,
484 .release = sysfs_release,
488 static int sysfs_attr_ns(struct kobject *kobj, const struct attribute *attr,
491 struct sysfs_dirent *dir_sd = kobj->sd;
492 const struct sysfs_ops *ops;
493 const void *ns = NULL;
497 WARN(1, KERN_ERR "sysfs: kobject %s without dirent\n",
503 if (!sysfs_ns_type(dir_sd))
509 ops = kobj->ktype->sysfs_ops;
516 ns = ops->namespace(kobj, attr);
519 WARN(1, KERN_ERR "missing sysfs namespace attribute operation for "
520 "kobject: %s\n", kobject_name(kobj));
526 int sysfs_add_file_mode(struct sysfs_dirent *dir_sd,
527 const struct attribute *attr, int type, umode_t amode)
529 umode_t mode = (amode & S_IALLUGO) | S_IFREG;
530 struct sysfs_addrm_cxt acxt;
531 struct sysfs_dirent *sd;
535 rc = sysfs_attr_ns(dir_sd->s_dir.kobj, attr, &ns);
539 sd = sysfs_new_dirent(attr->name, mode, type);
544 sd->s_attr.attr = (void *)attr;
545 sysfs_dirent_init_lockdep(sd);
547 sysfs_addrm_start(&acxt, dir_sd);
548 rc = sysfs_add_one(&acxt, sd);
549 sysfs_addrm_finish(&acxt);
558 int sysfs_add_file(struct sysfs_dirent *dir_sd, const struct attribute *attr,
561 return sysfs_add_file_mode(dir_sd, attr, type, attr->mode);
566 * sysfs_create_file - create an attribute file for an object.
567 * @kobj: object we're creating for.
568 * @attr: attribute descriptor.
570 int sysfs_create_file(struct kobject *kobj, const struct attribute *attr)
572 BUG_ON(!kobj || !kobj->sd || !attr);
574 return sysfs_add_file(kobj->sd, attr, SYSFS_KOBJ_ATTR);
577 EXPORT_SYMBOL_GPL(sysfs_create_file);
579 int sysfs_create_files(struct kobject *kobj, const struct attribute **ptr)
584 for (i = 0; ptr[i] && !err; i++)
585 err = sysfs_create_file(kobj, ptr[i]);
588 sysfs_remove_file(kobj, ptr[i]);
591 EXPORT_SYMBOL_GPL(sysfs_create_files);
594 * sysfs_add_file_to_group - add an attribute file to a pre-existing group.
595 * @kobj: object we're acting for.
596 * @attr: attribute descriptor.
597 * @group: group name.
599 int sysfs_add_file_to_group(struct kobject *kobj,
600 const struct attribute *attr, const char *group)
602 struct sysfs_dirent *dir_sd;
606 dir_sd = sysfs_get_dirent(kobj->sd, NULL, group);
608 dir_sd = sysfs_get(kobj->sd);
613 error = sysfs_add_file(dir_sd, attr, SYSFS_KOBJ_ATTR);
618 EXPORT_SYMBOL_GPL(sysfs_add_file_to_group);
621 * sysfs_chmod_file - update the modified mode value on an object attribute.
622 * @kobj: object we're acting for.
623 * @attr: attribute descriptor.
624 * @mode: file permissions.
627 int sysfs_chmod_file(struct kobject *kobj, const struct attribute *attr,
630 struct sysfs_dirent *sd;
631 struct iattr newattrs;
635 rc = sysfs_attr_ns(kobj, attr, &ns);
639 mutex_lock(&sysfs_mutex);
642 sd = sysfs_find_dirent(kobj->sd, ns, attr->name);
646 newattrs.ia_mode = (mode & S_IALLUGO) | (sd->s_mode & ~S_IALLUGO);
647 newattrs.ia_valid = ATTR_MODE;
648 rc = sysfs_sd_setattr(sd, &newattrs);
651 mutex_unlock(&sysfs_mutex);
654 EXPORT_SYMBOL_GPL(sysfs_chmod_file);
657 * sysfs_remove_file - remove an object attribute.
658 * @kobj: object we're acting for.
659 * @attr: attribute descriptor.
661 * Hash the attribute name and kill the victim.
663 void sysfs_remove_file(struct kobject *kobj, const struct attribute *attr)
667 if (sysfs_attr_ns(kobj, attr, &ns))
670 sysfs_hash_and_remove(kobj->sd, ns, attr->name);
672 EXPORT_SYMBOL_GPL(sysfs_remove_file);
674 void sysfs_remove_files(struct kobject *kobj, const struct attribute **ptr)
677 for (i = 0; ptr[i]; i++)
678 sysfs_remove_file(kobj, ptr[i]);
680 EXPORT_SYMBOL_GPL(sysfs_remove_files);
683 * sysfs_remove_file_from_group - remove an attribute file from a group.
684 * @kobj: object we're acting for.
685 * @attr: attribute descriptor.
686 * @group: group name.
688 void sysfs_remove_file_from_group(struct kobject *kobj,
689 const struct attribute *attr, const char *group)
691 struct sysfs_dirent *dir_sd;
694 dir_sd = sysfs_get_dirent(kobj->sd, NULL, group);
696 dir_sd = sysfs_get(kobj->sd);
698 sysfs_hash_and_remove(dir_sd, NULL, attr->name);
702 EXPORT_SYMBOL_GPL(sysfs_remove_file_from_group);
704 struct sysfs_schedule_callback_struct {
705 struct list_head workq_list;
706 struct kobject *kobj;
707 void (*func)(void *);
709 struct module *owner;
710 struct work_struct work;
713 static struct workqueue_struct *sysfs_workqueue;
714 static DEFINE_MUTEX(sysfs_workq_mutex);
715 static LIST_HEAD(sysfs_workq);
716 static void sysfs_schedule_callback_work(struct work_struct *work)
718 struct sysfs_schedule_callback_struct *ss = container_of(work,
719 struct sysfs_schedule_callback_struct, work);
721 (ss->func)(ss->data);
722 kobject_put(ss->kobj);
723 module_put(ss->owner);
724 mutex_lock(&sysfs_workq_mutex);
725 list_del(&ss->workq_list);
726 mutex_unlock(&sysfs_workq_mutex);
731 * sysfs_schedule_callback - helper to schedule a callback for a kobject
732 * @kobj: object we're acting for.
733 * @func: callback function to invoke later.
734 * @data: argument to pass to @func.
735 * @owner: module owning the callback code
737 * sysfs attribute methods must not unregister themselves or their parent
738 * kobject (which would amount to the same thing). Attempts to do so will
739 * deadlock, since unregistration is mutually exclusive with driver
742 * Instead methods can call this routine, which will attempt to allocate
743 * and schedule a workqueue request to call back @func with @data as its
744 * argument in the workqueue's process context. @kobj will be pinned
745 * until @func returns.
747 * Returns 0 if the request was submitted, -ENOMEM if storage could not
748 * be allocated, -ENODEV if a reference to @owner isn't available,
749 * -EAGAIN if a callback has already been scheduled for @kobj.
751 int sysfs_schedule_callback(struct kobject *kobj, void (*func)(void *),
752 void *data, struct module *owner)
754 struct sysfs_schedule_callback_struct *ss, *tmp;
756 if (!try_module_get(owner))
759 mutex_lock(&sysfs_workq_mutex);
760 list_for_each_entry_safe(ss, tmp, &sysfs_workq, workq_list)
761 if (ss->kobj == kobj) {
763 mutex_unlock(&sysfs_workq_mutex);
766 mutex_unlock(&sysfs_workq_mutex);
768 if (sysfs_workqueue == NULL) {
769 sysfs_workqueue = create_singlethread_workqueue("sysfsd");
770 if (sysfs_workqueue == NULL) {
776 ss = kmalloc(sizeof(*ss), GFP_KERNEL);
786 INIT_WORK(&ss->work, sysfs_schedule_callback_work);
787 INIT_LIST_HEAD(&ss->workq_list);
788 mutex_lock(&sysfs_workq_mutex);
789 list_add_tail(&ss->workq_list, &sysfs_workq);
790 mutex_unlock(&sysfs_workq_mutex);
791 queue_work(sysfs_workqueue, &ss->work);
794 EXPORT_SYMBOL_GPL(sysfs_schedule_callback);