xref: /openbmc/linux/fs/sysfs/file.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
1 /*
2  * file.c - operations for regular (text) files.
3  */
4 
5 #include <linux/module.h>
6 #include <linux/fsnotify.h>
7 #include <linux/kobject.h>
8 #include <linux/namei.h>
9 #include <linux/poll.h>
10 #include <linux/list.h>
11 #include <asm/uaccess.h>
12 #include <asm/semaphore.h>
13 
14 #include "sysfs.h"
15 
16 #define to_sattr(a) container_of(a,struct subsys_attribute, attr)
17 
18 /*
19  * Subsystem file operations.
20  * These operations allow subsystems to have files that can be
21  * read/written.
22  */
23 static ssize_t
24 subsys_attr_show(struct kobject * kobj, struct attribute * attr, char * page)
25 {
26 	struct kset *kset = to_kset(kobj);
27 	struct subsys_attribute * sattr = to_sattr(attr);
28 	ssize_t ret = -EIO;
29 
30 	if (sattr->show)
31 		ret = sattr->show(kset, page);
32 	return ret;
33 }
34 
35 static ssize_t
36 subsys_attr_store(struct kobject * kobj, struct attribute * attr,
37 		  const char * page, size_t count)
38 {
39 	struct kset *kset = to_kset(kobj);
40 	struct subsys_attribute * sattr = to_sattr(attr);
41 	ssize_t ret = -EIO;
42 
43 	if (sattr->store)
44 		ret = sattr->store(kset, page, count);
45 	return ret;
46 }
47 
48 static struct sysfs_ops subsys_sysfs_ops = {
49 	.show	= subsys_attr_show,
50 	.store	= subsys_attr_store,
51 };
52 
53 /**
54  *	add_to_collection - add buffer to a collection
55  *	@buffer:	buffer to be added
56  *	@node:		inode of set to add to
57  */
58 
59 static inline void
60 add_to_collection(struct sysfs_buffer *buffer, struct inode *node)
61 {
62 	struct sysfs_buffer_collection *set = node->i_private;
63 
64 	mutex_lock(&node->i_mutex);
65 	list_add(&buffer->associates, &set->associates);
66 	mutex_unlock(&node->i_mutex);
67 }
68 
69 static inline void
70 remove_from_collection(struct sysfs_buffer *buffer, struct inode *node)
71 {
72 	mutex_lock(&node->i_mutex);
73 	list_del(&buffer->associates);
74 	mutex_unlock(&node->i_mutex);
75 }
76 
77 /**
78  *	fill_read_buffer - allocate and fill buffer from object.
79  *	@dentry:	dentry pointer.
80  *	@buffer:	data buffer for file.
81  *
82  *	Allocate @buffer->page, if it hasn't been already, then call the
83  *	kobject's show() method to fill the buffer with this attribute's
84  *	data.
85  *	This is called only once, on the file's first read unless an error
86  *	is returned.
87  */
88 static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer)
89 {
90 	struct sysfs_dirent * sd = dentry->d_fsdata;
91 	struct attribute * attr = to_attr(dentry);
92 	struct kobject * kobj = to_kobj(dentry->d_parent);
93 	struct sysfs_ops * ops = buffer->ops;
94 	int ret = 0;
95 	ssize_t count;
96 
97 	if (!buffer->page)
98 		buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
99 	if (!buffer->page)
100 		return -ENOMEM;
101 
102 	buffer->event = atomic_read(&sd->s_event);
103 	count = ops->show(kobj,attr,buffer->page);
104 	BUG_ON(count > (ssize_t)PAGE_SIZE);
105 	if (count >= 0) {
106 		buffer->needs_read_fill = 0;
107 		buffer->count = count;
108 	} else {
109 		ret = count;
110 	}
111 	return ret;
112 }
113 
114 /**
115  *	sysfs_read_file - read an attribute.
116  *	@file:	file pointer.
117  *	@buf:	buffer to fill.
118  *	@count:	number of bytes to read.
119  *	@ppos:	starting offset in file.
120  *
121  *	Userspace wants to read an attribute file. The attribute descriptor
122  *	is in the file's ->d_fsdata. The target object is in the directory's
123  *	->d_fsdata.
124  *
125  *	We call fill_read_buffer() to allocate and fill the buffer from the
126  *	object's show() method exactly once (if the read is happening from
127  *	the beginning of the file). That should fill the entire buffer with
128  *	all the data the object has to offer for that attribute.
129  *	We then call flush_read_buffer() to copy the buffer to userspace
130  *	in the increments specified.
131  */
132 
133 static ssize_t
134 sysfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
135 {
136 	struct sysfs_buffer * buffer = file->private_data;
137 	ssize_t retval = 0;
138 
139 	down(&buffer->sem);
140 	if (buffer->needs_read_fill) {
141 		if (buffer->orphaned)
142 			retval = -ENODEV;
143 		else
144 			retval = fill_read_buffer(file->f_path.dentry,buffer);
145 		if (retval)
146 			goto out;
147 	}
148 	pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n",
149 		 __FUNCTION__, count, *ppos, buffer->page);
150 	retval = simple_read_from_buffer(buf, count, ppos, buffer->page,
151 					 buffer->count);
152 out:
153 	up(&buffer->sem);
154 	return retval;
155 }
156 
157 /**
158  *	fill_write_buffer - copy buffer from userspace.
159  *	@buffer:	data buffer for file.
160  *	@buf:		data from user.
161  *	@count:		number of bytes in @userbuf.
162  *
163  *	Allocate @buffer->page if it hasn't been already, then
164  *	copy the user-supplied buffer into it.
165  */
166 
167 static int
168 fill_write_buffer(struct sysfs_buffer * buffer, const char __user * buf, size_t count)
169 {
170 	int error;
171 
172 	if (!buffer->page)
173 		buffer->page = (char *)get_zeroed_page(GFP_KERNEL);
174 	if (!buffer->page)
175 		return -ENOMEM;
176 
177 	if (count >= PAGE_SIZE)
178 		count = PAGE_SIZE - 1;
179 	error = copy_from_user(buffer->page,buf,count);
180 	buffer->needs_read_fill = 1;
181 	/* if buf is assumed to contain a string, terminate it by \0,
182 	   so e.g. sscanf() can scan the string easily */
183 	buffer->page[count] = 0;
184 	return error ? -EFAULT : count;
185 }
186 
187 
188 /**
189  *	flush_write_buffer - push buffer to kobject.
190  *	@dentry:	dentry to the attribute
191  *	@buffer:	data buffer for file.
192  *	@count:		number of bytes
193  *
194  *	Get the correct pointers for the kobject and the attribute we're
195  *	dealing with, then call the store() method for the attribute,
196  *	passing the buffer that we acquired in fill_write_buffer().
197  */
198 
199 static int
200 flush_write_buffer(struct dentry * dentry, struct sysfs_buffer * buffer, size_t count)
201 {
202 	struct attribute * attr = to_attr(dentry);
203 	struct kobject * kobj = to_kobj(dentry->d_parent);
204 	struct sysfs_ops * ops = buffer->ops;
205 
206 	return ops->store(kobj,attr,buffer->page,count);
207 }
208 
209 
210 /**
211  *	sysfs_write_file - write an attribute.
212  *	@file:	file pointer
213  *	@buf:	data to write
214  *	@count:	number of bytes
215  *	@ppos:	starting offset
216  *
217  *	Similar to sysfs_read_file(), though working in the opposite direction.
218  *	We allocate and fill the data from the user in fill_write_buffer(),
219  *	then push it to the kobject in flush_write_buffer().
220  *	There is no easy way for us to know if userspace is only doing a partial
221  *	write, so we don't support them. We expect the entire buffer to come
222  *	on the first write.
223  *	Hint: if you're writing a value, first read the file, modify only the
224  *	the value you're changing, then write entire buffer back.
225  */
226 
227 static ssize_t
228 sysfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
229 {
230 	struct sysfs_buffer * buffer = file->private_data;
231 	ssize_t len;
232 
233 	down(&buffer->sem);
234 	if (buffer->orphaned) {
235 		len = -ENODEV;
236 		goto out;
237 	}
238 	len = fill_write_buffer(buffer, buf, count);
239 	if (len > 0)
240 		len = flush_write_buffer(file->f_path.dentry, buffer, len);
241 	if (len > 0)
242 		*ppos += len;
243 out:
244 	up(&buffer->sem);
245 	return len;
246 }
247 
248 static int sysfs_open_file(struct inode *inode, struct file *file)
249 {
250 	struct kobject *kobj = sysfs_get_kobject(file->f_path.dentry->d_parent);
251 	struct attribute * attr = to_attr(file->f_path.dentry);
252 	struct sysfs_buffer_collection *set;
253 	struct sysfs_buffer * buffer;
254 	struct sysfs_ops * ops = NULL;
255 	int error = 0;
256 
257 	if (!kobj || !attr)
258 		goto Einval;
259 
260 	/* Grab the module reference for this attribute if we have one */
261 	if (!try_module_get(attr->owner)) {
262 		error = -ENODEV;
263 		goto Done;
264 	}
265 
266 	/* if the kobject has no ktype, then we assume that it is a subsystem
267 	 * itself, and use ops for it.
268 	 */
269 	if (kobj->kset && kobj->kset->ktype)
270 		ops = kobj->kset->ktype->sysfs_ops;
271 	else if (kobj->ktype)
272 		ops = kobj->ktype->sysfs_ops;
273 	else
274 		ops = &subsys_sysfs_ops;
275 
276 	/* No sysfs operations, either from having no subsystem,
277 	 * or the subsystem have no operations.
278 	 */
279 	if (!ops)
280 		goto Eaccess;
281 
282 	/* make sure we have a collection to add our buffers to */
283 	mutex_lock(&inode->i_mutex);
284 	if (!(set = inode->i_private)) {
285 		if (!(set = inode->i_private = kmalloc(sizeof(struct sysfs_buffer_collection), GFP_KERNEL))) {
286 			error = -ENOMEM;
287 			goto Done;
288 		} else {
289 			INIT_LIST_HEAD(&set->associates);
290 		}
291 	}
292 	mutex_unlock(&inode->i_mutex);
293 
294 	/* File needs write support.
295 	 * The inode's perms must say it's ok,
296 	 * and we must have a store method.
297 	 */
298 	if (file->f_mode & FMODE_WRITE) {
299 
300 		if (!(inode->i_mode & S_IWUGO) || !ops->store)
301 			goto Eaccess;
302 
303 	}
304 
305 	/* File needs read support.
306 	 * The inode's perms must say it's ok, and we there
307 	 * must be a show method for it.
308 	 */
309 	if (file->f_mode & FMODE_READ) {
310 		if (!(inode->i_mode & S_IRUGO) || !ops->show)
311 			goto Eaccess;
312 	}
313 
314 	/* No error? Great, allocate a buffer for the file, and store it
315 	 * it in file->private_data for easy access.
316 	 */
317 	buffer = kzalloc(sizeof(struct sysfs_buffer), GFP_KERNEL);
318 	if (buffer) {
319 		INIT_LIST_HEAD(&buffer->associates);
320 		init_MUTEX(&buffer->sem);
321 		buffer->needs_read_fill = 1;
322 		buffer->ops = ops;
323 		add_to_collection(buffer, inode);
324 		file->private_data = buffer;
325 	} else
326 		error = -ENOMEM;
327 	goto Done;
328 
329  Einval:
330 	error = -EINVAL;
331 	goto Done;
332  Eaccess:
333 	error = -EACCES;
334 	module_put(attr->owner);
335  Done:
336 	if (error)
337 		kobject_put(kobj);
338 	return error;
339 }
340 
341 static int sysfs_release(struct inode * inode, struct file * filp)
342 {
343 	struct kobject * kobj = to_kobj(filp->f_path.dentry->d_parent);
344 	struct attribute * attr = to_attr(filp->f_path.dentry);
345 	struct module * owner = attr->owner;
346 	struct sysfs_buffer * buffer = filp->private_data;
347 
348 	if (buffer)
349 		remove_from_collection(buffer, inode);
350 	kobject_put(kobj);
351 	/* After this point, attr should not be accessed. */
352 	module_put(owner);
353 
354 	if (buffer) {
355 		if (buffer->page)
356 			free_page((unsigned long)buffer->page);
357 		kfree(buffer);
358 	}
359 	return 0;
360 }
361 
362 /* Sysfs attribute files are pollable.  The idea is that you read
363  * the content and then you use 'poll' or 'select' to wait for
364  * the content to change.  When the content changes (assuming the
365  * manager for the kobject supports notification), poll will
366  * return POLLERR|POLLPRI, and select will return the fd whether
367  * it is waiting for read, write, or exceptions.
368  * Once poll/select indicates that the value has changed, you
369  * need to close and re-open the file, as simply seeking and reading
370  * again will not get new data, or reset the state of 'poll'.
371  * Reminder: this only works for attributes which actively support
372  * it, and it is not possible to test an attribute from userspace
373  * to see if it supports poll (Nether 'poll' or 'select' return
374  * an appropriate error code).  When in doubt, set a suitable timeout value.
375  */
376 static unsigned int sysfs_poll(struct file *filp, poll_table *wait)
377 {
378 	struct sysfs_buffer * buffer = filp->private_data;
379 	struct kobject * kobj = to_kobj(filp->f_path.dentry->d_parent);
380 	struct sysfs_dirent * sd = filp->f_path.dentry->d_fsdata;
381 	int res = 0;
382 
383 	poll_wait(filp, &kobj->poll, wait);
384 
385 	if (buffer->event != atomic_read(&sd->s_event)) {
386 		res = POLLERR|POLLPRI;
387 		buffer->needs_read_fill = 1;
388 	}
389 
390 	return res;
391 }
392 
393 
394 static struct dentry *step_down(struct dentry *dir, const char * name)
395 {
396 	struct dentry * de;
397 
398 	if (dir == NULL || dir->d_inode == NULL)
399 		return NULL;
400 
401 	mutex_lock(&dir->d_inode->i_mutex);
402 	de = lookup_one_len(name, dir, strlen(name));
403 	mutex_unlock(&dir->d_inode->i_mutex);
404 	dput(dir);
405 	if (IS_ERR(de))
406 		return NULL;
407 	if (de->d_inode == NULL) {
408 		dput(de);
409 		return NULL;
410 	}
411 	return de;
412 }
413 
414 void sysfs_notify(struct kobject * k, char *dir, char *attr)
415 {
416 	struct dentry *de = k->dentry;
417 	if (de)
418 		dget(de);
419 	if (de && dir)
420 		de = step_down(de, dir);
421 	if (de && attr)
422 		de = step_down(de, attr);
423 	if (de) {
424 		struct sysfs_dirent * sd = de->d_fsdata;
425 		if (sd)
426 			atomic_inc(&sd->s_event);
427 		wake_up_interruptible(&k->poll);
428 		dput(de);
429 	}
430 }
431 EXPORT_SYMBOL_GPL(sysfs_notify);
432 
433 const struct file_operations sysfs_file_operations = {
434 	.read		= sysfs_read_file,
435 	.write		= sysfs_write_file,
436 	.llseek		= generic_file_llseek,
437 	.open		= sysfs_open_file,
438 	.release	= sysfs_release,
439 	.poll		= sysfs_poll,
440 };
441 
442 
443 int sysfs_add_file(struct dentry * dir, const struct attribute * attr, int type)
444 {
445 	struct sysfs_dirent * parent_sd = dir->d_fsdata;
446 	umode_t mode = (attr->mode & S_IALLUGO) | S_IFREG;
447 	int error = -EEXIST;
448 
449 	mutex_lock(&dir->d_inode->i_mutex);
450 	if (!sysfs_dirent_exist(parent_sd, attr->name))
451 		error = sysfs_make_dirent(parent_sd, NULL, (void *)attr,
452 					  mode, type);
453 	mutex_unlock(&dir->d_inode->i_mutex);
454 
455 	return error;
456 }
457 
458 
459 /**
460  *	sysfs_create_file - create an attribute file for an object.
461  *	@kobj:	object we're creating for.
462  *	@attr:	atrribute descriptor.
463  */
464 
465 int sysfs_create_file(struct kobject * kobj, const struct attribute * attr)
466 {
467 	BUG_ON(!kobj || !kobj->dentry || !attr);
468 
469 	return sysfs_add_file(kobj->dentry, attr, SYSFS_KOBJ_ATTR);
470 
471 }
472 
473 
474 /**
475  * sysfs_add_file_to_group - add an attribute file to a pre-existing group.
476  * @kobj: object we're acting for.
477  * @attr: attribute descriptor.
478  * @group: group name.
479  */
480 int sysfs_add_file_to_group(struct kobject *kobj,
481 		const struct attribute *attr, const char *group)
482 {
483 	struct dentry *dir;
484 	int error;
485 
486 	dir = lookup_one_len(group, kobj->dentry, strlen(group));
487 	if (IS_ERR(dir))
488 		error = PTR_ERR(dir);
489 	else {
490 		error = sysfs_add_file(dir, attr, SYSFS_KOBJ_ATTR);
491 		dput(dir);
492 	}
493 	return error;
494 }
495 EXPORT_SYMBOL_GPL(sysfs_add_file_to_group);
496 
497 
498 /**
499  * sysfs_update_file - update the modified timestamp on an object attribute.
500  * @kobj: object we're acting for.
501  * @attr: attribute descriptor.
502  */
503 int sysfs_update_file(struct kobject * kobj, const struct attribute * attr)
504 {
505 	struct dentry * dir = kobj->dentry;
506 	struct dentry * victim;
507 	int res = -ENOENT;
508 
509 	mutex_lock(&dir->d_inode->i_mutex);
510 	victim = lookup_one_len(attr->name, dir, strlen(attr->name));
511 	if (!IS_ERR(victim)) {
512 		/* make sure dentry is really there */
513 		if (victim->d_inode &&
514 		    (victim->d_parent->d_inode == dir->d_inode)) {
515 			victim->d_inode->i_mtime = CURRENT_TIME;
516 			fsnotify_modify(victim);
517 			res = 0;
518 		} else
519 			d_drop(victim);
520 
521 		/**
522 		 * Drop the reference acquired from lookup_one_len() above.
523 		 */
524 		dput(victim);
525 	}
526 	mutex_unlock(&dir->d_inode->i_mutex);
527 
528 	return res;
529 }
530 
531 
532 /**
533  * sysfs_chmod_file - update the modified mode value on an object attribute.
534  * @kobj: object we're acting for.
535  * @attr: attribute descriptor.
536  * @mode: file permissions.
537  *
538  */
539 int sysfs_chmod_file(struct kobject *kobj, struct attribute *attr, mode_t mode)
540 {
541 	struct dentry *dir = kobj->dentry;
542 	struct dentry *victim;
543 	struct inode * inode;
544 	struct iattr newattrs;
545 	int res = -ENOENT;
546 
547 	mutex_lock(&dir->d_inode->i_mutex);
548 	victim = lookup_one_len(attr->name, dir, strlen(attr->name));
549 	if (!IS_ERR(victim)) {
550 		if (victim->d_inode &&
551 		    (victim->d_parent->d_inode == dir->d_inode)) {
552 			inode = victim->d_inode;
553 			mutex_lock(&inode->i_mutex);
554 			newattrs.ia_mode = (mode & S_IALLUGO) |
555 						(inode->i_mode & ~S_IALLUGO);
556 			newattrs.ia_valid = ATTR_MODE | ATTR_CTIME;
557 			res = notify_change(victim, &newattrs);
558 			mutex_unlock(&inode->i_mutex);
559 		}
560 		dput(victim);
561 	}
562 	mutex_unlock(&dir->d_inode->i_mutex);
563 
564 	return res;
565 }
566 EXPORT_SYMBOL_GPL(sysfs_chmod_file);
567 
568 
569 /**
570  *	sysfs_remove_file - remove an object attribute.
571  *	@kobj:	object we're acting for.
572  *	@attr:	attribute descriptor.
573  *
574  *	Hash the attribute name and kill the victim.
575  */
576 
577 void sysfs_remove_file(struct kobject * kobj, const struct attribute * attr)
578 {
579 	sysfs_hash_and_remove(kobj->dentry, attr->name);
580 }
581 
582 
583 /**
584  * sysfs_remove_file_from_group - remove an attribute file from a group.
585  * @kobj: object we're acting for.
586  * @attr: attribute descriptor.
587  * @group: group name.
588  */
589 void sysfs_remove_file_from_group(struct kobject *kobj,
590 		const struct attribute *attr, const char *group)
591 {
592 	struct dentry *dir;
593 
594 	dir = lookup_one_len(group, kobj->dentry, strlen(group));
595 	if (!IS_ERR(dir)) {
596 		sysfs_hash_and_remove(dir, attr->name);
597 		dput(dir);
598 	}
599 }
600 EXPORT_SYMBOL_GPL(sysfs_remove_file_from_group);
601 
602 struct sysfs_schedule_callback_struct {
603 	struct kobject 		*kobj;
604 	void			(*func)(void *);
605 	void			*data;
606 	struct module		*owner;
607 	struct work_struct	work;
608 };
609 
610 static void sysfs_schedule_callback_work(struct work_struct *work)
611 {
612 	struct sysfs_schedule_callback_struct *ss = container_of(work,
613 			struct sysfs_schedule_callback_struct, work);
614 
615 	(ss->func)(ss->data);
616 	kobject_put(ss->kobj);
617 	module_put(ss->owner);
618 	kfree(ss);
619 }
620 
621 /**
622  * sysfs_schedule_callback - helper to schedule a callback for a kobject
623  * @kobj: object we're acting for.
624  * @func: callback function to invoke later.
625  * @data: argument to pass to @func.
626  * @owner: module owning the callback code
627  *
628  * sysfs attribute methods must not unregister themselves or their parent
629  * kobject (which would amount to the same thing).  Attempts to do so will
630  * deadlock, since unregistration is mutually exclusive with driver
631  * callbacks.
632  *
633  * Instead methods can call this routine, which will attempt to allocate
634  * and schedule a workqueue request to call back @func with @data as its
635  * argument in the workqueue's process context.  @kobj will be pinned
636  * until @func returns.
637  *
638  * Returns 0 if the request was submitted, -ENOMEM if storage could not
639  * be allocated, -ENODEV if a reference to @owner isn't available.
640  */
641 int sysfs_schedule_callback(struct kobject *kobj, void (*func)(void *),
642 		void *data, struct module *owner)
643 {
644 	struct sysfs_schedule_callback_struct *ss;
645 
646 	if (!try_module_get(owner))
647 		return -ENODEV;
648 	ss = kmalloc(sizeof(*ss), GFP_KERNEL);
649 	if (!ss) {
650 		module_put(owner);
651 		return -ENOMEM;
652 	}
653 	kobject_get(kobj);
654 	ss->kobj = kobj;
655 	ss->func = func;
656 	ss->data = data;
657 	ss->owner = owner;
658 	INIT_WORK(&ss->work, sysfs_schedule_callback_work);
659 	schedule_work(&ss->work);
660 	return 0;
661 }
662 EXPORT_SYMBOL_GPL(sysfs_schedule_callback);
663 
664 
665 EXPORT_SYMBOL_GPL(sysfs_create_file);
666 EXPORT_SYMBOL_GPL(sysfs_remove_file);
667 EXPORT_SYMBOL_GPL(sysfs_update_file);
668