1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * fs/kernfs/file.c - kernfs file implementation
4 *
5 * Copyright (c) 2001-3 Patrick Mochel
6 * Copyright (c) 2007 SUSE Linux Products GmbH
7 * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
8 */
9
10#include <linux/fs.h>
11#include <linux/seq_file.h>
12#include <linux/slab.h>
13#include <linux/poll.h>
14#include <linux/pagemap.h>
15#include <linux/sched/mm.h>
16#include <linux/fsnotify.h>
17#include <linux/uio.h>
18
19#include "kernfs-internal.h"
20
21struct kernfs_open_node {
22 struct rcu_head rcu_head;
23 atomic_t event;
24 wait_queue_head_t poll;
25 struct list_head files; /* goes through kernfs_open_file.list */
26 unsigned int nr_mmapped;
27 unsigned int nr_to_release;
28};
29
30/*
31 * kernfs_notify() may be called from any context and bounces notifications
32 * through a work item. To minimize space overhead in kernfs_node, the
33 * pending queue is implemented as a singly linked list of kernfs_nodes.
34 * The list is terminated with the self pointer so that whether a
35 * kernfs_node is on the list or not can be determined by testing the next
36 * pointer for %NULL.
37 */
38#define KERNFS_NOTIFY_EOL ((void *)&kernfs_notify_list)
39
40static DEFINE_SPINLOCK(kernfs_notify_lock);
41static struct kernfs_node *kernfs_notify_list = KERNFS_NOTIFY_EOL;
42
43static inline struct mutex *kernfs_open_file_mutex_ptr(struct kernfs_node *kn)
44{
45 int idx = hash_ptr(ptr: kn, NR_KERNFS_LOCK_BITS);
46
47 return &kernfs_locks->open_file_mutex[idx];
48}
49
50static inline struct mutex *kernfs_open_file_mutex_lock(struct kernfs_node *kn)
51{
52 struct mutex *lock;
53
54 lock = kernfs_open_file_mutex_ptr(kn);
55
56 mutex_lock(lock);
57
58 return lock;
59}
60
61/**
62 * of_on - Get the kernfs_open_node of the specified kernfs_open_file
63 * @of: target kernfs_open_file
64 *
65 * Return: the kernfs_open_node of the kernfs_open_file
66 */
67static struct kernfs_open_node *of_on(struct kernfs_open_file *of)
68{
69 return rcu_dereference_protected(of->kn->attr.open,
70 !list_empty(&of->list));
71}
72
73/**
74 * kernfs_deref_open_node_locked - Get kernfs_open_node corresponding to @kn
75 *
76 * @kn: target kernfs_node.
77 *
78 * Fetch and return ->attr.open of @kn when caller holds the
79 * kernfs_open_file_mutex_ptr(kn).
80 *
81 * Update of ->attr.open happens under kernfs_open_file_mutex_ptr(kn). So when
82 * the caller guarantees that this mutex is being held, other updaters can't
83 * change ->attr.open and this means that we can safely deref ->attr.open
84 * outside RCU read-side critical section.
85 *
86 * The caller needs to make sure that kernfs_open_file_mutex is held.
87 *
88 * Return: @kn->attr.open when kernfs_open_file_mutex is held.
89 */
90static struct kernfs_open_node *
91kernfs_deref_open_node_locked(struct kernfs_node *kn)
92{
93 return rcu_dereference_protected(kn->attr.open,
94 lockdep_is_held(kernfs_open_file_mutex_ptr(kn)));
95}
96
97static struct kernfs_open_file *kernfs_of(struct file *file)
98{
99 return ((struct seq_file *)file->private_data)->private;
100}
101
102/*
103 * Determine the kernfs_ops for the given kernfs_node. This function must
104 * be called while holding an active reference.
105 */
106static const struct kernfs_ops *kernfs_ops(struct kernfs_node *kn)
107{
108 if (kn->flags & KERNFS_LOCKDEP)
109 lockdep_assert_held(kn);
110 return kn->attr.ops;
111}
112
113/*
114 * As kernfs_seq_stop() is also called after kernfs_seq_start() or
115 * kernfs_seq_next() failure, it needs to distinguish whether it's stopping
116 * a seq_file iteration which is fully initialized with an active reference
117 * or an aborted kernfs_seq_start() due to get_active failure. The
118 * position pointer is the only context for each seq_file iteration and
119 * thus the stop condition should be encoded in it. As the return value is
120 * directly visible to userland, ERR_PTR(-ENODEV) is the only acceptable
121 * choice to indicate get_active failure.
122 *
123 * Unfortunately, this is complicated due to the optional custom seq_file
124 * operations which may return ERR_PTR(-ENODEV) too. kernfs_seq_stop()
125 * can't distinguish whether ERR_PTR(-ENODEV) is from get_active failure or
126 * custom seq_file operations and thus can't decide whether put_active
127 * should be performed or not only on ERR_PTR(-ENODEV).
128 *
129 * This is worked around by factoring out the custom seq_stop() and
130 * put_active part into kernfs_seq_stop_active(), skipping it from
131 * kernfs_seq_stop() if ERR_PTR(-ENODEV) while invoking it directly after
132 * custom seq_file operations fail with ERR_PTR(-ENODEV) - this ensures
133 * that kernfs_seq_stop_active() is skipped only after get_active failure.
134 */
135static void kernfs_seq_stop_active(struct seq_file *sf, void *v)
136{
137 struct kernfs_open_file *of = sf->private;
138 const struct kernfs_ops *ops = kernfs_ops(kn: of->kn);
139
140 if (ops->seq_stop)
141 ops->seq_stop(sf, v);
142 kernfs_put_active(kn: of->kn);
143}
144
145static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
146{
147 struct kernfs_open_file *of = sf->private;
148 const struct kernfs_ops *ops;
149
150 /*
151 * @of->mutex nests outside active ref and is primarily to ensure that
152 * the ops aren't called concurrently for the same open file.
153 */
154 mutex_lock(&of->mutex);
155 if (!kernfs_get_active(kn: of->kn))
156 return ERR_PTR(error: -ENODEV);
157
158 ops = kernfs_ops(kn: of->kn);
159 if (ops->seq_start) {
160 void *next = ops->seq_start(sf, ppos);
161 /* see the comment above kernfs_seq_stop_active() */
162 if (next == ERR_PTR(error: -ENODEV))
163 kernfs_seq_stop_active(sf, v: next);
164 return next;
165 }
166 return single_start(sf, ppos);
167}
168
169static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)
170{
171 struct kernfs_open_file *of = sf->private;
172 const struct kernfs_ops *ops = kernfs_ops(kn: of->kn);
173
174 if (ops->seq_next) {
175 void *next = ops->seq_next(sf, v, ppos);
176 /* see the comment above kernfs_seq_stop_active() */
177 if (next == ERR_PTR(error: -ENODEV))
178 kernfs_seq_stop_active(sf, v: next);
179 return next;
180 } else {
181 /*
182 * The same behavior and code as single_open(), always
183 * terminate after the initial read.
184 */
185 ++*ppos;
186 return NULL;
187 }
188}
189
190static void kernfs_seq_stop(struct seq_file *sf, void *v)
191{
192 struct kernfs_open_file *of = sf->private;
193
194 if (v != ERR_PTR(error: -ENODEV))
195 kernfs_seq_stop_active(sf, v);
196 mutex_unlock(lock: &of->mutex);
197}
198
199static int kernfs_seq_show(struct seq_file *sf, void *v)
200{
201 struct kernfs_open_file *of = sf->private;
202
203 of->event = atomic_read(v: &of_on(of)->event);
204
205 return of->kn->attr.ops->seq_show(sf, v);
206}
207
208static const struct seq_operations kernfs_seq_ops = {
209 .start = kernfs_seq_start,
210 .next = kernfs_seq_next,
211 .stop = kernfs_seq_stop,
212 .show = kernfs_seq_show,
213};
214
215/*
216 * As reading a bin file can have side-effects, the exact offset and bytes
217 * specified in read(2) call should be passed to the read callback making
218 * it difficult to use seq_file. Implement simplistic custom buffering for
219 * bin files.
220 */
221static ssize_t kernfs_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
222{
223 struct kernfs_open_file *of = kernfs_of(file: iocb->ki_filp);
224 ssize_t len = min_t(size_t, iov_iter_count(iter), PAGE_SIZE);
225 const struct kernfs_ops *ops;
226 char *buf;
227
228 buf = of->prealloc_buf;
229 if (buf)
230 mutex_lock(&of->prealloc_mutex);
231 else
232 buf = kmalloc(size: len, GFP_KERNEL);
233 if (!buf)
234 return -ENOMEM;
235
236 /*
237 * @of->mutex nests outside active ref and is used both to ensure that
238 * the ops aren't called concurrently for the same open file.
239 */
240 mutex_lock(&of->mutex);
241 if (!kernfs_get_active(kn: of->kn)) {
242 len = -ENODEV;
243 mutex_unlock(lock: &of->mutex);
244 goto out_free;
245 }
246
247 of->event = atomic_read(v: &of_on(of)->event);
248
249 ops = kernfs_ops(kn: of->kn);
250 if (ops->read)
251 len = ops->read(of, buf, len, iocb->ki_pos);
252 else
253 len = -EINVAL;
254
255 kernfs_put_active(kn: of->kn);
256 mutex_unlock(lock: &of->mutex);
257
258 if (len < 0)
259 goto out_free;
260
261 if (copy_to_iter(addr: buf, bytes: len, i: iter) != len) {
262 len = -EFAULT;
263 goto out_free;
264 }
265
266 iocb->ki_pos += len;
267
268 out_free:
269 if (buf == of->prealloc_buf)
270 mutex_unlock(lock: &of->prealloc_mutex);
271 else
272 kfree(objp: buf);
273 return len;
274}
275
276static ssize_t kernfs_fop_read_iter(struct kiocb *iocb, struct iov_iter *iter)
277{
278 if (kernfs_of(file: iocb->ki_filp)->kn->flags & KERNFS_HAS_SEQ_SHOW)
279 return seq_read_iter(iocb, iter);
280 return kernfs_file_read_iter(iocb, iter);
281}
282
283/*
284 * Copy data in from userland and pass it to the matching kernfs write
285 * operation.
286 *
287 * There is no easy way for us to know if userspace is only doing a partial
288 * write, so we don't support them. We expect the entire buffer to come on
289 * the first write. Hint: if you're writing a value, first read the file,
290 * modify only the value you're changing, then write entire buffer
291 * back.
292 */
293static ssize_t kernfs_fop_write_iter(struct kiocb *iocb, struct iov_iter *iter)
294{
295 struct kernfs_open_file *of = kernfs_of(file: iocb->ki_filp);
296 ssize_t len = iov_iter_count(i: iter);
297 const struct kernfs_ops *ops;
298 char *buf;
299
300 if (of->atomic_write_len) {
301 if (len > of->atomic_write_len)
302 return -E2BIG;
303 } else {
304 len = min_t(size_t, len, PAGE_SIZE);
305 }
306
307 buf = of->prealloc_buf;
308 if (buf)
309 mutex_lock(&of->prealloc_mutex);
310 else
311 buf = kmalloc(size: len + 1, GFP_KERNEL);
312 if (!buf)
313 return -ENOMEM;
314
315 if (copy_from_iter(addr: buf, bytes: len, i: iter) != len) {
316 len = -EFAULT;
317 goto out_free;
318 }
319 buf[len] = '\0'; /* guarantee string termination */
320
321 /*
322 * @of->mutex nests outside active ref and is used both to ensure that
323 * the ops aren't called concurrently for the same open file.
324 */
325 mutex_lock(&of->mutex);
326 if (!kernfs_get_active(kn: of->kn)) {
327 mutex_unlock(lock: &of->mutex);
328 len = -ENODEV;
329 goto out_free;
330 }
331
332 ops = kernfs_ops(kn: of->kn);
333 if (ops->write)
334 len = ops->write(of, buf, len, iocb->ki_pos);
335 else
336 len = -EINVAL;
337
338 kernfs_put_active(kn: of->kn);
339 mutex_unlock(lock: &of->mutex);
340
341 if (len > 0)
342 iocb->ki_pos += len;
343
344out_free:
345 if (buf == of->prealloc_buf)
346 mutex_unlock(lock: &of->prealloc_mutex);
347 else
348 kfree(objp: buf);
349 return len;
350}
351
352static void kernfs_vma_open(struct vm_area_struct *vma)
353{
354 struct file *file = vma->vm_file;
355 struct kernfs_open_file *of = kernfs_of(file);
356
357 if (!of->vm_ops)
358 return;
359
360 if (!kernfs_get_active(kn: of->kn))
361 return;
362
363 if (of->vm_ops->open)
364 of->vm_ops->open(vma);
365
366 kernfs_put_active(kn: of->kn);
367}
368
369static vm_fault_t kernfs_vma_fault(struct vm_fault *vmf)
370{
371 struct file *file = vmf->vma->vm_file;
372 struct kernfs_open_file *of = kernfs_of(file);
373 vm_fault_t ret;
374
375 if (!of->vm_ops)
376 return VM_FAULT_SIGBUS;
377
378 if (!kernfs_get_active(kn: of->kn))
379 return VM_FAULT_SIGBUS;
380
381 ret = VM_FAULT_SIGBUS;
382 if (of->vm_ops->fault)
383 ret = of->vm_ops->fault(vmf);
384
385 kernfs_put_active(kn: of->kn);
386 return ret;
387}
388
389static vm_fault_t kernfs_vma_page_mkwrite(struct vm_fault *vmf)
390{
391 struct file *file = vmf->vma->vm_file;
392 struct kernfs_open_file *of = kernfs_of(file);
393 vm_fault_t ret;
394
395 if (!of->vm_ops)
396 return VM_FAULT_SIGBUS;
397
398 if (!kernfs_get_active(kn: of->kn))
399 return VM_FAULT_SIGBUS;
400
401 ret = 0;
402 if (of->vm_ops->page_mkwrite)
403 ret = of->vm_ops->page_mkwrite(vmf);
404 else
405 file_update_time(file);
406
407 kernfs_put_active(kn: of->kn);
408 return ret;
409}
410
411static int kernfs_vma_access(struct vm_area_struct *vma, unsigned long addr,
412 void *buf, int len, int write)
413{
414 struct file *file = vma->vm_file;
415 struct kernfs_open_file *of = kernfs_of(file);
416 int ret;
417
418 if (!of->vm_ops)
419 return -EINVAL;
420
421 if (!kernfs_get_active(kn: of->kn))
422 return -EINVAL;
423
424 ret = -EINVAL;
425 if (of->vm_ops->access)
426 ret = of->vm_ops->access(vma, addr, buf, len, write);
427
428 kernfs_put_active(kn: of->kn);
429 return ret;
430}
431
432static const struct vm_operations_struct kernfs_vm_ops = {
433 .open = kernfs_vma_open,
434 .fault = kernfs_vma_fault,
435 .page_mkwrite = kernfs_vma_page_mkwrite,
436 .access = kernfs_vma_access,
437};
438
439static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
440{
441 struct kernfs_open_file *of = kernfs_of(file);
442 const struct kernfs_ops *ops;
443 int rc;
444
445 /*
446 * mmap path and of->mutex are prone to triggering spurious lockdep
447 * warnings and we don't want to add spurious locking dependency
448 * between the two. Check whether mmap is actually implemented
449 * without grabbing @of->mutex by testing HAS_MMAP flag. See the
450 * comment in kernfs_file_open() for more details.
451 */
452 if (!(of->kn->flags & KERNFS_HAS_MMAP))
453 return -ENODEV;
454
455 mutex_lock(&of->mutex);
456
457 rc = -ENODEV;
458 if (!kernfs_get_active(kn: of->kn))
459 goto out_unlock;
460
461 ops = kernfs_ops(kn: of->kn);
462 rc = ops->mmap(of, vma);
463 if (rc)
464 goto out_put;
465
466 /*
467 * PowerPC's pci_mmap of legacy_mem uses shmem_zero_setup()
468 * to satisfy versions of X which crash if the mmap fails: that
469 * substitutes a new vm_file, and we don't then want bin_vm_ops.
470 */
471 if (vma->vm_file != file)
472 goto out_put;
473
474 rc = -EINVAL;
475 if (of->mmapped && of->vm_ops != vma->vm_ops)
476 goto out_put;
477
478 /*
479 * It is not possible to successfully wrap close.
480 * So error if someone is trying to use close.
481 */
482 if (vma->vm_ops && vma->vm_ops->close)
483 goto out_put;
484
485 rc = 0;
486 of->mmapped = true;
487 of_on(of)->nr_mmapped++;
488 of->vm_ops = vma->vm_ops;
489 vma->vm_ops = &kernfs_vm_ops;
490out_put:
491 kernfs_put_active(kn: of->kn);
492out_unlock:
493 mutex_unlock(lock: &of->mutex);
494
495 return rc;
496}
497
498/**
499 * kernfs_get_open_node - get or create kernfs_open_node
500 * @kn: target kernfs_node
501 * @of: kernfs_open_file for this instance of open
502 *
503 * If @kn->attr.open exists, increment its reference count; otherwise,
504 * create one. @of is chained to the files list.
505 *
506 * Locking:
507 * Kernel thread context (may sleep).
508 *
509 * Return:
510 * %0 on success, -errno on failure.
511 */
512static int kernfs_get_open_node(struct kernfs_node *kn,
513 struct kernfs_open_file *of)
514{
515 struct kernfs_open_node *on;
516 struct mutex *mutex;
517
518 mutex = kernfs_open_file_mutex_lock(kn);
519 on = kernfs_deref_open_node_locked(kn);
520
521 if (!on) {
522 /* not there, initialize a new one */
523 on = kzalloc(size: sizeof(*on), GFP_KERNEL);
524 if (!on) {
525 mutex_unlock(lock: mutex);
526 return -ENOMEM;
527 }
528 atomic_set(v: &on->event, i: 1);
529 init_waitqueue_head(&on->poll);
530 INIT_LIST_HEAD(list: &on->files);
531 rcu_assign_pointer(kn->attr.open, on);
532 }
533
534 list_add_tail(new: &of->list, head: &on->files);
535 if (kn->flags & KERNFS_HAS_RELEASE)
536 on->nr_to_release++;
537
538 mutex_unlock(lock: mutex);
539 return 0;
540}
541
542/**
543 * kernfs_unlink_open_file - Unlink @of from @kn.
544 *
545 * @kn: target kernfs_node
546 * @of: associated kernfs_open_file
547 * @open_failed: ->open() failed, cancel ->release()
548 *
549 * Unlink @of from list of @kn's associated open files. If list of
550 * associated open files becomes empty, disassociate and free
551 * kernfs_open_node.
552 *
553 * LOCKING:
554 * None.
555 */
556static void kernfs_unlink_open_file(struct kernfs_node *kn,
557 struct kernfs_open_file *of,
558 bool open_failed)
559{
560 struct kernfs_open_node *on;
561 struct mutex *mutex;
562
563 mutex = kernfs_open_file_mutex_lock(kn);
564
565 on = kernfs_deref_open_node_locked(kn);
566 if (!on) {
567 mutex_unlock(lock: mutex);
568 return;
569 }
570
571 if (of) {
572 if (kn->flags & KERNFS_HAS_RELEASE) {
573 WARN_ON_ONCE(of->released == open_failed);
574 if (open_failed)
575 on->nr_to_release--;
576 }
577 if (of->mmapped)
578 on->nr_mmapped--;
579 list_del(entry: &of->list);
580 }
581
582 if (list_empty(head: &on->files)) {
583 rcu_assign_pointer(kn->attr.open, NULL);
584 kfree_rcu(on, rcu_head);
585 }
586
587 mutex_unlock(lock: mutex);
588}
589
590static int kernfs_fop_open(struct inode *inode, struct file *file)
591{
592 struct kernfs_node *kn = inode->i_private;
593 struct kernfs_root *root = kernfs_root(kn);
594 const struct kernfs_ops *ops;
595 struct kernfs_open_file *of;
596 bool has_read, has_write, has_mmap;
597 int error = -EACCES;
598
599 if (!kernfs_get_active(kn))
600 return -ENODEV;
601
602 ops = kernfs_ops(kn);
603
604 has_read = ops->seq_show || ops->read || ops->mmap;
605 has_write = ops->write || ops->mmap;
606 has_mmap = ops->mmap;
607
608 /* see the flag definition for details */
609 if (root->flags & KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK) {
610 if ((file->f_mode & FMODE_WRITE) &&
611 (!(inode->i_mode & S_IWUGO) || !has_write))
612 goto err_out;
613
614 if ((file->f_mode & FMODE_READ) &&
615 (!(inode->i_mode & S_IRUGO) || !has_read))
616 goto err_out;
617 }
618
619 /* allocate a kernfs_open_file for the file */
620 error = -ENOMEM;
621 of = kzalloc(size: sizeof(struct kernfs_open_file), GFP_KERNEL);
622 if (!of)
623 goto err_out;
624
625 /*
626 * The following is done to give a different lockdep key to
627 * @of->mutex for files which implement mmap. This is a rather
628 * crude way to avoid false positive lockdep warning around
629 * mm->mmap_lock - mmap nests @of->mutex under mm->mmap_lock and
630 * reading /sys/block/sda/trace/act_mask grabs sr_mutex, under
631 * which mm->mmap_lock nests, while holding @of->mutex. As each
632 * open file has a separate mutex, it's okay as long as those don't
633 * happen on the same file. At this point, we can't easily give
634 * each file a separate locking class. Let's differentiate on
635 * whether the file has mmap or not for now.
636 *
637 * Both paths of the branch look the same. They're supposed to
638 * look that way and give @of->mutex different static lockdep keys.
639 */
640 if (has_mmap)
641 mutex_init(&of->mutex);
642 else
643 mutex_init(&of->mutex);
644
645 of->kn = kn;
646 of->file = file;
647
648 /*
649 * Write path needs to atomic_write_len outside active reference.
650 * Cache it in open_file. See kernfs_fop_write_iter() for details.
651 */
652 of->atomic_write_len = ops->atomic_write_len;
653
654 error = -EINVAL;
655 /*
656 * ->seq_show is incompatible with ->prealloc,
657 * as seq_read does its own allocation.
658 * ->read must be used instead.
659 */
660 if (ops->prealloc && ops->seq_show)
661 goto err_free;
662 if (ops->prealloc) {
663 int len = of->atomic_write_len ?: PAGE_SIZE;
664 of->prealloc_buf = kmalloc(size: len + 1, GFP_KERNEL);
665 error = -ENOMEM;
666 if (!of->prealloc_buf)
667 goto err_free;
668 mutex_init(&of->prealloc_mutex);
669 }
670
671 /*
672 * Always instantiate seq_file even if read access doesn't use
673 * seq_file or is not requested. This unifies private data access
674 * and readable regular files are the vast majority anyway.
675 */
676 if (ops->seq_show)
677 error = seq_open(file, &kernfs_seq_ops);
678 else
679 error = seq_open(file, NULL);
680 if (error)
681 goto err_free;
682
683 of->seq_file = file->private_data;
684 of->seq_file->private = of;
685
686 /* seq_file clears PWRITE unconditionally, restore it if WRITE */
687 if (file->f_mode & FMODE_WRITE)
688 file->f_mode |= FMODE_PWRITE;
689
690 /* make sure we have open node struct */
691 error = kernfs_get_open_node(kn, of);
692 if (error)
693 goto err_seq_release;
694
695 if (ops->open) {
696 /* nobody has access to @of yet, skip @of->mutex */
697 error = ops->open(of);
698 if (error)
699 goto err_put_node;
700 }
701
702 /* open succeeded, put active references */
703 kernfs_put_active(kn);
704 return 0;
705
706err_put_node:
707 kernfs_unlink_open_file(kn, of, open_failed: true);
708err_seq_release:
709 seq_release(inode, file);
710err_free:
711 kfree(objp: of->prealloc_buf);
712 kfree(objp: of);
713err_out:
714 kernfs_put_active(kn);
715 return error;
716}
717
718/* used from release/drain to ensure that ->release() is called exactly once */
719static void kernfs_release_file(struct kernfs_node *kn,
720 struct kernfs_open_file *of)
721{
722 /*
723 * @of is guaranteed to have no other file operations in flight and
724 * we just want to synchronize release and drain paths.
725 * @kernfs_open_file_mutex_ptr(kn) is enough. @of->mutex can't be used
726 * here because drain path may be called from places which can
727 * cause circular dependency.
728 */
729 lockdep_assert_held(kernfs_open_file_mutex_ptr(kn));
730
731 if (!of->released) {
732 /*
733 * A file is never detached without being released and we
734 * need to be able to release files which are deactivated
735 * and being drained. Don't use kernfs_ops().
736 */
737 kn->attr.ops->release(of);
738 of->released = true;
739 of_on(of)->nr_to_release--;
740 }
741}
742
743static int kernfs_fop_release(struct inode *inode, struct file *filp)
744{
745 struct kernfs_node *kn = inode->i_private;
746 struct kernfs_open_file *of = kernfs_of(file: filp);
747
748 if (kn->flags & KERNFS_HAS_RELEASE) {
749 struct mutex *mutex;
750
751 mutex = kernfs_open_file_mutex_lock(kn);
752 kernfs_release_file(kn, of);
753 mutex_unlock(lock: mutex);
754 }
755
756 kernfs_unlink_open_file(kn, of, open_failed: false);
757 seq_release(inode, filp);
758 kfree(objp: of->prealloc_buf);
759 kfree(objp: of);
760
761 return 0;
762}
763
764bool kernfs_should_drain_open_files(struct kernfs_node *kn)
765{
766 struct kernfs_open_node *on;
767 bool ret;
768
769 /*
770 * @kn being deactivated guarantees that @kn->attr.open can't change
771 * beneath us making the lockless test below safe.
772 */
773 WARN_ON_ONCE(atomic_read(&kn->active) != KN_DEACTIVATED_BIAS);
774
775 rcu_read_lock();
776 on = rcu_dereference(kn->attr.open);
777 ret = on && (on->nr_mmapped || on->nr_to_release);
778 rcu_read_unlock();
779
780 return ret;
781}
782
783void kernfs_drain_open_files(struct kernfs_node *kn)
784{
785 struct kernfs_open_node *on;
786 struct kernfs_open_file *of;
787 struct mutex *mutex;
788
789 mutex = kernfs_open_file_mutex_lock(kn);
790 on = kernfs_deref_open_node_locked(kn);
791 if (!on) {
792 mutex_unlock(lock: mutex);
793 return;
794 }
795
796 list_for_each_entry(of, &on->files, list) {
797 struct inode *inode = file_inode(f: of->file);
798
799 if (of->mmapped) {
800 unmap_mapping_range(mapping: inode->i_mapping, holebegin: 0, holelen: 0, even_cows: 1);
801 of->mmapped = false;
802 on->nr_mmapped--;
803 }
804
805 if (kn->flags & KERNFS_HAS_RELEASE)
806 kernfs_release_file(kn, of);
807 }
808
809 WARN_ON_ONCE(on->nr_mmapped || on->nr_to_release);
810 mutex_unlock(lock: mutex);
811}
812
813/*
814 * Kernfs attribute files are pollable. The idea is that you read
815 * the content and then you use 'poll' or 'select' to wait for
816 * the content to change. When the content changes (assuming the
817 * manager for the kobject supports notification), poll will
818 * return EPOLLERR|EPOLLPRI, and select will return the fd whether
819 * it is waiting for read, write, or exceptions.
820 * Once poll/select indicates that the value has changed, you
821 * need to close and re-open the file, or seek to 0 and read again.
822 * Reminder: this only works for attributes which actively support
823 * it, and it is not possible to test an attribute from userspace
824 * to see if it supports poll (Neither 'poll' nor 'select' return
825 * an appropriate error code). When in doubt, set a suitable timeout value.
826 */
827__poll_t kernfs_generic_poll(struct kernfs_open_file *of, poll_table *wait)
828{
829 struct kernfs_open_node *on = of_on(of);
830
831 poll_wait(filp: of->file, wait_address: &on->poll, p: wait);
832
833 if (of->event != atomic_read(v: &on->event))
834 return DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;
835
836 return DEFAULT_POLLMASK;
837}
838
839static __poll_t kernfs_fop_poll(struct file *filp, poll_table *wait)
840{
841 struct kernfs_open_file *of = kernfs_of(file: filp);
842 struct kernfs_node *kn = kernfs_dentry_node(dentry: filp->f_path.dentry);
843 __poll_t ret;
844
845 if (!kernfs_get_active(kn))
846 return DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;
847
848 if (kn->attr.ops->poll)
849 ret = kn->attr.ops->poll(of, wait);
850 else
851 ret = kernfs_generic_poll(of, wait);
852
853 kernfs_put_active(kn);
854 return ret;
855}
856
857static loff_t kernfs_fop_llseek(struct file *file, loff_t offset, int whence)
858{
859 struct kernfs_open_file *of = kernfs_of(file);
860 const struct kernfs_ops *ops;
861 loff_t ret;
862
863 /*
864 * @of->mutex nests outside active ref and is primarily to ensure that
865 * the ops aren't called concurrently for the same open file.
866 */
867 mutex_lock(&of->mutex);
868 if (!kernfs_get_active(kn: of->kn)) {
869 mutex_unlock(lock: &of->mutex);
870 return -ENODEV;
871 }
872
873 ops = kernfs_ops(kn: of->kn);
874 if (ops->llseek)
875 ret = ops->llseek(of, offset, whence);
876 else
877 ret = generic_file_llseek(file, offset, whence);
878
879 kernfs_put_active(kn: of->kn);
880 mutex_unlock(lock: &of->mutex);
881 return ret;
882}
883
884static void kernfs_notify_workfn(struct work_struct *work)
885{
886 struct kernfs_node *kn;
887 struct kernfs_super_info *info;
888 struct kernfs_root *root;
889repeat:
890 /* pop one off the notify_list */
891 spin_lock_irq(lock: &kernfs_notify_lock);
892 kn = kernfs_notify_list;
893 if (kn == KERNFS_NOTIFY_EOL) {
894 spin_unlock_irq(lock: &kernfs_notify_lock);
895 return;
896 }
897 kernfs_notify_list = kn->attr.notify_next;
898 kn->attr.notify_next = NULL;
899 spin_unlock_irq(lock: &kernfs_notify_lock);
900
901 root = kernfs_root(kn);
902 /* kick fsnotify */
903
904 down_read(sem: &root->kernfs_supers_rwsem);
905 list_for_each_entry(info, &kernfs_root(kn)->supers, node) {
906 struct kernfs_node *parent;
907 struct inode *p_inode = NULL;
908 struct inode *inode;
909 struct qstr name;
910
911 /*
912 * We want fsnotify_modify() on @kn but as the
913 * modifications aren't originating from userland don't
914 * have the matching @file available. Look up the inodes
915 * and generate the events manually.
916 */
917 inode = ilookup(sb: info->sb, ino: kernfs_ino(kn));
918 if (!inode)
919 continue;
920
921 name = (struct qstr)QSTR_INIT(kn->name, strlen(kn->name));
922 parent = kernfs_get_parent(kn);
923 if (parent) {
924 p_inode = ilookup(sb: info->sb, ino: kernfs_ino(kn: parent));
925 if (p_inode) {
926 fsnotify(FS_MODIFY | FS_EVENT_ON_CHILD,
927 data: inode, data_type: FSNOTIFY_EVENT_INODE,
928 dir: p_inode, name: &name, inode, cookie: 0);
929 iput(p_inode);
930 }
931
932 kernfs_put(kn: parent);
933 }
934
935 if (!p_inode)
936 fsnotify_inode(inode, FS_MODIFY);
937
938 iput(inode);
939 }
940
941 up_read(sem: &root->kernfs_supers_rwsem);
942 kernfs_put(kn);
943 goto repeat;
944}
945
946/**
947 * kernfs_notify - notify a kernfs file
948 * @kn: file to notify
949 *
950 * Notify @kn such that poll(2) on @kn wakes up. Maybe be called from any
951 * context.
952 */
953void kernfs_notify(struct kernfs_node *kn)
954{
955 static DECLARE_WORK(kernfs_notify_work, kernfs_notify_workfn);
956 unsigned long flags;
957 struct kernfs_open_node *on;
958
959 if (WARN_ON(kernfs_type(kn) != KERNFS_FILE))
960 return;
961
962 /* kick poll immediately */
963 rcu_read_lock();
964 on = rcu_dereference(kn->attr.open);
965 if (on) {
966 atomic_inc(v: &on->event);
967 wake_up_interruptible(&on->poll);
968 }
969 rcu_read_unlock();
970
971 /* schedule work to kick fsnotify */
972 spin_lock_irqsave(&kernfs_notify_lock, flags);
973 if (!kn->attr.notify_next) {
974 kernfs_get(kn);
975 kn->attr.notify_next = kernfs_notify_list;
976 kernfs_notify_list = kn;
977 schedule_work(work: &kernfs_notify_work);
978 }
979 spin_unlock_irqrestore(lock: &kernfs_notify_lock, flags);
980}
981EXPORT_SYMBOL_GPL(kernfs_notify);
982
983const struct file_operations kernfs_file_fops = {
984 .read_iter = kernfs_fop_read_iter,
985 .write_iter = kernfs_fop_write_iter,
986 .llseek = kernfs_fop_llseek,
987 .mmap = kernfs_fop_mmap,
988 .open = kernfs_fop_open,
989 .release = kernfs_fop_release,
990 .poll = kernfs_fop_poll,
991 .fsync = noop_fsync,
992 .splice_read = copy_splice_read,
993 .splice_write = iter_file_splice_write,
994};
995
996/**
997 * __kernfs_create_file - kernfs internal function to create a file
998 * @parent: directory to create the file in
999 * @name: name of the file
1000 * @mode: mode of the file
1001 * @uid: uid of the file
1002 * @gid: gid of the file
1003 * @size: size of the file
1004 * @ops: kernfs operations for the file
1005 * @priv: private data for the file
1006 * @ns: optional namespace tag of the file
1007 * @key: lockdep key for the file's active_ref, %NULL to disable lockdep
1008 *
1009 * Return: the created node on success, ERR_PTR() value on error.
1010 */
1011struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
1012 const char *name,
1013 umode_t mode, kuid_t uid, kgid_t gid,
1014 loff_t size,
1015 const struct kernfs_ops *ops,
1016 void *priv, const void *ns,
1017 struct lock_class_key *key)
1018{
1019 struct kernfs_node *kn;
1020 unsigned flags;
1021 int rc;
1022
1023 flags = KERNFS_FILE;
1024
1025 kn = kernfs_new_node(parent, name, mode: (mode & S_IALLUGO) | S_IFREG,
1026 uid, gid, flags);
1027 if (!kn)
1028 return ERR_PTR(error: -ENOMEM);
1029
1030 kn->attr.ops = ops;
1031 kn->attr.size = size;
1032 kn->ns = ns;
1033 kn->priv = priv;
1034
1035#ifdef CONFIG_DEBUG_LOCK_ALLOC
1036 if (key) {
1037 lockdep_init_map(lock: &kn->dep_map, name: "kn->active", key, subclass: 0);
1038 kn->flags |= KERNFS_LOCKDEP;
1039 }
1040#endif
1041
1042 /*
1043 * kn->attr.ops is accessible only while holding active ref. We
1044 * need to know whether some ops are implemented outside active
1045 * ref. Cache their existence in flags.
1046 */
1047 if (ops->seq_show)
1048 kn->flags |= KERNFS_HAS_SEQ_SHOW;
1049 if (ops->mmap)
1050 kn->flags |= KERNFS_HAS_MMAP;
1051 if (ops->release)
1052 kn->flags |= KERNFS_HAS_RELEASE;
1053
1054 rc = kernfs_add_one(kn);
1055 if (rc) {
1056 kernfs_put(kn);
1057 return ERR_PTR(error: rc);
1058 }
1059 return kn;
1060}
1061

source code of linux/fs/kernfs/file.c