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Linux/fs/kernfs/file.c

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

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