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TOMOYO Linux Cross Reference
Linux/fs/kernfs/file.c

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  1 /*
  2  * fs/kernfs/file.c - kernfs file implementation
  3  *
  4  * Copyright (c) 2001-3 Patrick Mochel
  5  * Copyright (c) 2007 SUSE Linux Products GmbH
  6  * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
  7  *
  8  * This file is released under the GPLv2.
  9  */
 10 
 11 #include <linux/fs.h>
 12 #include <linux/seq_file.h>
 13 #include <linux/slab.h>
 14 #include <linux/poll.h>
 15 #include <linux/pagemap.h>
 16 #include <linux/sched/mm.h>
 17 #include <linux/fsnotify.h>
 18 
 19 #include "kernfs-internal.h"
 20 
 21 /*
 22  * There's one kernfs_open_file for each open file and one kernfs_open_node
 23  * for each kernfs_node with one or more open files.
 24  *
 25  * kernfs_node->attr.open points to kernfs_open_node.  attr.open is
 26  * protected by kernfs_open_node_lock.
 27  *
 28  * filp->private_data points to seq_file whose ->private points to
 29  * kernfs_open_file.  kernfs_open_files are chained at
 30  * kernfs_open_node->files, which is protected by kernfs_open_file_mutex.
 31  */
 32 static DEFINE_SPINLOCK(kernfs_open_node_lock);
 33 static DEFINE_MUTEX(kernfs_open_file_mutex);
 34 
 35 struct kernfs_open_node {
 36         atomic_t                refcnt;
 37         atomic_t                event;
 38         wait_queue_head_t       poll;
 39         struct list_head        files; /* goes through kernfs_open_file.list */
 40 };
 41 
 42 /*
 43  * kernfs_notify() may be called from any context and bounces notifications
 44  * through a work item.  To minimize space overhead in kernfs_node, the
 45  * pending queue is implemented as a singly linked list of kernfs_nodes.
 46  * The list is terminated with the self pointer so that whether a
 47  * kernfs_node is on the list or not can be determined by testing the next
 48  * pointer for NULL.
 49  */
 50 #define KERNFS_NOTIFY_EOL                       ((void *)&kernfs_notify_list)
 51 
 52 static DEFINE_SPINLOCK(kernfs_notify_lock);
 53 static struct kernfs_node *kernfs_notify_list = KERNFS_NOTIFY_EOL;
 54 
 55 static struct kernfs_open_file *kernfs_of(struct file *file)
 56 {
 57         return ((struct seq_file *)file->private_data)->private;
 58 }
 59 
 60 /*
 61  * Determine the kernfs_ops for the given kernfs_node.  This function must
 62  * be called while holding an active reference.
 63  */
 64 static const struct kernfs_ops *kernfs_ops(struct kernfs_node *kn)
 65 {
 66         if (kn->flags & KERNFS_LOCKDEP)
 67                 lockdep_assert_held(kn);
 68         return kn->attr.ops;
 69 }
 70 
 71 /*
 72  * As kernfs_seq_stop() is also called after kernfs_seq_start() or
 73  * kernfs_seq_next() failure, it needs to distinguish whether it's stopping
 74  * a seq_file iteration which is fully initialized with an active reference
 75  * or an aborted kernfs_seq_start() due to get_active failure.  The
 76  * position pointer is the only context for each seq_file iteration and
 77  * thus the stop condition should be encoded in it.  As the return value is
 78  * directly visible to userland, ERR_PTR(-ENODEV) is the only acceptable
 79  * choice to indicate get_active failure.
 80  *
 81  * Unfortunately, this is complicated due to the optional custom seq_file
 82  * operations which may return ERR_PTR(-ENODEV) too.  kernfs_seq_stop()
 83  * can't distinguish whether ERR_PTR(-ENODEV) is from get_active failure or
 84  * custom seq_file operations and thus can't decide whether put_active
 85  * should be performed or not only on ERR_PTR(-ENODEV).
 86  *
 87  * This is worked around by factoring out the custom seq_stop() and
 88  * put_active part into kernfs_seq_stop_active(), skipping it from
 89  * kernfs_seq_stop() if ERR_PTR(-ENODEV) while invoking it directly after
 90  * custom seq_file operations fail with ERR_PTR(-ENODEV) - this ensures
 91  * that kernfs_seq_stop_active() is skipped only after get_active failure.
 92  */
 93 static void kernfs_seq_stop_active(struct seq_file *sf, void *v)
 94 {
 95         struct kernfs_open_file *of = sf->private;
 96         const struct kernfs_ops *ops = kernfs_ops(of->kn);
 97 
 98         if (ops->seq_stop)
 99                 ops->seq_stop(sf, v);
100         kernfs_put_active(of->kn);
101 }
102 
103 static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
104 {
105         struct kernfs_open_file *of = sf->private;
106         const struct kernfs_ops *ops;
107 
108         /*
109          * @of->mutex nests outside active ref and is primarily to ensure that
110          * the ops aren't called concurrently for the same open file.
111          */
112         mutex_lock(&of->mutex);
113         if (!kernfs_get_active(of->kn))
114                 return ERR_PTR(-ENODEV);
115 
116         ops = kernfs_ops(of->kn);
117         if (ops->seq_start) {
118                 void *next = ops->seq_start(sf, ppos);
119                 /* see the comment above kernfs_seq_stop_active() */
120                 if (next == ERR_PTR(-ENODEV))
121                         kernfs_seq_stop_active(sf, next);
122                 return next;
123         } else {
124                 /*
125                  * The same behavior and code as single_open().  Returns
126                  * !NULL if pos is at the beginning; otherwise, NULL.
127                  */
128                 return NULL + !*ppos;
129         }
130 }
131 
132 static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)
133 {
134         struct kernfs_open_file *of = sf->private;
135         const struct kernfs_ops *ops = kernfs_ops(of->kn);
136 
137         if (ops->seq_next) {
138                 void *next = ops->seq_next(sf, v, ppos);
139                 /* see the comment above kernfs_seq_stop_active() */
140                 if (next == ERR_PTR(-ENODEV))
141                         kernfs_seq_stop_active(sf, next);
142                 return next;
143         } else {
144                 /*
145                  * The same behavior and code as single_open(), always
146                  * terminate after the initial read.
147                  */
148                 ++*ppos;
149                 return NULL;
150         }
151 }
152 
153 static void kernfs_seq_stop(struct seq_file *sf, void *v)
154 {
155         struct kernfs_open_file *of = sf->private;
156 
157         if (v != ERR_PTR(-ENODEV))
158                 kernfs_seq_stop_active(sf, v);
159         mutex_unlock(&of->mutex);
160 }
161 
162 static int kernfs_seq_show(struct seq_file *sf, void *v)
163 {
164         struct kernfs_open_file *of = sf->private;
165 
166         of->event = atomic_read(&of->kn->attr.open->event);
167 
168         return of->kn->attr.ops->seq_show(sf, v);
169 }
170 
171 static const struct seq_operations kernfs_seq_ops = {
172         .start = kernfs_seq_start,
173         .next = kernfs_seq_next,
174         .stop = kernfs_seq_stop,
175         .show = kernfs_seq_show,
176 };
177 
178 /*
179  * As reading a bin file can have side-effects, the exact offset and bytes
180  * specified in read(2) call should be passed to the read callback making
181  * it difficult to use seq_file.  Implement simplistic custom buffering for
182  * bin files.
183  */
184 static ssize_t kernfs_file_direct_read(struct kernfs_open_file *of,
185                                        char __user *user_buf, size_t count,
186                                        loff_t *ppos)
187 {
188         ssize_t len = min_t(size_t, count, PAGE_SIZE);
189         const struct kernfs_ops *ops;
190         char *buf;
191 
192         buf = of->prealloc_buf;
193         if (buf)
194                 mutex_lock(&of->prealloc_mutex);
195         else
196                 buf = kmalloc(len, GFP_KERNEL);
197         if (!buf)
198                 return -ENOMEM;
199 
200         /*
201          * @of->mutex nests outside active ref and is used both to ensure that
202          * the ops aren't called concurrently for the same open file.
203          */
204         mutex_lock(&of->mutex);
205         if (!kernfs_get_active(of->kn)) {
206                 len = -ENODEV;
207                 mutex_unlock(&of->mutex);
208                 goto out_free;
209         }
210 
211         of->event = atomic_read(&of->kn->attr.open->event);
212         ops = kernfs_ops(of->kn);
213         if (ops->read)
214                 len = ops->read(of, buf, len, *ppos);
215         else
216                 len = -EINVAL;
217 
218         kernfs_put_active(of->kn);
219         mutex_unlock(&of->mutex);
220 
221         if (len < 0)
222                 goto out_free;
223 
224         if (copy_to_user(user_buf, buf, len)) {
225                 len = -EFAULT;
226                 goto out_free;
227         }
228 
229         *ppos += len;
230 
231  out_free:
232         if (buf == of->prealloc_buf)
233                 mutex_unlock(&of->prealloc_mutex);
234         else
235                 kfree(buf);
236         return len;
237 }
238 
239 /**
240  * kernfs_fop_read - kernfs vfs read callback
241  * @file: file pointer
242  * @user_buf: data to write
243  * @count: number of bytes
244  * @ppos: starting offset
245  */
246 static ssize_t kernfs_fop_read(struct file *file, char __user *user_buf,
247                                size_t count, loff_t *ppos)
248 {
249         struct kernfs_open_file *of = kernfs_of(file);
250 
251         if (of->kn->flags & KERNFS_HAS_SEQ_SHOW)
252                 return seq_read(file, user_buf, count, ppos);
253         else
254                 return kernfs_file_direct_read(of, user_buf, count, ppos);
255 }
256 
257 /**
258  * kernfs_fop_write - kernfs vfs write callback
259  * @file: file pointer
260  * @user_buf: data to write
261  * @count: number of bytes
262  * @ppos: starting offset
263  *
264  * Copy data in from userland and pass it to the matching kernfs write
265  * operation.
266  *
267  * There is no easy way for us to know if userspace is only doing a partial
268  * write, so we don't support them. We expect the entire buffer to come on
269  * the first write.  Hint: if you're writing a value, first read the file,
270  * modify only the the value you're changing, then write entire buffer
271  * back.
272  */
273 static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,
274                                 size_t count, loff_t *ppos)
275 {
276         struct kernfs_open_file *of = kernfs_of(file);
277         const struct kernfs_ops *ops;
278         size_t len;
279         char *buf;
280 
281         if (of->atomic_write_len) {
282                 len = count;
283                 if (len > of->atomic_write_len)
284                         return -E2BIG;
285         } else {
286                 len = min_t(size_t, count, PAGE_SIZE);
287         }
288 
289         buf = of->prealloc_buf;
290         if (buf)
291                 mutex_lock(&of->prealloc_mutex);
292         else
293                 buf = kmalloc(len + 1, GFP_KERNEL);
294         if (!buf)
295                 return -ENOMEM;
296 
297         if (copy_from_user(buf, user_buf, len)) {
298                 len = -EFAULT;
299                 goto out_free;
300         }
301         buf[len] = '\0';        /* guarantee string termination */
302 
303         /*
304          * @of->mutex nests outside active ref and is used both to ensure that
305          * the ops aren't called concurrently for the same open file.
306          */
307         mutex_lock(&of->mutex);
308         if (!kernfs_get_active(of->kn)) {
309                 mutex_unlock(&of->mutex);
310                 len = -ENODEV;
311                 goto out_free;
312         }
313 
314         ops = kernfs_ops(of->kn);
315         if (ops->write)
316                 len = ops->write(of, buf, len, *ppos);
317         else
318                 len = -EINVAL;
319 
320         kernfs_put_active(of->kn);
321         mutex_unlock(&of->mutex);
322 
323         if (len > 0)
324                 *ppos += len;
325 
326 out_free:
327         if (buf == of->prealloc_buf)
328                 mutex_unlock(&of->prealloc_mutex);
329         else
330                 kfree(buf);
331         return len;
332 }
333 
334 static void kernfs_vma_open(struct vm_area_struct *vma)
335 {
336         struct file *file = vma->vm_file;
337         struct kernfs_open_file *of = kernfs_of(file);
338 
339         if (!of->vm_ops)
340                 return;
341 
342         if (!kernfs_get_active(of->kn))
343                 return;
344 
345         if (of->vm_ops->open)
346                 of->vm_ops->open(vma);
347 
348         kernfs_put_active(of->kn);
349 }
350 
351 static int kernfs_vma_fault(struct vm_fault *vmf)
352 {
353         struct file *file = vmf->vma->vm_file;
354         struct kernfs_open_file *of = kernfs_of(file);
355         int ret;
356 
357         if (!of->vm_ops)
358                 return VM_FAULT_SIGBUS;
359 
360         if (!kernfs_get_active(of->kn))
361                 return VM_FAULT_SIGBUS;
362 
363         ret = VM_FAULT_SIGBUS;
364         if (of->vm_ops->fault)
365                 ret = of->vm_ops->fault(vmf);
366 
367         kernfs_put_active(of->kn);
368         return ret;
369 }
370 
371 static int kernfs_vma_page_mkwrite(struct vm_fault *vmf)
372 {
373         struct file *file = vmf->vma->vm_file;
374         struct kernfs_open_file *of = kernfs_of(file);
375         int ret;
376 
377         if (!of->vm_ops)
378                 return VM_FAULT_SIGBUS;
379 
380         if (!kernfs_get_active(of->kn))
381                 return VM_FAULT_SIGBUS;
382 
383         ret = 0;
384         if (of->vm_ops->page_mkwrite)
385                 ret = of->vm_ops->page_mkwrite(vmf);
386         else
387                 file_update_time(file);
388 
389         kernfs_put_active(of->kn);
390         return ret;
391 }
392 
393 static int kernfs_vma_access(struct vm_area_struct *vma, unsigned long addr,
394                              void *buf, int len, int write)
395 {
396         struct file *file = vma->vm_file;
397         struct kernfs_open_file *of = kernfs_of(file);
398         int ret;
399 
400         if (!of->vm_ops)
401                 return -EINVAL;
402 
403         if (!kernfs_get_active(of->kn))
404                 return -EINVAL;
405 
406         ret = -EINVAL;
407         if (of->vm_ops->access)
408                 ret = of->vm_ops->access(vma, addr, buf, len, write);
409 
410         kernfs_put_active(of->kn);
411         return ret;
412 }
413 
414 #ifdef CONFIG_NUMA
415 static int kernfs_vma_set_policy(struct vm_area_struct *vma,
416                                  struct mempolicy *new)
417 {
418         struct file *file = vma->vm_file;
419         struct kernfs_open_file *of = kernfs_of(file);
420         int ret;
421 
422         if (!of->vm_ops)
423                 return 0;
424 
425         if (!kernfs_get_active(of->kn))
426                 return -EINVAL;
427 
428         ret = 0;
429         if (of->vm_ops->set_policy)
430                 ret = of->vm_ops->set_policy(vma, new);
431 
432         kernfs_put_active(of->kn);
433         return ret;
434 }
435 
436 static struct mempolicy *kernfs_vma_get_policy(struct vm_area_struct *vma,
437                                                unsigned long addr)
438 {
439         struct file *file = vma->vm_file;
440         struct kernfs_open_file *of = kernfs_of(file);
441         struct mempolicy *pol;
442 
443         if (!of->vm_ops)
444                 return vma->vm_policy;
445 
446         if (!kernfs_get_active(of->kn))
447                 return vma->vm_policy;
448 
449         pol = vma->vm_policy;
450         if (of->vm_ops->get_policy)
451                 pol = of->vm_ops->get_policy(vma, addr);
452 
453         kernfs_put_active(of->kn);
454         return pol;
455 }
456 
457 #endif
458 
459 static const struct vm_operations_struct kernfs_vm_ops = {
460         .open           = kernfs_vma_open,
461         .fault          = kernfs_vma_fault,
462         .page_mkwrite   = kernfs_vma_page_mkwrite,
463         .access         = kernfs_vma_access,
464 #ifdef CONFIG_NUMA
465         .set_policy     = kernfs_vma_set_policy,
466         .get_policy     = kernfs_vma_get_policy,
467 #endif
468 };
469 
470 static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
471 {
472         struct kernfs_open_file *of = kernfs_of(file);
473         const struct kernfs_ops *ops;
474         int rc;
475 
476         /*
477          * mmap path and of->mutex are prone to triggering spurious lockdep
478          * warnings and we don't want to add spurious locking dependency
479          * between the two.  Check whether mmap is actually implemented
480          * without grabbing @of->mutex by testing HAS_MMAP flag.  See the
481          * comment in kernfs_file_open() for more details.
482          */
483         if (!(of->kn->flags & KERNFS_HAS_MMAP))
484                 return -ENODEV;
485 
486         mutex_lock(&of->mutex);
487 
488         rc = -ENODEV;
489         if (!kernfs_get_active(of->kn))
490                 goto out_unlock;
491 
492         ops = kernfs_ops(of->kn);
493         rc = ops->mmap(of, vma);
494         if (rc)
495                 goto out_put;
496 
497         /*
498          * PowerPC's pci_mmap of legacy_mem uses shmem_zero_setup()
499          * to satisfy versions of X which crash if the mmap fails: that
500          * substitutes a new vm_file, and we don't then want bin_vm_ops.
501          */
502         if (vma->vm_file != file)
503                 goto out_put;
504 
505         rc = -EINVAL;
506         if (of->mmapped && of->vm_ops != vma->vm_ops)
507                 goto out_put;
508 
509         /*
510          * It is not possible to successfully wrap close.
511          * So error if someone is trying to use close.
512          */
513         rc = -EINVAL;
514         if (vma->vm_ops && vma->vm_ops->close)
515                 goto out_put;
516 
517         rc = 0;
518         of->mmapped = true;
519         of->vm_ops = vma->vm_ops;
520         vma->vm_ops = &kernfs_vm_ops;
521 out_put:
522         kernfs_put_active(of->kn);
523 out_unlock:
524         mutex_unlock(&of->mutex);
525 
526         return rc;
527 }
528 
529 /**
530  *      kernfs_get_open_node - get or create kernfs_open_node
531  *      @kn: target kernfs_node
532  *      @of: kernfs_open_file for this instance of open
533  *
534  *      If @kn->attr.open exists, increment its reference count; otherwise,
535  *      create one.  @of is chained to the files list.
536  *
537  *      LOCKING:
538  *      Kernel thread context (may sleep).
539  *
540  *      RETURNS:
541  *      0 on success, -errno on failure.
542  */
543 static int kernfs_get_open_node(struct kernfs_node *kn,
544                                 struct kernfs_open_file *of)
545 {
546         struct kernfs_open_node *on, *new_on = NULL;
547 
548  retry:
549         mutex_lock(&kernfs_open_file_mutex);
550         spin_lock_irq(&kernfs_open_node_lock);
551 
552         if (!kn->attr.open && new_on) {
553                 kn->attr.open = new_on;
554                 new_on = NULL;
555         }
556 
557         on = kn->attr.open;
558         if (on) {
559                 atomic_inc(&on->refcnt);
560                 list_add_tail(&of->list, &on->files);
561         }
562 
563         spin_unlock_irq(&kernfs_open_node_lock);
564         mutex_unlock(&kernfs_open_file_mutex);
565 
566         if (on) {
567                 kfree(new_on);
568                 return 0;
569         }
570 
571         /* not there, initialize a new one and retry */
572         new_on = kmalloc(sizeof(*new_on), GFP_KERNEL);
573         if (!new_on)
574                 return -ENOMEM;
575 
576         atomic_set(&new_on->refcnt, 0);
577         atomic_set(&new_on->event, 1);
578         init_waitqueue_head(&new_on->poll);
579         INIT_LIST_HEAD(&new_on->files);
580         goto retry;
581 }
582 
583 /**
584  *      kernfs_put_open_node - put kernfs_open_node
585  *      @kn: target kernfs_nodet
586  *      @of: associated kernfs_open_file
587  *
588  *      Put @kn->attr.open and unlink @of from the files list.  If
589  *      reference count reaches zero, disassociate and free it.
590  *
591  *      LOCKING:
592  *      None.
593  */
594 static void kernfs_put_open_node(struct kernfs_node *kn,
595                                  struct kernfs_open_file *of)
596 {
597         struct kernfs_open_node *on = kn->attr.open;
598         unsigned long flags;
599 
600         mutex_lock(&kernfs_open_file_mutex);
601         spin_lock_irqsave(&kernfs_open_node_lock, flags);
602 
603         if (of)
604                 list_del(&of->list);
605 
606         if (atomic_dec_and_test(&on->refcnt))
607                 kn->attr.open = NULL;
608         else
609                 on = NULL;
610 
611         spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
612         mutex_unlock(&kernfs_open_file_mutex);
613 
614         kfree(on);
615 }
616 
617 static int kernfs_fop_open(struct inode *inode, struct file *file)
618 {
619         struct kernfs_node *kn = file->f_path.dentry->d_fsdata;
620         struct kernfs_root *root = kernfs_root(kn);
621         const struct kernfs_ops *ops;
622         struct kernfs_open_file *of;
623         bool has_read, has_write, has_mmap;
624         int error = -EACCES;
625 
626         if (!kernfs_get_active(kn))
627                 return -ENODEV;
628 
629         ops = kernfs_ops(kn);
630 
631         has_read = ops->seq_show || ops->read || ops->mmap;
632         has_write = ops->write || ops->mmap;
633         has_mmap = ops->mmap;
634 
635         /* see the flag definition for details */
636         if (root->flags & KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK) {
637                 if ((file->f_mode & FMODE_WRITE) &&
638                     (!(inode->i_mode & S_IWUGO) || !has_write))
639                         goto err_out;
640 
641                 if ((file->f_mode & FMODE_READ) &&
642                     (!(inode->i_mode & S_IRUGO) || !has_read))
643                         goto err_out;
644         }
645 
646         /* allocate a kernfs_open_file for the file */
647         error = -ENOMEM;
648         of = kzalloc(sizeof(struct kernfs_open_file), GFP_KERNEL);
649         if (!of)
650                 goto err_out;
651 
652         /*
653          * The following is done to give a different lockdep key to
654          * @of->mutex for files which implement mmap.  This is a rather
655          * crude way to avoid false positive lockdep warning around
656          * mm->mmap_sem - mmap nests @of->mutex under mm->mmap_sem and
657          * reading /sys/block/sda/trace/act_mask grabs sr_mutex, under
658          * which mm->mmap_sem nests, while holding @of->mutex.  As each
659          * open file has a separate mutex, it's okay as long as those don't
660          * happen on the same file.  At this point, we can't easily give
661          * each file a separate locking class.  Let's differentiate on
662          * whether the file has mmap or not for now.
663          *
664          * Both paths of the branch look the same.  They're supposed to
665          * look that way and give @of->mutex different static lockdep keys.
666          */
667         if (has_mmap)
668                 mutex_init(&of->mutex);
669         else
670                 mutex_init(&of->mutex);
671 
672         of->kn = kn;
673         of->file = file;
674 
675         /*
676          * Write path needs to atomic_write_len outside active reference.
677          * Cache it in open_file.  See kernfs_fop_write() for details.
678          */
679         of->atomic_write_len = ops->atomic_write_len;
680 
681         error = -EINVAL;
682         /*
683          * ->seq_show is incompatible with ->prealloc,
684          * as seq_read does its own allocation.
685          * ->read must be used instead.
686          */
687         if (ops->prealloc && ops->seq_show)
688                 goto err_free;
689         if (ops->prealloc) {
690                 int len = of->atomic_write_len ?: PAGE_SIZE;
691                 of->prealloc_buf = kmalloc(len + 1, GFP_KERNEL);
692                 error = -ENOMEM;
693                 if (!of->prealloc_buf)
694                         goto err_free;
695                 mutex_init(&of->prealloc_mutex);
696         }
697 
698         /*
699          * Always instantiate seq_file even if read access doesn't use
700          * seq_file or is not requested.  This unifies private data access
701          * and readable regular files are the vast majority anyway.
702          */
703         if (ops->seq_show)
704                 error = seq_open(file, &kernfs_seq_ops);
705         else
706                 error = seq_open(file, NULL);
707         if (error)
708                 goto err_free;
709 
710         of->seq_file = file->private_data;
711         of->seq_file->private = of;
712 
713         /* seq_file clears PWRITE unconditionally, restore it if WRITE */
714         if (file->f_mode & FMODE_WRITE)
715                 file->f_mode |= FMODE_PWRITE;
716 
717         /* make sure we have open node struct */
718         error = kernfs_get_open_node(kn, of);
719         if (error)
720                 goto err_seq_release;
721 
722         if (ops->open) {
723                 /* nobody has access to @of yet, skip @of->mutex */
724                 error = ops->open(of);
725                 if (error)
726                         goto err_put_node;
727         }
728 
729         /* open succeeded, put active references */
730         kernfs_put_active(kn);
731         return 0;
732 
733 err_put_node:
734         kernfs_put_open_node(kn, of);
735 err_seq_release:
736         seq_release(inode, file);
737 err_free:
738         kfree(of->prealloc_buf);
739         kfree(of);
740 err_out:
741         kernfs_put_active(kn);
742         return error;
743 }
744 
745 /* used from release/drain to ensure that ->release() is called exactly once */
746 static void kernfs_release_file(struct kernfs_node *kn,
747                                 struct kernfs_open_file *of)
748 {
749         /*
750          * @of is guaranteed to have no other file operations in flight and
751          * we just want to synchronize release and drain paths.
752          * @kernfs_open_file_mutex is enough.  @of->mutex can't be used
753          * here because drain path may be called from places which can
754          * cause circular dependency.
755          */
756         lockdep_assert_held(&kernfs_open_file_mutex);
757 
758         if (!of->released) {
759                 /*
760                  * A file is never detached without being released and we
761                  * need to be able to release files which are deactivated
762                  * and being drained.  Don't use kernfs_ops().
763                  */
764                 kn->attr.ops->release(of);
765                 of->released = true;
766         }
767 }
768 
769 static int kernfs_fop_release(struct inode *inode, struct file *filp)
770 {
771         struct kernfs_node *kn = filp->f_path.dentry->d_fsdata;
772         struct kernfs_open_file *of = kernfs_of(filp);
773 
774         if (kn->flags & KERNFS_HAS_RELEASE) {
775                 mutex_lock(&kernfs_open_file_mutex);
776                 kernfs_release_file(kn, of);
777                 mutex_unlock(&kernfs_open_file_mutex);
778         }
779 
780         kernfs_put_open_node(kn, of);
781         seq_release(inode, filp);
782         kfree(of->prealloc_buf);
783         kfree(of);
784 
785         return 0;
786 }
787 
788 void kernfs_drain_open_files(struct kernfs_node *kn)
789 {
790         struct kernfs_open_node *on;
791         struct kernfs_open_file *of;
792 
793         if (!(kn->flags & (KERNFS_HAS_MMAP | KERNFS_HAS_RELEASE)))
794                 return;
795 
796         spin_lock_irq(&kernfs_open_node_lock);
797         on = kn->attr.open;
798         if (on)
799                 atomic_inc(&on->refcnt);
800         spin_unlock_irq(&kernfs_open_node_lock);
801         if (!on)
802                 return;
803 
804         mutex_lock(&kernfs_open_file_mutex);
805 
806         list_for_each_entry(of, &on->files, list) {
807                 struct inode *inode = file_inode(of->file);
808 
809                 if (kn->flags & KERNFS_HAS_MMAP)
810                         unmap_mapping_range(inode->i_mapping, 0, 0, 1);
811 
812                 if (kn->flags & KERNFS_HAS_RELEASE)
813                         kernfs_release_file(kn, of);
814         }
815 
816         mutex_unlock(&kernfs_open_file_mutex);
817 
818         kernfs_put_open_node(kn, NULL);
819 }
820 
821 /*
822  * Kernfs attribute files are pollable.  The idea is that you read
823  * the content and then you use 'poll' or 'select' to wait for
824  * the content to change.  When the content changes (assuming the
825  * manager for the kobject supports notification), poll will
826  * return POLLERR|POLLPRI, and select will return the fd whether
827  * it is waiting for read, write, or exceptions.
828  * Once poll/select indicates that the value has changed, you
829  * need to close and re-open the file, or seek to 0 and read again.
830  * Reminder: this only works for attributes which actively support
831  * it, and it is not possible to test an attribute from userspace
832  * to see if it supports poll (Neither 'poll' nor 'select' return
833  * an appropriate error code).  When in doubt, set a suitable timeout value.
834  */
835 static unsigned int kernfs_fop_poll(struct file *filp, poll_table *wait)
836 {
837         struct kernfs_open_file *of = kernfs_of(filp);
838         struct kernfs_node *kn = filp->f_path.dentry->d_fsdata;
839         struct kernfs_open_node *on = kn->attr.open;
840 
841         if (!kernfs_get_active(kn))
842                 goto trigger;
843 
844         poll_wait(filp, &on->poll, wait);
845 
846         kernfs_put_active(kn);
847 
848         if (of->event != atomic_read(&on->event))
849                 goto trigger;
850 
851         return DEFAULT_POLLMASK;
852 
853  trigger:
854         return DEFAULT_POLLMASK|POLLERR|POLLPRI;
855 }
856 
857 static void kernfs_notify_workfn(struct work_struct *work)
858 {
859         struct kernfs_node *kn;
860         struct kernfs_open_node *on;
861         struct kernfs_super_info *info;
862 repeat:
863         /* pop one off the notify_list */
864         spin_lock_irq(&kernfs_notify_lock);
865         kn = kernfs_notify_list;
866         if (kn == KERNFS_NOTIFY_EOL) {
867                 spin_unlock_irq(&kernfs_notify_lock);
868                 return;
869         }
870         kernfs_notify_list = kn->attr.notify_next;
871         kn->attr.notify_next = NULL;
872         spin_unlock_irq(&kernfs_notify_lock);
873 
874         /* kick poll */
875         spin_lock_irq(&kernfs_open_node_lock);
876 
877         on = kn->attr.open;
878         if (on) {
879                 atomic_inc(&on->event);
880                 wake_up_interruptible(&on->poll);
881         }
882 
883         spin_unlock_irq(&kernfs_open_node_lock);
884 
885         /* kick fsnotify */
886         mutex_lock(&kernfs_mutex);
887 
888         list_for_each_entry(info, &kernfs_root(kn)->supers, node) {
889                 struct kernfs_node *parent;
890                 struct inode *inode;
891 
892                 /*
893                  * We want fsnotify_modify() on @kn but as the
894                  * modifications aren't originating from userland don't
895                  * have the matching @file available.  Look up the inodes
896                  * and generate the events manually.
897                  */
898                 inode = ilookup(info->sb, kn->ino);
899                 if (!inode)
900                         continue;
901 
902                 parent = kernfs_get_parent(kn);
903                 if (parent) {
904                         struct inode *p_inode;
905 
906                         p_inode = ilookup(info->sb, parent->ino);
907                         if (p_inode) {
908                                 fsnotify(p_inode, FS_MODIFY | FS_EVENT_ON_CHILD,
909                                          inode, FSNOTIFY_EVENT_INODE, kn->name, 0);
910                                 iput(p_inode);
911                         }
912 
913                         kernfs_put(parent);
914                 }
915 
916                 fsnotify(inode, FS_MODIFY, inode, FSNOTIFY_EVENT_INODE,
917                          kn->name, 0);
918                 iput(inode);
919         }
920 
921         mutex_unlock(&kernfs_mutex);
922         kernfs_put(kn);
923         goto repeat;
924 }
925 
926 /**
927  * kernfs_notify - notify a kernfs file
928  * @kn: file to notify
929  *
930  * Notify @kn such that poll(2) on @kn wakes up.  Maybe be called from any
931  * context.
932  */
933 void kernfs_notify(struct kernfs_node *kn)
934 {
935         static DECLARE_WORK(kernfs_notify_work, kernfs_notify_workfn);
936         unsigned long flags;
937 
938         if (WARN_ON(kernfs_type(kn) != KERNFS_FILE))
939                 return;
940 
941         spin_lock_irqsave(&kernfs_notify_lock, flags);
942         if (!kn->attr.notify_next) {
943                 kernfs_get(kn);
944                 kn->attr.notify_next = kernfs_notify_list;
945                 kernfs_notify_list = kn;
946                 schedule_work(&kernfs_notify_work);
947         }
948         spin_unlock_irqrestore(&kernfs_notify_lock, flags);
949 }
950 EXPORT_SYMBOL_GPL(kernfs_notify);
951 
952 const struct file_operations kernfs_file_fops = {
953         .read           = kernfs_fop_read,
954         .write          = kernfs_fop_write,
955         .llseek         = generic_file_llseek,
956         .mmap           = kernfs_fop_mmap,
957         .open           = kernfs_fop_open,
958         .release        = kernfs_fop_release,
959         .poll           = kernfs_fop_poll,
960         .fsync          = noop_fsync,
961 };
962 
963 /**
964  * __kernfs_create_file - kernfs internal function to create a file
965  * @parent: directory to create the file in
966  * @name: name of the file
967  * @mode: mode of the file
968  * @size: size of the file
969  * @ops: kernfs operations for the file
970  * @priv: private data for the file
971  * @ns: optional namespace tag of the file
972  * @key: lockdep key for the file's active_ref, %NULL to disable lockdep
973  *
974  * Returns the created node on success, ERR_PTR() value on error.
975  */
976 struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
977                                          const char *name,
978                                          umode_t mode, loff_t size,
979                                          const struct kernfs_ops *ops,
980                                          void *priv, const void *ns,
981                                          struct lock_class_key *key)
982 {
983         struct kernfs_node *kn;
984         unsigned flags;
985         int rc;
986 
987         flags = KERNFS_FILE;
988 
989         kn = kernfs_new_node(parent, name, (mode & S_IALLUGO) | S_IFREG, flags);
990         if (!kn)
991                 return ERR_PTR(-ENOMEM);
992 
993         kn->attr.ops = ops;
994         kn->attr.size = size;
995         kn->ns = ns;
996         kn->priv = priv;
997 
998 #ifdef CONFIG_DEBUG_LOCK_ALLOC
999         if (key) {
1000                 lockdep_init_map(&kn->dep_map, "s_active", key, 0);
1001                 kn->flags |= KERNFS_LOCKDEP;
1002         }
1003 #endif
1004 
1005         /*
1006          * kn->attr.ops is accesible only while holding active ref.  We
1007          * need to know whether some ops are implemented outside active
1008          * ref.  Cache their existence in flags.
1009          */
1010         if (ops->seq_show)
1011                 kn->flags |= KERNFS_HAS_SEQ_SHOW;
1012         if (ops->mmap)
1013                 kn->flags |= KERNFS_HAS_MMAP;
1014         if (ops->release)
1015                 kn->flags |= KERNFS_HAS_RELEASE;
1016 
1017         rc = kernfs_add_one(kn);
1018         if (rc) {
1019                 kernfs_put(kn);
1020                 return ERR_PTR(rc);
1021         }
1022         return kn;
1023 }
1024 

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