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TOMOYO Linux Cross Reference
Linux/fs/select.c

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  1 /*
  2  * This file contains the procedures for the handling of select and poll
  3  *
  4  * Created for Linux based loosely upon Mathius Lattner's minix
  5  * patches by Peter MacDonald. Heavily edited by Linus.
  6  *
  7  *  4 February 1994
  8  *     COFF/ELF binary emulation. If the process has the STICKY_TIMEOUTS
  9  *     flag set in its personality we do *not* modify the given timeout
 10  *     parameter to reflect time remaining.
 11  *
 12  *  24 January 2000
 13  *     Changed sys_poll()/do_poll() to use PAGE_SIZE chunk-based allocation 
 14  *     of fds to overcome nfds < 16390 descriptors limit (Tigran Aivazian).
 15  */
 16 
 17 #include <linux/kernel.h>
 18 #include <linux/sched.h>
 19 #include <linux/syscalls.h>
 20 #include <linux/export.h>
 21 #include <linux/slab.h>
 22 #include <linux/poll.h>
 23 #include <linux/personality.h> /* for STICKY_TIMEOUTS */
 24 #include <linux/file.h>
 25 #include <linux/fdtable.h>
 26 #include <linux/fs.h>
 27 #include <linux/rcupdate.h>
 28 #include <linux/hrtimer.h>
 29 #include <linux/sched/rt.h>
 30 
 31 #include <asm/uaccess.h>
 32 
 33 
 34 /*
 35  * Estimate expected accuracy in ns from a timeval.
 36  *
 37  * After quite a bit of churning around, we've settled on
 38  * a simple thing of taking 0.1% of the timeout as the
 39  * slack, with a cap of 100 msec.
 40  * "nice" tasks get a 0.5% slack instead.
 41  *
 42  * Consider this comment an open invitation to come up with even
 43  * better solutions..
 44  */
 45 
 46 #define MAX_SLACK       (100 * NSEC_PER_MSEC)
 47 
 48 static long __estimate_accuracy(struct timespec *tv)
 49 {
 50         long slack;
 51         int divfactor = 1000;
 52 
 53         if (tv->tv_sec < 0)
 54                 return 0;
 55 
 56         if (task_nice(current) > 0)
 57                 divfactor = divfactor / 5;
 58 
 59         if (tv->tv_sec > MAX_SLACK / (NSEC_PER_SEC/divfactor))
 60                 return MAX_SLACK;
 61 
 62         slack = tv->tv_nsec / divfactor;
 63         slack += tv->tv_sec * (NSEC_PER_SEC/divfactor);
 64 
 65         if (slack > MAX_SLACK)
 66                 return MAX_SLACK;
 67 
 68         return slack;
 69 }
 70 
 71 long select_estimate_accuracy(struct timespec *tv)
 72 {
 73         unsigned long ret;
 74         struct timespec now;
 75 
 76         /*
 77          * Realtime tasks get a slack of 0 for obvious reasons.
 78          */
 79 
 80         if (rt_task(current))
 81                 return 0;
 82 
 83         ktime_get_ts(&now);
 84         now = timespec_sub(*tv, now);
 85         ret = __estimate_accuracy(&now);
 86         if (ret < current->timer_slack_ns)
 87                 return current->timer_slack_ns;
 88         return ret;
 89 }
 90 
 91 
 92 
 93 struct poll_table_page {
 94         struct poll_table_page * next;
 95         struct poll_table_entry * entry;
 96         struct poll_table_entry entries[0];
 97 };
 98 
 99 #define POLL_TABLE_FULL(table) \
100         ((unsigned long)((table)->entry+1) > PAGE_SIZE + (unsigned long)(table))
101 
102 /*
103  * Ok, Peter made a complicated, but straightforward multiple_wait() function.
104  * I have rewritten this, taking some shortcuts: This code may not be easy to
105  * follow, but it should be free of race-conditions, and it's practical. If you
106  * understand what I'm doing here, then you understand how the linux
107  * sleep/wakeup mechanism works.
108  *
109  * Two very simple procedures, poll_wait() and poll_freewait() make all the
110  * work.  poll_wait() is an inline-function defined in <linux/poll.h>,
111  * as all select/poll functions have to call it to add an entry to the
112  * poll table.
113  */
114 static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
115                        poll_table *p);
116 
117 void poll_initwait(struct poll_wqueues *pwq)
118 {
119         init_poll_funcptr(&pwq->pt, __pollwait);
120         pwq->polling_task = current;
121         pwq->triggered = 0;
122         pwq->error = 0;
123         pwq->table = NULL;
124         pwq->inline_index = 0;
125 }
126 EXPORT_SYMBOL(poll_initwait);
127 
128 static void free_poll_entry(struct poll_table_entry *entry)
129 {
130         remove_wait_queue(entry->wait_address, &entry->wait);
131         fput(entry->filp);
132 }
133 
134 void poll_freewait(struct poll_wqueues *pwq)
135 {
136         struct poll_table_page * p = pwq->table;
137         int i;
138         for (i = 0; i < pwq->inline_index; i++)
139                 free_poll_entry(pwq->inline_entries + i);
140         while (p) {
141                 struct poll_table_entry * entry;
142                 struct poll_table_page *old;
143 
144                 entry = p->entry;
145                 do {
146                         entry--;
147                         free_poll_entry(entry);
148                 } while (entry > p->entries);
149                 old = p;
150                 p = p->next;
151                 free_page((unsigned long) old);
152         }
153 }
154 EXPORT_SYMBOL(poll_freewait);
155 
156 static struct poll_table_entry *poll_get_entry(struct poll_wqueues *p)
157 {
158         struct poll_table_page *table = p->table;
159 
160         if (p->inline_index < N_INLINE_POLL_ENTRIES)
161                 return p->inline_entries + p->inline_index++;
162 
163         if (!table || POLL_TABLE_FULL(table)) {
164                 struct poll_table_page *new_table;
165 
166                 new_table = (struct poll_table_page *) __get_free_page(GFP_KERNEL);
167                 if (!new_table) {
168                         p->error = -ENOMEM;
169                         return NULL;
170                 }
171                 new_table->entry = new_table->entries;
172                 new_table->next = table;
173                 p->table = new_table;
174                 table = new_table;
175         }
176 
177         return table->entry++;
178 }
179 
180 static int __pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key)
181 {
182         struct poll_wqueues *pwq = wait->private;
183         DECLARE_WAITQUEUE(dummy_wait, pwq->polling_task);
184 
185         /*
186          * Although this function is called under waitqueue lock, LOCK
187          * doesn't imply write barrier and the users expect write
188          * barrier semantics on wakeup functions.  The following
189          * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
190          * and is paired with set_mb() in poll_schedule_timeout.
191          */
192         smp_wmb();
193         pwq->triggered = 1;
194 
195         /*
196          * Perform the default wake up operation using a dummy
197          * waitqueue.
198          *
199          * TODO: This is hacky but there currently is no interface to
200          * pass in @sync.  @sync is scheduled to be removed and once
201          * that happens, wake_up_process() can be used directly.
202          */
203         return default_wake_function(&dummy_wait, mode, sync, key);
204 }
205 
206 static int pollwake(wait_queue_t *wait, unsigned mode, int sync, void *key)
207 {
208         struct poll_table_entry *entry;
209 
210         entry = container_of(wait, struct poll_table_entry, wait);
211         if (key && !((unsigned long)key & entry->key))
212                 return 0;
213         return __pollwake(wait, mode, sync, key);
214 }
215 
216 /* Add a new entry */
217 static void __pollwait(struct file *filp, wait_queue_head_t *wait_address,
218                                 poll_table *p)
219 {
220         struct poll_wqueues *pwq = container_of(p, struct poll_wqueues, pt);
221         struct poll_table_entry *entry = poll_get_entry(pwq);
222         if (!entry)
223                 return;
224         entry->filp = get_file(filp);
225         entry->wait_address = wait_address;
226         entry->key = p->_key;
227         init_waitqueue_func_entry(&entry->wait, pollwake);
228         entry->wait.private = pwq;
229         add_wait_queue(wait_address, &entry->wait);
230 }
231 
232 int poll_schedule_timeout(struct poll_wqueues *pwq, int state,
233                           ktime_t *expires, unsigned long slack)
234 {
235         int rc = -EINTR;
236 
237         set_current_state(state);
238         if (!pwq->triggered)
239                 rc = schedule_hrtimeout_range(expires, slack, HRTIMER_MODE_ABS);
240         __set_current_state(TASK_RUNNING);
241 
242         /*
243          * Prepare for the next iteration.
244          *
245          * The following set_mb() serves two purposes.  First, it's
246          * the counterpart rmb of the wmb in pollwake() such that data
247          * written before wake up is always visible after wake up.
248          * Second, the full barrier guarantees that triggered clearing
249          * doesn't pass event check of the next iteration.  Note that
250          * this problem doesn't exist for the first iteration as
251          * add_wait_queue() has full barrier semantics.
252          */
253         set_mb(pwq->triggered, 0);
254 
255         return rc;
256 }
257 EXPORT_SYMBOL(poll_schedule_timeout);
258 
259 /**
260  * poll_select_set_timeout - helper function to setup the timeout value
261  * @to:         pointer to timespec variable for the final timeout
262  * @sec:        seconds (from user space)
263  * @nsec:       nanoseconds (from user space)
264  *
265  * Note, we do not use a timespec for the user space value here, That
266  * way we can use the function for timeval and compat interfaces as well.
267  *
268  * Returns -EINVAL if sec/nsec are not normalized. Otherwise 0.
269  */
270 int poll_select_set_timeout(struct timespec *to, long sec, long nsec)
271 {
272         struct timespec ts = {.tv_sec = sec, .tv_nsec = nsec};
273 
274         if (!timespec_valid(&ts))
275                 return -EINVAL;
276 
277         /* Optimize for the zero timeout value here */
278         if (!sec && !nsec) {
279                 to->tv_sec = to->tv_nsec = 0;
280         } else {
281                 ktime_get_ts(to);
282                 *to = timespec_add_safe(*to, ts);
283         }
284         return 0;
285 }
286 
287 static int poll_select_copy_remaining(struct timespec *end_time, void __user *p,
288                                       int timeval, int ret)
289 {
290         struct timespec rts;
291         struct timeval rtv;
292 
293         if (!p)
294                 return ret;
295 
296         if (current->personality & STICKY_TIMEOUTS)
297                 goto sticky;
298 
299         /* No update for zero timeout */
300         if (!end_time->tv_sec && !end_time->tv_nsec)
301                 return ret;
302 
303         ktime_get_ts(&rts);
304         rts = timespec_sub(*end_time, rts);
305         if (rts.tv_sec < 0)
306                 rts.tv_sec = rts.tv_nsec = 0;
307 
308         if (timeval) {
309                 if (sizeof(rtv) > sizeof(rtv.tv_sec) + sizeof(rtv.tv_usec))
310                         memset(&rtv, 0, sizeof(rtv));
311                 rtv.tv_sec = rts.tv_sec;
312                 rtv.tv_usec = rts.tv_nsec / NSEC_PER_USEC;
313 
314                 if (!copy_to_user(p, &rtv, sizeof(rtv)))
315                         return ret;
316 
317         } else if (!copy_to_user(p, &rts, sizeof(rts)))
318                 return ret;
319 
320         /*
321          * If an application puts its timeval in read-only memory, we
322          * don't want the Linux-specific update to the timeval to
323          * cause a fault after the select has completed
324          * successfully. However, because we're not updating the
325          * timeval, we can't restart the system call.
326          */
327 
328 sticky:
329         if (ret == -ERESTARTNOHAND)
330                 ret = -EINTR;
331         return ret;
332 }
333 
334 #define FDS_IN(fds, n)          (fds->in + n)
335 #define FDS_OUT(fds, n)         (fds->out + n)
336 #define FDS_EX(fds, n)          (fds->ex + n)
337 
338 #define BITS(fds, n)    (*FDS_IN(fds, n)|*FDS_OUT(fds, n)|*FDS_EX(fds, n))
339 
340 static int max_select_fd(unsigned long n, fd_set_bits *fds)
341 {
342         unsigned long *open_fds;
343         unsigned long set;
344         int max;
345         struct fdtable *fdt;
346 
347         /* handle last in-complete long-word first */
348         set = ~(~0UL << (n & (BITS_PER_LONG-1)));
349         n /= BITS_PER_LONG;
350         fdt = files_fdtable(current->files);
351         open_fds = fdt->open_fds + n;
352         max = 0;
353         if (set) {
354                 set &= BITS(fds, n);
355                 if (set) {
356                         if (!(set & ~*open_fds))
357                                 goto get_max;
358                         return -EBADF;
359                 }
360         }
361         while (n) {
362                 open_fds--;
363                 n--;
364                 set = BITS(fds, n);
365                 if (!set)
366                         continue;
367                 if (set & ~*open_fds)
368                         return -EBADF;
369                 if (max)
370                         continue;
371 get_max:
372                 do {
373                         max++;
374                         set >>= 1;
375                 } while (set);
376                 max += n * BITS_PER_LONG;
377         }
378 
379         return max;
380 }
381 
382 #define POLLIN_SET (POLLRDNORM | POLLRDBAND | POLLIN | POLLHUP | POLLERR)
383 #define POLLOUT_SET (POLLWRBAND | POLLWRNORM | POLLOUT | POLLERR)
384 #define POLLEX_SET (POLLPRI)
385 
386 static inline void wait_key_set(poll_table *wait, unsigned long in,
387                                 unsigned long out, unsigned long bit)
388 {
389         wait->_key = POLLEX_SET;
390         if (in & bit)
391                 wait->_key |= POLLIN_SET;
392         if (out & bit)
393                 wait->_key |= POLLOUT_SET;
394 }
395 
396 int do_select(int n, fd_set_bits *fds, struct timespec *end_time)
397 {
398         ktime_t expire, *to = NULL;
399         struct poll_wqueues table;
400         poll_table *wait;
401         int retval, i, timed_out = 0;
402         unsigned long slack = 0;
403 
404         rcu_read_lock();
405         retval = max_select_fd(n, fds);
406         rcu_read_unlock();
407 
408         if (retval < 0)
409                 return retval;
410         n = retval;
411 
412         poll_initwait(&table);
413         wait = &table.pt;
414         if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {
415                 wait->_qproc = NULL;
416                 timed_out = 1;
417         }
418 
419         if (end_time && !timed_out)
420                 slack = select_estimate_accuracy(end_time);
421 
422         retval = 0;
423         for (;;) {
424                 unsigned long *rinp, *routp, *rexp, *inp, *outp, *exp;
425 
426                 inp = fds->in; outp = fds->out; exp = fds->ex;
427                 rinp = fds->res_in; routp = fds->res_out; rexp = fds->res_ex;
428 
429                 for (i = 0; i < n; ++rinp, ++routp, ++rexp) {
430                         unsigned long in, out, ex, all_bits, bit = 1, mask, j;
431                         unsigned long res_in = 0, res_out = 0, res_ex = 0;
432 
433                         in = *inp++; out = *outp++; ex = *exp++;
434                         all_bits = in | out | ex;
435                         if (all_bits == 0) {
436                                 i += BITS_PER_LONG;
437                                 continue;
438                         }
439 
440                         for (j = 0; j < BITS_PER_LONG; ++j, ++i, bit <<= 1) {
441                                 struct fd f;
442                                 if (i >= n)
443                                         break;
444                                 if (!(bit & all_bits))
445                                         continue;
446                                 f = fdget(i);
447                                 if (f.file) {
448                                         const struct file_operations *f_op;
449                                         f_op = f.file->f_op;
450                                         mask = DEFAULT_POLLMASK;
451                                         if (f_op && f_op->poll) {
452                                                 wait_key_set(wait, in, out, bit);
453                                                 mask = (*f_op->poll)(f.file, wait);
454                                         }
455                                         fdput(f);
456                                         if ((mask & POLLIN_SET) && (in & bit)) {
457                                                 res_in |= bit;
458                                                 retval++;
459                                                 wait->_qproc = NULL;
460                                         }
461                                         if ((mask & POLLOUT_SET) && (out & bit)) {
462                                                 res_out |= bit;
463                                                 retval++;
464                                                 wait->_qproc = NULL;
465                                         }
466                                         if ((mask & POLLEX_SET) && (ex & bit)) {
467                                                 res_ex |= bit;
468                                                 retval++;
469                                                 wait->_qproc = NULL;
470                                         }
471                                 }
472                         }
473                         if (res_in)
474                                 *rinp = res_in;
475                         if (res_out)
476                                 *routp = res_out;
477                         if (res_ex)
478                                 *rexp = res_ex;
479                         cond_resched();
480                 }
481                 wait->_qproc = NULL;
482                 if (retval || timed_out || signal_pending(current))
483                         break;
484                 if (table.error) {
485                         retval = table.error;
486                         break;
487                 }
488 
489                 /*
490                  * If this is the first loop and we have a timeout
491                  * given, then we convert to ktime_t and set the to
492                  * pointer to the expiry value.
493                  */
494                 if (end_time && !to) {
495                         expire = timespec_to_ktime(*end_time);
496                         to = &expire;
497                 }
498 
499                 if (!poll_schedule_timeout(&table, TASK_INTERRUPTIBLE,
500                                            to, slack))
501                         timed_out = 1;
502         }
503 
504         poll_freewait(&table);
505 
506         return retval;
507 }
508 
509 /*
510  * We can actually return ERESTARTSYS instead of EINTR, but I'd
511  * like to be certain this leads to no problems. So I return
512  * EINTR just for safety.
513  *
514  * Update: ERESTARTSYS breaks at least the xview clock binary, so
515  * I'm trying ERESTARTNOHAND which restart only when you want to.
516  */
517 int core_sys_select(int n, fd_set __user *inp, fd_set __user *outp,
518                            fd_set __user *exp, struct timespec *end_time)
519 {
520         fd_set_bits fds;
521         void *bits;
522         int ret, max_fds;
523         unsigned int size;
524         struct fdtable *fdt;
525         /* Allocate small arguments on the stack to save memory and be faster */
526         long stack_fds[SELECT_STACK_ALLOC/sizeof(long)];
527 
528         ret = -EINVAL;
529         if (n < 0)
530                 goto out_nofds;
531 
532         /* max_fds can increase, so grab it once to avoid race */
533         rcu_read_lock();
534         fdt = files_fdtable(current->files);
535         max_fds = fdt->max_fds;
536         rcu_read_unlock();
537         if (n > max_fds)
538                 n = max_fds;
539 
540         /*
541          * We need 6 bitmaps (in/out/ex for both incoming and outgoing),
542          * since we used fdset we need to allocate memory in units of
543          * long-words. 
544          */
545         size = FDS_BYTES(n);
546         bits = stack_fds;
547         if (size > sizeof(stack_fds) / 6) {
548                 /* Not enough space in on-stack array; must use kmalloc */
549                 ret = -ENOMEM;
550                 bits = kmalloc(6 * size, GFP_KERNEL);
551                 if (!bits)
552                         goto out_nofds;
553         }
554         fds.in      = bits;
555         fds.out     = bits +   size;
556         fds.ex      = bits + 2*size;
557         fds.res_in  = bits + 3*size;
558         fds.res_out = bits + 4*size;
559         fds.res_ex  = bits + 5*size;
560 
561         if ((ret = get_fd_set(n, inp, fds.in)) ||
562             (ret = get_fd_set(n, outp, fds.out)) ||
563             (ret = get_fd_set(n, exp, fds.ex)))
564                 goto out;
565         zero_fd_set(n, fds.res_in);
566         zero_fd_set(n, fds.res_out);
567         zero_fd_set(n, fds.res_ex);
568 
569         ret = do_select(n, &fds, end_time);
570 
571         if (ret < 0)
572                 goto out;
573         if (!ret) {
574                 ret = -ERESTARTNOHAND;
575                 if (signal_pending(current))
576                         goto out;
577                 ret = 0;
578         }
579 
580         if (set_fd_set(n, inp, fds.res_in) ||
581             set_fd_set(n, outp, fds.res_out) ||
582             set_fd_set(n, exp, fds.res_ex))
583                 ret = -EFAULT;
584 
585 out:
586         if (bits != stack_fds)
587                 kfree(bits);
588 out_nofds:
589         return ret;
590 }
591 
592 SYSCALL_DEFINE5(select, int, n, fd_set __user *, inp, fd_set __user *, outp,
593                 fd_set __user *, exp, struct timeval __user *, tvp)
594 {
595         struct timespec end_time, *to = NULL;
596         struct timeval tv;
597         int ret;
598 
599         if (tvp) {
600                 if (copy_from_user(&tv, tvp, sizeof(tv)))
601                         return -EFAULT;
602 
603                 to = &end_time;
604                 if (poll_select_set_timeout(to,
605                                 tv.tv_sec + (tv.tv_usec / USEC_PER_SEC),
606                                 (tv.tv_usec % USEC_PER_SEC) * NSEC_PER_USEC))
607                         return -EINVAL;
608         }
609 
610         ret = core_sys_select(n, inp, outp, exp, to);
611         ret = poll_select_copy_remaining(&end_time, tvp, 1, ret);
612 
613         return ret;
614 }
615 
616 static long do_pselect(int n, fd_set __user *inp, fd_set __user *outp,
617                        fd_set __user *exp, struct timespec __user *tsp,
618                        const sigset_t __user *sigmask, size_t sigsetsize)
619 {
620         sigset_t ksigmask, sigsaved;
621         struct timespec ts, end_time, *to = NULL;
622         int ret;
623 
624         if (tsp) {
625                 if (copy_from_user(&ts, tsp, sizeof(ts)))
626                         return -EFAULT;
627 
628                 to = &end_time;
629                 if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec))
630                         return -EINVAL;
631         }
632 
633         if (sigmask) {
634                 /* XXX: Don't preclude handling different sized sigset_t's.  */
635                 if (sigsetsize != sizeof(sigset_t))
636                         return -EINVAL;
637                 if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
638                         return -EFAULT;
639 
640                 sigdelsetmask(&ksigmask, sigmask(SIGKILL)|sigmask(SIGSTOP));
641                 sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
642         }
643 
644         ret = core_sys_select(n, inp, outp, exp, to);
645         ret = poll_select_copy_remaining(&end_time, tsp, 0, ret);
646 
647         if (ret == -ERESTARTNOHAND) {
648                 /*
649                  * Don't restore the signal mask yet. Let do_signal() deliver
650                  * the signal on the way back to userspace, before the signal
651                  * mask is restored.
652                  */
653                 if (sigmask) {
654                         memcpy(&current->saved_sigmask, &sigsaved,
655                                         sizeof(sigsaved));
656                         set_restore_sigmask();
657                 }
658         } else if (sigmask)
659                 sigprocmask(SIG_SETMASK, &sigsaved, NULL);
660 
661         return ret;
662 }
663 
664 /*
665  * Most architectures can't handle 7-argument syscalls. So we provide a
666  * 6-argument version where the sixth argument is a pointer to a structure
667  * which has a pointer to the sigset_t itself followed by a size_t containing
668  * the sigset size.
669  */
670 SYSCALL_DEFINE6(pselect6, int, n, fd_set __user *, inp, fd_set __user *, outp,
671                 fd_set __user *, exp, struct timespec __user *, tsp,
672                 void __user *, sig)
673 {
674         size_t sigsetsize = 0;
675         sigset_t __user *up = NULL;
676 
677         if (sig) {
678                 if (!access_ok(VERIFY_READ, sig, sizeof(void *)+sizeof(size_t))
679                     || __get_user(up, (sigset_t __user * __user *)sig)
680                     || __get_user(sigsetsize,
681                                 (size_t __user *)(sig+sizeof(void *))))
682                         return -EFAULT;
683         }
684 
685         return do_pselect(n, inp, outp, exp, tsp, up, sigsetsize);
686 }
687 
688 #ifdef __ARCH_WANT_SYS_OLD_SELECT
689 struct sel_arg_struct {
690         unsigned long n;
691         fd_set __user *inp, *outp, *exp;
692         struct timeval __user *tvp;
693 };
694 
695 SYSCALL_DEFINE1(old_select, struct sel_arg_struct __user *, arg)
696 {
697         struct sel_arg_struct a;
698 
699         if (copy_from_user(&a, arg, sizeof(a)))
700                 return -EFAULT;
701         return sys_select(a.n, a.inp, a.outp, a.exp, a.tvp);
702 }
703 #endif
704 
705 struct poll_list {
706         struct poll_list *next;
707         int len;
708         struct pollfd entries[0];
709 };
710 
711 #define POLLFD_PER_PAGE  ((PAGE_SIZE-sizeof(struct poll_list)) / sizeof(struct pollfd))
712 
713 /*
714  * Fish for pollable events on the pollfd->fd file descriptor. We're only
715  * interested in events matching the pollfd->events mask, and the result
716  * matching that mask is both recorded in pollfd->revents and returned. The
717  * pwait poll_table will be used by the fd-provided poll handler for waiting,
718  * if pwait->_qproc is non-NULL.
719  */
720 static inline unsigned int do_pollfd(struct pollfd *pollfd, poll_table *pwait)
721 {
722         unsigned int mask;
723         int fd;
724 
725         mask = 0;
726         fd = pollfd->fd;
727         if (fd >= 0) {
728                 struct fd f = fdget(fd);
729                 mask = POLLNVAL;
730                 if (f.file) {
731                         mask = DEFAULT_POLLMASK;
732                         if (f.file->f_op && f.file->f_op->poll) {
733                                 pwait->_key = pollfd->events|POLLERR|POLLHUP;
734                                 mask = f.file->f_op->poll(f.file, pwait);
735                         }
736                         /* Mask out unneeded events. */
737                         mask &= pollfd->events | POLLERR | POLLHUP;
738                         fdput(f);
739                 }
740         }
741         pollfd->revents = mask;
742 
743         return mask;
744 }
745 
746 static int do_poll(unsigned int nfds,  struct poll_list *list,
747                    struct poll_wqueues *wait, struct timespec *end_time)
748 {
749         poll_table* pt = &wait->pt;
750         ktime_t expire, *to = NULL;
751         int timed_out = 0, count = 0;
752         unsigned long slack = 0;
753 
754         /* Optimise the no-wait case */
755         if (end_time && !end_time->tv_sec && !end_time->tv_nsec) {
756                 pt->_qproc = NULL;
757                 timed_out = 1;
758         }
759 
760         if (end_time && !timed_out)
761                 slack = select_estimate_accuracy(end_time);
762 
763         for (;;) {
764                 struct poll_list *walk;
765 
766                 for (walk = list; walk != NULL; walk = walk->next) {
767                         struct pollfd * pfd, * pfd_end;
768 
769                         pfd = walk->entries;
770                         pfd_end = pfd + walk->len;
771                         for (; pfd != pfd_end; pfd++) {
772                                 /*
773                                  * Fish for events. If we found one, record it
774                                  * and kill poll_table->_qproc, so we don't
775                                  * needlessly register any other waiters after
776                                  * this. They'll get immediately deregistered
777                                  * when we break out and return.
778                                  */
779                                 if (do_pollfd(pfd, pt)) {
780                                         count++;
781                                         pt->_qproc = NULL;
782                                 }
783                         }
784                 }
785                 /*
786                  * All waiters have already been registered, so don't provide
787                  * a poll_table->_qproc to them on the next loop iteration.
788                  */
789                 pt->_qproc = NULL;
790                 if (!count) {
791                         count = wait->error;
792                         if (signal_pending(current))
793                                 count = -EINTR;
794                 }
795                 if (count || timed_out)
796                         break;
797 
798                 /*
799                  * If this is the first loop and we have a timeout
800                  * given, then we convert to ktime_t and set the to
801                  * pointer to the expiry value.
802                  */
803                 if (end_time && !to) {
804                         expire = timespec_to_ktime(*end_time);
805                         to = &expire;
806                 }
807 
808                 if (!poll_schedule_timeout(wait, TASK_INTERRUPTIBLE, to, slack))
809                         timed_out = 1;
810         }
811         return count;
812 }
813 
814 #define N_STACK_PPS ((sizeof(stack_pps) - sizeof(struct poll_list))  / \
815                         sizeof(struct pollfd))
816 
817 int do_sys_poll(struct pollfd __user *ufds, unsigned int nfds,
818                 struct timespec *end_time)
819 {
820         struct poll_wqueues table;
821         int err = -EFAULT, fdcount, len, size;
822         /* Allocate small arguments on the stack to save memory and be
823            faster - use long to make sure the buffer is aligned properly
824            on 64 bit archs to avoid unaligned access */
825         long stack_pps[POLL_STACK_ALLOC/sizeof(long)];
826         struct poll_list *const head = (struct poll_list *)stack_pps;
827         struct poll_list *walk = head;
828         unsigned long todo = nfds;
829 
830         if (nfds > rlimit(RLIMIT_NOFILE))
831                 return -EINVAL;
832 
833         len = min_t(unsigned int, nfds, N_STACK_PPS);
834         for (;;) {
835                 walk->next = NULL;
836                 walk->len = len;
837                 if (!len)
838                         break;
839 
840                 if (copy_from_user(walk->entries, ufds + nfds-todo,
841                                         sizeof(struct pollfd) * walk->len))
842                         goto out_fds;
843 
844                 todo -= walk->len;
845                 if (!todo)
846                         break;
847 
848                 len = min(todo, POLLFD_PER_PAGE);
849                 size = sizeof(struct poll_list) + sizeof(struct pollfd) * len;
850                 walk = walk->next = kmalloc(size, GFP_KERNEL);
851                 if (!walk) {
852                         err = -ENOMEM;
853                         goto out_fds;
854                 }
855         }
856 
857         poll_initwait(&table);
858         fdcount = do_poll(nfds, head, &table, end_time);
859         poll_freewait(&table);
860 
861         for (walk = head; walk; walk = walk->next) {
862                 struct pollfd *fds = walk->entries;
863                 int j;
864 
865                 for (j = 0; j < walk->len; j++, ufds++)
866                         if (__put_user(fds[j].revents, &ufds->revents))
867                                 goto out_fds;
868         }
869 
870         err = fdcount;
871 out_fds:
872         walk = head->next;
873         while (walk) {
874                 struct poll_list *pos = walk;
875                 walk = walk->next;
876                 kfree(pos);
877         }
878 
879         return err;
880 }
881 
882 static long do_restart_poll(struct restart_block *restart_block)
883 {
884         struct pollfd __user *ufds = restart_block->poll.ufds;
885         int nfds = restart_block->poll.nfds;
886         struct timespec *to = NULL, end_time;
887         int ret;
888 
889         if (restart_block->poll.has_timeout) {
890                 end_time.tv_sec = restart_block->poll.tv_sec;
891                 end_time.tv_nsec = restart_block->poll.tv_nsec;
892                 to = &end_time;
893         }
894 
895         ret = do_sys_poll(ufds, nfds, to);
896 
897         if (ret == -EINTR) {
898                 restart_block->fn = do_restart_poll;
899                 ret = -ERESTART_RESTARTBLOCK;
900         }
901         return ret;
902 }
903 
904 SYSCALL_DEFINE3(poll, struct pollfd __user *, ufds, unsigned int, nfds,
905                 int, timeout_msecs)
906 {
907         struct timespec end_time, *to = NULL;
908         int ret;
909 
910         if (timeout_msecs >= 0) {
911                 to = &end_time;
912                 poll_select_set_timeout(to, timeout_msecs / MSEC_PER_SEC,
913                         NSEC_PER_MSEC * (timeout_msecs % MSEC_PER_SEC));
914         }
915 
916         ret = do_sys_poll(ufds, nfds, to);
917 
918         if (ret == -EINTR) {
919                 struct restart_block *restart_block;
920 
921                 restart_block = &current_thread_info()->restart_block;
922                 restart_block->fn = do_restart_poll;
923                 restart_block->poll.ufds = ufds;
924                 restart_block->poll.nfds = nfds;
925 
926                 if (timeout_msecs >= 0) {
927                         restart_block->poll.tv_sec = end_time.tv_sec;
928                         restart_block->poll.tv_nsec = end_time.tv_nsec;
929                         restart_block->poll.has_timeout = 1;
930                 } else
931                         restart_block->poll.has_timeout = 0;
932 
933                 ret = -ERESTART_RESTARTBLOCK;
934         }
935         return ret;
936 }
937 
938 SYSCALL_DEFINE5(ppoll, struct pollfd __user *, ufds, unsigned int, nfds,
939                 struct timespec __user *, tsp, const sigset_t __user *, sigmask,
940                 size_t, sigsetsize)
941 {
942         sigset_t ksigmask, sigsaved;
943         struct timespec ts, end_time, *to = NULL;
944         int ret;
945 
946         if (tsp) {
947                 if (copy_from_user(&ts, tsp, sizeof(ts)))
948                         return -EFAULT;
949 
950                 to = &end_time;
951                 if (poll_select_set_timeout(to, ts.tv_sec, ts.tv_nsec))
952                         return -EINVAL;
953         }
954 
955         if (sigmask) {
956                 /* XXX: Don't preclude handling different sized sigset_t's.  */
957                 if (sigsetsize != sizeof(sigset_t))
958                         return -EINVAL;
959                 if (copy_from_user(&ksigmask, sigmask, sizeof(ksigmask)))
960                         return -EFAULT;
961 
962                 sigdelsetmask(&ksigmask, sigmask(SIGKILL)|sigmask(SIGSTOP));
963                 sigprocmask(SIG_SETMASK, &ksigmask, &sigsaved);
964         }
965 
966         ret = do_sys_poll(ufds, nfds, to);
967 
968         /* We can restart this syscall, usually */
969         if (ret == -EINTR) {
970                 /*
971                  * Don't restore the signal mask yet. Let do_signal() deliver
972                  * the signal on the way back to userspace, before the signal
973                  * mask is restored.
974                  */
975                 if (sigmask) {
976                         memcpy(&current->saved_sigmask, &sigsaved,
977                                         sizeof(sigsaved));
978                         set_restore_sigmask();
979                 }
980                 ret = -ERESTARTNOHAND;
981         } else if (sigmask)
982                 sigprocmask(SIG_SETMASK, &sigsaved, NULL);
983 
984         ret = poll_select_copy_remaining(&end_time, tsp, 0, ret);
985 
986         return ret;
987 }
988 

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