xref: /freebsd/sys/kern/sys_pipe.c (revision b197d4b893974c9eb4d7b38704c6d5c486235d6f)
1 /*-
2  * SPDX-License-Identifier: BSD-4-Clause
3  *
4  * Copyright (c) 1996 John S. Dyson
5  * Copyright (c) 2012 Giovanni Trematerra
6  * All rights reserved.
7  *
8  * Redistribution and use in source and binary forms, with or without
9  * modification, are permitted provided that the following conditions
10  * are met:
11  * 1. Redistributions of source code must retain the above copyright
12  *    notice immediately at the beginning of the file, without modification,
13  *    this list of conditions, and the following disclaimer.
14  * 2. Redistributions in binary form must reproduce the above copyright
15  *    notice, this list of conditions and the following disclaimer in the
16  *    documentation and/or other materials provided with the distribution.
17  * 3. Absolutely no warranty of function or purpose is made by the author
18  *    John S. Dyson.
19  * 4. Modifications may be freely made to this file if the above conditions
20  *    are met.
21  */
22 
23 /*
24  * This file contains a high-performance replacement for the socket-based
25  * pipes scheme originally used in FreeBSD/4.4Lite.  It does not support
26  * all features of sockets, but does do everything that pipes normally
27  * do.
28  */
29 
30 /*
31  * This code has two modes of operation, a small write mode and a large
32  * write mode.  The small write mode acts like conventional pipes with
33  * a kernel buffer.  If the buffer is less than PIPE_MINDIRECT, then the
34  * "normal" pipe buffering is done.  If the buffer is between PIPE_MINDIRECT
35  * and PIPE_SIZE in size, the sending process pins the underlying pages in
36  * memory, and the receiving process copies directly from these pinned pages
37  * in the sending process.
38  *
39  * If the sending process receives a signal, it is possible that it will
40  * go away, and certainly its address space can change, because control
41  * is returned back to the user-mode side.  In that case, the pipe code
42  * arranges to copy the buffer supplied by the user process, to a pageable
43  * kernel buffer, and the receiving process will grab the data from the
44  * pageable kernel buffer.  Since signals don't happen all that often,
45  * the copy operation is normally eliminated.
46  *
47  * The constant PIPE_MINDIRECT is chosen to make sure that buffering will
48  * happen for small transfers so that the system will not spend all of
49  * its time context switching.
50  *
51  * In order to limit the resource use of pipes, two sysctls exist:
52  *
53  * kern.ipc.maxpipekva - This is a hard limit on the amount of pageable
54  * address space available to us in pipe_map. This value is normally
55  * autotuned, but may also be loader tuned.
56  *
57  * kern.ipc.pipekva - This read-only sysctl tracks the current amount of
58  * memory in use by pipes.
59  *
60  * Based on how large pipekva is relative to maxpipekva, the following
61  * will happen:
62  *
63  * 0% - 50%:
64  *     New pipes are given 16K of memory backing, pipes may dynamically
65  *     grow to as large as 64K where needed.
66  * 50% - 75%:
67  *     New pipes are given 4K (or PAGE_SIZE) of memory backing,
68  *     existing pipes may NOT grow.
69  * 75% - 100%:
70  *     New pipes are given 4K (or PAGE_SIZE) of memory backing,
71  *     existing pipes will be shrunk down to 4K whenever possible.
72  *
73  * Resizing may be disabled by setting kern.ipc.piperesizeallowed=0.  If
74  * that is set,  the only resize that will occur is the 0 -> SMALL_PIPE_SIZE
75  * resize which MUST occur for reverse-direction pipes when they are
76  * first used.
77  *
78  * Additional information about the current state of pipes may be obtained
79  * from kern.ipc.pipes, kern.ipc.pipefragretry, kern.ipc.pipeallocfail,
80  * and kern.ipc.piperesizefail.
81  *
82  * Locking rules:  There are two locks present here:  A mutex, used via
83  * PIPE_LOCK, and a flag, used via pipelock().  All locking is done via
84  * the flag, as mutexes can not persist over uiomove.  The mutex
85  * exists only to guard access to the flag, and is not in itself a
86  * locking mechanism.  Also note that there is only a single mutex for
87  * both directions of a pipe.
88  *
89  * As pipelock() may have to sleep before it can acquire the flag, it
90  * is important to reread all data after a call to pipelock(); everything
91  * in the structure may have changed.
92  */
93 
94 #include <sys/cdefs.h>
95 __FBSDID("$FreeBSD$");
96 
97 #include <sys/param.h>
98 #include <sys/systm.h>
99 #include <sys/conf.h>
100 #include <sys/fcntl.h>
101 #include <sys/file.h>
102 #include <sys/filedesc.h>
103 #include <sys/filio.h>
104 #include <sys/kernel.h>
105 #include <sys/lock.h>
106 #include <sys/mutex.h>
107 #include <sys/ttycom.h>
108 #include <sys/stat.h>
109 #include <sys/malloc.h>
110 #include <sys/poll.h>
111 #include <sys/selinfo.h>
112 #include <sys/signalvar.h>
113 #include <sys/syscallsubr.h>
114 #include <sys/sysctl.h>
115 #include <sys/sysproto.h>
116 #include <sys/pipe.h>
117 #include <sys/proc.h>
118 #include <sys/vnode.h>
119 #include <sys/uio.h>
120 #include <sys/user.h>
121 #include <sys/event.h>
122 
123 #include <security/mac/mac_framework.h>
124 
125 #include <vm/vm.h>
126 #include <vm/vm_param.h>
127 #include <vm/vm_object.h>
128 #include <vm/vm_kern.h>
129 #include <vm/vm_extern.h>
130 #include <vm/pmap.h>
131 #include <vm/vm_map.h>
132 #include <vm/vm_page.h>
133 #include <vm/uma.h>
134 
135 /*
136  * Use this define if you want to disable *fancy* VM things.  Expect an
137  * approx 30% decrease in transfer rate.  This could be useful for
138  * NetBSD or OpenBSD.
139  */
140 /* #define PIPE_NODIRECT */
141 
142 #define PIPE_PEER(pipe)	\
143 	(((pipe)->pipe_type & PIPE_TYPE_NAMED) ? (pipe) : ((pipe)->pipe_peer))
144 
145 /*
146  * interfaces to the outside world
147  */
148 static fo_rdwr_t	pipe_read;
149 static fo_rdwr_t	pipe_write;
150 static fo_truncate_t	pipe_truncate;
151 static fo_ioctl_t	pipe_ioctl;
152 static fo_poll_t	pipe_poll;
153 static fo_kqfilter_t	pipe_kqfilter;
154 static fo_stat_t	pipe_stat;
155 static fo_close_t	pipe_close;
156 static fo_chmod_t	pipe_chmod;
157 static fo_chown_t	pipe_chown;
158 static fo_fill_kinfo_t	pipe_fill_kinfo;
159 
160 struct fileops pipeops = {
161 	.fo_read = pipe_read,
162 	.fo_write = pipe_write,
163 	.fo_truncate = pipe_truncate,
164 	.fo_ioctl = pipe_ioctl,
165 	.fo_poll = pipe_poll,
166 	.fo_kqfilter = pipe_kqfilter,
167 	.fo_stat = pipe_stat,
168 	.fo_close = pipe_close,
169 	.fo_chmod = pipe_chmod,
170 	.fo_chown = pipe_chown,
171 	.fo_sendfile = invfo_sendfile,
172 	.fo_fill_kinfo = pipe_fill_kinfo,
173 	.fo_flags = DFLAG_PASSABLE
174 };
175 
176 static void	filt_pipedetach(struct knote *kn);
177 static void	filt_pipedetach_notsup(struct knote *kn);
178 static int	filt_pipenotsup(struct knote *kn, long hint);
179 static int	filt_piperead(struct knote *kn, long hint);
180 static int	filt_pipewrite(struct knote *kn, long hint);
181 
182 static struct filterops pipe_nfiltops = {
183 	.f_isfd = 1,
184 	.f_detach = filt_pipedetach_notsup,
185 	.f_event = filt_pipenotsup
186 };
187 static struct filterops pipe_rfiltops = {
188 	.f_isfd = 1,
189 	.f_detach = filt_pipedetach,
190 	.f_event = filt_piperead
191 };
192 static struct filterops pipe_wfiltops = {
193 	.f_isfd = 1,
194 	.f_detach = filt_pipedetach,
195 	.f_event = filt_pipewrite
196 };
197 
198 /*
199  * Default pipe buffer size(s), this can be kind-of large now because pipe
200  * space is pageable.  The pipe code will try to maintain locality of
201  * reference for performance reasons, so small amounts of outstanding I/O
202  * will not wipe the cache.
203  */
204 #define MINPIPESIZE (PIPE_SIZE/3)
205 #define MAXPIPESIZE (2*PIPE_SIZE/3)
206 
207 static long amountpipekva;
208 static int pipefragretry;
209 static int pipeallocfail;
210 static int piperesizefail;
211 static int piperesizeallowed = 1;
212 static long pipe_mindirect = PIPE_MINDIRECT;
213 
214 SYSCTL_LONG(_kern_ipc, OID_AUTO, maxpipekva, CTLFLAG_RDTUN | CTLFLAG_NOFETCH,
215 	   &maxpipekva, 0, "Pipe KVA limit");
216 SYSCTL_LONG(_kern_ipc, OID_AUTO, pipekva, CTLFLAG_RD,
217 	   &amountpipekva, 0, "Pipe KVA usage");
218 SYSCTL_INT(_kern_ipc, OID_AUTO, pipefragretry, CTLFLAG_RD,
219 	  &pipefragretry, 0, "Pipe allocation retries due to fragmentation");
220 SYSCTL_INT(_kern_ipc, OID_AUTO, pipeallocfail, CTLFLAG_RD,
221 	  &pipeallocfail, 0, "Pipe allocation failures");
222 SYSCTL_INT(_kern_ipc, OID_AUTO, piperesizefail, CTLFLAG_RD,
223 	  &piperesizefail, 0, "Pipe resize failures");
224 SYSCTL_INT(_kern_ipc, OID_AUTO, piperesizeallowed, CTLFLAG_RW,
225 	  &piperesizeallowed, 0, "Pipe resizing allowed");
226 
227 static void pipeinit(void *dummy __unused);
228 static void pipeclose(struct pipe *cpipe);
229 static void pipe_free_kmem(struct pipe *cpipe);
230 static int pipe_create(struct pipe *pipe, bool backing);
231 static int pipe_paircreate(struct thread *td, struct pipepair **p_pp);
232 static __inline int pipelock(struct pipe *cpipe, int catch);
233 static __inline void pipeunlock(struct pipe *cpipe);
234 static void pipe_timestamp(struct timespec *tsp);
235 #ifndef PIPE_NODIRECT
236 static int pipe_build_write_buffer(struct pipe *wpipe, struct uio *uio);
237 static void pipe_destroy_write_buffer(struct pipe *wpipe);
238 static int pipe_direct_write(struct pipe *wpipe, struct uio *uio);
239 static void pipe_clone_write_buffer(struct pipe *wpipe);
240 #endif
241 static int pipespace(struct pipe *cpipe, int size);
242 static int pipespace_new(struct pipe *cpipe, int size);
243 
244 static int	pipe_zone_ctor(void *mem, int size, void *arg, int flags);
245 static int	pipe_zone_init(void *mem, int size, int flags);
246 static void	pipe_zone_fini(void *mem, int size);
247 
248 static uma_zone_t pipe_zone;
249 static struct unrhdr64 pipeino_unr;
250 static dev_t pipedev_ino;
251 
252 SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_ANY, pipeinit, NULL);
253 
254 static void
255 pipeinit(void *dummy __unused)
256 {
257 
258 	pipe_zone = uma_zcreate("pipe", sizeof(struct pipepair),
259 	    pipe_zone_ctor, NULL, pipe_zone_init, pipe_zone_fini,
260 	    UMA_ALIGN_PTR, 0);
261 	KASSERT(pipe_zone != NULL, ("pipe_zone not initialized"));
262 	new_unrhdr64(&pipeino_unr, 1);
263 	pipedev_ino = devfs_alloc_cdp_inode();
264 	KASSERT(pipedev_ino > 0, ("pipe dev inode not initialized"));
265 }
266 
267 static int
268 sysctl_handle_pipe_mindirect(SYSCTL_HANDLER_ARGS)
269 {
270 	int error = 0;
271 	long tmp_pipe_mindirect = pipe_mindirect;
272 
273 	error = sysctl_handle_long(oidp, &tmp_pipe_mindirect, arg2, req);
274 	if (error != 0 || req->newptr == NULL)
275 		return (error);
276 
277 	/*
278 	 * Don't allow pipe_mindirect to be set so low that we violate
279 	 * atomicity requirements.
280 	 */
281 	if (tmp_pipe_mindirect <= PIPE_BUF)
282 		return (EINVAL);
283 	pipe_mindirect = tmp_pipe_mindirect;
284 	return (0);
285 }
286 SYSCTL_OID(_kern_ipc, OID_AUTO, pipe_mindirect, CTLTYPE_LONG | CTLFLAG_RW,
287     &pipe_mindirect, 0, sysctl_handle_pipe_mindirect, "L",
288     "Minimum write size triggering VM optimization");
289 
290 static int
291 pipe_zone_ctor(void *mem, int size, void *arg, int flags)
292 {
293 	struct pipepair *pp;
294 	struct pipe *rpipe, *wpipe;
295 
296 	KASSERT(size == sizeof(*pp), ("pipe_zone_ctor: wrong size"));
297 
298 	pp = (struct pipepair *)mem;
299 
300 	/*
301 	 * We zero both pipe endpoints to make sure all the kmem pointers
302 	 * are NULL, flag fields are zero'd, etc.  We timestamp both
303 	 * endpoints with the same time.
304 	 */
305 	rpipe = &pp->pp_rpipe;
306 	bzero(rpipe, sizeof(*rpipe));
307 	pipe_timestamp(&rpipe->pipe_ctime);
308 	rpipe->pipe_atime = rpipe->pipe_mtime = rpipe->pipe_ctime;
309 
310 	wpipe = &pp->pp_wpipe;
311 	bzero(wpipe, sizeof(*wpipe));
312 	wpipe->pipe_ctime = rpipe->pipe_ctime;
313 	wpipe->pipe_atime = wpipe->pipe_mtime = rpipe->pipe_ctime;
314 
315 	rpipe->pipe_peer = wpipe;
316 	rpipe->pipe_pair = pp;
317 	wpipe->pipe_peer = rpipe;
318 	wpipe->pipe_pair = pp;
319 
320 	/*
321 	 * Mark both endpoints as present; they will later get free'd
322 	 * one at a time.  When both are free'd, then the whole pair
323 	 * is released.
324 	 */
325 	rpipe->pipe_present = PIPE_ACTIVE;
326 	wpipe->pipe_present = PIPE_ACTIVE;
327 
328 	/*
329 	 * Eventually, the MAC Framework may initialize the label
330 	 * in ctor or init, but for now we do it elswhere to avoid
331 	 * blocking in ctor or init.
332 	 */
333 	pp->pp_label = NULL;
334 
335 	return (0);
336 }
337 
338 static int
339 pipe_zone_init(void *mem, int size, int flags)
340 {
341 	struct pipepair *pp;
342 
343 	KASSERT(size == sizeof(*pp), ("pipe_zone_init: wrong size"));
344 
345 	pp = (struct pipepair *)mem;
346 
347 	mtx_init(&pp->pp_mtx, "pipe mutex", NULL, MTX_DEF | MTX_NEW);
348 	return (0);
349 }
350 
351 static void
352 pipe_zone_fini(void *mem, int size)
353 {
354 	struct pipepair *pp;
355 
356 	KASSERT(size == sizeof(*pp), ("pipe_zone_fini: wrong size"));
357 
358 	pp = (struct pipepair *)mem;
359 
360 	mtx_destroy(&pp->pp_mtx);
361 }
362 
363 static int
364 pipe_paircreate(struct thread *td, struct pipepair **p_pp)
365 {
366 	struct pipepair *pp;
367 	struct pipe *rpipe, *wpipe;
368 	int error;
369 
370 	*p_pp = pp = uma_zalloc(pipe_zone, M_WAITOK);
371 #ifdef MAC
372 	/*
373 	 * The MAC label is shared between the connected endpoints.  As a
374 	 * result mac_pipe_init() and mac_pipe_create() are called once
375 	 * for the pair, and not on the endpoints.
376 	 */
377 	mac_pipe_init(pp);
378 	mac_pipe_create(td->td_ucred, pp);
379 #endif
380 	rpipe = &pp->pp_rpipe;
381 	wpipe = &pp->pp_wpipe;
382 
383 	knlist_init_mtx(&rpipe->pipe_sel.si_note, PIPE_MTX(rpipe));
384 	knlist_init_mtx(&wpipe->pipe_sel.si_note, PIPE_MTX(wpipe));
385 
386 	/*
387 	 * Only the forward direction pipe is backed by big buffer by
388 	 * default.
389 	 */
390 	error = pipe_create(rpipe, true);
391 	if (error != 0)
392 		goto fail;
393 	error = pipe_create(wpipe, false);
394 	if (error != 0) {
395 		/*
396 		 * This cleanup leaves the pipe inode number for rpipe
397 		 * still allocated, but never used.  We do not free
398 		 * inode numbers for opened pipes, which is required
399 		 * for correctness because numbers must be unique.
400 		 * But also it avoids any memory use by the unr
401 		 * allocator, so stashing away the transient inode
402 		 * number is reasonable.
403 		 */
404 		pipe_free_kmem(rpipe);
405 		goto fail;
406 	}
407 
408 	rpipe->pipe_state |= PIPE_DIRECTOK;
409 	wpipe->pipe_state |= PIPE_DIRECTOK;
410 	return (0);
411 
412 fail:
413 	knlist_destroy(&rpipe->pipe_sel.si_note);
414 	knlist_destroy(&wpipe->pipe_sel.si_note);
415 #ifdef MAC
416 	mac_pipe_destroy(pp);
417 #endif
418 	uma_zfree(pipe_zone, pp);
419 	return (error);
420 }
421 
422 int
423 pipe_named_ctor(struct pipe **ppipe, struct thread *td)
424 {
425 	struct pipepair *pp;
426 	int error;
427 
428 	error = pipe_paircreate(td, &pp);
429 	if (error != 0)
430 		return (error);
431 	pp->pp_rpipe.pipe_type |= PIPE_TYPE_NAMED;
432 	*ppipe = &pp->pp_rpipe;
433 	return (0);
434 }
435 
436 void
437 pipe_dtor(struct pipe *dpipe)
438 {
439 	struct pipe *peer;
440 
441 	peer = (dpipe->pipe_type & PIPE_TYPE_NAMED) != 0 ? dpipe->pipe_peer : NULL;
442 	funsetown(&dpipe->pipe_sigio);
443 	pipeclose(dpipe);
444 	if (peer != NULL) {
445 		funsetown(&peer->pipe_sigio);
446 		pipeclose(peer);
447 	}
448 }
449 
450 /*
451  * Get a timestamp.
452  *
453  * This used to be vfs_timestamp but the higher precision is unnecessary and
454  * can very negatively affect performance in virtualized environments (e.g., on
455  * vms running on amd64 when using the rdtscp instruction).
456  */
457 static void
458 pipe_timestamp(struct timespec *tsp)
459 {
460 
461 	getnanotime(tsp);
462 }
463 
464 /*
465  * The pipe system call for the DTYPE_PIPE type of pipes.  If we fail, let
466  * the zone pick up the pieces via pipeclose().
467  */
468 int
469 kern_pipe(struct thread *td, int fildes[2], int flags, struct filecaps *fcaps1,
470     struct filecaps *fcaps2)
471 {
472 	struct file *rf, *wf;
473 	struct pipe *rpipe, *wpipe;
474 	struct pipepair *pp;
475 	int fd, fflags, error;
476 
477 	error = pipe_paircreate(td, &pp);
478 	if (error != 0)
479 		return (error);
480 	rpipe = &pp->pp_rpipe;
481 	wpipe = &pp->pp_wpipe;
482 	error = falloc_caps(td, &rf, &fd, flags, fcaps1);
483 	if (error) {
484 		pipeclose(rpipe);
485 		pipeclose(wpipe);
486 		return (error);
487 	}
488 	/* An extra reference on `rf' has been held for us by falloc_caps(). */
489 	fildes[0] = fd;
490 
491 	fflags = FREAD | FWRITE;
492 	if ((flags & O_NONBLOCK) != 0)
493 		fflags |= FNONBLOCK;
494 
495 	/*
496 	 * Warning: once we've gotten past allocation of the fd for the
497 	 * read-side, we can only drop the read side via fdrop() in order
498 	 * to avoid races against processes which manage to dup() the read
499 	 * side while we are blocked trying to allocate the write side.
500 	 */
501 	finit(rf, fflags, DTYPE_PIPE, rpipe, &pipeops);
502 	error = falloc_caps(td, &wf, &fd, flags, fcaps2);
503 	if (error) {
504 		fdclose(td, rf, fildes[0]);
505 		fdrop(rf, td);
506 		/* rpipe has been closed by fdrop(). */
507 		pipeclose(wpipe);
508 		return (error);
509 	}
510 	/* An extra reference on `wf' has been held for us by falloc_caps(). */
511 	finit(wf, fflags, DTYPE_PIPE, wpipe, &pipeops);
512 	fdrop(wf, td);
513 	fildes[1] = fd;
514 	fdrop(rf, td);
515 
516 	return (0);
517 }
518 
519 #ifdef COMPAT_FREEBSD10
520 /* ARGSUSED */
521 int
522 freebsd10_pipe(struct thread *td, struct freebsd10_pipe_args *uap __unused)
523 {
524 	int error;
525 	int fildes[2];
526 
527 	error = kern_pipe(td, fildes, 0, NULL, NULL);
528 	if (error)
529 		return (error);
530 
531 	td->td_retval[0] = fildes[0];
532 	td->td_retval[1] = fildes[1];
533 
534 	return (0);
535 }
536 #endif
537 
538 int
539 sys_pipe2(struct thread *td, struct pipe2_args *uap)
540 {
541 	int error, fildes[2];
542 
543 	if (uap->flags & ~(O_CLOEXEC | O_NONBLOCK))
544 		return (EINVAL);
545 	error = kern_pipe(td, fildes, uap->flags, NULL, NULL);
546 	if (error)
547 		return (error);
548 	error = copyout(fildes, uap->fildes, 2 * sizeof(int));
549 	if (error) {
550 		(void)kern_close(td, fildes[0]);
551 		(void)kern_close(td, fildes[1]);
552 	}
553 	return (error);
554 }
555 
556 /*
557  * Allocate kva for pipe circular buffer, the space is pageable
558  * This routine will 'realloc' the size of a pipe safely, if it fails
559  * it will retain the old buffer.
560  * If it fails it will return ENOMEM.
561  */
562 static int
563 pipespace_new(struct pipe *cpipe, int size)
564 {
565 	caddr_t buffer;
566 	int error, cnt, firstseg;
567 	static int curfail = 0;
568 	static struct timeval lastfail;
569 
570 	KASSERT(!mtx_owned(PIPE_MTX(cpipe)), ("pipespace: pipe mutex locked"));
571 	KASSERT(!(cpipe->pipe_state & PIPE_DIRECTW),
572 		("pipespace: resize of direct writes not allowed"));
573 retry:
574 	cnt = cpipe->pipe_buffer.cnt;
575 	if (cnt > size)
576 		size = cnt;
577 
578 	size = round_page(size);
579 	buffer = (caddr_t) vm_map_min(pipe_map);
580 
581 	error = vm_map_find(pipe_map, NULL, 0, (vm_offset_t *)&buffer, size, 0,
582 	    VMFS_ANY_SPACE, VM_PROT_RW, VM_PROT_RW, 0);
583 	if (error != KERN_SUCCESS) {
584 		if (cpipe->pipe_buffer.buffer == NULL &&
585 		    size > SMALL_PIPE_SIZE) {
586 			size = SMALL_PIPE_SIZE;
587 			pipefragretry++;
588 			goto retry;
589 		}
590 		if (cpipe->pipe_buffer.buffer == NULL) {
591 			pipeallocfail++;
592 			if (ppsratecheck(&lastfail, &curfail, 1))
593 				printf("kern.ipc.maxpipekva exceeded; see tuning(7)\n");
594 		} else {
595 			piperesizefail++;
596 		}
597 		return (ENOMEM);
598 	}
599 
600 	/* copy data, then free old resources if we're resizing */
601 	if (cnt > 0) {
602 		if (cpipe->pipe_buffer.in <= cpipe->pipe_buffer.out) {
603 			firstseg = cpipe->pipe_buffer.size - cpipe->pipe_buffer.out;
604 			bcopy(&cpipe->pipe_buffer.buffer[cpipe->pipe_buffer.out],
605 				buffer, firstseg);
606 			if ((cnt - firstseg) > 0)
607 				bcopy(cpipe->pipe_buffer.buffer, &buffer[firstseg],
608 					cpipe->pipe_buffer.in);
609 		} else {
610 			bcopy(&cpipe->pipe_buffer.buffer[cpipe->pipe_buffer.out],
611 				buffer, cnt);
612 		}
613 	}
614 	pipe_free_kmem(cpipe);
615 	cpipe->pipe_buffer.buffer = buffer;
616 	cpipe->pipe_buffer.size = size;
617 	cpipe->pipe_buffer.in = cnt;
618 	cpipe->pipe_buffer.out = 0;
619 	cpipe->pipe_buffer.cnt = cnt;
620 	atomic_add_long(&amountpipekva, cpipe->pipe_buffer.size);
621 	return (0);
622 }
623 
624 /*
625  * Wrapper for pipespace_new() that performs locking assertions.
626  */
627 static int
628 pipespace(struct pipe *cpipe, int size)
629 {
630 
631 	KASSERT(cpipe->pipe_state & PIPE_LOCKFL,
632 	    ("Unlocked pipe passed to pipespace"));
633 	return (pipespace_new(cpipe, size));
634 }
635 
636 /*
637  * lock a pipe for I/O, blocking other access
638  */
639 static __inline int
640 pipelock(struct pipe *cpipe, int catch)
641 {
642 	int error, prio;
643 
644 	PIPE_LOCK_ASSERT(cpipe, MA_OWNED);
645 
646 	prio = PRIBIO;
647 	if (catch)
648 		prio |= PCATCH;
649 	while (cpipe->pipe_state & PIPE_LOCKFL) {
650 		KASSERT(cpipe->pipe_waiters >= 0,
651 		    ("%s: bad waiter count %d", __func__,
652 		    cpipe->pipe_waiters));
653 		cpipe->pipe_waiters++;
654 		error = msleep(&cpipe->pipe_waiters, PIPE_MTX(cpipe), prio,
655 		    "pipelk", 0);
656 		cpipe->pipe_waiters--;
657 		if (error != 0)
658 			return (error);
659 	}
660 	cpipe->pipe_state |= PIPE_LOCKFL;
661 	return (0);
662 }
663 
664 /*
665  * unlock a pipe I/O lock
666  */
667 static __inline void
668 pipeunlock(struct pipe *cpipe)
669 {
670 
671 	PIPE_LOCK_ASSERT(cpipe, MA_OWNED);
672 	KASSERT(cpipe->pipe_state & PIPE_LOCKFL,
673 		("Unlocked pipe passed to pipeunlock"));
674 	KASSERT(cpipe->pipe_waiters >= 0,
675 	    ("%s: bad waiter count %d", __func__,
676 	    cpipe->pipe_waiters));
677 	cpipe->pipe_state &= ~PIPE_LOCKFL;
678 	if (cpipe->pipe_waiters > 0)
679 		wakeup_one(&cpipe->pipe_waiters);
680 }
681 
682 void
683 pipeselwakeup(struct pipe *cpipe)
684 {
685 
686 	PIPE_LOCK_ASSERT(cpipe, MA_OWNED);
687 	if (cpipe->pipe_state & PIPE_SEL) {
688 		selwakeuppri(&cpipe->pipe_sel, PSOCK);
689 		if (!SEL_WAITING(&cpipe->pipe_sel))
690 			cpipe->pipe_state &= ~PIPE_SEL;
691 	}
692 	if ((cpipe->pipe_state & PIPE_ASYNC) && cpipe->pipe_sigio)
693 		pgsigio(&cpipe->pipe_sigio, SIGIO, 0);
694 	KNOTE_LOCKED(&cpipe->pipe_sel.si_note, 0);
695 }
696 
697 /*
698  * Initialize and allocate VM and memory for pipe.  The structure
699  * will start out zero'd from the ctor, so we just manage the kmem.
700  */
701 static int
702 pipe_create(struct pipe *pipe, bool large_backing)
703 {
704 	int error;
705 
706 	error = pipespace_new(pipe, !large_backing || amountpipekva >
707 	    maxpipekva / 2 ? SMALL_PIPE_SIZE : PIPE_SIZE);
708 	if (error == 0)
709 		pipe->pipe_ino = alloc_unr64(&pipeino_unr);
710 	return (error);
711 }
712 
713 /* ARGSUSED */
714 static int
715 pipe_read(struct file *fp, struct uio *uio, struct ucred *active_cred,
716     int flags, struct thread *td)
717 {
718 	struct pipe *rpipe;
719 	int error;
720 	int nread = 0;
721 	int size;
722 
723 	rpipe = fp->f_data;
724 
725 	/*
726 	 * Try to avoid locking the pipe if we have nothing to do.
727 	 *
728 	 * There are programs which share one pipe amongst multiple processes
729 	 * and perform non-blocking reads in parallel, even if the pipe is
730 	 * empty.  This in particular is the case with BSD make, which when
731 	 * spawned with a high -j number can find itself with over half of the
732 	 * calls failing to find anything.
733 	 */
734 	if ((fp->f_flag & FNONBLOCK) != 0 && !mac_pipe_check_read_enabled()) {
735 		if (__predict_false(uio->uio_resid == 0))
736 			return (0);
737 		if ((atomic_load_short(&rpipe->pipe_state) & PIPE_EOF) == 0 &&
738 		    atomic_load_int(&rpipe->pipe_buffer.cnt) == 0 &&
739 		    atomic_load_int(&rpipe->pipe_pages.cnt) == 0)
740 			return (EAGAIN);
741 	}
742 
743 	PIPE_LOCK(rpipe);
744 	++rpipe->pipe_busy;
745 	error = pipelock(rpipe, 1);
746 	if (error)
747 		goto unlocked_error;
748 
749 #ifdef MAC
750 	error = mac_pipe_check_read(active_cred, rpipe->pipe_pair);
751 	if (error)
752 		goto locked_error;
753 #endif
754 	if (amountpipekva > (3 * maxpipekva) / 4) {
755 		if ((rpipe->pipe_state & PIPE_DIRECTW) == 0 &&
756 		    rpipe->pipe_buffer.size > SMALL_PIPE_SIZE &&
757 		    rpipe->pipe_buffer.cnt <= SMALL_PIPE_SIZE &&
758 		    piperesizeallowed == 1) {
759 			PIPE_UNLOCK(rpipe);
760 			pipespace(rpipe, SMALL_PIPE_SIZE);
761 			PIPE_LOCK(rpipe);
762 		}
763 	}
764 
765 	while (uio->uio_resid) {
766 		/*
767 		 * normal pipe buffer receive
768 		 */
769 		if (rpipe->pipe_buffer.cnt > 0) {
770 			size = rpipe->pipe_buffer.size - rpipe->pipe_buffer.out;
771 			if (size > rpipe->pipe_buffer.cnt)
772 				size = rpipe->pipe_buffer.cnt;
773 			if (size > uio->uio_resid)
774 				size = uio->uio_resid;
775 
776 			PIPE_UNLOCK(rpipe);
777 			error = uiomove(
778 			    &rpipe->pipe_buffer.buffer[rpipe->pipe_buffer.out],
779 			    size, uio);
780 			PIPE_LOCK(rpipe);
781 			if (error)
782 				break;
783 
784 			rpipe->pipe_buffer.out += size;
785 			if (rpipe->pipe_buffer.out >= rpipe->pipe_buffer.size)
786 				rpipe->pipe_buffer.out = 0;
787 
788 			rpipe->pipe_buffer.cnt -= size;
789 
790 			/*
791 			 * If there is no more to read in the pipe, reset
792 			 * its pointers to the beginning.  This improves
793 			 * cache hit stats.
794 			 */
795 			if (rpipe->pipe_buffer.cnt == 0) {
796 				rpipe->pipe_buffer.in = 0;
797 				rpipe->pipe_buffer.out = 0;
798 			}
799 			nread += size;
800 #ifndef PIPE_NODIRECT
801 		/*
802 		 * Direct copy, bypassing a kernel buffer.
803 		 */
804 		} else if ((size = rpipe->pipe_pages.cnt) != 0) {
805 			if (size > uio->uio_resid)
806 				size = (u_int) uio->uio_resid;
807 			PIPE_UNLOCK(rpipe);
808 			error = uiomove_fromphys(rpipe->pipe_pages.ms,
809 			    rpipe->pipe_pages.pos, size, uio);
810 			PIPE_LOCK(rpipe);
811 			if (error)
812 				break;
813 			nread += size;
814 			rpipe->pipe_pages.pos += size;
815 			rpipe->pipe_pages.cnt -= size;
816 			if (rpipe->pipe_pages.cnt == 0) {
817 				rpipe->pipe_state &= ~PIPE_WANTW;
818 				wakeup(rpipe);
819 			}
820 #endif
821 		} else {
822 			/*
823 			 * detect EOF condition
824 			 * read returns 0 on EOF, no need to set error
825 			 */
826 			if (rpipe->pipe_state & PIPE_EOF)
827 				break;
828 
829 			/*
830 			 * If the "write-side" has been blocked, wake it up now.
831 			 */
832 			if (rpipe->pipe_state & PIPE_WANTW) {
833 				rpipe->pipe_state &= ~PIPE_WANTW;
834 				wakeup(rpipe);
835 			}
836 
837 			/*
838 			 * Break if some data was read.
839 			 */
840 			if (nread > 0)
841 				break;
842 
843 			/*
844 			 * Unlock the pipe buffer for our remaining processing.
845 			 * We will either break out with an error or we will
846 			 * sleep and relock to loop.
847 			 */
848 			pipeunlock(rpipe);
849 
850 			/*
851 			 * Handle non-blocking mode operation or
852 			 * wait for more data.
853 			 */
854 			if (fp->f_flag & FNONBLOCK) {
855 				error = EAGAIN;
856 			} else {
857 				rpipe->pipe_state |= PIPE_WANTR;
858 				if ((error = msleep(rpipe, PIPE_MTX(rpipe),
859 				    PRIBIO | PCATCH,
860 				    "piperd", 0)) == 0)
861 					error = pipelock(rpipe, 1);
862 			}
863 			if (error)
864 				goto unlocked_error;
865 		}
866 	}
867 #ifdef MAC
868 locked_error:
869 #endif
870 	pipeunlock(rpipe);
871 
872 	/* XXX: should probably do this before getting any locks. */
873 	if (error == 0)
874 		pipe_timestamp(&rpipe->pipe_atime);
875 unlocked_error:
876 	--rpipe->pipe_busy;
877 
878 	/*
879 	 * PIPE_WANT processing only makes sense if pipe_busy is 0.
880 	 */
881 	if ((rpipe->pipe_busy == 0) && (rpipe->pipe_state & PIPE_WANT)) {
882 		rpipe->pipe_state &= ~(PIPE_WANT|PIPE_WANTW);
883 		wakeup(rpipe);
884 	} else if (rpipe->pipe_buffer.cnt < MINPIPESIZE) {
885 		/*
886 		 * Handle write blocking hysteresis.
887 		 */
888 		if (rpipe->pipe_state & PIPE_WANTW) {
889 			rpipe->pipe_state &= ~PIPE_WANTW;
890 			wakeup(rpipe);
891 		}
892 	}
893 
894 	/*
895 	 * Only wake up writers if there was actually something read.
896 	 * Otherwise, when calling read(2) at EOF, a spurious wakeup occurs.
897 	 */
898 	if (nread > 0 &&
899 	    rpipe->pipe_buffer.size - rpipe->pipe_buffer.cnt >= PIPE_BUF)
900 		pipeselwakeup(rpipe);
901 
902 	PIPE_UNLOCK(rpipe);
903 	if (nread > 0)
904 		td->td_ru.ru_msgrcv++;
905 	return (error);
906 }
907 
908 #ifndef PIPE_NODIRECT
909 /*
910  * Map the sending processes' buffer into kernel space and wire it.
911  * This is similar to a physical write operation.
912  */
913 static int
914 pipe_build_write_buffer(struct pipe *wpipe, struct uio *uio)
915 {
916 	u_int size;
917 	int i;
918 
919 	PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
920 	KASSERT((wpipe->pipe_state & PIPE_DIRECTW) == 0,
921 	    ("%s: PIPE_DIRECTW set on %p", __func__, wpipe));
922 	KASSERT(wpipe->pipe_pages.cnt == 0,
923 	    ("%s: pipe map for %p contains residual data", __func__, wpipe));
924 
925 	if (uio->uio_iov->iov_len > wpipe->pipe_buffer.size)
926                 size = wpipe->pipe_buffer.size;
927 	else
928                 size = uio->uio_iov->iov_len;
929 
930 	wpipe->pipe_state |= PIPE_DIRECTW;
931 	PIPE_UNLOCK(wpipe);
932 	i = vm_fault_quick_hold_pages(&curproc->p_vmspace->vm_map,
933 	    (vm_offset_t)uio->uio_iov->iov_base, size, VM_PROT_READ,
934 	    wpipe->pipe_pages.ms, PIPENPAGES);
935 	PIPE_LOCK(wpipe);
936 	if (i < 0) {
937 		wpipe->pipe_state &= ~PIPE_DIRECTW;
938 		return (EFAULT);
939 	}
940 
941 	wpipe->pipe_pages.npages = i;
942 	wpipe->pipe_pages.pos =
943 	    ((vm_offset_t) uio->uio_iov->iov_base) & PAGE_MASK;
944 	wpipe->pipe_pages.cnt = size;
945 
946 	uio->uio_iov->iov_len -= size;
947 	uio->uio_iov->iov_base = (char *)uio->uio_iov->iov_base + size;
948 	if (uio->uio_iov->iov_len == 0)
949 		uio->uio_iov++;
950 	uio->uio_resid -= size;
951 	uio->uio_offset += size;
952 	return (0);
953 }
954 
955 /*
956  * Unwire the process buffer.
957  */
958 static void
959 pipe_destroy_write_buffer(struct pipe *wpipe)
960 {
961 
962 	PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
963 	KASSERT((wpipe->pipe_state & PIPE_DIRECTW) != 0,
964 	    ("%s: PIPE_DIRECTW not set on %p", __func__, wpipe));
965 	KASSERT(wpipe->pipe_pages.cnt == 0,
966 	    ("%s: pipe map for %p contains residual data", __func__, wpipe));
967 
968 	wpipe->pipe_state &= ~PIPE_DIRECTW;
969 	vm_page_unhold_pages(wpipe->pipe_pages.ms, wpipe->pipe_pages.npages);
970 	wpipe->pipe_pages.npages = 0;
971 }
972 
973 /*
974  * In the case of a signal, the writing process might go away.  This
975  * code copies the data into the circular buffer so that the source
976  * pages can be freed without loss of data.
977  */
978 static void
979 pipe_clone_write_buffer(struct pipe *wpipe)
980 {
981 	struct uio uio;
982 	struct iovec iov;
983 	int size;
984 	int pos;
985 
986 	PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
987 	KASSERT((wpipe->pipe_state & PIPE_DIRECTW) != 0,
988 	    ("%s: PIPE_DIRECTW not set on %p", __func__, wpipe));
989 
990 	size = wpipe->pipe_pages.cnt;
991 	pos = wpipe->pipe_pages.pos;
992 	wpipe->pipe_pages.cnt = 0;
993 
994 	wpipe->pipe_buffer.in = size;
995 	wpipe->pipe_buffer.out = 0;
996 	wpipe->pipe_buffer.cnt = size;
997 
998 	PIPE_UNLOCK(wpipe);
999 	iov.iov_base = wpipe->pipe_buffer.buffer;
1000 	iov.iov_len = size;
1001 	uio.uio_iov = &iov;
1002 	uio.uio_iovcnt = 1;
1003 	uio.uio_offset = 0;
1004 	uio.uio_resid = size;
1005 	uio.uio_segflg = UIO_SYSSPACE;
1006 	uio.uio_rw = UIO_READ;
1007 	uio.uio_td = curthread;
1008 	uiomove_fromphys(wpipe->pipe_pages.ms, pos, size, &uio);
1009 	PIPE_LOCK(wpipe);
1010 	pipe_destroy_write_buffer(wpipe);
1011 }
1012 
1013 /*
1014  * This implements the pipe buffer write mechanism.  Note that only
1015  * a direct write OR a normal pipe write can be pending at any given time.
1016  * If there are any characters in the pipe buffer, the direct write will
1017  * be deferred until the receiving process grabs all of the bytes from
1018  * the pipe buffer.  Then the direct mapping write is set-up.
1019  */
1020 static int
1021 pipe_direct_write(struct pipe *wpipe, struct uio *uio)
1022 {
1023 	int error;
1024 
1025 retry:
1026 	PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
1027 	if ((wpipe->pipe_state & PIPE_EOF) != 0) {
1028 		error = EPIPE;
1029 		goto error1;
1030 	}
1031 	if (wpipe->pipe_state & PIPE_DIRECTW) {
1032 		if (wpipe->pipe_state & PIPE_WANTR) {
1033 			wpipe->pipe_state &= ~PIPE_WANTR;
1034 			wakeup(wpipe);
1035 		}
1036 		pipeselwakeup(wpipe);
1037 		wpipe->pipe_state |= PIPE_WANTW;
1038 		pipeunlock(wpipe);
1039 		error = msleep(wpipe, PIPE_MTX(wpipe),
1040 		    PRIBIO | PCATCH, "pipdww", 0);
1041 		pipelock(wpipe, 0);
1042 		if (error != 0)
1043 			goto error1;
1044 		goto retry;
1045 	}
1046 	if (wpipe->pipe_buffer.cnt > 0) {
1047 		if (wpipe->pipe_state & PIPE_WANTR) {
1048 			wpipe->pipe_state &= ~PIPE_WANTR;
1049 			wakeup(wpipe);
1050 		}
1051 		pipeselwakeup(wpipe);
1052 		wpipe->pipe_state |= PIPE_WANTW;
1053 		pipeunlock(wpipe);
1054 		error = msleep(wpipe, PIPE_MTX(wpipe),
1055 		    PRIBIO | PCATCH, "pipdwc", 0);
1056 		pipelock(wpipe, 0);
1057 		if (error != 0)
1058 			goto error1;
1059 		goto retry;
1060 	}
1061 
1062 	error = pipe_build_write_buffer(wpipe, uio);
1063 	if (error) {
1064 		goto error1;
1065 	}
1066 
1067 	while (wpipe->pipe_pages.cnt != 0 &&
1068 	    (wpipe->pipe_state & PIPE_EOF) == 0) {
1069 		if (wpipe->pipe_state & PIPE_WANTR) {
1070 			wpipe->pipe_state &= ~PIPE_WANTR;
1071 			wakeup(wpipe);
1072 		}
1073 		pipeselwakeup(wpipe);
1074 		wpipe->pipe_state |= PIPE_WANTW;
1075 		pipeunlock(wpipe);
1076 		error = msleep(wpipe, PIPE_MTX(wpipe), PRIBIO | PCATCH,
1077 		    "pipdwt", 0);
1078 		pipelock(wpipe, 0);
1079 		if (error != 0)
1080 			break;
1081 	}
1082 
1083 	if ((wpipe->pipe_state & PIPE_EOF) != 0) {
1084 		wpipe->pipe_pages.cnt = 0;
1085 		pipe_destroy_write_buffer(wpipe);
1086 		pipeselwakeup(wpipe);
1087 		error = EPIPE;
1088 	} else if (error == EINTR || error == ERESTART) {
1089 		pipe_clone_write_buffer(wpipe);
1090 	} else {
1091 		pipe_destroy_write_buffer(wpipe);
1092 	}
1093 	KASSERT((wpipe->pipe_state & PIPE_DIRECTW) == 0,
1094 	    ("pipe %p leaked PIPE_DIRECTW", wpipe));
1095 	return (error);
1096 
1097 error1:
1098 	wakeup(wpipe);
1099 	return (error);
1100 }
1101 #endif
1102 
1103 static int
1104 pipe_write(struct file *fp, struct uio *uio, struct ucred *active_cred,
1105     int flags, struct thread *td)
1106 {
1107 	struct pipe *wpipe, *rpipe;
1108 	ssize_t orig_resid;
1109 	int desiredsize, error;
1110 
1111 	rpipe = fp->f_data;
1112 	wpipe = PIPE_PEER(rpipe);
1113 	PIPE_LOCK(rpipe);
1114 	error = pipelock(wpipe, 1);
1115 	if (error) {
1116 		PIPE_UNLOCK(rpipe);
1117 		return (error);
1118 	}
1119 	/*
1120 	 * detect loss of pipe read side, issue SIGPIPE if lost.
1121 	 */
1122 	if (wpipe->pipe_present != PIPE_ACTIVE ||
1123 	    (wpipe->pipe_state & PIPE_EOF)) {
1124 		pipeunlock(wpipe);
1125 		PIPE_UNLOCK(rpipe);
1126 		return (EPIPE);
1127 	}
1128 #ifdef MAC
1129 	error = mac_pipe_check_write(active_cred, wpipe->pipe_pair);
1130 	if (error) {
1131 		pipeunlock(wpipe);
1132 		PIPE_UNLOCK(rpipe);
1133 		return (error);
1134 	}
1135 #endif
1136 	++wpipe->pipe_busy;
1137 
1138 	/* Choose a larger size if it's advantageous */
1139 	desiredsize = max(SMALL_PIPE_SIZE, wpipe->pipe_buffer.size);
1140 	while (desiredsize < wpipe->pipe_buffer.cnt + uio->uio_resid) {
1141 		if (piperesizeallowed != 1)
1142 			break;
1143 		if (amountpipekva > maxpipekva / 2)
1144 			break;
1145 		if (desiredsize == BIG_PIPE_SIZE)
1146 			break;
1147 		desiredsize = desiredsize * 2;
1148 	}
1149 
1150 	/* Choose a smaller size if we're in a OOM situation */
1151 	if (amountpipekva > (3 * maxpipekva) / 4 &&
1152 	    wpipe->pipe_buffer.size > SMALL_PIPE_SIZE &&
1153 	    wpipe->pipe_buffer.cnt <= SMALL_PIPE_SIZE &&
1154 	    piperesizeallowed == 1)
1155 		desiredsize = SMALL_PIPE_SIZE;
1156 
1157 	/* Resize if the above determined that a new size was necessary */
1158 	if (desiredsize != wpipe->pipe_buffer.size &&
1159 	    (wpipe->pipe_state & PIPE_DIRECTW) == 0) {
1160 		PIPE_UNLOCK(wpipe);
1161 		pipespace(wpipe, desiredsize);
1162 		PIPE_LOCK(wpipe);
1163 	}
1164 	MPASS(wpipe->pipe_buffer.size != 0);
1165 
1166 	orig_resid = uio->uio_resid;
1167 
1168 	while (uio->uio_resid) {
1169 		int space;
1170 
1171 		if (wpipe->pipe_state & PIPE_EOF) {
1172 			error = EPIPE;
1173 			break;
1174 		}
1175 #ifndef PIPE_NODIRECT
1176 		/*
1177 		 * If the transfer is large, we can gain performance if
1178 		 * we do process-to-process copies directly.
1179 		 * If the write is non-blocking, we don't use the
1180 		 * direct write mechanism.
1181 		 *
1182 		 * The direct write mechanism will detect the reader going
1183 		 * away on us.
1184 		 */
1185 		if (uio->uio_segflg == UIO_USERSPACE &&
1186 		    uio->uio_iov->iov_len >= pipe_mindirect &&
1187 		    wpipe->pipe_buffer.size >= pipe_mindirect &&
1188 		    (fp->f_flag & FNONBLOCK) == 0) {
1189 			error = pipe_direct_write(wpipe, uio);
1190 			if (error != 0)
1191 				break;
1192 			continue;
1193 		}
1194 #endif
1195 
1196 		/*
1197 		 * Pipe buffered writes cannot be coincidental with
1198 		 * direct writes.  We wait until the currently executing
1199 		 * direct write is completed before we start filling the
1200 		 * pipe buffer.  We break out if a signal occurs or the
1201 		 * reader goes away.
1202 		 */
1203 		if (wpipe->pipe_pages.cnt != 0) {
1204 			if (wpipe->pipe_state & PIPE_WANTR) {
1205 				wpipe->pipe_state &= ~PIPE_WANTR;
1206 				wakeup(wpipe);
1207 			}
1208 			pipeselwakeup(wpipe);
1209 			wpipe->pipe_state |= PIPE_WANTW;
1210 			pipeunlock(wpipe);
1211 			error = msleep(wpipe, PIPE_MTX(rpipe), PRIBIO | PCATCH,
1212 			    "pipbww", 0);
1213 			pipelock(wpipe, 0);
1214 			if (error != 0)
1215 				break;
1216 			continue;
1217 		}
1218 
1219 		space = wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt;
1220 
1221 		/* Writes of size <= PIPE_BUF must be atomic. */
1222 		if ((space < uio->uio_resid) && (orig_resid <= PIPE_BUF))
1223 			space = 0;
1224 
1225 		if (space > 0) {
1226 			int size;	/* Transfer size */
1227 			int segsize;	/* first segment to transfer */
1228 
1229 			/*
1230 			 * Transfer size is minimum of uio transfer
1231 			 * and free space in pipe buffer.
1232 			 */
1233 			if (space > uio->uio_resid)
1234 				size = uio->uio_resid;
1235 			else
1236 				size = space;
1237 			/*
1238 			 * First segment to transfer is minimum of
1239 			 * transfer size and contiguous space in
1240 			 * pipe buffer.  If first segment to transfer
1241 			 * is less than the transfer size, we've got
1242 			 * a wraparound in the buffer.
1243 			 */
1244 			segsize = wpipe->pipe_buffer.size -
1245 				wpipe->pipe_buffer.in;
1246 			if (segsize > size)
1247 				segsize = size;
1248 
1249 			/* Transfer first segment */
1250 
1251 			PIPE_UNLOCK(rpipe);
1252 			error = uiomove(&wpipe->pipe_buffer.buffer[wpipe->pipe_buffer.in],
1253 					segsize, uio);
1254 			PIPE_LOCK(rpipe);
1255 
1256 			if (error == 0 && segsize < size) {
1257 				KASSERT(wpipe->pipe_buffer.in + segsize ==
1258 					wpipe->pipe_buffer.size,
1259 					("Pipe buffer wraparound disappeared"));
1260 				/*
1261 				 * Transfer remaining part now, to
1262 				 * support atomic writes.  Wraparound
1263 				 * happened.
1264 				 */
1265 
1266 				PIPE_UNLOCK(rpipe);
1267 				error = uiomove(
1268 				    &wpipe->pipe_buffer.buffer[0],
1269 				    size - segsize, uio);
1270 				PIPE_LOCK(rpipe);
1271 			}
1272 			if (error == 0) {
1273 				wpipe->pipe_buffer.in += size;
1274 				if (wpipe->pipe_buffer.in >=
1275 				    wpipe->pipe_buffer.size) {
1276 					KASSERT(wpipe->pipe_buffer.in ==
1277 						size - segsize +
1278 						wpipe->pipe_buffer.size,
1279 						("Expected wraparound bad"));
1280 					wpipe->pipe_buffer.in = size - segsize;
1281 				}
1282 
1283 				wpipe->pipe_buffer.cnt += size;
1284 				KASSERT(wpipe->pipe_buffer.cnt <=
1285 					wpipe->pipe_buffer.size,
1286 					("Pipe buffer overflow"));
1287 			}
1288 			if (error != 0)
1289 				break;
1290 			continue;
1291 		} else {
1292 			/*
1293 			 * If the "read-side" has been blocked, wake it up now.
1294 			 */
1295 			if (wpipe->pipe_state & PIPE_WANTR) {
1296 				wpipe->pipe_state &= ~PIPE_WANTR;
1297 				wakeup(wpipe);
1298 			}
1299 
1300 			/*
1301 			 * don't block on non-blocking I/O
1302 			 */
1303 			if (fp->f_flag & FNONBLOCK) {
1304 				error = EAGAIN;
1305 				break;
1306 			}
1307 
1308 			/*
1309 			 * We have no more space and have something to offer,
1310 			 * wake up select/poll.
1311 			 */
1312 			pipeselwakeup(wpipe);
1313 
1314 			wpipe->pipe_state |= PIPE_WANTW;
1315 			pipeunlock(wpipe);
1316 			error = msleep(wpipe, PIPE_MTX(rpipe),
1317 			    PRIBIO | PCATCH, "pipewr", 0);
1318 			pipelock(wpipe, 0);
1319 			if (error != 0)
1320 				break;
1321 			continue;
1322 		}
1323 	}
1324 
1325 	--wpipe->pipe_busy;
1326 
1327 	if ((wpipe->pipe_busy == 0) && (wpipe->pipe_state & PIPE_WANT)) {
1328 		wpipe->pipe_state &= ~(PIPE_WANT | PIPE_WANTR);
1329 		wakeup(wpipe);
1330 	} else if (wpipe->pipe_buffer.cnt > 0) {
1331 		/*
1332 		 * If we have put any characters in the buffer, we wake up
1333 		 * the reader.
1334 		 */
1335 		if (wpipe->pipe_state & PIPE_WANTR) {
1336 			wpipe->pipe_state &= ~PIPE_WANTR;
1337 			wakeup(wpipe);
1338 		}
1339 	}
1340 
1341 	/*
1342 	 * Don't return EPIPE if any byte was written.
1343 	 * EINTR and other interrupts are handled by generic I/O layer.
1344 	 * Do not pretend that I/O succeeded for obvious user error
1345 	 * like EFAULT.
1346 	 */
1347 	if (uio->uio_resid != orig_resid && error == EPIPE)
1348 		error = 0;
1349 
1350 	if (error == 0)
1351 		pipe_timestamp(&wpipe->pipe_mtime);
1352 
1353 	/*
1354 	 * We have something to offer,
1355 	 * wake up select/poll.
1356 	 */
1357 	if (wpipe->pipe_buffer.cnt)
1358 		pipeselwakeup(wpipe);
1359 
1360 	pipeunlock(wpipe);
1361 	PIPE_UNLOCK(rpipe);
1362 	if (uio->uio_resid != orig_resid)
1363 		td->td_ru.ru_msgsnd++;
1364 	return (error);
1365 }
1366 
1367 /* ARGSUSED */
1368 static int
1369 pipe_truncate(struct file *fp, off_t length, struct ucred *active_cred,
1370     struct thread *td)
1371 {
1372 	struct pipe *cpipe;
1373 	int error;
1374 
1375 	cpipe = fp->f_data;
1376 	if (cpipe->pipe_type & PIPE_TYPE_NAMED)
1377 		error = vnops.fo_truncate(fp, length, active_cred, td);
1378 	else
1379 		error = invfo_truncate(fp, length, active_cred, td);
1380 	return (error);
1381 }
1382 
1383 /*
1384  * we implement a very minimal set of ioctls for compatibility with sockets.
1385  */
1386 static int
1387 pipe_ioctl(struct file *fp, u_long cmd, void *data, struct ucred *active_cred,
1388     struct thread *td)
1389 {
1390 	struct pipe *mpipe = fp->f_data;
1391 	int error;
1392 
1393 	PIPE_LOCK(mpipe);
1394 
1395 #ifdef MAC
1396 	error = mac_pipe_check_ioctl(active_cred, mpipe->pipe_pair, cmd, data);
1397 	if (error) {
1398 		PIPE_UNLOCK(mpipe);
1399 		return (error);
1400 	}
1401 #endif
1402 
1403 	error = 0;
1404 	switch (cmd) {
1405 	case FIONBIO:
1406 		break;
1407 
1408 	case FIOASYNC:
1409 		if (*(int *)data) {
1410 			mpipe->pipe_state |= PIPE_ASYNC;
1411 		} else {
1412 			mpipe->pipe_state &= ~PIPE_ASYNC;
1413 		}
1414 		break;
1415 
1416 	case FIONREAD:
1417 		if (!(fp->f_flag & FREAD)) {
1418 			*(int *)data = 0;
1419 			PIPE_UNLOCK(mpipe);
1420 			return (0);
1421 		}
1422 		if (mpipe->pipe_pages.cnt != 0)
1423 			*(int *)data = mpipe->pipe_pages.cnt;
1424 		else
1425 			*(int *)data = mpipe->pipe_buffer.cnt;
1426 		break;
1427 
1428 	case FIOSETOWN:
1429 		PIPE_UNLOCK(mpipe);
1430 		error = fsetown(*(int *)data, &mpipe->pipe_sigio);
1431 		goto out_unlocked;
1432 
1433 	case FIOGETOWN:
1434 		*(int *)data = fgetown(&mpipe->pipe_sigio);
1435 		break;
1436 
1437 	/* This is deprecated, FIOSETOWN should be used instead. */
1438 	case TIOCSPGRP:
1439 		PIPE_UNLOCK(mpipe);
1440 		error = fsetown(-(*(int *)data), &mpipe->pipe_sigio);
1441 		goto out_unlocked;
1442 
1443 	/* This is deprecated, FIOGETOWN should be used instead. */
1444 	case TIOCGPGRP:
1445 		*(int *)data = -fgetown(&mpipe->pipe_sigio);
1446 		break;
1447 
1448 	default:
1449 		error = ENOTTY;
1450 		break;
1451 	}
1452 	PIPE_UNLOCK(mpipe);
1453 out_unlocked:
1454 	return (error);
1455 }
1456 
1457 static int
1458 pipe_poll(struct file *fp, int events, struct ucred *active_cred,
1459     struct thread *td)
1460 {
1461 	struct pipe *rpipe;
1462 	struct pipe *wpipe;
1463 	int levents, revents;
1464 #ifdef MAC
1465 	int error;
1466 #endif
1467 
1468 	revents = 0;
1469 	rpipe = fp->f_data;
1470 	wpipe = PIPE_PEER(rpipe);
1471 	PIPE_LOCK(rpipe);
1472 #ifdef MAC
1473 	error = mac_pipe_check_poll(active_cred, rpipe->pipe_pair);
1474 	if (error)
1475 		goto locked_error;
1476 #endif
1477 	if (fp->f_flag & FREAD && events & (POLLIN | POLLRDNORM))
1478 		if (rpipe->pipe_pages.cnt > 0 || rpipe->pipe_buffer.cnt > 0)
1479 			revents |= events & (POLLIN | POLLRDNORM);
1480 
1481 	if (fp->f_flag & FWRITE && events & (POLLOUT | POLLWRNORM))
1482 		if (wpipe->pipe_present != PIPE_ACTIVE ||
1483 		    (wpipe->pipe_state & PIPE_EOF) ||
1484 		    ((wpipe->pipe_state & PIPE_DIRECTW) == 0 &&
1485 		     ((wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt) >= PIPE_BUF ||
1486 			 wpipe->pipe_buffer.size == 0)))
1487 			revents |= events & (POLLOUT | POLLWRNORM);
1488 
1489 	levents = events &
1490 	    (POLLIN | POLLINIGNEOF | POLLPRI | POLLRDNORM | POLLRDBAND);
1491 	if (rpipe->pipe_type & PIPE_TYPE_NAMED && fp->f_flag & FREAD && levents &&
1492 	    fp->f_pipegen == rpipe->pipe_wgen)
1493 		events |= POLLINIGNEOF;
1494 
1495 	if ((events & POLLINIGNEOF) == 0) {
1496 		if (rpipe->pipe_state & PIPE_EOF) {
1497 			if (fp->f_flag & FREAD)
1498 				revents |= (events & (POLLIN | POLLRDNORM));
1499 			if (wpipe->pipe_present != PIPE_ACTIVE ||
1500 			    (wpipe->pipe_state & PIPE_EOF))
1501 				revents |= POLLHUP;
1502 		}
1503 	}
1504 
1505 	if (revents == 0) {
1506 		/*
1507 		 * Add ourselves regardless of eventmask as we have to return
1508 		 * POLLHUP even if it was not asked for.
1509 		 */
1510 		if ((fp->f_flag & FREAD) != 0) {
1511 			selrecord(td, &rpipe->pipe_sel);
1512 			if (SEL_WAITING(&rpipe->pipe_sel))
1513 				rpipe->pipe_state |= PIPE_SEL;
1514 		}
1515 
1516 		if ((fp->f_flag & FWRITE) != 0 &&
1517 		    wpipe->pipe_present == PIPE_ACTIVE) {
1518 			selrecord(td, &wpipe->pipe_sel);
1519 			if (SEL_WAITING(&wpipe->pipe_sel))
1520 				wpipe->pipe_state |= PIPE_SEL;
1521 		}
1522 	}
1523 #ifdef MAC
1524 locked_error:
1525 #endif
1526 	PIPE_UNLOCK(rpipe);
1527 
1528 	return (revents);
1529 }
1530 
1531 /*
1532  * We shouldn't need locks here as we're doing a read and this should
1533  * be a natural race.
1534  */
1535 static int
1536 pipe_stat(struct file *fp, struct stat *ub, struct ucred *active_cred)
1537 {
1538 	struct pipe *pipe;
1539 #ifdef MAC
1540 	int error;
1541 #endif
1542 
1543 	pipe = fp->f_data;
1544 #ifdef MAC
1545 	if (mac_pipe_check_stat_enabled()) {
1546 		PIPE_LOCK(pipe);
1547 		error = mac_pipe_check_stat(active_cred, pipe->pipe_pair);
1548 		PIPE_UNLOCK(pipe);
1549 		if (error) {
1550 			return (error);
1551 		}
1552 	}
1553 #endif
1554 
1555 	/* For named pipes ask the underlying filesystem. */
1556 	if (pipe->pipe_type & PIPE_TYPE_NAMED) {
1557 		return (vnops.fo_stat(fp, ub, active_cred));
1558 	}
1559 
1560 	bzero(ub, sizeof(*ub));
1561 	ub->st_mode = S_IFIFO;
1562 	ub->st_blksize = PAGE_SIZE;
1563 	if (pipe->pipe_pages.cnt != 0)
1564 		ub->st_size = pipe->pipe_pages.cnt;
1565 	else
1566 		ub->st_size = pipe->pipe_buffer.cnt;
1567 	ub->st_blocks = howmany(ub->st_size, ub->st_blksize);
1568 	ub->st_atim = pipe->pipe_atime;
1569 	ub->st_mtim = pipe->pipe_mtime;
1570 	ub->st_ctim = pipe->pipe_ctime;
1571 	ub->st_uid = fp->f_cred->cr_uid;
1572 	ub->st_gid = fp->f_cred->cr_gid;
1573 	ub->st_dev = pipedev_ino;
1574 	ub->st_ino = pipe->pipe_ino;
1575 	/*
1576 	 * Left as 0: st_nlink, st_rdev, st_flags, st_gen.
1577 	 */
1578 	return (0);
1579 }
1580 
1581 /* ARGSUSED */
1582 static int
1583 pipe_close(struct file *fp, struct thread *td)
1584 {
1585 
1586 	if (fp->f_vnode != NULL)
1587 		return vnops.fo_close(fp, td);
1588 	fp->f_ops = &badfileops;
1589 	pipe_dtor(fp->f_data);
1590 	fp->f_data = NULL;
1591 	return (0);
1592 }
1593 
1594 static int
1595 pipe_chmod(struct file *fp, mode_t mode, struct ucred *active_cred, struct thread *td)
1596 {
1597 	struct pipe *cpipe;
1598 	int error;
1599 
1600 	cpipe = fp->f_data;
1601 	if (cpipe->pipe_type & PIPE_TYPE_NAMED)
1602 		error = vn_chmod(fp, mode, active_cred, td);
1603 	else
1604 		error = invfo_chmod(fp, mode, active_cred, td);
1605 	return (error);
1606 }
1607 
1608 static int
1609 pipe_chown(struct file *fp, uid_t uid, gid_t gid, struct ucred *active_cred,
1610     struct thread *td)
1611 {
1612 	struct pipe *cpipe;
1613 	int error;
1614 
1615 	cpipe = fp->f_data;
1616 	if (cpipe->pipe_type & PIPE_TYPE_NAMED)
1617 		error = vn_chown(fp, uid, gid, active_cred, td);
1618 	else
1619 		error = invfo_chown(fp, uid, gid, active_cred, td);
1620 	return (error);
1621 }
1622 
1623 static int
1624 pipe_fill_kinfo(struct file *fp, struct kinfo_file *kif, struct filedesc *fdp)
1625 {
1626 	struct pipe *pi;
1627 
1628 	if (fp->f_type == DTYPE_FIFO)
1629 		return (vn_fill_kinfo(fp, kif, fdp));
1630 	kif->kf_type = KF_TYPE_PIPE;
1631 	pi = fp->f_data;
1632 	kif->kf_un.kf_pipe.kf_pipe_addr = (uintptr_t)pi;
1633 	kif->kf_un.kf_pipe.kf_pipe_peer = (uintptr_t)pi->pipe_peer;
1634 	kif->kf_un.kf_pipe.kf_pipe_buffer_cnt = pi->pipe_buffer.cnt;
1635 	kif->kf_un.kf_pipe.kf_pipe_buffer_in = pi->pipe_buffer.in;
1636 	kif->kf_un.kf_pipe.kf_pipe_buffer_out = pi->pipe_buffer.out;
1637 	kif->kf_un.kf_pipe.kf_pipe_buffer_size = pi->pipe_buffer.size;
1638 	return (0);
1639 }
1640 
1641 static void
1642 pipe_free_kmem(struct pipe *cpipe)
1643 {
1644 
1645 	KASSERT(!mtx_owned(PIPE_MTX(cpipe)),
1646 	    ("pipe_free_kmem: pipe mutex locked"));
1647 
1648 	if (cpipe->pipe_buffer.buffer != NULL) {
1649 		atomic_subtract_long(&amountpipekva, cpipe->pipe_buffer.size);
1650 		vm_map_remove(pipe_map,
1651 		    (vm_offset_t)cpipe->pipe_buffer.buffer,
1652 		    (vm_offset_t)cpipe->pipe_buffer.buffer + cpipe->pipe_buffer.size);
1653 		cpipe->pipe_buffer.buffer = NULL;
1654 	}
1655 #ifndef PIPE_NODIRECT
1656 	{
1657 		cpipe->pipe_pages.cnt = 0;
1658 		cpipe->pipe_pages.pos = 0;
1659 		cpipe->pipe_pages.npages = 0;
1660 	}
1661 #endif
1662 }
1663 
1664 /*
1665  * shutdown the pipe
1666  */
1667 static void
1668 pipeclose(struct pipe *cpipe)
1669 {
1670 #ifdef MAC
1671 	struct pipepair *pp;
1672 #endif
1673 	struct pipe *ppipe;
1674 
1675 	KASSERT(cpipe != NULL, ("pipeclose: cpipe == NULL"));
1676 
1677 	PIPE_LOCK(cpipe);
1678 	pipelock(cpipe, 0);
1679 #ifdef MAC
1680 	pp = cpipe->pipe_pair;
1681 #endif
1682 
1683 	/*
1684 	 * If the other side is blocked, wake it up saying that
1685 	 * we want to close it down.
1686 	 */
1687 	cpipe->pipe_state |= PIPE_EOF;
1688 	while (cpipe->pipe_busy) {
1689 		wakeup(cpipe);
1690 		cpipe->pipe_state |= PIPE_WANT;
1691 		pipeunlock(cpipe);
1692 		msleep(cpipe, PIPE_MTX(cpipe), PRIBIO, "pipecl", 0);
1693 		pipelock(cpipe, 0);
1694 	}
1695 
1696 	pipeselwakeup(cpipe);
1697 
1698 	/*
1699 	 * Disconnect from peer, if any.
1700 	 */
1701 	ppipe = cpipe->pipe_peer;
1702 	if (ppipe->pipe_present == PIPE_ACTIVE) {
1703 		ppipe->pipe_state |= PIPE_EOF;
1704 		wakeup(ppipe);
1705 		pipeselwakeup(ppipe);
1706 	}
1707 
1708 	/*
1709 	 * Mark this endpoint as free.  Release kmem resources.  We
1710 	 * don't mark this endpoint as unused until we've finished
1711 	 * doing that, or the pipe might disappear out from under
1712 	 * us.
1713 	 */
1714 	PIPE_UNLOCK(cpipe);
1715 	pipe_free_kmem(cpipe);
1716 	PIPE_LOCK(cpipe);
1717 	cpipe->pipe_present = PIPE_CLOSING;
1718 	pipeunlock(cpipe);
1719 
1720 	/*
1721 	 * knlist_clear() may sleep dropping the PIPE_MTX. Set the
1722 	 * PIPE_FINALIZED, that allows other end to free the
1723 	 * pipe_pair, only after the knotes are completely dismantled.
1724 	 */
1725 	knlist_clear(&cpipe->pipe_sel.si_note, 1);
1726 	cpipe->pipe_present = PIPE_FINALIZED;
1727 	seldrain(&cpipe->pipe_sel);
1728 	knlist_destroy(&cpipe->pipe_sel.si_note);
1729 
1730 	/*
1731 	 * If both endpoints are now closed, release the memory for the
1732 	 * pipe pair.  If not, unlock.
1733 	 */
1734 	if (ppipe->pipe_present == PIPE_FINALIZED) {
1735 		PIPE_UNLOCK(cpipe);
1736 #ifdef MAC
1737 		mac_pipe_destroy(pp);
1738 #endif
1739 		uma_zfree(pipe_zone, cpipe->pipe_pair);
1740 	} else
1741 		PIPE_UNLOCK(cpipe);
1742 }
1743 
1744 /*ARGSUSED*/
1745 static int
1746 pipe_kqfilter(struct file *fp, struct knote *kn)
1747 {
1748 	struct pipe *cpipe;
1749 
1750 	/*
1751 	 * If a filter is requested that is not supported by this file
1752 	 * descriptor, don't return an error, but also don't ever generate an
1753 	 * event.
1754 	 */
1755 	if ((kn->kn_filter == EVFILT_READ) && !(fp->f_flag & FREAD)) {
1756 		kn->kn_fop = &pipe_nfiltops;
1757 		return (0);
1758 	}
1759 	if ((kn->kn_filter == EVFILT_WRITE) && !(fp->f_flag & FWRITE)) {
1760 		kn->kn_fop = &pipe_nfiltops;
1761 		return (0);
1762 	}
1763 	cpipe = fp->f_data;
1764 	PIPE_LOCK(cpipe);
1765 	switch (kn->kn_filter) {
1766 	case EVFILT_READ:
1767 		kn->kn_fop = &pipe_rfiltops;
1768 		break;
1769 	case EVFILT_WRITE:
1770 		kn->kn_fop = &pipe_wfiltops;
1771 		if (cpipe->pipe_peer->pipe_present != PIPE_ACTIVE) {
1772 			/* other end of pipe has been closed */
1773 			PIPE_UNLOCK(cpipe);
1774 			return (EPIPE);
1775 		}
1776 		cpipe = PIPE_PEER(cpipe);
1777 		break;
1778 	default:
1779 		if ((cpipe->pipe_type & PIPE_TYPE_NAMED) != 0) {
1780 			PIPE_UNLOCK(cpipe);
1781 			return (vnops.fo_kqfilter(fp, kn));
1782 		}
1783 		PIPE_UNLOCK(cpipe);
1784 		return (EINVAL);
1785 	}
1786 
1787 	kn->kn_hook = cpipe;
1788 	knlist_add(&cpipe->pipe_sel.si_note, kn, 1);
1789 	PIPE_UNLOCK(cpipe);
1790 	return (0);
1791 }
1792 
1793 static void
1794 filt_pipedetach(struct knote *kn)
1795 {
1796 	struct pipe *cpipe = kn->kn_hook;
1797 
1798 	PIPE_LOCK(cpipe);
1799 	knlist_remove(&cpipe->pipe_sel.si_note, kn, 1);
1800 	PIPE_UNLOCK(cpipe);
1801 }
1802 
1803 /*ARGSUSED*/
1804 static int
1805 filt_piperead(struct knote *kn, long hint)
1806 {
1807 	struct file *fp = kn->kn_fp;
1808 	struct pipe *rpipe = kn->kn_hook;
1809 
1810 	PIPE_LOCK_ASSERT(rpipe, MA_OWNED);
1811 	kn->kn_data = rpipe->pipe_buffer.cnt;
1812 	if (kn->kn_data == 0)
1813 		kn->kn_data = rpipe->pipe_pages.cnt;
1814 
1815 	if ((rpipe->pipe_state & PIPE_EOF) != 0 &&
1816 	    ((rpipe->pipe_type & PIPE_TYPE_NAMED) == 0 ||
1817 	    fp->f_pipegen != rpipe->pipe_wgen)) {
1818 		kn->kn_flags |= EV_EOF;
1819 		return (1);
1820 	}
1821 	kn->kn_flags &= ~EV_EOF;
1822 	return (kn->kn_data > 0);
1823 }
1824 
1825 /*ARGSUSED*/
1826 static int
1827 filt_pipewrite(struct knote *kn, long hint)
1828 {
1829 	struct pipe *wpipe = kn->kn_hook;
1830 
1831 	/*
1832 	 * If this end of the pipe is closed, the knote was removed from the
1833 	 * knlist and the list lock (i.e., the pipe lock) is therefore not held.
1834 	 */
1835 	if (wpipe->pipe_present == PIPE_ACTIVE ||
1836 	    (wpipe->pipe_type & PIPE_TYPE_NAMED) != 0) {
1837 		PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
1838 
1839 		if (wpipe->pipe_state & PIPE_DIRECTW) {
1840 			kn->kn_data = 0;
1841 		} else if (wpipe->pipe_buffer.size > 0) {
1842 			kn->kn_data = wpipe->pipe_buffer.size -
1843 			    wpipe->pipe_buffer.cnt;
1844 		} else {
1845 			kn->kn_data = PIPE_BUF;
1846 		}
1847 	}
1848 
1849 	if (wpipe->pipe_present != PIPE_ACTIVE ||
1850 	    (wpipe->pipe_state & PIPE_EOF)) {
1851 		kn->kn_flags |= EV_EOF;
1852 		return (1);
1853 	}
1854 	kn->kn_flags &= ~EV_EOF;
1855 	return (kn->kn_data >= PIPE_BUF);
1856 }
1857 
1858 static void
1859 filt_pipedetach_notsup(struct knote *kn)
1860 {
1861 
1862 }
1863 
1864 static int
1865 filt_pipenotsup(struct knote *kn, long hint)
1866 {
1867 
1868 	return (0);
1869 }
1870