The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/sys_pipe.c

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    1 /*-
    2  * Copyright (c) 1996 John S. Dyson
    3  * Copyright (c) 2012 Giovanni Trematerra
    4  * All rights reserved.
    5  *
    6  * Redistribution and use in source and binary forms, with or without
    7  * modification, are permitted provided that the following conditions
    8  * are met:
    9  * 1. Redistributions of source code must retain the above copyright
   10  *    notice immediately at the beginning of the file, without modification,
   11  *    this list of conditions, and the following disclaimer.
   12  * 2. Redistributions in binary form must reproduce the above copyright
   13  *    notice, this list of conditions and the following disclaimer in the
   14  *    documentation and/or other materials provided with the distribution.
   15  * 3. Absolutely no warranty of function or purpose is made by the author
   16  *    John S. Dyson.
   17  * 4. Modifications may be freely made to this file if the above conditions
   18  *    are met.
   19  */
   20 
   21 /*
   22  * This file contains a high-performance replacement for the socket-based
   23  * pipes scheme originally used in FreeBSD/4.4Lite.  It does not support
   24  * all features of sockets, but does do everything that pipes normally
   25  * do.
   26  */
   27 
   28 /*
   29  * This code has two modes of operation, a small write mode and a large
   30  * write mode.  The small write mode acts like conventional pipes with
   31  * a kernel buffer.  If the buffer is less than PIPE_MINDIRECT, then the
   32  * "normal" pipe buffering is done.  If the buffer is between PIPE_MINDIRECT
   33  * and PIPE_SIZE in size, the sending process pins the underlying pages in
   34  * memory, and the receiving process copies directly from these pinned pages
   35  * in the sending process.
   36  *
   37  * If the sending process receives a signal, it is possible that it will
   38  * go away, and certainly its address space can change, because control
   39  * is returned back to the user-mode side.  In that case, the pipe code
   40  * arranges to copy the buffer supplied by the user process, to a pageable
   41  * kernel buffer, and the receiving process will grab the data from the
   42  * pageable kernel buffer.  Since signals don't happen all that often,
   43  * the copy operation is normally eliminated.
   44  *
   45  * The constant PIPE_MINDIRECT is chosen to make sure that buffering will
   46  * happen for small transfers so that the system will not spend all of
   47  * its time context switching.
   48  *
   49  * In order to limit the resource use of pipes, two sysctls exist:
   50  *
   51  * kern.ipc.maxpipekva - This is a hard limit on the amount of pageable
   52  * address space available to us in pipe_map. This value is normally
   53  * autotuned, but may also be loader tuned.
   54  *
   55  * kern.ipc.pipekva - This read-only sysctl tracks the current amount of
   56  * memory in use by pipes.
   57  *
   58  * Based on how large pipekva is relative to maxpipekva, the following
   59  * will happen:
   60  *
   61  * 0% - 50%:
   62  *     New pipes are given 16K of memory backing, pipes may dynamically
   63  *     grow to as large as 64K where needed.
   64  * 50% - 75%:
   65  *     New pipes are given 4K (or PAGE_SIZE) of memory backing,
   66  *     existing pipes may NOT grow.
   67  * 75% - 100%:
   68  *     New pipes are given 4K (or PAGE_SIZE) of memory backing,
   69  *     existing pipes will be shrunk down to 4K whenever possible.
   70  *
   71  * Resizing may be disabled by setting kern.ipc.piperesizeallowed=0.  If
   72  * that is set,  the only resize that will occur is the 0 -> SMALL_PIPE_SIZE
   73  * resize which MUST occur for reverse-direction pipes when they are
   74  * first used.
   75  *
   76  * Additional information about the current state of pipes may be obtained
   77  * from kern.ipc.pipes, kern.ipc.pipefragretry, kern.ipc.pipeallocfail,
   78  * and kern.ipc.piperesizefail.
   79  *
   80  * Locking rules:  There are two locks present here:  A mutex, used via
   81  * PIPE_LOCK, and a flag, used via pipelock().  All locking is done via
   82  * the flag, as mutexes can not persist over uiomove.  The mutex
   83  * exists only to guard access to the flag, and is not in itself a
   84  * locking mechanism.  Also note that there is only a single mutex for
   85  * both directions of a pipe.
   86  *
   87  * As pipelock() may have to sleep before it can acquire the flag, it
   88  * is important to reread all data after a call to pipelock(); everything
   89  * in the structure may have changed.
   90  */
   91 
   92 #include "opt_compat.h"
   93 
   94 #include <sys/cdefs.h>
   95 __FBSDID("$FreeBSD: releng/11.2/sys/kern/sys_pipe.c 302095 2016-06-22 21:18:19Z brooks $");
   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_state & PIPE_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 
  213 SYSCTL_LONG(_kern_ipc, OID_AUTO, maxpipekva, CTLFLAG_RDTUN | CTLFLAG_NOFETCH,
  214            &maxpipekva, 0, "Pipe KVA limit");
  215 SYSCTL_LONG(_kern_ipc, OID_AUTO, pipekva, CTLFLAG_RD,
  216            &amountpipekva, 0, "Pipe KVA usage");
  217 SYSCTL_INT(_kern_ipc, OID_AUTO, pipefragretry, CTLFLAG_RD,
  218           &pipefragretry, 0, "Pipe allocation retries due to fragmentation");
  219 SYSCTL_INT(_kern_ipc, OID_AUTO, pipeallocfail, CTLFLAG_RD,
  220           &pipeallocfail, 0, "Pipe allocation failures");
  221 SYSCTL_INT(_kern_ipc, OID_AUTO, piperesizefail, CTLFLAG_RD,
  222           &piperesizefail, 0, "Pipe resize failures");
  223 SYSCTL_INT(_kern_ipc, OID_AUTO, piperesizeallowed, CTLFLAG_RW,
  224           &piperesizeallowed, 0, "Pipe resizing allowed");
  225 
  226 static void pipeinit(void *dummy __unused);
  227 static void pipeclose(struct pipe *cpipe);
  228 static void pipe_free_kmem(struct pipe *cpipe);
  229 static void pipe_create(struct pipe *pipe, int backing);
  230 static void pipe_paircreate(struct thread *td, struct pipepair **p_pp);
  231 static __inline int pipelock(struct pipe *cpipe, int catch);
  232 static __inline void pipeunlock(struct pipe *cpipe);
  233 #ifndef PIPE_NODIRECT
  234 static int pipe_build_write_buffer(struct pipe *wpipe, struct uio *uio);
  235 static void pipe_destroy_write_buffer(struct pipe *wpipe);
  236 static int pipe_direct_write(struct pipe *wpipe, struct uio *uio);
  237 static void pipe_clone_write_buffer(struct pipe *wpipe);
  238 #endif
  239 static int pipespace(struct pipe *cpipe, int size);
  240 static int pipespace_new(struct pipe *cpipe, int size);
  241 
  242 static int      pipe_zone_ctor(void *mem, int size, void *arg, int flags);
  243 static int      pipe_zone_init(void *mem, int size, int flags);
  244 static void     pipe_zone_fini(void *mem, int size);
  245 
  246 static uma_zone_t pipe_zone;
  247 static struct unrhdr *pipeino_unr;
  248 static dev_t pipedev_ino;
  249 
  250 SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_ANY, pipeinit, NULL);
  251 
  252 static void
  253 pipeinit(void *dummy __unused)
  254 {
  255 
  256         pipe_zone = uma_zcreate("pipe", sizeof(struct pipepair),
  257             pipe_zone_ctor, NULL, pipe_zone_init, pipe_zone_fini,
  258             UMA_ALIGN_PTR, 0);
  259         KASSERT(pipe_zone != NULL, ("pipe_zone not initialized"));
  260         pipeino_unr = new_unrhdr(1, INT32_MAX, NULL);
  261         KASSERT(pipeino_unr != NULL, ("pipe fake inodes not initialized"));
  262         pipedev_ino = devfs_alloc_cdp_inode();
  263         KASSERT(pipedev_ino > 0, ("pipe dev inode not initialized"));
  264 }
  265 
  266 static int
  267 pipe_zone_ctor(void *mem, int size, void *arg, int flags)
  268 {
  269         struct pipepair *pp;
  270         struct pipe *rpipe, *wpipe;
  271 
  272         KASSERT(size == sizeof(*pp), ("pipe_zone_ctor: wrong size"));
  273 
  274         pp = (struct pipepair *)mem;
  275 
  276         /*
  277          * We zero both pipe endpoints to make sure all the kmem pointers
  278          * are NULL, flag fields are zero'd, etc.  We timestamp both
  279          * endpoints with the same time.
  280          */
  281         rpipe = &pp->pp_rpipe;
  282         bzero(rpipe, sizeof(*rpipe));
  283         vfs_timestamp(&rpipe->pipe_ctime);
  284         rpipe->pipe_atime = rpipe->pipe_mtime = rpipe->pipe_ctime;
  285 
  286         wpipe = &pp->pp_wpipe;
  287         bzero(wpipe, sizeof(*wpipe));
  288         wpipe->pipe_ctime = rpipe->pipe_ctime;
  289         wpipe->pipe_atime = wpipe->pipe_mtime = rpipe->pipe_ctime;
  290 
  291         rpipe->pipe_peer = wpipe;
  292         rpipe->pipe_pair = pp;
  293         wpipe->pipe_peer = rpipe;
  294         wpipe->pipe_pair = pp;
  295 
  296         /*
  297          * Mark both endpoints as present; they will later get free'd
  298          * one at a time.  When both are free'd, then the whole pair
  299          * is released.
  300          */
  301         rpipe->pipe_present = PIPE_ACTIVE;
  302         wpipe->pipe_present = PIPE_ACTIVE;
  303 
  304         /*
  305          * Eventually, the MAC Framework may initialize the label
  306          * in ctor or init, but for now we do it elswhere to avoid
  307          * blocking in ctor or init.
  308          */
  309         pp->pp_label = NULL;
  310 
  311         return (0);
  312 }
  313 
  314 static int
  315 pipe_zone_init(void *mem, int size, int flags)
  316 {
  317         struct pipepair *pp;
  318 
  319         KASSERT(size == sizeof(*pp), ("pipe_zone_init: wrong size"));
  320 
  321         pp = (struct pipepair *)mem;
  322 
  323         mtx_init(&pp->pp_mtx, "pipe mutex", NULL, MTX_DEF | MTX_NEW);
  324         return (0);
  325 }
  326 
  327 static void
  328 pipe_zone_fini(void *mem, int size)
  329 {
  330         struct pipepair *pp;
  331 
  332         KASSERT(size == sizeof(*pp), ("pipe_zone_fini: wrong size"));
  333 
  334         pp = (struct pipepair *)mem;
  335 
  336         mtx_destroy(&pp->pp_mtx);
  337 }
  338 
  339 static void
  340 pipe_paircreate(struct thread *td, struct pipepair **p_pp)
  341 {
  342         struct pipepair *pp;
  343         struct pipe *rpipe, *wpipe;
  344 
  345         *p_pp = pp = uma_zalloc(pipe_zone, M_WAITOK);
  346 #ifdef MAC
  347         /*
  348          * The MAC label is shared between the connected endpoints.  As a
  349          * result mac_pipe_init() and mac_pipe_create() are called once
  350          * for the pair, and not on the endpoints.
  351          */
  352         mac_pipe_init(pp);
  353         mac_pipe_create(td->td_ucred, pp);
  354 #endif
  355         rpipe = &pp->pp_rpipe;
  356         wpipe = &pp->pp_wpipe;
  357 
  358         knlist_init_mtx(&rpipe->pipe_sel.si_note, PIPE_MTX(rpipe));
  359         knlist_init_mtx(&wpipe->pipe_sel.si_note, PIPE_MTX(wpipe));
  360 
  361         /* Only the forward direction pipe is backed by default */
  362         pipe_create(rpipe, 1);
  363         pipe_create(wpipe, 0);
  364 
  365         rpipe->pipe_state |= PIPE_DIRECTOK;
  366         wpipe->pipe_state |= PIPE_DIRECTOK;
  367 }
  368 
  369 void
  370 pipe_named_ctor(struct pipe **ppipe, struct thread *td)
  371 {
  372         struct pipepair *pp;
  373 
  374         pipe_paircreate(td, &pp);
  375         pp->pp_rpipe.pipe_state |= PIPE_NAMED;
  376         *ppipe = &pp->pp_rpipe;
  377 }
  378 
  379 void
  380 pipe_dtor(struct pipe *dpipe)
  381 {
  382         struct pipe *peer;
  383         ino_t ino;
  384 
  385         ino = dpipe->pipe_ino;
  386         peer = (dpipe->pipe_state & PIPE_NAMED) != 0 ? dpipe->pipe_peer : NULL;
  387         funsetown(&dpipe->pipe_sigio);
  388         pipeclose(dpipe);
  389         if (peer != NULL) {
  390                 funsetown(&peer->pipe_sigio);
  391                 pipeclose(peer);
  392         }
  393         if (ino != 0 && ino != (ino_t)-1)
  394                 free_unr(pipeino_unr, ino);
  395 }
  396 
  397 /*
  398  * The pipe system call for the DTYPE_PIPE type of pipes.  If we fail, let
  399  * the zone pick up the pieces via pipeclose().
  400  */
  401 int
  402 kern_pipe(struct thread *td, int fildes[2], int flags, struct filecaps *fcaps1,
  403     struct filecaps *fcaps2)
  404 {
  405         struct file *rf, *wf;
  406         struct pipe *rpipe, *wpipe;
  407         struct pipepair *pp;
  408         int fd, fflags, error;
  409 
  410         pipe_paircreate(td, &pp);
  411         rpipe = &pp->pp_rpipe;
  412         wpipe = &pp->pp_wpipe;
  413         error = falloc_caps(td, &rf, &fd, flags, fcaps1);
  414         if (error) {
  415                 pipeclose(rpipe);
  416                 pipeclose(wpipe);
  417                 return (error);
  418         }
  419         /* An extra reference on `rf' has been held for us by falloc_caps(). */
  420         fildes[0] = fd;
  421 
  422         fflags = FREAD | FWRITE;
  423         if ((flags & O_NONBLOCK) != 0)
  424                 fflags |= FNONBLOCK;
  425 
  426         /*
  427          * Warning: once we've gotten past allocation of the fd for the
  428          * read-side, we can only drop the read side via fdrop() in order
  429          * to avoid races against processes which manage to dup() the read
  430          * side while we are blocked trying to allocate the write side.
  431          */
  432         finit(rf, fflags, DTYPE_PIPE, rpipe, &pipeops);
  433         error = falloc_caps(td, &wf, &fd, flags, fcaps2);
  434         if (error) {
  435                 fdclose(td, rf, fildes[0]);
  436                 fdrop(rf, td);
  437                 /* rpipe has been closed by fdrop(). */
  438                 pipeclose(wpipe);
  439                 return (error);
  440         }
  441         /* An extra reference on `wf' has been held for us by falloc_caps(). */
  442         finit(wf, fflags, DTYPE_PIPE, wpipe, &pipeops);
  443         fdrop(wf, td);
  444         fildes[1] = fd;
  445         fdrop(rf, td);
  446 
  447         return (0);
  448 }
  449 
  450 #ifdef COMPAT_FREEBSD10
  451 /* ARGSUSED */
  452 int
  453 freebsd10_pipe(struct thread *td, struct freebsd10_pipe_args *uap __unused)
  454 {
  455         int error;
  456         int fildes[2];
  457 
  458         error = kern_pipe(td, fildes, 0, NULL, NULL);
  459         if (error)
  460                 return (error);
  461 
  462         td->td_retval[0] = fildes[0];
  463         td->td_retval[1] = fildes[1];
  464 
  465         return (0);
  466 }
  467 #endif
  468 
  469 int
  470 sys_pipe2(struct thread *td, struct pipe2_args *uap)
  471 {
  472         int error, fildes[2];
  473 
  474         if (uap->flags & ~(O_CLOEXEC | O_NONBLOCK))
  475                 return (EINVAL);
  476         error = kern_pipe(td, fildes, uap->flags, NULL, NULL);
  477         if (error)
  478                 return (error);
  479         error = copyout(fildes, uap->fildes, 2 * sizeof(int));
  480         if (error) {
  481                 (void)kern_close(td, fildes[0]);
  482                 (void)kern_close(td, fildes[1]);
  483         }
  484         return (error);
  485 }
  486 
  487 /*
  488  * Allocate kva for pipe circular buffer, the space is pageable
  489  * This routine will 'realloc' the size of a pipe safely, if it fails
  490  * it will retain the old buffer.
  491  * If it fails it will return ENOMEM.
  492  */
  493 static int
  494 pipespace_new(cpipe, size)
  495         struct pipe *cpipe;
  496         int size;
  497 {
  498         caddr_t buffer;
  499         int error, cnt, firstseg;
  500         static int curfail = 0;
  501         static struct timeval lastfail;
  502 
  503         KASSERT(!mtx_owned(PIPE_MTX(cpipe)), ("pipespace: pipe mutex locked"));
  504         KASSERT(!(cpipe->pipe_state & PIPE_DIRECTW),
  505                 ("pipespace: resize of direct writes not allowed"));
  506 retry:
  507         cnt = cpipe->pipe_buffer.cnt;
  508         if (cnt > size)
  509                 size = cnt;
  510 
  511         size = round_page(size);
  512         buffer = (caddr_t) vm_map_min(pipe_map);
  513 
  514         error = vm_map_find(pipe_map, NULL, 0,
  515                 (vm_offset_t *) &buffer, size, 0, VMFS_ANY_SPACE,
  516                 VM_PROT_ALL, VM_PROT_ALL, 0);
  517         if (error != KERN_SUCCESS) {
  518                 if ((cpipe->pipe_buffer.buffer == NULL) &&
  519                         (size > SMALL_PIPE_SIZE)) {
  520                         size = SMALL_PIPE_SIZE;
  521                         pipefragretry++;
  522                         goto retry;
  523                 }
  524                 if (cpipe->pipe_buffer.buffer == NULL) {
  525                         pipeallocfail++;
  526                         if (ppsratecheck(&lastfail, &curfail, 1))
  527                                 printf("kern.ipc.maxpipekva exceeded; see tuning(7)\n");
  528                 } else {
  529                         piperesizefail++;
  530                 }
  531                 return (ENOMEM);
  532         }
  533 
  534         /* copy data, then free old resources if we're resizing */
  535         if (cnt > 0) {
  536                 if (cpipe->pipe_buffer.in <= cpipe->pipe_buffer.out) {
  537                         firstseg = cpipe->pipe_buffer.size - cpipe->pipe_buffer.out;
  538                         bcopy(&cpipe->pipe_buffer.buffer[cpipe->pipe_buffer.out],
  539                                 buffer, firstseg);
  540                         if ((cnt - firstseg) > 0)
  541                                 bcopy(cpipe->pipe_buffer.buffer, &buffer[firstseg],
  542                                         cpipe->pipe_buffer.in);
  543                 } else {
  544                         bcopy(&cpipe->pipe_buffer.buffer[cpipe->pipe_buffer.out],
  545                                 buffer, cnt);
  546                 }
  547         }
  548         pipe_free_kmem(cpipe);
  549         cpipe->pipe_buffer.buffer = buffer;
  550         cpipe->pipe_buffer.size = size;
  551         cpipe->pipe_buffer.in = cnt;
  552         cpipe->pipe_buffer.out = 0;
  553         cpipe->pipe_buffer.cnt = cnt;
  554         atomic_add_long(&amountpipekva, cpipe->pipe_buffer.size);
  555         return (0);
  556 }
  557 
  558 /*
  559  * Wrapper for pipespace_new() that performs locking assertions.
  560  */
  561 static int
  562 pipespace(cpipe, size)
  563         struct pipe *cpipe;
  564         int size;
  565 {
  566 
  567         KASSERT(cpipe->pipe_state & PIPE_LOCKFL,
  568                 ("Unlocked pipe passed to pipespace"));
  569         return (pipespace_new(cpipe, size));
  570 }
  571 
  572 /*
  573  * lock a pipe for I/O, blocking other access
  574  */
  575 static __inline int
  576 pipelock(cpipe, catch)
  577         struct pipe *cpipe;
  578         int catch;
  579 {
  580         int error;
  581 
  582         PIPE_LOCK_ASSERT(cpipe, MA_OWNED);
  583         while (cpipe->pipe_state & PIPE_LOCKFL) {
  584                 cpipe->pipe_state |= PIPE_LWANT;
  585                 error = msleep(cpipe, PIPE_MTX(cpipe),
  586                     catch ? (PRIBIO | PCATCH) : PRIBIO,
  587                     "pipelk", 0);
  588                 if (error != 0)
  589                         return (error);
  590         }
  591         cpipe->pipe_state |= PIPE_LOCKFL;
  592         return (0);
  593 }
  594 
  595 /*
  596  * unlock a pipe I/O lock
  597  */
  598 static __inline void
  599 pipeunlock(cpipe)
  600         struct pipe *cpipe;
  601 {
  602 
  603         PIPE_LOCK_ASSERT(cpipe, MA_OWNED);
  604         KASSERT(cpipe->pipe_state & PIPE_LOCKFL,
  605                 ("Unlocked pipe passed to pipeunlock"));
  606         cpipe->pipe_state &= ~PIPE_LOCKFL;
  607         if (cpipe->pipe_state & PIPE_LWANT) {
  608                 cpipe->pipe_state &= ~PIPE_LWANT;
  609                 wakeup(cpipe);
  610         }
  611 }
  612 
  613 void
  614 pipeselwakeup(cpipe)
  615         struct pipe *cpipe;
  616 {
  617 
  618         PIPE_LOCK_ASSERT(cpipe, MA_OWNED);
  619         if (cpipe->pipe_state & PIPE_SEL) {
  620                 selwakeuppri(&cpipe->pipe_sel, PSOCK);
  621                 if (!SEL_WAITING(&cpipe->pipe_sel))
  622                         cpipe->pipe_state &= ~PIPE_SEL;
  623         }
  624         if ((cpipe->pipe_state & PIPE_ASYNC) && cpipe->pipe_sigio)
  625                 pgsigio(&cpipe->pipe_sigio, SIGIO, 0);
  626         KNOTE_LOCKED(&cpipe->pipe_sel.si_note, 0);
  627 }
  628 
  629 /*
  630  * Initialize and allocate VM and memory for pipe.  The structure
  631  * will start out zero'd from the ctor, so we just manage the kmem.
  632  */
  633 static void
  634 pipe_create(pipe, backing)
  635         struct pipe *pipe;
  636         int backing;
  637 {
  638 
  639         if (backing) {
  640                 /*
  641                  * Note that these functions can fail if pipe map is exhausted
  642                  * (as a result of too many pipes created), but we ignore the
  643                  * error as it is not fatal and could be provoked by
  644                  * unprivileged users. The only consequence is worse performance
  645                  * with given pipe.
  646                  */
  647                 if (amountpipekva > maxpipekva / 2)
  648                         (void)pipespace_new(pipe, SMALL_PIPE_SIZE);
  649                 else
  650                         (void)pipespace_new(pipe, PIPE_SIZE);
  651         }
  652 
  653         pipe->pipe_ino = -1;
  654 }
  655 
  656 /* ARGSUSED */
  657 static int
  658 pipe_read(fp, uio, active_cred, flags, td)
  659         struct file *fp;
  660         struct uio *uio;
  661         struct ucred *active_cred;
  662         struct thread *td;
  663         int flags;
  664 {
  665         struct pipe *rpipe;
  666         int error;
  667         int nread = 0;
  668         int size;
  669 
  670         rpipe = fp->f_data;
  671         PIPE_LOCK(rpipe);
  672         ++rpipe->pipe_busy;
  673         error = pipelock(rpipe, 1);
  674         if (error)
  675                 goto unlocked_error;
  676 
  677 #ifdef MAC
  678         error = mac_pipe_check_read(active_cred, rpipe->pipe_pair);
  679         if (error)
  680                 goto locked_error;
  681 #endif
  682         if (amountpipekva > (3 * maxpipekva) / 4) {
  683                 if (!(rpipe->pipe_state & PIPE_DIRECTW) &&
  684                         (rpipe->pipe_buffer.size > SMALL_PIPE_SIZE) &&
  685                         (rpipe->pipe_buffer.cnt <= SMALL_PIPE_SIZE) &&
  686                         (piperesizeallowed == 1)) {
  687                         PIPE_UNLOCK(rpipe);
  688                         pipespace(rpipe, SMALL_PIPE_SIZE);
  689                         PIPE_LOCK(rpipe);
  690                 }
  691         }
  692 
  693         while (uio->uio_resid) {
  694                 /*
  695                  * normal pipe buffer receive
  696                  */
  697                 if (rpipe->pipe_buffer.cnt > 0) {
  698                         size = rpipe->pipe_buffer.size - rpipe->pipe_buffer.out;
  699                         if (size > rpipe->pipe_buffer.cnt)
  700                                 size = rpipe->pipe_buffer.cnt;
  701                         if (size > uio->uio_resid)
  702                                 size = uio->uio_resid;
  703 
  704                         PIPE_UNLOCK(rpipe);
  705                         error = uiomove(
  706                             &rpipe->pipe_buffer.buffer[rpipe->pipe_buffer.out],
  707                             size, uio);
  708                         PIPE_LOCK(rpipe);
  709                         if (error)
  710                                 break;
  711 
  712                         rpipe->pipe_buffer.out += size;
  713                         if (rpipe->pipe_buffer.out >= rpipe->pipe_buffer.size)
  714                                 rpipe->pipe_buffer.out = 0;
  715 
  716                         rpipe->pipe_buffer.cnt -= size;
  717 
  718                         /*
  719                          * If there is no more to read in the pipe, reset
  720                          * its pointers to the beginning.  This improves
  721                          * cache hit stats.
  722                          */
  723                         if (rpipe->pipe_buffer.cnt == 0) {
  724                                 rpipe->pipe_buffer.in = 0;
  725                                 rpipe->pipe_buffer.out = 0;
  726                         }
  727                         nread += size;
  728 #ifndef PIPE_NODIRECT
  729                 /*
  730                  * Direct copy, bypassing a kernel buffer.
  731                  */
  732                 } else if ((size = rpipe->pipe_map.cnt) &&
  733                            (rpipe->pipe_state & PIPE_DIRECTW)) {
  734                         if (size > uio->uio_resid)
  735                                 size = (u_int) uio->uio_resid;
  736 
  737                         PIPE_UNLOCK(rpipe);
  738                         error = uiomove_fromphys(rpipe->pipe_map.ms,
  739                             rpipe->pipe_map.pos, size, uio);
  740                         PIPE_LOCK(rpipe);
  741                         if (error)
  742                                 break;
  743                         nread += size;
  744                         rpipe->pipe_map.pos += size;
  745                         rpipe->pipe_map.cnt -= size;
  746                         if (rpipe->pipe_map.cnt == 0) {
  747                                 rpipe->pipe_state &= ~(PIPE_DIRECTW|PIPE_WANTW);
  748                                 wakeup(rpipe);
  749                         }
  750 #endif
  751                 } else {
  752                         /*
  753                          * detect EOF condition
  754                          * read returns 0 on EOF, no need to set error
  755                          */
  756                         if (rpipe->pipe_state & PIPE_EOF)
  757                                 break;
  758 
  759                         /*
  760                          * If the "write-side" has been blocked, wake it up now.
  761                          */
  762                         if (rpipe->pipe_state & PIPE_WANTW) {
  763                                 rpipe->pipe_state &= ~PIPE_WANTW;
  764                                 wakeup(rpipe);
  765                         }
  766 
  767                         /*
  768                          * Break if some data was read.
  769                          */
  770                         if (nread > 0)
  771                                 break;
  772 
  773                         /*
  774                          * Unlock the pipe buffer for our remaining processing.
  775                          * We will either break out with an error or we will
  776                          * sleep and relock to loop.
  777                          */
  778                         pipeunlock(rpipe);
  779 
  780                         /*
  781                          * Handle non-blocking mode operation or
  782                          * wait for more data.
  783                          */
  784                         if (fp->f_flag & FNONBLOCK) {
  785                                 error = EAGAIN;
  786                         } else {
  787                                 rpipe->pipe_state |= PIPE_WANTR;
  788                                 if ((error = msleep(rpipe, PIPE_MTX(rpipe),
  789                                     PRIBIO | PCATCH,
  790                                     "piperd", 0)) == 0)
  791                                         error = pipelock(rpipe, 1);
  792                         }
  793                         if (error)
  794                                 goto unlocked_error;
  795                 }
  796         }
  797 #ifdef MAC
  798 locked_error:
  799 #endif
  800         pipeunlock(rpipe);
  801 
  802         /* XXX: should probably do this before getting any locks. */
  803         if (error == 0)
  804                 vfs_timestamp(&rpipe->pipe_atime);
  805 unlocked_error:
  806         --rpipe->pipe_busy;
  807 
  808         /*
  809          * PIPE_WANT processing only makes sense if pipe_busy is 0.
  810          */
  811         if ((rpipe->pipe_busy == 0) && (rpipe->pipe_state & PIPE_WANT)) {
  812                 rpipe->pipe_state &= ~(PIPE_WANT|PIPE_WANTW);
  813                 wakeup(rpipe);
  814         } else if (rpipe->pipe_buffer.cnt < MINPIPESIZE) {
  815                 /*
  816                  * Handle write blocking hysteresis.
  817                  */
  818                 if (rpipe->pipe_state & PIPE_WANTW) {
  819                         rpipe->pipe_state &= ~PIPE_WANTW;
  820                         wakeup(rpipe);
  821                 }
  822         }
  823 
  824         if ((rpipe->pipe_buffer.size - rpipe->pipe_buffer.cnt) >= PIPE_BUF)
  825                 pipeselwakeup(rpipe);
  826 
  827         PIPE_UNLOCK(rpipe);
  828         return (error);
  829 }
  830 
  831 #ifndef PIPE_NODIRECT
  832 /*
  833  * Map the sending processes' buffer into kernel space and wire it.
  834  * This is similar to a physical write operation.
  835  */
  836 static int
  837 pipe_build_write_buffer(wpipe, uio)
  838         struct pipe *wpipe;
  839         struct uio *uio;
  840 {
  841         u_int size;
  842         int i;
  843 
  844         PIPE_LOCK_ASSERT(wpipe, MA_NOTOWNED);
  845         KASSERT(wpipe->pipe_state & PIPE_DIRECTW,
  846                 ("Clone attempt on non-direct write pipe!"));
  847 
  848         if (uio->uio_iov->iov_len > wpipe->pipe_buffer.size)
  849                 size = wpipe->pipe_buffer.size;
  850         else
  851                 size = uio->uio_iov->iov_len;
  852 
  853         if ((i = vm_fault_quick_hold_pages(&curproc->p_vmspace->vm_map,
  854             (vm_offset_t)uio->uio_iov->iov_base, size, VM_PROT_READ,
  855             wpipe->pipe_map.ms, PIPENPAGES)) < 0)
  856                 return (EFAULT);
  857 
  858 /*
  859  * set up the control block
  860  */
  861         wpipe->pipe_map.npages = i;
  862         wpipe->pipe_map.pos =
  863             ((vm_offset_t) uio->uio_iov->iov_base) & PAGE_MASK;
  864         wpipe->pipe_map.cnt = size;
  865 
  866 /*
  867  * and update the uio data
  868  */
  869 
  870         uio->uio_iov->iov_len -= size;
  871         uio->uio_iov->iov_base = (char *)uio->uio_iov->iov_base + size;
  872         if (uio->uio_iov->iov_len == 0)
  873                 uio->uio_iov++;
  874         uio->uio_resid -= size;
  875         uio->uio_offset += size;
  876         return (0);
  877 }
  878 
  879 /*
  880  * unmap and unwire the process buffer
  881  */
  882 static void
  883 pipe_destroy_write_buffer(wpipe)
  884         struct pipe *wpipe;
  885 {
  886 
  887         PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
  888         vm_page_unhold_pages(wpipe->pipe_map.ms, wpipe->pipe_map.npages);
  889         wpipe->pipe_map.npages = 0;
  890 }
  891 
  892 /*
  893  * In the case of a signal, the writing process might go away.  This
  894  * code copies the data into the circular buffer so that the source
  895  * pages can be freed without loss of data.
  896  */
  897 static void
  898 pipe_clone_write_buffer(wpipe)
  899         struct pipe *wpipe;
  900 {
  901         struct uio uio;
  902         struct iovec iov;
  903         int size;
  904         int pos;
  905 
  906         PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
  907         size = wpipe->pipe_map.cnt;
  908         pos = wpipe->pipe_map.pos;
  909 
  910         wpipe->pipe_buffer.in = size;
  911         wpipe->pipe_buffer.out = 0;
  912         wpipe->pipe_buffer.cnt = size;
  913         wpipe->pipe_state &= ~PIPE_DIRECTW;
  914 
  915         PIPE_UNLOCK(wpipe);
  916         iov.iov_base = wpipe->pipe_buffer.buffer;
  917         iov.iov_len = size;
  918         uio.uio_iov = &iov;
  919         uio.uio_iovcnt = 1;
  920         uio.uio_offset = 0;
  921         uio.uio_resid = size;
  922         uio.uio_segflg = UIO_SYSSPACE;
  923         uio.uio_rw = UIO_READ;
  924         uio.uio_td = curthread;
  925         uiomove_fromphys(wpipe->pipe_map.ms, pos, size, &uio);
  926         PIPE_LOCK(wpipe);
  927         pipe_destroy_write_buffer(wpipe);
  928 }
  929 
  930 /*
  931  * This implements the pipe buffer write mechanism.  Note that only
  932  * a direct write OR a normal pipe write can be pending at any given time.
  933  * If there are any characters in the pipe buffer, the direct write will
  934  * be deferred until the receiving process grabs all of the bytes from
  935  * the pipe buffer.  Then the direct mapping write is set-up.
  936  */
  937 static int
  938 pipe_direct_write(wpipe, uio)
  939         struct pipe *wpipe;
  940         struct uio *uio;
  941 {
  942         int error;
  943 
  944 retry:
  945         PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
  946         error = pipelock(wpipe, 1);
  947         if (error != 0)
  948                 goto error1;
  949         if ((wpipe->pipe_state & PIPE_EOF) != 0) {
  950                 error = EPIPE;
  951                 pipeunlock(wpipe);
  952                 goto error1;
  953         }
  954         while (wpipe->pipe_state & PIPE_DIRECTW) {
  955                 if (wpipe->pipe_state & PIPE_WANTR) {
  956                         wpipe->pipe_state &= ~PIPE_WANTR;
  957                         wakeup(wpipe);
  958                 }
  959                 pipeselwakeup(wpipe);
  960                 wpipe->pipe_state |= PIPE_WANTW;
  961                 pipeunlock(wpipe);
  962                 error = msleep(wpipe, PIPE_MTX(wpipe),
  963                     PRIBIO | PCATCH, "pipdww", 0);
  964                 if (error)
  965                         goto error1;
  966                 else
  967                         goto retry;
  968         }
  969         wpipe->pipe_map.cnt = 0;        /* transfer not ready yet */
  970         if (wpipe->pipe_buffer.cnt > 0) {
  971                 if (wpipe->pipe_state & PIPE_WANTR) {
  972                         wpipe->pipe_state &= ~PIPE_WANTR;
  973                         wakeup(wpipe);
  974                 }
  975                 pipeselwakeup(wpipe);
  976                 wpipe->pipe_state |= PIPE_WANTW;
  977                 pipeunlock(wpipe);
  978                 error = msleep(wpipe, PIPE_MTX(wpipe),
  979                     PRIBIO | PCATCH, "pipdwc", 0);
  980                 if (error)
  981                         goto error1;
  982                 else
  983                         goto retry;
  984         }
  985 
  986         wpipe->pipe_state |= PIPE_DIRECTW;
  987 
  988         PIPE_UNLOCK(wpipe);
  989         error = pipe_build_write_buffer(wpipe, uio);
  990         PIPE_LOCK(wpipe);
  991         if (error) {
  992                 wpipe->pipe_state &= ~PIPE_DIRECTW;
  993                 pipeunlock(wpipe);
  994                 goto error1;
  995         }
  996 
  997         error = 0;
  998         while (!error && (wpipe->pipe_state & PIPE_DIRECTW)) {
  999                 if (wpipe->pipe_state & PIPE_EOF) {
 1000                         pipe_destroy_write_buffer(wpipe);
 1001                         pipeselwakeup(wpipe);
 1002                         pipeunlock(wpipe);
 1003                         error = EPIPE;
 1004                         goto error1;
 1005                 }
 1006                 if (wpipe->pipe_state & PIPE_WANTR) {
 1007                         wpipe->pipe_state &= ~PIPE_WANTR;
 1008                         wakeup(wpipe);
 1009                 }
 1010                 pipeselwakeup(wpipe);
 1011                 wpipe->pipe_state |= PIPE_WANTW;
 1012                 pipeunlock(wpipe);
 1013                 error = msleep(wpipe, PIPE_MTX(wpipe), PRIBIO | PCATCH,
 1014                     "pipdwt", 0);
 1015                 pipelock(wpipe, 0);
 1016         }
 1017 
 1018         if (wpipe->pipe_state & PIPE_EOF)
 1019                 error = EPIPE;
 1020         if (wpipe->pipe_state & PIPE_DIRECTW) {
 1021                 /*
 1022                  * this bit of trickery substitutes a kernel buffer for
 1023                  * the process that might be going away.
 1024                  */
 1025                 pipe_clone_write_buffer(wpipe);
 1026         } else {
 1027                 pipe_destroy_write_buffer(wpipe);
 1028         }
 1029         pipeunlock(wpipe);
 1030         return (error);
 1031 
 1032 error1:
 1033         wakeup(wpipe);
 1034         return (error);
 1035 }
 1036 #endif
 1037 
 1038 static int
 1039 pipe_write(fp, uio, active_cred, flags, td)
 1040         struct file *fp;
 1041         struct uio *uio;
 1042         struct ucred *active_cred;
 1043         struct thread *td;
 1044         int flags;
 1045 {
 1046         int error = 0;
 1047         int desiredsize;
 1048         ssize_t orig_resid;
 1049         struct pipe *wpipe, *rpipe;
 1050 
 1051         rpipe = fp->f_data;
 1052         wpipe = PIPE_PEER(rpipe);
 1053         PIPE_LOCK(rpipe);
 1054         error = pipelock(wpipe, 1);
 1055         if (error) {
 1056                 PIPE_UNLOCK(rpipe);
 1057                 return (error);
 1058         }
 1059         /*
 1060          * detect loss of pipe read side, issue SIGPIPE if lost.
 1061          */
 1062         if (wpipe->pipe_present != PIPE_ACTIVE ||
 1063             (wpipe->pipe_state & PIPE_EOF)) {
 1064                 pipeunlock(wpipe);
 1065                 PIPE_UNLOCK(rpipe);
 1066                 return (EPIPE);
 1067         }
 1068 #ifdef MAC
 1069         error = mac_pipe_check_write(active_cred, wpipe->pipe_pair);
 1070         if (error) {
 1071                 pipeunlock(wpipe);
 1072                 PIPE_UNLOCK(rpipe);
 1073                 return (error);
 1074         }
 1075 #endif
 1076         ++wpipe->pipe_busy;
 1077 
 1078         /* Choose a larger size if it's advantageous */
 1079         desiredsize = max(SMALL_PIPE_SIZE, wpipe->pipe_buffer.size);
 1080         while (desiredsize < wpipe->pipe_buffer.cnt + uio->uio_resid) {
 1081                 if (piperesizeallowed != 1)
 1082                         break;
 1083                 if (amountpipekva > maxpipekva / 2)
 1084                         break;
 1085                 if (desiredsize == BIG_PIPE_SIZE)
 1086                         break;
 1087                 desiredsize = desiredsize * 2;
 1088         }
 1089 
 1090         /* Choose a smaller size if we're in a OOM situation */
 1091         if ((amountpipekva > (3 * maxpipekva) / 4) &&
 1092                 (wpipe->pipe_buffer.size > SMALL_PIPE_SIZE) &&
 1093                 (wpipe->pipe_buffer.cnt <= SMALL_PIPE_SIZE) &&
 1094                 (piperesizeallowed == 1))
 1095                 desiredsize = SMALL_PIPE_SIZE;
 1096 
 1097         /* Resize if the above determined that a new size was necessary */
 1098         if ((desiredsize != wpipe->pipe_buffer.size) &&
 1099                 ((wpipe->pipe_state & PIPE_DIRECTW) == 0)) {
 1100                 PIPE_UNLOCK(wpipe);
 1101                 pipespace(wpipe, desiredsize);
 1102                 PIPE_LOCK(wpipe);
 1103         }
 1104         if (wpipe->pipe_buffer.size == 0) {
 1105                 /*
 1106                  * This can only happen for reverse direction use of pipes
 1107                  * in a complete OOM situation.
 1108                  */
 1109                 error = ENOMEM;
 1110                 --wpipe->pipe_busy;
 1111                 pipeunlock(wpipe);
 1112                 PIPE_UNLOCK(wpipe);
 1113                 return (error);
 1114         }
 1115 
 1116         pipeunlock(wpipe);
 1117 
 1118         orig_resid = uio->uio_resid;
 1119 
 1120         while (uio->uio_resid) {
 1121                 int space;
 1122 
 1123                 pipelock(wpipe, 0);
 1124                 if (wpipe->pipe_state & PIPE_EOF) {
 1125                         pipeunlock(wpipe);
 1126                         error = EPIPE;
 1127                         break;
 1128                 }
 1129 #ifndef PIPE_NODIRECT
 1130                 /*
 1131                  * If the transfer is large, we can gain performance if
 1132                  * we do process-to-process copies directly.
 1133                  * If the write is non-blocking, we don't use the
 1134                  * direct write mechanism.
 1135                  *
 1136                  * The direct write mechanism will detect the reader going
 1137                  * away on us.
 1138                  */
 1139                 if (uio->uio_segflg == UIO_USERSPACE &&
 1140                     uio->uio_iov->iov_len >= PIPE_MINDIRECT &&
 1141                     wpipe->pipe_buffer.size >= PIPE_MINDIRECT &&
 1142                     (fp->f_flag & FNONBLOCK) == 0) {
 1143                         pipeunlock(wpipe);
 1144                         error = pipe_direct_write(wpipe, uio);
 1145                         if (error)
 1146                                 break;
 1147                         continue;
 1148                 }
 1149 #endif
 1150 
 1151                 /*
 1152                  * Pipe buffered writes cannot be coincidental with
 1153                  * direct writes.  We wait until the currently executing
 1154                  * direct write is completed before we start filling the
 1155                  * pipe buffer.  We break out if a signal occurs or the
 1156                  * reader goes away.
 1157                  */
 1158                 if (wpipe->pipe_state & PIPE_DIRECTW) {
 1159                         if (wpipe->pipe_state & PIPE_WANTR) {
 1160                                 wpipe->pipe_state &= ~PIPE_WANTR;
 1161                                 wakeup(wpipe);
 1162                         }
 1163                         pipeselwakeup(wpipe);
 1164                         wpipe->pipe_state |= PIPE_WANTW;
 1165                         pipeunlock(wpipe);
 1166                         error = msleep(wpipe, PIPE_MTX(rpipe), PRIBIO | PCATCH,
 1167                             "pipbww", 0);
 1168                         if (error)
 1169                                 break;
 1170                         else
 1171                                 continue;
 1172                 }
 1173 
 1174                 space = wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt;
 1175 
 1176                 /* Writes of size <= PIPE_BUF must be atomic. */
 1177                 if ((space < uio->uio_resid) && (orig_resid <= PIPE_BUF))
 1178                         space = 0;
 1179 
 1180                 if (space > 0) {
 1181                         int size;       /* Transfer size */
 1182                         int segsize;    /* first segment to transfer */
 1183 
 1184                         /*
 1185                          * Transfer size is minimum of uio transfer
 1186                          * and free space in pipe buffer.
 1187                          */
 1188                         if (space > uio->uio_resid)
 1189                                 size = uio->uio_resid;
 1190                         else
 1191                                 size = space;
 1192                         /*
 1193                          * First segment to transfer is minimum of
 1194                          * transfer size and contiguous space in
 1195                          * pipe buffer.  If first segment to transfer
 1196                          * is less than the transfer size, we've got
 1197                          * a wraparound in the buffer.
 1198                          */
 1199                         segsize = wpipe->pipe_buffer.size -
 1200                                 wpipe->pipe_buffer.in;
 1201                         if (segsize > size)
 1202                                 segsize = size;
 1203 
 1204                         /* Transfer first segment */
 1205 
 1206                         PIPE_UNLOCK(rpipe);
 1207                         error = uiomove(&wpipe->pipe_buffer.buffer[wpipe->pipe_buffer.in],
 1208                                         segsize, uio);
 1209                         PIPE_LOCK(rpipe);
 1210 
 1211                         if (error == 0 && segsize < size) {
 1212                                 KASSERT(wpipe->pipe_buffer.in + segsize ==
 1213                                         wpipe->pipe_buffer.size,
 1214                                         ("Pipe buffer wraparound disappeared"));
 1215                                 /*
 1216                                  * Transfer remaining part now, to
 1217                                  * support atomic writes.  Wraparound
 1218                                  * happened.
 1219                                  */
 1220 
 1221                                 PIPE_UNLOCK(rpipe);
 1222                                 error = uiomove(
 1223                                     &wpipe->pipe_buffer.buffer[0],
 1224                                     size - segsize, uio);
 1225                                 PIPE_LOCK(rpipe);
 1226                         }
 1227                         if (error == 0) {
 1228                                 wpipe->pipe_buffer.in += size;
 1229                                 if (wpipe->pipe_buffer.in >=
 1230                                     wpipe->pipe_buffer.size) {
 1231                                         KASSERT(wpipe->pipe_buffer.in ==
 1232                                                 size - segsize +
 1233                                                 wpipe->pipe_buffer.size,
 1234                                                 ("Expected wraparound bad"));
 1235                                         wpipe->pipe_buffer.in = size - segsize;
 1236                                 }
 1237 
 1238                                 wpipe->pipe_buffer.cnt += size;
 1239                                 KASSERT(wpipe->pipe_buffer.cnt <=
 1240                                         wpipe->pipe_buffer.size,
 1241                                         ("Pipe buffer overflow"));
 1242                         }
 1243                         pipeunlock(wpipe);
 1244                         if (error != 0)
 1245                                 break;
 1246                 } else {
 1247                         /*
 1248                          * If the "read-side" has been blocked, wake it up now.
 1249                          */
 1250                         if (wpipe->pipe_state & PIPE_WANTR) {
 1251                                 wpipe->pipe_state &= ~PIPE_WANTR;
 1252                                 wakeup(wpipe);
 1253                         }
 1254 
 1255                         /*
 1256                          * don't block on non-blocking I/O
 1257                          */
 1258                         if (fp->f_flag & FNONBLOCK) {
 1259                                 error = EAGAIN;
 1260                                 pipeunlock(wpipe);
 1261                                 break;
 1262                         }
 1263 
 1264                         /*
 1265                          * We have no more space and have something to offer,
 1266                          * wake up select/poll.
 1267                          */
 1268                         pipeselwakeup(wpipe);
 1269 
 1270                         wpipe->pipe_state |= PIPE_WANTW;
 1271                         pipeunlock(wpipe);
 1272                         error = msleep(wpipe, PIPE_MTX(rpipe),
 1273                             PRIBIO | PCATCH, "pipewr", 0);
 1274                         if (error != 0)
 1275                                 break;
 1276                 }
 1277         }
 1278 
 1279         pipelock(wpipe, 0);
 1280         --wpipe->pipe_busy;
 1281 
 1282         if ((wpipe->pipe_busy == 0) && (wpipe->pipe_state & PIPE_WANT)) {
 1283                 wpipe->pipe_state &= ~(PIPE_WANT | PIPE_WANTR);
 1284                 wakeup(wpipe);
 1285         } else if (wpipe->pipe_buffer.cnt > 0) {
 1286                 /*
 1287                  * If we have put any characters in the buffer, we wake up
 1288                  * the reader.
 1289                  */
 1290                 if (wpipe->pipe_state & PIPE_WANTR) {
 1291                         wpipe->pipe_state &= ~PIPE_WANTR;
 1292                         wakeup(wpipe);
 1293                 }
 1294         }
 1295 
 1296         /*
 1297          * Don't return EPIPE if any byte was written.
 1298          * EINTR and other interrupts are handled by generic I/O layer.
 1299          * Do not pretend that I/O succeeded for obvious user error
 1300          * like EFAULT.
 1301          */
 1302         if (uio->uio_resid != orig_resid && error == EPIPE)
 1303                 error = 0;
 1304 
 1305         if (error == 0)
 1306                 vfs_timestamp(&wpipe->pipe_mtime);
 1307 
 1308         /*
 1309          * We have something to offer,
 1310          * wake up select/poll.
 1311          */
 1312         if (wpipe->pipe_buffer.cnt)
 1313                 pipeselwakeup(wpipe);
 1314 
 1315         pipeunlock(wpipe);
 1316         PIPE_UNLOCK(rpipe);
 1317         return (error);
 1318 }
 1319 
 1320 /* ARGSUSED */
 1321 static int
 1322 pipe_truncate(fp, length, active_cred, td)
 1323         struct file *fp;
 1324         off_t length;
 1325         struct ucred *active_cred;
 1326         struct thread *td;
 1327 {
 1328         struct pipe *cpipe;
 1329         int error;
 1330 
 1331         cpipe = fp->f_data;
 1332         if (cpipe->pipe_state & PIPE_NAMED)
 1333                 error = vnops.fo_truncate(fp, length, active_cred, td);
 1334         else
 1335                 error = invfo_truncate(fp, length, active_cred, td);
 1336         return (error);
 1337 }
 1338 
 1339 /*
 1340  * we implement a very minimal set of ioctls for compatibility with sockets.
 1341  */
 1342 static int
 1343 pipe_ioctl(fp, cmd, data, active_cred, td)
 1344         struct file *fp;
 1345         u_long cmd;
 1346         void *data;
 1347         struct ucred *active_cred;
 1348         struct thread *td;
 1349 {
 1350         struct pipe *mpipe = fp->f_data;
 1351         int error;
 1352 
 1353         PIPE_LOCK(mpipe);
 1354 
 1355 #ifdef MAC
 1356         error = mac_pipe_check_ioctl(active_cred, mpipe->pipe_pair, cmd, data);
 1357         if (error) {
 1358                 PIPE_UNLOCK(mpipe);
 1359                 return (error);
 1360         }
 1361 #endif
 1362 
 1363         error = 0;
 1364         switch (cmd) {
 1365 
 1366         case FIONBIO:
 1367                 break;
 1368 
 1369         case FIOASYNC:
 1370                 if (*(int *)data) {
 1371                         mpipe->pipe_state |= PIPE_ASYNC;
 1372                 } else {
 1373                         mpipe->pipe_state &= ~PIPE_ASYNC;
 1374                 }
 1375                 break;
 1376 
 1377         case FIONREAD:
 1378                 if (!(fp->f_flag & FREAD)) {
 1379                         *(int *)data = 0;
 1380                         PIPE_UNLOCK(mpipe);
 1381                         return (0);
 1382                 }
 1383                 if (mpipe->pipe_state & PIPE_DIRECTW)
 1384                         *(int *)data = mpipe->pipe_map.cnt;
 1385                 else
 1386                         *(int *)data = mpipe->pipe_buffer.cnt;
 1387                 break;
 1388 
 1389         case FIOSETOWN:
 1390                 PIPE_UNLOCK(mpipe);
 1391                 error = fsetown(*(int *)data, &mpipe->pipe_sigio);
 1392                 goto out_unlocked;
 1393 
 1394         case FIOGETOWN:
 1395                 *(int *)data = fgetown(&mpipe->pipe_sigio);
 1396                 break;
 1397 
 1398         /* This is deprecated, FIOSETOWN should be used instead. */
 1399         case TIOCSPGRP:
 1400                 PIPE_UNLOCK(mpipe);
 1401                 error = fsetown(-(*(int *)data), &mpipe->pipe_sigio);
 1402                 goto out_unlocked;
 1403 
 1404         /* This is deprecated, FIOGETOWN should be used instead. */
 1405         case TIOCGPGRP:
 1406                 *(int *)data = -fgetown(&mpipe->pipe_sigio);
 1407                 break;
 1408 
 1409         default:
 1410                 error = ENOTTY;
 1411                 break;
 1412         }
 1413         PIPE_UNLOCK(mpipe);
 1414 out_unlocked:
 1415         return (error);
 1416 }
 1417 
 1418 static int
 1419 pipe_poll(fp, events, active_cred, td)
 1420         struct file *fp;
 1421         int events;
 1422         struct ucred *active_cred;
 1423         struct thread *td;
 1424 {
 1425         struct pipe *rpipe;
 1426         struct pipe *wpipe;
 1427         int levents, revents;
 1428 #ifdef MAC
 1429         int error;
 1430 #endif
 1431 
 1432         revents = 0;
 1433         rpipe = fp->f_data;
 1434         wpipe = PIPE_PEER(rpipe);
 1435         PIPE_LOCK(rpipe);
 1436 #ifdef MAC
 1437         error = mac_pipe_check_poll(active_cred, rpipe->pipe_pair);
 1438         if (error)
 1439                 goto locked_error;
 1440 #endif
 1441         if (fp->f_flag & FREAD && events & (POLLIN | POLLRDNORM))
 1442                 if ((rpipe->pipe_state & PIPE_DIRECTW) ||
 1443                     (rpipe->pipe_buffer.cnt > 0))
 1444                         revents |= events & (POLLIN | POLLRDNORM);
 1445 
 1446         if (fp->f_flag & FWRITE && events & (POLLOUT | POLLWRNORM))
 1447                 if (wpipe->pipe_present != PIPE_ACTIVE ||
 1448                     (wpipe->pipe_state & PIPE_EOF) ||
 1449                     (((wpipe->pipe_state & PIPE_DIRECTW) == 0) &&
 1450                      ((wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt) >= PIPE_BUF ||
 1451                          wpipe->pipe_buffer.size == 0)))
 1452                         revents |= events & (POLLOUT | POLLWRNORM);
 1453 
 1454         levents = events &
 1455             (POLLIN | POLLINIGNEOF | POLLPRI | POLLRDNORM | POLLRDBAND);
 1456         if (rpipe->pipe_state & PIPE_NAMED && fp->f_flag & FREAD && levents &&
 1457             fp->f_seqcount == rpipe->pipe_wgen)
 1458                 events |= POLLINIGNEOF;
 1459 
 1460         if ((events & POLLINIGNEOF) == 0) {
 1461                 if (rpipe->pipe_state & PIPE_EOF) {
 1462                         revents |= (events & (POLLIN | POLLRDNORM));
 1463                         if (wpipe->pipe_present != PIPE_ACTIVE ||
 1464                             (wpipe->pipe_state & PIPE_EOF))
 1465                                 revents |= POLLHUP;
 1466                 }
 1467         }
 1468 
 1469         if (revents == 0) {
 1470                 if (fp->f_flag & FREAD && events & (POLLIN | POLLRDNORM)) {
 1471                         selrecord(td, &rpipe->pipe_sel);
 1472                         if (SEL_WAITING(&rpipe->pipe_sel))
 1473                                 rpipe->pipe_state |= PIPE_SEL;
 1474                 }
 1475 
 1476                 if (fp->f_flag & FWRITE && events & (POLLOUT | POLLWRNORM)) {
 1477                         selrecord(td, &wpipe->pipe_sel);
 1478                         if (SEL_WAITING(&wpipe->pipe_sel))
 1479                                 wpipe->pipe_state |= PIPE_SEL;
 1480                 }
 1481         }
 1482 #ifdef MAC
 1483 locked_error:
 1484 #endif
 1485         PIPE_UNLOCK(rpipe);
 1486 
 1487         return (revents);
 1488 }
 1489 
 1490 /*
 1491  * We shouldn't need locks here as we're doing a read and this should
 1492  * be a natural race.
 1493  */
 1494 static int
 1495 pipe_stat(fp, ub, active_cred, td)
 1496         struct file *fp;
 1497         struct stat *ub;
 1498         struct ucred *active_cred;
 1499         struct thread *td;
 1500 {
 1501         struct pipe *pipe;
 1502         int new_unr;
 1503 #ifdef MAC
 1504         int error;
 1505 #endif
 1506 
 1507         pipe = fp->f_data;
 1508         PIPE_LOCK(pipe);
 1509 #ifdef MAC
 1510         error = mac_pipe_check_stat(active_cred, pipe->pipe_pair);
 1511         if (error) {
 1512                 PIPE_UNLOCK(pipe);
 1513                 return (error);
 1514         }
 1515 #endif
 1516 
 1517         /* For named pipes ask the underlying filesystem. */
 1518         if (pipe->pipe_state & PIPE_NAMED) {
 1519                 PIPE_UNLOCK(pipe);
 1520                 return (vnops.fo_stat(fp, ub, active_cred, td));
 1521         }
 1522 
 1523         /*
 1524          * Lazily allocate an inode number for the pipe.  Most pipe
 1525          * users do not call fstat(2) on the pipe, which means that
 1526          * postponing the inode allocation until it is must be
 1527          * returned to userland is useful.  If alloc_unr failed,
 1528          * assign st_ino zero instead of returning an error.
 1529          * Special pipe_ino values:
 1530          *  -1 - not yet initialized;
 1531          *  0  - alloc_unr failed, return 0 as st_ino forever.
 1532          */
 1533         if (pipe->pipe_ino == (ino_t)-1) {
 1534                 new_unr = alloc_unr(pipeino_unr);
 1535                 if (new_unr != -1)
 1536                         pipe->pipe_ino = new_unr;
 1537                 else
 1538                         pipe->pipe_ino = 0;
 1539         }
 1540         PIPE_UNLOCK(pipe);
 1541 
 1542         bzero(ub, sizeof(*ub));
 1543         ub->st_mode = S_IFIFO;
 1544         ub->st_blksize = PAGE_SIZE;
 1545         if (pipe->pipe_state & PIPE_DIRECTW)
 1546                 ub->st_size = pipe->pipe_map.cnt;
 1547         else
 1548                 ub->st_size = pipe->pipe_buffer.cnt;
 1549         ub->st_blocks = howmany(ub->st_size, ub->st_blksize);
 1550         ub->st_atim = pipe->pipe_atime;
 1551         ub->st_mtim = pipe->pipe_mtime;
 1552         ub->st_ctim = pipe->pipe_ctime;
 1553         ub->st_uid = fp->f_cred->cr_uid;
 1554         ub->st_gid = fp->f_cred->cr_gid;
 1555         ub->st_dev = pipedev_ino;
 1556         ub->st_ino = pipe->pipe_ino;
 1557         /*
 1558          * Left as 0: st_nlink, st_rdev, st_flags, st_gen.
 1559          */
 1560         return (0);
 1561 }
 1562 
 1563 /* ARGSUSED */
 1564 static int
 1565 pipe_close(fp, td)
 1566         struct file *fp;
 1567         struct thread *td;
 1568 {
 1569 
 1570         if (fp->f_vnode != NULL) 
 1571                 return vnops.fo_close(fp, td);
 1572         fp->f_ops = &badfileops;
 1573         pipe_dtor(fp->f_data);
 1574         fp->f_data = NULL;
 1575         return (0);
 1576 }
 1577 
 1578 static int
 1579 pipe_chmod(struct file *fp, mode_t mode, struct ucred *active_cred, struct thread *td)
 1580 {
 1581         struct pipe *cpipe;
 1582         int error;
 1583 
 1584         cpipe = fp->f_data;
 1585         if (cpipe->pipe_state & PIPE_NAMED)
 1586                 error = vn_chmod(fp, mode, active_cred, td);
 1587         else
 1588                 error = invfo_chmod(fp, mode, active_cred, td);
 1589         return (error);
 1590 }
 1591 
 1592 static int
 1593 pipe_chown(fp, uid, gid, active_cred, td)
 1594         struct file *fp;
 1595         uid_t uid;
 1596         gid_t gid;
 1597         struct ucred *active_cred;
 1598         struct thread *td;
 1599 {
 1600         struct pipe *cpipe;
 1601         int error;
 1602 
 1603         cpipe = fp->f_data;
 1604         if (cpipe->pipe_state & PIPE_NAMED)
 1605                 error = vn_chown(fp, uid, gid, active_cred, td);
 1606         else
 1607                 error = invfo_chown(fp, uid, gid, active_cred, td);
 1608         return (error);
 1609 }
 1610 
 1611 static int
 1612 pipe_fill_kinfo(struct file *fp, struct kinfo_file *kif, struct filedesc *fdp)
 1613 {
 1614         struct pipe *pi;
 1615 
 1616         if (fp->f_type == DTYPE_FIFO)
 1617                 return (vn_fill_kinfo(fp, kif, fdp));
 1618         kif->kf_type = KF_TYPE_PIPE;
 1619         pi = fp->f_data;
 1620         kif->kf_un.kf_pipe.kf_pipe_addr = (uintptr_t)pi;
 1621         kif->kf_un.kf_pipe.kf_pipe_peer = (uintptr_t)pi->pipe_peer;
 1622         kif->kf_un.kf_pipe.kf_pipe_buffer_cnt = pi->pipe_buffer.cnt;
 1623         return (0);
 1624 }
 1625 
 1626 static void
 1627 pipe_free_kmem(cpipe)
 1628         struct pipe *cpipe;
 1629 {
 1630 
 1631         KASSERT(!mtx_owned(PIPE_MTX(cpipe)),
 1632             ("pipe_free_kmem: pipe mutex locked"));
 1633 
 1634         if (cpipe->pipe_buffer.buffer != NULL) {
 1635                 atomic_subtract_long(&amountpipekva, cpipe->pipe_buffer.size);
 1636                 vm_map_remove(pipe_map,
 1637                     (vm_offset_t)cpipe->pipe_buffer.buffer,
 1638                     (vm_offset_t)cpipe->pipe_buffer.buffer + cpipe->pipe_buffer.size);
 1639                 cpipe->pipe_buffer.buffer = NULL;
 1640         }
 1641 #ifndef PIPE_NODIRECT
 1642         {
 1643                 cpipe->pipe_map.cnt = 0;
 1644                 cpipe->pipe_map.pos = 0;
 1645                 cpipe->pipe_map.npages = 0;
 1646         }
 1647 #endif
 1648 }
 1649 
 1650 /*
 1651  * shutdown the pipe
 1652  */
 1653 static void
 1654 pipeclose(cpipe)
 1655         struct pipe *cpipe;
 1656 {
 1657         struct pipepair *pp;
 1658         struct pipe *ppipe;
 1659 
 1660         KASSERT(cpipe != NULL, ("pipeclose: cpipe == NULL"));
 1661 
 1662         PIPE_LOCK(cpipe);
 1663         pipelock(cpipe, 0);
 1664         pp = cpipe->pipe_pair;
 1665 
 1666         pipeselwakeup(cpipe);
 1667 
 1668         /*
 1669          * If the other side is blocked, wake it up saying that
 1670          * we want to close it down.
 1671          */
 1672         cpipe->pipe_state |= PIPE_EOF;
 1673         while (cpipe->pipe_busy) {
 1674                 wakeup(cpipe);
 1675                 cpipe->pipe_state |= PIPE_WANT;
 1676                 pipeunlock(cpipe);
 1677                 msleep(cpipe, PIPE_MTX(cpipe), PRIBIO, "pipecl", 0);
 1678                 pipelock(cpipe, 0);
 1679         }
 1680 
 1681 
 1682         /*
 1683          * Disconnect from peer, if any.
 1684          */
 1685         ppipe = cpipe->pipe_peer;
 1686         if (ppipe->pipe_present == PIPE_ACTIVE) {
 1687                 pipeselwakeup(ppipe);
 1688 
 1689                 ppipe->pipe_state |= PIPE_EOF;
 1690                 wakeup(ppipe);
 1691                 KNOTE_LOCKED(&ppipe->pipe_sel.si_note, 0);
 1692         }
 1693 
 1694         /*
 1695          * Mark this endpoint as free.  Release kmem resources.  We
 1696          * don't mark this endpoint as unused until we've finished
 1697          * doing that, or the pipe might disappear out from under
 1698          * us.
 1699          */
 1700         PIPE_UNLOCK(cpipe);
 1701         pipe_free_kmem(cpipe);
 1702         PIPE_LOCK(cpipe);
 1703         cpipe->pipe_present = PIPE_CLOSING;
 1704         pipeunlock(cpipe);
 1705 
 1706         /*
 1707          * knlist_clear() may sleep dropping the PIPE_MTX. Set the
 1708          * PIPE_FINALIZED, that allows other end to free the
 1709          * pipe_pair, only after the knotes are completely dismantled.
 1710          */
 1711         knlist_clear(&cpipe->pipe_sel.si_note, 1);
 1712         cpipe->pipe_present = PIPE_FINALIZED;
 1713         seldrain(&cpipe->pipe_sel);
 1714         knlist_destroy(&cpipe->pipe_sel.si_note);
 1715 
 1716         /*
 1717          * If both endpoints are now closed, release the memory for the
 1718          * pipe pair.  If not, unlock.
 1719          */
 1720         if (ppipe->pipe_present == PIPE_FINALIZED) {
 1721                 PIPE_UNLOCK(cpipe);
 1722 #ifdef MAC
 1723                 mac_pipe_destroy(pp);
 1724 #endif
 1725                 uma_zfree(pipe_zone, cpipe->pipe_pair);
 1726         } else
 1727                 PIPE_UNLOCK(cpipe);
 1728 }
 1729 
 1730 /*ARGSUSED*/
 1731 static int
 1732 pipe_kqfilter(struct file *fp, struct knote *kn)
 1733 {
 1734         struct pipe *cpipe;
 1735 
 1736         /*
 1737          * If a filter is requested that is not supported by this file
 1738          * descriptor, don't return an error, but also don't ever generate an
 1739          * event.
 1740          */
 1741         if ((kn->kn_filter == EVFILT_READ) && !(fp->f_flag & FREAD)) {
 1742                 kn->kn_fop = &pipe_nfiltops;
 1743                 return (0);
 1744         }
 1745         if ((kn->kn_filter == EVFILT_WRITE) && !(fp->f_flag & FWRITE)) {
 1746                 kn->kn_fop = &pipe_nfiltops;
 1747                 return (0);
 1748         }
 1749         cpipe = fp->f_data;
 1750         PIPE_LOCK(cpipe);
 1751         switch (kn->kn_filter) {
 1752         case EVFILT_READ:
 1753                 kn->kn_fop = &pipe_rfiltops;
 1754                 break;
 1755         case EVFILT_WRITE:
 1756                 kn->kn_fop = &pipe_wfiltops;
 1757                 if (cpipe->pipe_peer->pipe_present != PIPE_ACTIVE) {
 1758                         /* other end of pipe has been closed */
 1759                         PIPE_UNLOCK(cpipe);
 1760                         return (EPIPE);
 1761                 }
 1762                 cpipe = PIPE_PEER(cpipe);
 1763                 break;
 1764         default:
 1765                 PIPE_UNLOCK(cpipe);
 1766                 return (EINVAL);
 1767         }
 1768 
 1769         kn->kn_hook = cpipe; 
 1770         knlist_add(&cpipe->pipe_sel.si_note, kn, 1);
 1771         PIPE_UNLOCK(cpipe);
 1772         return (0);
 1773 }
 1774 
 1775 static void
 1776 filt_pipedetach(struct knote *kn)
 1777 {
 1778         struct pipe *cpipe = kn->kn_hook;
 1779 
 1780         PIPE_LOCK(cpipe);
 1781         knlist_remove(&cpipe->pipe_sel.si_note, kn, 1);
 1782         PIPE_UNLOCK(cpipe);
 1783 }
 1784 
 1785 /*ARGSUSED*/
 1786 static int
 1787 filt_piperead(struct knote *kn, long hint)
 1788 {
 1789         struct pipe *rpipe = kn->kn_hook;
 1790         struct pipe *wpipe = rpipe->pipe_peer;
 1791         int ret;
 1792 
 1793         PIPE_LOCK_ASSERT(rpipe, MA_OWNED);
 1794         kn->kn_data = rpipe->pipe_buffer.cnt;
 1795         if ((kn->kn_data == 0) && (rpipe->pipe_state & PIPE_DIRECTW))
 1796                 kn->kn_data = rpipe->pipe_map.cnt;
 1797 
 1798         if ((rpipe->pipe_state & PIPE_EOF) ||
 1799             wpipe->pipe_present != PIPE_ACTIVE ||
 1800             (wpipe->pipe_state & PIPE_EOF)) {
 1801                 kn->kn_flags |= EV_EOF;
 1802                 return (1);
 1803         }
 1804         ret = kn->kn_data > 0;
 1805         return ret;
 1806 }
 1807 
 1808 /*ARGSUSED*/
 1809 static int
 1810 filt_pipewrite(struct knote *kn, long hint)
 1811 {
 1812         struct pipe *wpipe;
 1813    
 1814         wpipe = kn->kn_hook;
 1815         PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
 1816         if (wpipe->pipe_present != PIPE_ACTIVE ||
 1817             (wpipe->pipe_state & PIPE_EOF)) {
 1818                 kn->kn_data = 0;
 1819                 kn->kn_flags |= EV_EOF;
 1820                 return (1);
 1821         }
 1822         kn->kn_data = (wpipe->pipe_buffer.size > 0) ?
 1823             (wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt) : PIPE_BUF;
 1824         if (wpipe->pipe_state & PIPE_DIRECTW)
 1825                 kn->kn_data = 0;
 1826 
 1827         return (kn->kn_data >= PIPE_BUF);
 1828 }
 1829 
 1830 static void
 1831 filt_pipedetach_notsup(struct knote *kn)
 1832 {
 1833 
 1834 }
 1835 
 1836 static int
 1837 filt_pipenotsup(struct knote *kn, long hint)
 1838 {
 1839 
 1840         return (0);
 1841 }

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