sys/kern/sys_pipe.c

   1 /*
   2  * Copyright (c) 1996 John S. Dyson
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice immediately at the beginning of the file, without modification,
  10  *    this list of conditions, and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  * 3. Absolutely no warranty of function or purpose is made by the author
  15  *    John S. Dyson.
  16  * 4. Modifications may be freely made to this file if the above conditions
  17  *    are met.
  18  *
  19  * $FreeBSD: src/sys/kern/sys_pipe.c,v 1.60.2.13 2002/08/05 15:05:15 des Exp $
  20  * $DragonFly: src/sys/kern/sys_pipe.c,v 1.50 2008/09/09 04:06:13 dillon Exp $
  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 #include <sys/param.h>
  30 #include <sys/systm.h>
  31 #include <sys/kernel.h>
  32 #include <sys/proc.h>
  33 #include <sys/fcntl.h>
  34 #include <sys/file.h>
  35 #include <sys/filedesc.h>
  36 #include <sys/filio.h>
  37 #include <sys/ttycom.h>
  38 #include <sys/stat.h>
  39 #include <sys/poll.h>
  40 #include <sys/select.h>
  41 #include <sys/signalvar.h>
  42 #include <sys/sysproto.h>
  43 #include <sys/pipe.h>
  44 #include <sys/vnode.h>
  45 #include <sys/uio.h>
  46 #include <sys/event.h>
  47 #include <sys/globaldata.h>
  48 #include <sys/module.h>
  49 #include <sys/malloc.h>
  50 #include <sys/sysctl.h>
  51 #include <sys/socket.h>
  52
  53 #include <vm/vm.h>
  54 #include <vm/vm_param.h>
  55 #include <sys/lock.h>
  56 #include <vm/vm_object.h>
  57 #include <vm/vm_kern.h>
  58 #include <vm/vm_extern.h>
  59 #include <vm/pmap.h>
  60 #include <vm/vm_map.h>
  61 #include <vm/vm_page.h>
  62 #include <vm/vm_zone.h>
  63
  64 #include <sys/file2.h>
  65
  66 #include <machine/cpufunc.h>
  67
  68 /*
  69  * interfaces to the outside world
  70  */
  71 static int pipe_read (struct file *fp, struct uio *uio,
  72                 struct ucred *cred, int flags);
  73 static int pipe_write (struct file *fp, struct uio *uio,
  74                 struct ucred *cred, int flags);
  75 static int pipe_close (struct file *fp);
  76 static int pipe_shutdown (struct file *fp, int how);
  77 static int pipe_poll (struct file *fp, int events, struct ucred *cred);
  78 static int pipe_kqfilter (struct file *fp, struct knote *kn);
  79 static int pipe_stat (struct file *fp, struct stat *sb, struct ucred *cred);
  80 static int pipe_ioctl (struct file *fp, u_long cmd, caddr_t data, struct ucred *cred);
  81
  82 static struct fileops pipeops = {
  83         .fo_read = pipe_read,
  84         .fo_write = pipe_write,
  85         .fo_ioctl = pipe_ioctl,
  86         .fo_poll = pipe_poll,
  87         .fo_kqfilter = pipe_kqfilter,
  88         .fo_stat = pipe_stat,
  89         .fo_close = pipe_close,
  90         .fo_shutdown = pipe_shutdown
  91 };
  92
  93 static void     filt_pipedetach(struct knote *kn);
  94 static int      filt_piperead(struct knote *kn, long hint);
  95 static int      filt_pipewrite(struct knote *kn, long hint);
  96
  97 static struct filterops pipe_rfiltops =
  98         { 1, NULL, filt_pipedetach, filt_piperead };
  99 static struct filterops pipe_wfiltops =
 100         { 1, NULL, filt_pipedetach, filt_pipewrite };
 101
 102 MALLOC_DEFINE(M_PIPE, "pipe", "pipe structures");
 103
 104 /*
 105  * Default pipe buffer size(s), this can be kind-of large now because pipe
 106  * space is pageable.  The pipe code will try to maintain locality of
 107  * reference for performance reasons, so small amounts of outstanding I/O
 108  * will not wipe the cache.
 109  */
 110 #define MINPIPESIZE (PIPE_SIZE/3)
 111 #define MAXPIPESIZE (2*PIPE_SIZE/3)
 112
 113 /*
 114  * Limit the number of "big" pipes
 115  */
 116 #define LIMITBIGPIPES   64
 117 #define PIPEQ_MAX_CACHE 16      /* per-cpu pipe structure cache */
 118
 119 static int pipe_maxbig = LIMITBIGPIPES;
 120 static int pipe_maxcache = PIPEQ_MAX_CACHE;
 121 static int pipe_bigcount;
 122 static int pipe_nbig;
 123 static int pipe_bcache_alloc;
 124 static int pipe_bkmem_alloc;
 125
 126 SYSCTL_NODE(_kern, OID_AUTO, pipe, CTLFLAG_RW, 0, "Pipe operation");
 127 SYSCTL_INT(_kern_pipe, OID_AUTO, nbig,
 128         CTLFLAG_RD, &pipe_nbig, 0, "numer of big pipes allocated");
 129 SYSCTL_INT(_kern_pipe, OID_AUTO, bigcount,
 130         CTLFLAG_RW, &pipe_bigcount, 0, "number of times pipe expanded");
 131 SYSCTL_INT(_kern_pipe, OID_AUTO, maxcache,
 132         CTLFLAG_RW, &pipe_maxcache, 0, "max pipes cached per-cpu");
 133 SYSCTL_INT(_kern_pipe, OID_AUTO, maxbig,
 134         CTLFLAG_RW, &pipe_maxbig, 0, "max number of big pipes");
 135 #ifdef SMP
 136 static int pipe_mpsafe = 0;
 137 SYSCTL_INT(_kern_pipe, OID_AUTO, mpsafe,
 138         CTLFLAG_RW, &pipe_mpsafe, 0, "");
 139 #endif
 140 #if !defined(NO_PIPE_SYSCTL_STATS)
 141 SYSCTL_INT(_kern_pipe, OID_AUTO, bcache_alloc,
 142         CTLFLAG_RW, &pipe_bcache_alloc, 0, "pipe buffer from pcpu cache");
 143 SYSCTL_INT(_kern_pipe, OID_AUTO, bkmem_alloc,
 144         CTLFLAG_RW, &pipe_bkmem_alloc, 0, "pipe buffer from kmem");
 145 #endif
 146
 147 static void pipeclose (struct pipe *cpipe);
 148 static void pipe_free_kmem (struct pipe *cpipe);
 149 static int pipe_create (struct pipe **cpipep);
 150 static __inline void pipeselwakeup (struct pipe *cpipe);
 151 static int pipespace (struct pipe *cpipe, int size);
 152
 153 static __inline void
 154 pipeselwakeup(struct pipe *cpipe)
 155 {
 156         if (cpipe->pipe_state & PIPE_SEL) {
 157                 get_mplock();
 158                 cpipe->pipe_state &= ~PIPE_SEL;
 159                 selwakeup(&cpipe->pipe_sel);
 160                 rel_mplock();
 161         }
 162         if ((cpipe->pipe_state & PIPE_ASYNC) && cpipe->pipe_sigio) {
 163                 get_mplock();
 164                 pgsigio(cpipe->pipe_sigio, SIGIO, 0);
 165                 rel_mplock();
 166         }
 167         if (SLIST_FIRST(&cpipe->pipe_sel.si_note)) {
 168                 get_mplock();
 169                 KNOTE(&cpipe->pipe_sel.si_note, 0);
 170                 rel_mplock();
 171         }
 172 }
 173
 174 /*
 175  * These routines are called before and after a UIO.  The UIO
 176  * may block, causing our held tokens to be lost temporarily.
 177  *
 178  * We use these routines to serialize reads against other reads
 179  * and writes against other writes.
 180  *
 181  * The read token is held on entry so *ipp does not race.
 182  */
 183 static __inline int
 184 pipe_start_uio(struct pipe *cpipe, u_int *ipp)
 185 {
 186         int error;
 187
 188         while (*ipp) {
 189                 *ipp = -1;
 190                 error = tsleep(ipp, PCATCH, "pipexx", 0);
 191                 if (error)
 192                         return (error);
 193         }
 194         *ipp = 1;
 195         return (0);
 196 }
 197
 198 static __inline void
 199 pipe_end_uio(struct pipe *cpipe, u_int *ipp)
 200 {
 201         if (*ipp < 0) {
 202                 *ipp = 0;
 203                 wakeup(ipp);
 204         } else {
 205                 *ipp = 0;
 206         }
 207 }
 208
 209 static __inline void
 210 pipe_get_mplock(int *save)
 211 {
 212 #ifdef SMP
 213         if (pipe_mpsafe == 0) {
 214                 get_mplock();
 215                 *save = 1;
 216         } else
 217 #endif
 218         {
 219                 *save = 0;
 220         }
 221 }
 222
 223 static __inline void
 224 pipe_rel_mplock(int *save)
 225 {
 226 #ifdef SMP
 227         if (*save)
 228                 rel_mplock();
 229 #endif
 230 }
 231
 232
 233 /*
 234  * The pipe system call for the DTYPE_PIPE type of pipes
 235  *
 236  * pipe_ARgs(int dummy)
 237  */
 238
 239 /* ARGSUSED */
 240 int
 241 sys_pipe(struct pipe_args *uap)
 242 {
 243         struct thread *td = curthread;
 244         struct proc *p = td->td_proc;
 245         struct file *rf, *wf;
 246         struct pipe *rpipe, *wpipe;
 247         int fd1, fd2, error;
 248
 249         KKASSERT(p);
 250
 251         rpipe = wpipe = NULL;
 252         if (pipe_create(&rpipe) || pipe_create(&wpipe)) {
 253                 pipeclose(rpipe);
 254                 pipeclose(wpipe);
 255                 return (ENFILE);
 256         }
 257
 258         error = falloc(p, &rf, &fd1);
 259         if (error) {
 260                 pipeclose(rpipe);
 261                 pipeclose(wpipe);
 262                 return (error);
 263         }
 264         uap->sysmsg_fds[0] = fd1;
 265
 266         /*
 267          * Warning: once we've gotten past allocation of the fd for the
 268          * read-side, we can only drop the read side via fdrop() in order
 269          * to avoid races against processes which manage to dup() the read
 270          * side while we are blocked trying to allocate the write side.
 271          */
 272         rf->f_type = DTYPE_PIPE;
 273         rf->f_flag = FREAD | FWRITE;
 274         rf->f_ops = &pipeops;
 275         rf->f_data = rpipe;
 276         error = falloc(p, &wf, &fd2);
 277         if (error) {
 278                 fsetfd(p, NULL, fd1);
 279                 fdrop(rf);
 280                 /* rpipe has been closed by fdrop(). */
 281                 pipeclose(wpipe);
 282                 return (error);
 283         }
 284         wf->f_type = DTYPE_PIPE;
 285         wf->f_flag = FREAD | FWRITE;
 286         wf->f_ops = &pipeops;
 287         wf->f_data = wpipe;
 288         uap->sysmsg_fds[1] = fd2;
 289
 290         rpipe->pipe_slock = kmalloc(sizeof(struct lock),
 291                                     M_PIPE, M_WAITOK|M_ZERO);
 292         wpipe->pipe_slock = rpipe->pipe_slock;
 293         rpipe->pipe_peer = wpipe;
 294         wpipe->pipe_peer = rpipe;
 295         lockinit(rpipe->pipe_slock, "pipecl", 0, 0);
 296
 297         /*
 298          * Once activated the peer relationship remains valid until
 299          * both sides are closed.
 300          */
 301         fsetfd(p, rf, fd1);
 302         fsetfd(p, wf, fd2);
 303         fdrop(rf);
 304         fdrop(wf);
 305
 306         return (0);
 307 }
 308
 309 /*
 310  * Allocate kva for pipe circular buffer, the space is pageable
 311  * This routine will 'realloc' the size of a pipe safely, if it fails
 312  * it will retain the old buffer.
 313  * If it fails it will return ENOMEM.
 314  */
 315 static int
 316 pipespace(struct pipe *cpipe, int size)
 317 {
 318         struct vm_object *object;
 319         caddr_t buffer;
 320         int npages, error;
 321
 322         npages = round_page(size) / PAGE_SIZE;
 323         object = cpipe->pipe_buffer.object;
 324
 325         /*
 326          * [re]create the object if necessary and reserve space for it
 327          * in the kernel_map.  The object and memory are pageable.  On
 328          * success, free the old resources before assigning the new
 329          * ones.
 330          */
 331         if (object == NULL || object->size != npages) {
 332                 get_mplock();
 333                 object = vm_object_allocate(OBJT_DEFAULT, npages);
 334                 buffer = (caddr_t)vm_map_min(&kernel_map);
 335
 336                 error = vm_map_find(&kernel_map, object, 0,
 337                                     (vm_offset_t *)&buffer, size,
 338                                     1,
 339                                     VM_MAPTYPE_NORMAL,
 340                                     VM_PROT_ALL, VM_PROT_ALL,
 341                                     0);
 342
 343                 if (error != KERN_SUCCESS) {
 344                         vm_object_deallocate(object);
 345                         rel_mplock();
 346                         return (ENOMEM);
 347                 }
 348                 pipe_free_kmem(cpipe);
 349                 rel_mplock();
 350                 cpipe->pipe_buffer.object = object;
 351                 cpipe->pipe_buffer.buffer = buffer;
 352                 cpipe->pipe_buffer.size = size;
 353                 ++pipe_bkmem_alloc;
 354         } else {
 355                 ++pipe_bcache_alloc;
 356         }
 357         cpipe->pipe_buffer.rindex = 0;
 358         cpipe->pipe_buffer.windex = 0;
 359         return (0);
 360 }
 361
 362 /*
 363  * Initialize and allocate VM and memory for pipe, pulling the pipe from
 364  * our per-cpu cache if possible.  For now make sure it is sized for the
 365  * smaller PIPE_SIZE default.
 366  */
 367 static int
 368 pipe_create(struct pipe **cpipep)
 369 {
 370         globaldata_t gd = mycpu;
 371         struct pipe *cpipe;
 372         int error;
 373
 374         if ((cpipe = gd->gd_pipeq) != NULL) {
 375                 gd->gd_pipeq = cpipe->pipe_peer;
 376                 --gd->gd_pipeqcount;
 377                 cpipe->pipe_peer = NULL;
 378                 cpipe->pipe_wantwcnt = 0;
 379         } else {
 380                 cpipe = kmalloc(sizeof(struct pipe), M_PIPE, M_WAITOK|M_ZERO);
 381         }
 382         *cpipep = cpipe;
 383         if ((error = pipespace(cpipe, PIPE_SIZE)) != 0)
 384                 return (error);
 385         vfs_timestamp(&cpipe->pipe_ctime);
 386         cpipe->pipe_atime = cpipe->pipe_ctime;
 387         cpipe->pipe_mtime = cpipe->pipe_ctime;
 388         lwkt_token_init(&cpipe->pipe_rlock);
 389         lwkt_token_init(&cpipe->pipe_wlock);
 390         return (0);
 391 }
 392
 393 /*
 394  * MPALMOSTSAFE (acquires mplock)
 395  */
 396 static int
 397 pipe_read(struct file *fp, struct uio *uio, struct ucred *cred, int fflags)
 398 {
 399         struct pipe *rpipe;
 400         int error;
 401         int nread = 0;
 402         int nbio;
 403         u_int size;     /* total bytes available */
 404         u_int nsize;    /* total bytes to read */
 405         u_int rindex;   /* contiguous bytes available */
 406         u_int half_way;
 407         lwkt_tokref rlock;
 408         lwkt_tokref wlock;
 409         int mpsave;
 410
 411         /*
 412          * Degenerate case
 413          */
 414         if (uio->uio_resid == 0)
 415                 return(0);
 416
 417         /*
 418          * Setup locks, calculate nbio
 419          */
 420         pipe_get_mplock(&mpsave);
 421         rpipe = (struct pipe *)fp->f_data;
 422         lwkt_gettoken(&rlock, &rpipe->pipe_rlock);
 423
 424         if (fflags & O_FBLOCKING)
 425                 nbio = 0;
 426         else if (fflags & O_FNONBLOCKING)
 427                 nbio = 1;
 428         else if (fp->f_flag & O_NONBLOCK)
 429                 nbio = 1;
 430         else
 431                 nbio = 0;
 432
 433         /*
 434          * Reads are serialized.  Note howeverthat pipe_buffer.buffer and
 435          * pipe_buffer.size can change out from under us when the number
 436          * of bytes in the buffer are zero due to the write-side doing a
 437          * pipespace().
 438          */
 439         error = pipe_start_uio(rpipe, &rpipe->pipe_rip);
 440         if (error) {
 441                 pipe_rel_mplock(&mpsave);
 442                 lwkt_reltoken(&rlock);
 443                 return (error);
 444         }
 445         while (uio->uio_resid) {
 446                 size = rpipe->pipe_buffer.windex - rpipe->pipe_buffer.rindex;
 447                 cpu_lfence();
 448                 if (size) {
 449                         rindex = rpipe->pipe_buffer.rindex &
 450                                  (rpipe->pipe_buffer.size - 1);
 451                         nsize = size;
 452                         if (nsize > rpipe->pipe_buffer.size - rindex)
 453                                 nsize = rpipe->pipe_buffer.size - rindex;
 454                         if (nsize > (u_int)uio->uio_resid)
 455                                 nsize = (u_int)uio->uio_resid;
 456
 457                         error = uiomove(&rpipe->pipe_buffer.buffer[rindex],
 458                                         nsize, uio);
 459                         if (error)
 460                                 break;
 461                         cpu_mfence();
 462                         rpipe->pipe_buffer.rindex += nsize;
 463                         nread += nsize;
 464
 465                         /*
 466                          * Shortcut to the loop-up if there is no writer
 467                          * waiting or if we have not transitioned across
 468                          * the half-way point.
 469                          */
 470                         half_way = rpipe->pipe_buffer.size >> 1;
 471                         if ((rpipe->pipe_state & PIPE_WANTW) == 0 ||
 472                             size <= half_way || size - nsize > half_way) {
 473                         } {
 474                                 continue;
 475                         }
 476                 }
 477
 478                 /*
 479                  * If the "write-side" was blocked we wake it up.  This code
 480                  * is reached either when the buffer is completely emptied
 481                  * or if it becomes more then half-empty.
 482                  *
 483                  * Pipe_state can only be modified if both the rlock and
 484                  * wlock are held.
 485                  */
 486                 if (rpipe->pipe_state & PIPE_WANTW) {
 487                         lwkt_gettoken(&wlock, &rpipe->pipe_wlock);
 488                         if (rpipe->pipe_state & PIPE_WANTW) {
 489                                 rpipe->pipe_state &= ~PIPE_WANTW;
 490                                 lwkt_reltoken(&wlock);
 491                                 wakeup(rpipe);
 492                         } else {
 493                                 lwkt_reltoken(&wlock);
 494                         }
 495                 }
 496
 497                 /*
 498                  * Pick up our copy loop again if the writer sent data to
 499                  * us.
 500                  */
 501                 size = rpipe->pipe_buffer.windex - rpipe->pipe_buffer.rindex;
 502                 if (size)
 503                         continue;
 504
 505                 /*
 506                  * Detect EOF condition, do not set error.
 507                  */
 508                 if (rpipe->pipe_state & PIPE_REOF)
 509                         break;
 510
 511 #ifdef SMP
 512                 /*
 513                  * Gravy train if SMP box.  This saves a ton of IPIs and
 514                  * allows two cpus to operate in lockstep.
 515                  *
 516                  * XXX check pipe_wip also?
 517                  */
 518                 DELAY(1);
 519                 size = rpipe->pipe_buffer.windex - rpipe->pipe_buffer.rindex;
 520                 if (size)
 521                         continue;
 522 #endif
 523
 524                 /*
 525                  * Break if some data was read, or if this was a non-blocking
 526                  * read.
 527                  */
 528                 if (nread > 0)
 529                         break;
 530
 531                 if (nbio) {
 532                         error = EAGAIN;
 533                         break;
 534                 }
 535
 536                 /*
 537                  * Last chance, interlock with WANTR.
 538                  */
 539                 lwkt_gettoken(&wlock, &rpipe->pipe_wlock);
 540                 size = rpipe->pipe_buffer.windex - rpipe->pipe_buffer.rindex;
 541                 if (size) {
 542                         lwkt_reltoken(&wlock);
 543                         continue;
 544                 }
 545
 546                 /*
 547                  * If there is no more to read in the pipe, reset its
 548                  * pointers to the beginning.  This improves cache hit
 549                  * stats.
 550                  *
 551                  * We need both locks to modify both pointers, and there
 552                  * must also not be a write in progress or the uiomove()
 553                  * in the write might block and temporarily release
 554                  * its wlock, then reacquire and update windex.  We are
 555                  * only serialized against reads, not writes.
 556                  *
 557                  * XXX should we even bother resetting the indices?  It
 558                  *     might actually be more cache efficient not to.
 559                  */
 560                 if (rpipe->pipe_buffer.rindex == rpipe->pipe_buffer.windex &&
 561                     rpipe->pipe_wip == 0) {
 562                         rpipe->pipe_buffer.rindex = 0;
 563                         rpipe->pipe_buffer.windex = 0;
 564                 }
 565
 566                 /*
 567                  * Wait for more data.
 568                  *
 569                  * Pipe_state can only be set if both the rlock and wlock
 570                  * are held.
 571                  */
 572                 rpipe->pipe_state |= PIPE_WANTR;
 573                 tsleep_interlock(rpipe);
 574                 lwkt_reltoken(&wlock);
 575                 error = tsleep(rpipe, PCATCH, "piperd", 0);
 576                 if (error)
 577                         break;
 578         }
 579         pipe_end_uio(rpipe, &rpipe->pipe_rip);
 580
 581         /*
 582          * Uptime last access time
 583          */
 584         if (error == 0 && nread)
 585                 vfs_timestamp(&rpipe->pipe_atime);
 586
 587 #if 0
 588         /*
 589          * Handle write blocking hysteresis.  size can only increase while
 590          * we hold the rlock.
 591          *
 592          * XXX shouldn't need this any more.  We will wakeup the writer
 593          *     when we've drained past half-way.  The worst the writer
 594          *     can do is fill the buffer up, not make it smaller, so
 595          *     we are guaranteed our half-way test.
 596          */
 597         if (rpipe->pipe_state & PIPE_WANTW) {
 598                 size = rpipe->pipe_buffer.windex - rpipe->pipe_buffer.rindex;
 599                 if (size <= (rpipe->pipe_buffer.size >> 1)) {
 600                         lwkt_gettoken(&wlock, &rpipe->pipe_wlock);
 601                         if (rpipe->pipe_state & PIPE_WANTW) {
 602                                 rpipe->pipe_state &= ~PIPE_WANTW;
 603                                 lwkt_reltoken(&wlock);
 604                                 wakeup(rpipe);
 605                         } else {
 606                                 lwkt_reltoken(&wlock);
 607                         }
 608                 }
 609         }
 610 #endif
 611         size = rpipe->pipe_buffer.windex - rpipe->pipe_buffer.rindex;
 612         lwkt_reltoken(&rlock);
 613
 614         /*
 615          * If enough space is available in buffer then wakeup sel writers?
 616          */
 617         if ((rpipe->pipe_buffer.size - size) >= PIPE_BUF)
 618                 pipeselwakeup(rpipe);
 619         pipe_rel_mplock(&mpsave);
 620         return (error);
 621 }
 622
 623 /*
 624  * MPALMOSTSAFE - acquires mplock
 625  */
 626 static int
 627 pipe_write(struct file *fp, struct uio *uio, struct ucred *cred, int fflags)
 628 {
 629         int error;
 630         int orig_resid;
 631         int nbio;
 632         struct pipe *wpipe, *rpipe;
 633         lwkt_tokref rlock;
 634         lwkt_tokref wlock;
 635         u_int windex;
 636         u_int space;
 637         u_int wcount;
 638         int mpsave;
 639
 640         pipe_get_mplock(&mpsave);
 641
 642         /*
 643          * Writes go to the peer.  The peer will always exist.
 644          */
 645         rpipe = (struct pipe *) fp->f_data;
 646         wpipe = rpipe->pipe_peer;
 647         lwkt_gettoken(&wlock, &wpipe->pipe_wlock);
 648         if (wpipe->pipe_state & PIPE_WEOF) {
 649                 pipe_rel_mplock(&mpsave);
 650                 lwkt_reltoken(&wlock);
 651                 return (EPIPE);
 652         }
 653
 654         /*
 655          * Degenerate case (EPIPE takes prec)
 656          */
 657         if (uio->uio_resid == 0) {
 658                 pipe_rel_mplock(&mpsave);
 659                 lwkt_reltoken(&wlock);
 660                 return(0);
 661         }
 662
 663         /*
 664          * Writes are serialized (start_uio must be called with wlock)
 665          */
 666         error = pipe_start_uio(wpipe, &wpipe->pipe_wip);
 667         if (error) {
 668                 pipe_rel_mplock(&mpsave);
 669                 lwkt_reltoken(&wlock);
 670                 return (error);
 671         }
 672
 673         if (fflags & O_FBLOCKING)
 674                 nbio = 0;
 675         else if (fflags & O_FNONBLOCKING)
 676                 nbio = 1;
 677         else if (fp->f_flag & O_NONBLOCK)
 678                 nbio = 1;
 679         else
 680                 nbio = 0;
 681
 682         /*
 683          * If it is advantageous to resize the pipe buffer, do
 684          * so.  We are write-serialized so we can block safely.
 685          */
 686         if ((wpipe->pipe_buffer.size <= PIPE_SIZE) &&
 687             (pipe_nbig < pipe_maxbig) &&
 688             wpipe->pipe_wantwcnt > 4 &&
 689             (wpipe->pipe_buffer.rindex == wpipe->pipe_buffer.windex)) {
 690                 /*
 691                  * Recheck after lock.
 692                  */
 693                 lwkt_gettoken(&rlock, &wpipe->pipe_rlock);
 694                 if ((wpipe->pipe_buffer.size <= PIPE_SIZE) &&
 695                     (pipe_nbig < pipe_maxbig) &&
 696                     (wpipe->pipe_buffer.rindex == wpipe->pipe_buffer.windex)) {
 697                         if (pipespace(wpipe, BIG_PIPE_SIZE) == 0) {
 698                                 ++pipe_bigcount;
 699                                 pipe_nbig++;
 700                         }
 701                 }
 702                 lwkt_reltoken(&rlock);
 703         }
 704
 705         orig_resid = uio->uio_resid;
 706         wcount = 0;
 707
 708         while (uio->uio_resid) {
 709                 if (wpipe->pipe_state & PIPE_WEOF) {
 710                         error = EPIPE;
 711                         break;
 712                 }
 713
 714                 windex = wpipe->pipe_buffer.windex &
 715                          (wpipe->pipe_buffer.size - 1);
 716                 space = wpipe->pipe_buffer.size -
 717                         (wpipe->pipe_buffer.windex - wpipe->pipe_buffer.rindex);
 718                 cpu_lfence();
 719
 720                 /* Writes of size <= PIPE_BUF must be atomic. */
 721                 if ((space < uio->uio_resid) && (orig_resid <= PIPE_BUF))
 722                         space = 0;
 723
 724                 /*
 725                  * Write to fill, read size handles write hysteresis.  Also
 726                  * additional restrictions can cause select-based non-blocking
 727                  * writes to spin.
 728                  */
 729                 if (space > 0) {
 730                         u_int segsize;
 731
 732                         /*
 733                          * Transfer size is minimum of uio transfer
 734                          * and free space in pipe buffer.
 735                          *
 736                          * Limit each uiocopy to no more then PIPE_SIZE
 737                          * so we can keep the gravy train going on a
 738                          * SMP box.  This doubles the performance for
 739                          * write sizes > 16K.  Otherwise large writes
 740                          * wind up doing an inefficient synchronous
 741                          * ping-pong.
 742                          */
 743                         if (space > (u_int)uio->uio_resid)
 744                                 space = (u_int)uio->uio_resid;
 745                         if (space > PIPE_SIZE)
 746                                 space = PIPE_SIZE;
 747
 748                         /*
 749                          * First segment to transfer is minimum of
 750                          * transfer size and contiguous space in
 751                          * pipe buffer.  If first segment to transfer
 752                          * is less than the transfer size, we've got
 753                          * a wraparound in the buffer.
 754                          */
 755                         segsize = wpipe->pipe_buffer.size - windex;
 756                         if (segsize > space)
 757                                 segsize = space;
 758
 759                         /*
 760                          * If this is the first loop and the reader is
 761                          * blocked, do a preemptive wakeup of the reader.
 762                          *
 763                          * This works for both SMP and UP.  On SMP the IPI
 764                          * latency plus the wlock interlock on the reader
 765                          * side is the fastest way to get the reader going.
 766                          * (The scheduler will hard loop on lock tokens).
 767                          *
 768                          * NOTE: We can't clear WANTR here without acquiring
 769                          * the rlock, which we don't want to do here!
 770                          */
 771                         if (wpipe->pipe_state & PIPE_WANTR)
 772                                 wakeup(wpipe);
 773
 774                         /*
 775                          * Transfer first segment
 776                          */
 777                         error = uiomove(&wpipe->pipe_buffer.buffer[windex],
 778                                         segsize, uio);
 779                         cpu_mfence();
 780                         wpipe->pipe_buffer.windex += segsize;
 781
 782                         if (error == 0 && segsize < space) {
 783                                 /*
 784                                  * Transfer remaining part now, to
 785                                  * support atomic writes.  Wraparound
 786                                  * happened.
 787                                  */
 788                                 segsize = space - segsize;
 789                                 error = uiomove(&wpipe->pipe_buffer.buffer[0],
 790                                                 segsize, uio);
 791                                 cpu_mfence();
 792                                 wpipe->pipe_buffer.windex += segsize;
 793                         }
 794                         if (error)
 795                                 break;
 796                         wcount += space;
 797                         continue;
 798                 }
 799
 800                 /*
 801                  * We need both the rlock and the wlock to interlock against
 802                  * the EOF, WANTW, and size checks, and to modify pipe_state.
 803                  *
 804                  * These are token locks so we do not have to worry about
 805                  * deadlocks.
 806                  */
 807                 lwkt_gettoken(&rlock, &wpipe->pipe_rlock);
 808
 809                 /*
 810                  * If the "read-side" has been blocked, wake it up now
 811                  * and yield to let it drain synchronously rather
 812                  * then block.
 813                  */
 814                 if (wpipe->pipe_state & PIPE_WANTR) {
 815                         wpipe->pipe_state &= ~PIPE_WANTR;
 816                         wakeup(wpipe);
 817                 }
 818
 819                 /*
 820                  * don't block on non-blocking I/O
 821                  */
 822                 if (nbio) {
 823                         lwkt_reltoken(&rlock);
 824                         error = EAGAIN;
 825                         break;
 826                 }
 827
 828                 /*
 829                  * We have no more space and have something to offer,
 830                  * wake up select/poll.
 831                  */
 832                 pipeselwakeup(wpipe);
 833
 834                 ++wpipe->pipe_wantwcnt; /* don't care about overflow */
 835                 wpipe->pipe_state |= PIPE_WANTW;
 836                 error = tsleep(wpipe, PCATCH, "pipewr", 0);
 837                 lwkt_reltoken(&rlock);
 838
 839                 /*
 840                  * Break out if we errored or the read side wants us to go
 841                  * away.
 842                  */
 843                 if (error)
 844                         break;
 845                 if (wpipe->pipe_state & PIPE_WEOF) {
 846                         error = EPIPE;
 847                         break;
 848                 }
 849         }
 850         pipe_end_uio(wpipe, &wpipe->pipe_wip);
 851
 852         /*
 853          * If we have put any characters in the buffer, we wake up
 854          * the reader.
 855          *
 856          * Both rlock and wlock are required to be able to modify pipe_state.
 857          */
 858         if (wpipe->pipe_buffer.windex != wpipe->pipe_buffer.rindex) {
 859                 if (wpipe->pipe_state & PIPE_WANTR) {
 860                         lwkt_gettoken(&rlock, &wpipe->pipe_rlock);
 861                         if (wpipe->pipe_state & PIPE_WANTR) {
 862                                 wpipe->pipe_state &= ~PIPE_WANTR;
 863                                 lwkt_reltoken(&rlock);
 864                                 wakeup(wpipe);
 865                         } else {
 866                                 lwkt_reltoken(&rlock);
 867                         }
 868                 }
 869         }
 870
 871         /*
 872          * Don't return EPIPE if I/O was successful
 873          */
 874         if ((wpipe->pipe_buffer.rindex == wpipe->pipe_buffer.windex) &&
 875             (uio->uio_resid == 0) &&
 876             (error == EPIPE)) {
 877                 error = 0;
 878         }
 879
 880         if (error == 0)
 881                 vfs_timestamp(&wpipe->pipe_mtime);
 882
 883         /*
 884          * We have something to offer,
 885          * wake up select/poll.
 886          */
 887         space = wpipe->pipe_buffer.windex - wpipe->pipe_buffer.rindex;
 888         lwkt_reltoken(&wlock);
 889         if (space)
 890                 pipeselwakeup(wpipe);
 891         pipe_rel_mplock(&mpsave);
 892         return (error);
 893 }
 894
 895 /*
 896  * MPALMOSTSAFE - acquires mplock
 897  *
 898  * we implement a very minimal set of ioctls for compatibility with sockets.
 899  */
 900 int
 901 pipe_ioctl(struct file *fp, u_long cmd, caddr_t data, struct ucred *cred)
 902 {
 903         struct pipe *mpipe;
 904         int error;
 905
 906         get_mplock();
 907         mpipe = (struct pipe *)fp->f_data;
 908
 909         switch (cmd) {
 910         case FIOASYNC:
 911                 if (*(int *)data) {
 912                         mpipe->pipe_state |= PIPE_ASYNC;
 913                 } else {
 914                         mpipe->pipe_state &= ~PIPE_ASYNC;
 915                 }
 916                 error = 0;
 917                 break;
 918         case FIONREAD:
 919                 *(int *)data = mpipe->pipe_buffer.windex -
 920                                 mpipe->pipe_buffer.rindex;
 921                 error = 0;
 922                 break;
 923         case FIOSETOWN:
 924                 error = fsetown(*(int *)data, &mpipe->pipe_sigio);
 925                 break;
 926         case FIOGETOWN:
 927                 *(int *)data = fgetown(mpipe->pipe_sigio);
 928                 error = 0;
 929                 break;
 930         case TIOCSPGRP:
 931                 /* This is deprecated, FIOSETOWN should be used instead. */
 932                 error = fsetown(-(*(int *)data), &mpipe->pipe_sigio);
 933                 break;
 934
 935         case TIOCGPGRP:
 936                 /* This is deprecated, FIOGETOWN should be used instead. */
 937                 *(int *)data = -fgetown(mpipe->pipe_sigio);
 938                 error = 0;
 939                 break;
 940         default:
 941                 error = ENOTTY;
 942                 break;
 943         }
 944         rel_mplock();
 945         return (error);
 946 }
 947
 948 /*
 949  * MPALMOSTSAFE - acquires mplock
 950  */
 951 int
 952 pipe_poll(struct file *fp, int events, struct ucred *cred)
 953 {
 954         struct pipe *rpipe;
 955         struct pipe *wpipe;
 956         int revents = 0;
 957         u_int space;
 958         int mpsave;
 959
 960         pipe_get_mplock(&mpsave);
 961         rpipe = (struct pipe *)fp->f_data;
 962         wpipe = rpipe->pipe_peer;
 963         if (events & (POLLIN | POLLRDNORM)) {
 964                 if ((rpipe->pipe_buffer.windex != rpipe->pipe_buffer.rindex) ||
 965                     (rpipe->pipe_state & PIPE_REOF)) {
 966                         revents |= events & (POLLIN | POLLRDNORM);
 967                 }
 968         }
 969
 970         if (events & (POLLOUT | POLLWRNORM)) {
 971                 if (wpipe == NULL || (wpipe->pipe_state & PIPE_WEOF)) {
 972                         revents |= events & (POLLOUT | POLLWRNORM);
 973                 } else {
 974                         space = wpipe->pipe_buffer.windex -
 975                                 wpipe->pipe_buffer.rindex;
 976                         space = wpipe->pipe_buffer.size - space;
 977                         if (space >= PIPE_BUF)
 978                                 revents |= events & (POLLOUT | POLLWRNORM);
 979                 }
 980         }
 981
 982         if ((rpipe->pipe_state & PIPE_REOF) ||
 983             (wpipe == NULL) ||
 984             (wpipe->pipe_state & PIPE_WEOF))
 985                 revents |= POLLHUP;
 986
 987         if (revents == 0) {
 988                 if (events & (POLLIN | POLLRDNORM)) {
 989                         selrecord(curthread, &rpipe->pipe_sel);
 990                         rpipe->pipe_state |= PIPE_SEL;
 991                 }
 992
 993                 if (events & (POLLOUT | POLLWRNORM)) {
 994                         selrecord(curthread, &wpipe->pipe_sel);
 995                         wpipe->pipe_state |= PIPE_SEL;
 996                 }
 997         }
 998         pipe_rel_mplock(&mpsave);
 999         return (revents);
1000 }
1001
1002 /*
1003  * MPALMOSTSAFE - acquires mplock
1004  */
1005 static int
1006 pipe_stat(struct file *fp, struct stat *ub, struct ucred *cred)
1007 {
1008         struct pipe *pipe;
1009         int mpsave;
1010
1011         pipe_get_mplock(&mpsave);
1012         pipe = (struct pipe *)fp->f_data;
1013
1014         bzero((caddr_t)ub, sizeof(*ub));
1015         ub->st_mode = S_IFIFO;
1016         ub->st_blksize = pipe->pipe_buffer.size;
1017         ub->st_size = pipe->pipe_buffer.windex - pipe->pipe_buffer.rindex;
1018         ub->st_blocks = (ub->st_size + ub->st_blksize - 1) / ub->st_blksize;
1019         ub->st_atimespec = pipe->pipe_atime;
1020         ub->st_mtimespec = pipe->pipe_mtime;
1021         ub->st_ctimespec = pipe->pipe_ctime;
1022         /*
1023          * Left as 0: st_dev, st_ino, st_nlink, st_uid, st_gid, st_rdev,
1024          * st_flags, st_gen.
1025          * XXX (st_dev, st_ino) should be unique.
1026          */
1027         pipe_rel_mplock(&mpsave);
1028         return (0);
1029 }
1030
1031 /*
1032  * MPALMOSTSAFE - acquires mplock
1033  */
1034 static int
1035 pipe_close(struct file *fp)
1036 {
1037         struct pipe *cpipe;
1038
1039         get_mplock();
1040         cpipe = (struct pipe *)fp->f_data;
1041         fp->f_ops = &badfileops;
1042         fp->f_data = NULL;
1043         funsetown(cpipe->pipe_sigio);
1044         pipeclose(cpipe);
1045         rel_mplock();
1046         return (0);
1047 }
1048
1049 /*
1050  * Shutdown one or both directions of a full-duplex pipe.
1051  *
1052  * MPALMOSTSAFE - acquires mplock
1053  */
1054 static int
1055 pipe_shutdown(struct file *fp, int how)
1056 {
1057         struct pipe *rpipe;
1058         struct pipe *wpipe;
1059         int error = EPIPE;
1060         lwkt_tokref rpipe_rlock;
1061         lwkt_tokref rpipe_wlock;
1062         lwkt_tokref wpipe_rlock;
1063         lwkt_tokref wpipe_wlock;
1064         int mpsave;
1065
1066         pipe_get_mplock(&mpsave);
1067         rpipe = (struct pipe *)fp->f_data;
1068         wpipe = rpipe->pipe_peer;
1069
1070         /*
1071          * We modify pipe_state on both pipes, which means we need
1072          * all four tokens!
1073          */
1074         lwkt_gettoken(&rpipe_rlock, &rpipe->pipe_rlock);
1075         lwkt_gettoken(&rpipe_wlock, &rpipe->pipe_wlock);
1076         lwkt_gettoken(&wpipe_rlock, &wpipe->pipe_rlock);
1077         lwkt_gettoken(&wpipe_wlock, &wpipe->pipe_wlock);
1078
1079         switch(how) {
1080         case SHUT_RDWR:
1081         case SHUT_RD:
1082                 rpipe->pipe_state |= PIPE_REOF;
1083                 wpipe->pipe_state |= PIPE_WEOF;
1084                 if (rpipe->pipe_state & PIPE_WANTR) {
1085                         rpipe->pipe_state &= ~PIPE_WANTR;
1086                         wakeup(rpipe);
1087                 }
1088                 if (wpipe->pipe_state & PIPE_WANTW) {
1089                         wpipe->pipe_state &= ~PIPE_WANTW;
1090                         wakeup(wpipe);
1091                 }
1092                 pipeselwakeup(rpipe);
1093                 error = 0;
1094                 if (how == SHUT_RD)
1095                         break;
1096                 /* fall through */
1097         case SHUT_WR:
1098                 wpipe->pipe_state |= PIPE_WEOF;
1099                 rpipe->pipe_state |= PIPE_REOF;
1100                 if (wpipe->pipe_state & PIPE_WANTW) {
1101                         wpipe->pipe_state &= ~PIPE_WANTW;
1102                         wakeup(wpipe);
1103                 }
1104                 if (rpipe->pipe_state & PIPE_WANTR) {
1105                         rpipe->pipe_state &= ~PIPE_WANTR;
1106                         wakeup(rpipe);
1107                 }
1108                 pipeselwakeup(wpipe);
1109                 error = 0;
1110                 break;
1111         }
1112
1113         lwkt_reltoken(&rpipe_rlock);
1114         lwkt_reltoken(&rpipe_wlock);
1115         lwkt_reltoken(&wpipe_rlock);
1116         lwkt_reltoken(&wpipe_wlock);
1117
1118         pipe_rel_mplock(&mpsave);
1119         return (error);
1120 }
1121
1122 static void
1123 pipe_free_kmem(struct pipe *cpipe)
1124 {
1125         if (cpipe->pipe_buffer.buffer != NULL) {
1126                 if (cpipe->pipe_buffer.size > PIPE_SIZE)
1127                         --pipe_nbig;
1128                 kmem_free(&kernel_map,
1129                         (vm_offset_t)cpipe->pipe_buffer.buffer,
1130                         cpipe->pipe_buffer.size);
1131                 cpipe->pipe_buffer.buffer = NULL;
1132                 cpipe->pipe_buffer.object = NULL;
1133         }
1134 }
1135
1136 /*
1137  * Close the pipe.  The slock must be held to interlock against simultanious
1138  * closes.  The rlock and wlock must be held to adjust the pipe_state.
1139  */
1140 static void
1141 pipeclose(struct pipe *cpipe)
1142 {
1143         globaldata_t gd;
1144         struct pipe *ppipe;
1145         lwkt_tokref cpipe_rlock;
1146         lwkt_tokref cpipe_wlock;
1147         lwkt_tokref ppipe_rlock;
1148         lwkt_tokref ppipe_wlock;
1149
1150         if (cpipe == NULL)
1151                 return;
1152
1153         /*
1154          * The slock may not have been allocated yet (close during
1155          * initialization)
1156          *
1157          * We need both the read and write tokens to modify pipe_state.
1158          */
1159         if (cpipe->pipe_slock)
1160                 lockmgr(cpipe->pipe_slock, LK_EXCLUSIVE);
1161         lwkt_gettoken(&cpipe_rlock, &cpipe->pipe_rlock);
1162         lwkt_gettoken(&cpipe_wlock, &cpipe->pipe_wlock);
1163
1164         /*
1165          * Set our state, wakeup anyone waiting in select, and
1166          * wakeup anyone blocked on our pipe.
1167          */
1168         cpipe->pipe_state |= PIPE_CLOSED | PIPE_REOF | PIPE_WEOF;
1169         pipeselwakeup(cpipe);
1170         if (cpipe->pipe_state & (PIPE_WANTR | PIPE_WANTW)) {
1171                 cpipe->pipe_state &= ~(PIPE_WANTR | PIPE_WANTW);
1172                 wakeup(cpipe);
1173         }
1174
1175         /*
1176          * Disconnect from peer
1177          */
1178         if ((ppipe = cpipe->pipe_peer) != NULL) {
1179                 lwkt_gettoken(&ppipe_rlock, &ppipe->pipe_rlock);
1180                 lwkt_gettoken(&ppipe_wlock, &ppipe->pipe_wlock);
1181                 ppipe->pipe_state |= PIPE_REOF;
1182                 pipeselwakeup(ppipe);
1183                 if (ppipe->pipe_state & (PIPE_WANTR | PIPE_WANTW)) {
1184                         ppipe->pipe_state &= ~(PIPE_WANTR | PIPE_WANTW);
1185                         wakeup(ppipe);
1186                 }
1187                 if (SLIST_FIRST(&ppipe->pipe_sel.si_note)) {
1188                         get_mplock();
1189                         KNOTE(&ppipe->pipe_sel.si_note, 0);
1190                         rel_mplock();
1191                 }
1192                 lwkt_reltoken(&ppipe_rlock);
1193                 lwkt_reltoken(&ppipe_wlock);
1194         }
1195
1196         /*
1197          * If the peer is also closed we can free resources for both
1198          * sides, otherwise we leave our side intact to deal with any
1199          * races (since we only have the slock).
1200          */
1201         if (ppipe && (ppipe->pipe_state & PIPE_CLOSED)) {
1202                 cpipe->pipe_peer = NULL;
1203                 ppipe->pipe_peer = NULL;
1204                 ppipe->pipe_slock = NULL;       /* we will free the slock */
1205                 pipeclose(ppipe);
1206                 ppipe = NULL;
1207         }
1208
1209         lwkt_reltoken(&cpipe_rlock);
1210         lwkt_reltoken(&cpipe_wlock);
1211         if (cpipe->pipe_slock)
1212                 lockmgr(cpipe->pipe_slock, LK_RELEASE);
1213
1214         /*
1215          * If we disassociated from our peer we can free resources
1216          */
1217         if (ppipe == NULL) {
1218                 gd = mycpu;
1219                 if (cpipe->pipe_slock) {
1220                         kfree(cpipe->pipe_slock, M_PIPE);
1221                         cpipe->pipe_slock = NULL;
1222                 }
1223                 if (gd->gd_pipeqcount >= pipe_maxcache ||
1224                     cpipe->pipe_buffer.size != PIPE_SIZE
1225                 ) {
1226                         pipe_free_kmem(cpipe);
1227                         kfree(cpipe, M_PIPE);
1228                 } else {
1229                         cpipe->pipe_state = 0;
1230                         cpipe->pipe_peer = gd->gd_pipeq;
1231                         gd->gd_pipeq = cpipe;
1232                         ++gd->gd_pipeqcount;
1233                 }
1234         }
1235 }
1236
1237 /*
1238  * MPALMOSTSAFE - acquires mplock
1239  */
1240 static int
1241 pipe_kqfilter(struct file *fp, struct knote *kn)
1242 {
1243         struct pipe *cpipe;
1244
1245         get_mplock();
1246         cpipe = (struct pipe *)kn->kn_fp->f_data;
1247
1248         switch (kn->kn_filter) {
1249         case EVFILT_READ:
1250                 kn->kn_fop = &pipe_rfiltops;
1251                 break;
1252         case EVFILT_WRITE:
1253                 kn->kn_fop = &pipe_wfiltops;
1254                 cpipe = cpipe->pipe_peer;
1255                 if (cpipe == NULL) {
1256                         /* other end of pipe has been closed */
1257                         rel_mplock();
1258                         return (EPIPE);
1259                 }
1260                 break;
1261         default:
1262                 return (1);
1263         }
1264         kn->kn_hook = (caddr_t)cpipe;
1265
1266         SLIST_INSERT_HEAD(&cpipe->pipe_sel.si_note, kn, kn_selnext);
1267         rel_mplock();
1268         return (0);
1269 }
1270
1271 static void
1272 filt_pipedetach(struct knote *kn)
1273 {
1274         struct pipe *cpipe = (struct pipe *)kn->kn_hook;
1275
1276         SLIST_REMOVE(&cpipe->pipe_sel.si_note, kn, knote, kn_selnext);
1277 }
1278
1279 /*ARGSUSED*/
1280 static int
1281 filt_piperead(struct knote *kn, long hint)
1282 {
1283         struct pipe *rpipe = (struct pipe *)kn->kn_fp->f_data;
1284
1285         kn->kn_data = rpipe->pipe_buffer.windex - rpipe->pipe_buffer.rindex;
1286
1287         /* XXX RACE */
1288         if (rpipe->pipe_state & PIPE_REOF) {
1289                 kn->kn_flags |= EV_EOF;
1290                 return (1);
1291         }
1292         return (kn->kn_data > 0);
1293 }
1294
1295 /*ARGSUSED*/
1296 static int
1297 filt_pipewrite(struct knote *kn, long hint)
1298 {
1299         struct pipe *rpipe = (struct pipe *)kn->kn_fp->f_data;
1300         struct pipe *wpipe = rpipe->pipe_peer;
1301         u_int32_t space;
1302
1303         /* XXX RACE */
1304         if ((wpipe == NULL) || (wpipe->pipe_state & PIPE_WEOF)) {
1305                 kn->kn_data = 0;
1306                 kn->kn_flags |= EV_EOF;
1307                 return (1);
1308         }
1309         space = wpipe->pipe_buffer.windex -
1310                 wpipe->pipe_buffer.rindex;
1311         space = wpipe->pipe_buffer.size - space;
1312         kn->kn_data = space;
1313         return (kn->kn_data >= PIPE_BUF);
1314 }