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  * 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 
   20 /*
   21  * This file contains a high-performance replacement for the socket-based
   22  * pipes scheme originally used in FreeBSD/4.4Lite.  It does not support
   23  * all features of sockets, but does do everything that pipes normally
   24  * do.
   25  */
   26 
   27 /*
   28  * This code has two modes of operation, a small write mode and a large
   29  * write mode.  The small write mode acts like conventional pipes with
   30  * a kernel buffer.  If the buffer is less than PIPE_MINDIRECT, then the
   31  * "normal" pipe buffering is done.  If the buffer is between PIPE_MINDIRECT
   32  * and PIPE_SIZE in size, it is fully mapped and wired into the kernel, and
   33  * the receiving process can copy it directly from the pages in the sending
   34  * process.
   35  *
   36  * If the sending process receives a signal, it is possible that it will
   37  * go away, and certainly its address space can change, because control
   38  * is returned back to the user-mode side.  In that case, the pipe code
   39  * arranges to copy the buffer supplied by the user process, to a pageable
   40  * kernel buffer, and the receiving process will grab the data from the
   41  * pageable kernel buffer.  Since signals don't happen all that often,
   42  * the copy operation is normally eliminated.
   43  *
   44  * The constant PIPE_MINDIRECT is chosen to make sure that buffering will
   45  * happen for small transfers so that the system will not spend all of
   46  * its time context switching.
   47  *
   48  * In order to limit the resource use of pipes, two sysctls exist:
   49  *
   50  * kern.ipc.maxpipekva - This is a hard limit on the amount of pageable
   51  * address space available to us in pipe_map. This value is normally
   52  * autotuned, but may also be loader tuned.
   53  *
   54  * kern.ipc.pipekva - This read-only sysctl tracks the current amount of
   55  * memory in use by pipes.
   56  *
   57  * Based on how large pipekva is relative to maxpipekva, the following
   58  * will happen:
   59  *
   60  * 0% - 50%:
   61  *     New pipes are given 16K of memory backing, pipes may dynamically
   62  *     grow to as large as 64K where needed.
   63  * 50% - 75%:
   64  *     New pipes are given 4K (or PAGE_SIZE) of memory backing,
   65  *     existing pipes may NOT grow.
   66  * 75% - 100%:
   67  *     New pipes are given 4K (or PAGE_SIZE) of memory backing,
   68  *     existing pipes will be shrunk down to 4K whenever possible.
   69  *
   70  * Resizing may be disabled by setting kern.ipc.piperesizeallowed=0.  If
   71  * that is set,  the only resize that will occur is the 0 -> SMALL_PIPE_SIZE
   72  * resize which MUST occur for reverse-direction pipes when they are
   73  * first used.
   74  *
   75  * Additional information about the current state of pipes may be obtained
   76  * from kern.ipc.pipes, kern.ipc.pipefragretry, kern.ipc.pipeallocfail,
   77  * and kern.ipc.piperesizefail.
   78  *
   79  * Locking rules:  There are two locks present here:  A mutex, used via
   80  * PIPE_LOCK, and a flag, used via pipelock().  All locking is done via
   81  * the flag, as mutexes can not persist over uiomove.  The mutex
   82  * exists only to guard access to the flag, and is not in itself a
   83  * locking mechanism.  Also note that there is only a single mutex for
   84  * both directions of a pipe.
   85  *
   86  * As pipelock() may have to sleep before it can acquire the flag, it
   87  * is important to reread all data after a call to pipelock(); everything
   88  * in the structure may have changed.
   89  */
   90 
   91 #include <sys/cdefs.h>
   92 __FBSDID("$FreeBSD: releng/7.4/sys/kern/sys_pipe.c 202814 2010-01-22 17:02:07Z jhb $");
   93 
   94 #include "opt_mac.h"
   95 
   96 #include <sys/param.h>
   97 #include <sys/systm.h>
   98 #include <sys/fcntl.h>
   99 #include <sys/file.h>
  100 #include <sys/filedesc.h>
  101 #include <sys/filio.h>
  102 #include <sys/kernel.h>
  103 #include <sys/lock.h>
  104 #include <sys/mutex.h>
  105 #include <sys/ttycom.h>
  106 #include <sys/stat.h>
  107 #include <sys/malloc.h>
  108 #include <sys/poll.h>
  109 #include <sys/selinfo.h>
  110 #include <sys/signalvar.h>
  111 #include <sys/sysctl.h>
  112 #include <sys/sysproto.h>
  113 #include <sys/pipe.h>
  114 #include <sys/proc.h>
  115 #include <sys/vnode.h>
  116 #include <sys/uio.h>
  117 #include <sys/event.h>
  118 
  119 #include <security/mac/mac_framework.h>
  120 
  121 #include <vm/vm.h>
  122 #include <vm/vm_param.h>
  123 #include <vm/vm_object.h>
  124 #include <vm/vm_kern.h>
  125 #include <vm/vm_extern.h>
  126 #include <vm/pmap.h>
  127 #include <vm/vm_map.h>
  128 #include <vm/vm_page.h>
  129 #include <vm/uma.h>
  130 
  131 /*
  132  * Use this define if you want to disable *fancy* VM things.  Expect an
  133  * approx 30% decrease in transfer rate.  This could be useful for
  134  * NetBSD or OpenBSD.
  135  */
  136 /* #define PIPE_NODIRECT */
  137 
  138 /*
  139  * interfaces to the outside world
  140  */
  141 static fo_rdwr_t        pipe_read;
  142 static fo_rdwr_t        pipe_write;
  143 static fo_ioctl_t       pipe_ioctl;
  144 static fo_poll_t        pipe_poll;
  145 static fo_kqfilter_t    pipe_kqfilter;
  146 static fo_stat_t        pipe_stat;
  147 static fo_close_t       pipe_close;
  148 
  149 static struct fileops pipeops = {
  150         .fo_read = pipe_read,
  151         .fo_write = pipe_write,
  152         .fo_ioctl = pipe_ioctl,
  153         .fo_poll = pipe_poll,
  154         .fo_kqfilter = pipe_kqfilter,
  155         .fo_stat = pipe_stat,
  156         .fo_close = pipe_close,
  157         .fo_flags = DFLAG_PASSABLE
  158 };
  159 
  160 static void     filt_pipedetach(struct knote *kn);
  161 static int      filt_piperead(struct knote *kn, long hint);
  162 static int      filt_pipewrite(struct knote *kn, long hint);
  163 
  164 static struct filterops pipe_rfiltops =
  165         { 1, NULL, filt_pipedetach, filt_piperead };
  166 static struct filterops pipe_wfiltops =
  167         { 1, NULL, filt_pipedetach, filt_pipewrite };
  168 
  169 /*
  170  * Default pipe buffer size(s), this can be kind-of large now because pipe
  171  * space is pageable.  The pipe code will try to maintain locality of
  172  * reference for performance reasons, so small amounts of outstanding I/O
  173  * will not wipe the cache.
  174  */
  175 #define MINPIPESIZE (PIPE_SIZE/3)
  176 #define MAXPIPESIZE (2*PIPE_SIZE/3)
  177 
  178 static long amountpipekva;
  179 static int pipefragretry;
  180 static int pipeallocfail;
  181 static int piperesizefail;
  182 static int piperesizeallowed = 1;
  183 
  184 SYSCTL_LONG(_kern_ipc, OID_AUTO, maxpipekva, CTLFLAG_RDTUN,
  185            &maxpipekva, 0, "Pipe KVA limit");
  186 SYSCTL_LONG(_kern_ipc, OID_AUTO, pipekva, CTLFLAG_RD,
  187            &amountpipekva, 0, "Pipe KVA usage");
  188 SYSCTL_INT(_kern_ipc, OID_AUTO, pipefragretry, CTLFLAG_RD,
  189           &pipefragretry, 0, "Pipe allocation retries due to fragmentation");
  190 SYSCTL_INT(_kern_ipc, OID_AUTO, pipeallocfail, CTLFLAG_RD,
  191           &pipeallocfail, 0, "Pipe allocation failures");
  192 SYSCTL_INT(_kern_ipc, OID_AUTO, piperesizefail, CTLFLAG_RD,
  193           &piperesizefail, 0, "Pipe resize failures");
  194 SYSCTL_INT(_kern_ipc, OID_AUTO, piperesizeallowed, CTLFLAG_RW,
  195           &piperesizeallowed, 0, "Pipe resizing allowed");
  196 
  197 static void pipeinit(void *dummy __unused);
  198 static void pipeclose(struct pipe *cpipe);
  199 static void pipe_free_kmem(struct pipe *cpipe);
  200 static int pipe_create(struct pipe *pipe, int backing);
  201 static __inline int pipelock(struct pipe *cpipe, int catch);
  202 static __inline void pipeunlock(struct pipe *cpipe);
  203 static __inline void pipeselwakeup(struct pipe *cpipe);
  204 #ifndef PIPE_NODIRECT
  205 static int pipe_build_write_buffer(struct pipe *wpipe, struct uio *uio);
  206 static void pipe_destroy_write_buffer(struct pipe *wpipe);
  207 static int pipe_direct_write(struct pipe *wpipe, struct uio *uio);
  208 static void pipe_clone_write_buffer(struct pipe *wpipe);
  209 #endif
  210 static int pipespace(struct pipe *cpipe, int size);
  211 static int pipespace_new(struct pipe *cpipe, int size);
  212 
  213 static int      pipe_zone_ctor(void *mem, int size, void *arg, int flags);
  214 static int      pipe_zone_init(void *mem, int size, int flags);
  215 static void     pipe_zone_fini(void *mem, int size);
  216 
  217 static uma_zone_t pipe_zone;
  218 
  219 SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_ANY, pipeinit, NULL);
  220 
  221 static void
  222 pipeinit(void *dummy __unused)
  223 {
  224 
  225         pipe_zone = uma_zcreate("pipe", sizeof(struct pipepair),
  226             pipe_zone_ctor, NULL, pipe_zone_init, pipe_zone_fini,
  227             UMA_ALIGN_PTR, 0);
  228         KASSERT(pipe_zone != NULL, ("pipe_zone not initialized"));
  229 }
  230 
  231 static int
  232 pipe_zone_ctor(void *mem, int size, void *arg, int flags)
  233 {
  234         struct pipepair *pp;
  235         struct pipe *rpipe, *wpipe;
  236 
  237         KASSERT(size == sizeof(*pp), ("pipe_zone_ctor: wrong size"));
  238 
  239         pp = (struct pipepair *)mem;
  240 
  241         /*
  242          * We zero both pipe endpoints to make sure all the kmem pointers
  243          * are NULL, flag fields are zero'd, etc.  We timestamp both
  244          * endpoints with the same time.
  245          */
  246         rpipe = &pp->pp_rpipe;
  247         bzero(rpipe, sizeof(*rpipe));
  248         vfs_timestamp(&rpipe->pipe_ctime);
  249         rpipe->pipe_atime = rpipe->pipe_mtime = rpipe->pipe_ctime;
  250 
  251         wpipe = &pp->pp_wpipe;
  252         bzero(wpipe, sizeof(*wpipe));
  253         wpipe->pipe_ctime = rpipe->pipe_ctime;
  254         wpipe->pipe_atime = wpipe->pipe_mtime = rpipe->pipe_ctime;
  255 
  256         rpipe->pipe_peer = wpipe;
  257         rpipe->pipe_pair = pp;
  258         wpipe->pipe_peer = rpipe;
  259         wpipe->pipe_pair = pp;
  260 
  261         /*
  262          * Mark both endpoints as present; they will later get free'd
  263          * one at a time.  When both are free'd, then the whole pair
  264          * is released.
  265          */
  266         rpipe->pipe_present = PIPE_ACTIVE;
  267         wpipe->pipe_present = PIPE_ACTIVE;
  268 
  269         /*
  270          * Eventually, the MAC Framework may initialize the label
  271          * in ctor or init, but for now we do it elswhere to avoid
  272          * blocking in ctor or init.
  273          */
  274         pp->pp_label = NULL;
  275 
  276         return (0);
  277 }
  278 
  279 static int
  280 pipe_zone_init(void *mem, int size, int flags)
  281 {
  282         struct pipepair *pp;
  283 
  284         KASSERT(size == sizeof(*pp), ("pipe_zone_init: wrong size"));
  285 
  286         pp = (struct pipepair *)mem;
  287 
  288         mtx_init(&pp->pp_mtx, "pipe mutex", NULL, MTX_DEF | MTX_RECURSE);
  289         return (0);
  290 }
  291 
  292 static void
  293 pipe_zone_fini(void *mem, int size)
  294 {
  295         struct pipepair *pp;
  296 
  297         KASSERT(size == sizeof(*pp), ("pipe_zone_fini: wrong size"));
  298 
  299         pp = (struct pipepair *)mem;
  300 
  301         mtx_destroy(&pp->pp_mtx);
  302 }
  303 
  304 /*
  305  * The pipe system call for the DTYPE_PIPE type of pipes.  If we fail, let
  306  * the zone pick up the pieces via pipeclose().
  307  */
  308 /* ARGSUSED */
  309 int
  310 pipe(td, uap)
  311         struct thread *td;
  312         struct pipe_args /* {
  313                 int     dummy;
  314         } */ *uap;
  315 {
  316         struct filedesc *fdp = td->td_proc->p_fd;
  317         struct file *rf, *wf;
  318         struct pipepair *pp;
  319         struct pipe *rpipe, *wpipe;
  320         int fd, error;
  321 
  322         pp = uma_zalloc(pipe_zone, M_WAITOK);
  323 #ifdef MAC
  324         /*
  325          * The MAC label is shared between the connected endpoints.  As a
  326          * result mac_init_pipe() and mac_create_pipe() are called once
  327          * for the pair, and not on the endpoints.
  328          */
  329         mac_init_pipe(pp);
  330         mac_create_pipe(td->td_ucred, pp);
  331 #endif
  332         rpipe = &pp->pp_rpipe;
  333         wpipe = &pp->pp_wpipe;
  334 
  335         knlist_init_mtx(&rpipe->pipe_sel.si_note, PIPE_MTX(rpipe));
  336         knlist_init_mtx(&wpipe->pipe_sel.si_note, PIPE_MTX(wpipe));
  337 
  338         /* Only the forward direction pipe is backed by default */
  339         if ((error = pipe_create(rpipe, 1)) != 0 ||
  340             (error = pipe_create(wpipe, 0)) != 0) {
  341                 pipeclose(rpipe);
  342                 pipeclose(wpipe);
  343                 return (error);
  344         }
  345 
  346         rpipe->pipe_state |= PIPE_DIRECTOK;
  347         wpipe->pipe_state |= PIPE_DIRECTOK;
  348 
  349         error = falloc(td, &rf, &fd);
  350         if (error) {
  351                 pipeclose(rpipe);
  352                 pipeclose(wpipe);
  353                 return (error);
  354         }
  355         /* An extra reference on `rf' has been held for us by falloc(). */
  356         td->td_retval[0] = fd;
  357 
  358         /*
  359          * Warning: once we've gotten past allocation of the fd for the
  360          * read-side, we can only drop the read side via fdrop() in order
  361          * to avoid races against processes which manage to dup() the read
  362          * side while we are blocked trying to allocate the write side.
  363          */
  364         FILE_LOCK(rf);
  365         rf->f_flag = FREAD | FWRITE;
  366         rf->f_type = DTYPE_PIPE;
  367         rf->f_data = rpipe;
  368         rf->f_ops = &pipeops;
  369         FILE_UNLOCK(rf);
  370         error = falloc(td, &wf, &fd);
  371         if (error) {
  372                 fdclose(fdp, rf, td->td_retval[0], td);
  373                 fdrop(rf, td);
  374                 /* rpipe has been closed by fdrop(). */
  375                 pipeclose(wpipe);
  376                 return (error);
  377         }
  378         /* An extra reference on `wf' has been held for us by falloc(). */
  379         FILE_LOCK(wf);
  380         wf->f_flag = FREAD | FWRITE;
  381         wf->f_type = DTYPE_PIPE;
  382         wf->f_data = wpipe;
  383         wf->f_ops = &pipeops;
  384         FILE_UNLOCK(wf);
  385         fdrop(wf, td);
  386         td->td_retval[1] = fd;
  387         fdrop(rf, td);
  388 
  389         return (0);
  390 }
  391 
  392 /*
  393  * Allocate kva for pipe circular buffer, the space is pageable
  394  * This routine will 'realloc' the size of a pipe safely, if it fails
  395  * it will retain the old buffer.
  396  * If it fails it will return ENOMEM.
  397  */
  398 static int
  399 pipespace_new(cpipe, size)
  400         struct pipe *cpipe;
  401         int size;
  402 {
  403         caddr_t buffer;
  404         int error, cnt, firstseg;
  405         static int curfail = 0;
  406         static struct timeval lastfail;
  407 
  408         KASSERT(!mtx_owned(PIPE_MTX(cpipe)), ("pipespace: pipe mutex locked"));
  409         KASSERT(!(cpipe->pipe_state & PIPE_DIRECTW),
  410                 ("pipespace: resize of direct writes not allowed"));
  411 retry:
  412         cnt = cpipe->pipe_buffer.cnt;
  413         if (cnt > size)
  414                 size = cnt;
  415 
  416         size = round_page(size);
  417         buffer = (caddr_t) vm_map_min(pipe_map);
  418 
  419         error = vm_map_find(pipe_map, NULL, 0,
  420                 (vm_offset_t *) &buffer, size, 1,
  421                 VM_PROT_ALL, VM_PROT_ALL, 0);
  422         if (error != KERN_SUCCESS) {
  423                 if ((cpipe->pipe_buffer.buffer == NULL) &&
  424                         (size > SMALL_PIPE_SIZE)) {
  425                         size = SMALL_PIPE_SIZE;
  426                         pipefragretry++;
  427                         goto retry;
  428                 }
  429                 if (cpipe->pipe_buffer.buffer == NULL) {
  430                         pipeallocfail++;
  431                         if (ppsratecheck(&lastfail, &curfail, 1))
  432                                 printf("kern.ipc.maxpipekva exceeded; see tuning(7)\n");
  433                 } else {
  434                         piperesizefail++;
  435                 }
  436                 return (ENOMEM);
  437         }
  438 
  439         /* copy data, then free old resources if we're resizing */
  440         if (cnt > 0) {
  441                 if (cpipe->pipe_buffer.in <= cpipe->pipe_buffer.out) {
  442                         firstseg = cpipe->pipe_buffer.size - cpipe->pipe_buffer.out;
  443                         bcopy(&cpipe->pipe_buffer.buffer[cpipe->pipe_buffer.out],
  444                                 buffer, firstseg);
  445                         if ((cnt - firstseg) > 0)
  446                                 bcopy(cpipe->pipe_buffer.buffer, &buffer[firstseg],
  447                                         cpipe->pipe_buffer.in);
  448                 } else {
  449                         bcopy(&cpipe->pipe_buffer.buffer[cpipe->pipe_buffer.out],
  450                                 buffer, cnt);
  451                 }
  452         }
  453         pipe_free_kmem(cpipe);
  454         cpipe->pipe_buffer.buffer = buffer;
  455         cpipe->pipe_buffer.size = size;
  456         cpipe->pipe_buffer.in = cnt;
  457         cpipe->pipe_buffer.out = 0;
  458         cpipe->pipe_buffer.cnt = cnt;
  459         atomic_add_long(&amountpipekva, cpipe->pipe_buffer.size);
  460         return (0);
  461 }
  462 
  463 /*
  464  * Wrapper for pipespace_new() that performs locking assertions.
  465  */
  466 static int
  467 pipespace(cpipe, size)
  468         struct pipe *cpipe;
  469         int size;
  470 {
  471 
  472         KASSERT(cpipe->pipe_state & PIPE_LOCKFL,
  473                 ("Unlocked pipe passed to pipespace"));
  474         return (pipespace_new(cpipe, size));
  475 }
  476 
  477 /*
  478  * lock a pipe for I/O, blocking other access
  479  */
  480 static __inline int
  481 pipelock(cpipe, catch)
  482         struct pipe *cpipe;
  483         int catch;
  484 {
  485         int error;
  486 
  487         PIPE_LOCK_ASSERT(cpipe, MA_OWNED);
  488         while (cpipe->pipe_state & PIPE_LOCKFL) {
  489                 cpipe->pipe_state |= PIPE_LWANT;
  490                 error = msleep(cpipe, PIPE_MTX(cpipe),
  491                     catch ? (PRIBIO | PCATCH) : PRIBIO,
  492                     "pipelk", 0);
  493                 if (error != 0)
  494                         return (error);
  495         }
  496         cpipe->pipe_state |= PIPE_LOCKFL;
  497         return (0);
  498 }
  499 
  500 /*
  501  * unlock a pipe I/O lock
  502  */
  503 static __inline void
  504 pipeunlock(cpipe)
  505         struct pipe *cpipe;
  506 {
  507 
  508         PIPE_LOCK_ASSERT(cpipe, MA_OWNED);
  509         KASSERT(cpipe->pipe_state & PIPE_LOCKFL,
  510                 ("Unlocked pipe passed to pipeunlock"));
  511         cpipe->pipe_state &= ~PIPE_LOCKFL;
  512         if (cpipe->pipe_state & PIPE_LWANT) {
  513                 cpipe->pipe_state &= ~PIPE_LWANT;
  514                 wakeup(cpipe);
  515         }
  516 }
  517 
  518 static __inline void
  519 pipeselwakeup(cpipe)
  520         struct pipe *cpipe;
  521 {
  522 
  523         PIPE_LOCK_ASSERT(cpipe, MA_OWNED);
  524         if (cpipe->pipe_state & PIPE_SEL) {
  525                 cpipe->pipe_state &= ~PIPE_SEL;
  526                 selwakeuppri(&cpipe->pipe_sel, PSOCK);
  527         }
  528         if ((cpipe->pipe_state & PIPE_ASYNC) && cpipe->pipe_sigio)
  529                 pgsigio(&cpipe->pipe_sigio, SIGIO, 0);
  530         KNOTE_LOCKED(&cpipe->pipe_sel.si_note, 0);
  531 }
  532 
  533 /*
  534  * Initialize and allocate VM and memory for pipe.  The structure
  535  * will start out zero'd from the ctor, so we just manage the kmem.
  536  */
  537 static int
  538 pipe_create(pipe, backing)
  539         struct pipe *pipe;
  540         int backing;
  541 {
  542         int error;
  543 
  544         if (backing) {
  545                 if (amountpipekva > maxpipekva / 2)
  546                         error = pipespace_new(pipe, SMALL_PIPE_SIZE);
  547                 else
  548                         error = pipespace_new(pipe, PIPE_SIZE);
  549         } else {
  550                 /* If we're not backing this pipe, no need to do anything. */
  551                 error = 0;
  552         }
  553         return (error);
  554 }
  555 
  556 /* ARGSUSED */
  557 static int
  558 pipe_read(fp, uio, active_cred, flags, td)
  559         struct file *fp;
  560         struct uio *uio;
  561         struct ucred *active_cred;
  562         struct thread *td;
  563         int flags;
  564 {
  565         struct pipe *rpipe = fp->f_data;
  566         int error;
  567         int nread = 0;
  568         u_int size;
  569 
  570         PIPE_LOCK(rpipe);
  571         ++rpipe->pipe_busy;
  572         error = pipelock(rpipe, 1);
  573         if (error)
  574                 goto unlocked_error;
  575 
  576 #ifdef MAC
  577         error = mac_check_pipe_read(active_cred, rpipe->pipe_pair);
  578         if (error)
  579                 goto locked_error;
  580 #endif
  581         if (amountpipekva > (3 * maxpipekva) / 4) {
  582                 if (!(rpipe->pipe_state & PIPE_DIRECTW) &&
  583                         (rpipe->pipe_buffer.size > SMALL_PIPE_SIZE) &&
  584                         (rpipe->pipe_buffer.cnt <= SMALL_PIPE_SIZE) &&
  585                         (piperesizeallowed == 1)) {
  586                         PIPE_UNLOCK(rpipe);
  587                         pipespace(rpipe, SMALL_PIPE_SIZE);
  588                         PIPE_LOCK(rpipe);
  589                 }
  590         }
  591 
  592         while (uio->uio_resid) {
  593                 /*
  594                  * normal pipe buffer receive
  595                  */
  596                 if (rpipe->pipe_buffer.cnt > 0) {
  597                         size = rpipe->pipe_buffer.size - rpipe->pipe_buffer.out;
  598                         if (size > rpipe->pipe_buffer.cnt)
  599                                 size = rpipe->pipe_buffer.cnt;
  600                         if (size > (u_int) uio->uio_resid)
  601                                 size = (u_int) uio->uio_resid;
  602 
  603                         PIPE_UNLOCK(rpipe);
  604                         error = uiomove(
  605                             &rpipe->pipe_buffer.buffer[rpipe->pipe_buffer.out],
  606                             size, uio);
  607                         PIPE_LOCK(rpipe);
  608                         if (error)
  609                                 break;
  610 
  611                         rpipe->pipe_buffer.out += size;
  612                         if (rpipe->pipe_buffer.out >= rpipe->pipe_buffer.size)
  613                                 rpipe->pipe_buffer.out = 0;
  614 
  615                         rpipe->pipe_buffer.cnt -= size;
  616 
  617                         /*
  618                          * If there is no more to read in the pipe, reset
  619                          * its pointers to the beginning.  This improves
  620                          * cache hit stats.
  621                          */
  622                         if (rpipe->pipe_buffer.cnt == 0) {
  623                                 rpipe->pipe_buffer.in = 0;
  624                                 rpipe->pipe_buffer.out = 0;
  625                         }
  626                         nread += size;
  627 #ifndef PIPE_NODIRECT
  628                 /*
  629                  * Direct copy, bypassing a kernel buffer.
  630                  */
  631                 } else if ((size = rpipe->pipe_map.cnt) &&
  632                            (rpipe->pipe_state & PIPE_DIRECTW)) {
  633                         if (size > (u_int) uio->uio_resid)
  634                                 size = (u_int) uio->uio_resid;
  635 
  636                         PIPE_UNLOCK(rpipe);
  637                         error = uiomove_fromphys(rpipe->pipe_map.ms,
  638                             rpipe->pipe_map.pos, size, uio);
  639                         PIPE_LOCK(rpipe);
  640                         if (error)
  641                                 break;
  642                         nread += size;
  643                         rpipe->pipe_map.pos += size;
  644                         rpipe->pipe_map.cnt -= size;
  645                         if (rpipe->pipe_map.cnt == 0) {
  646                                 rpipe->pipe_state &= ~PIPE_DIRECTW;
  647                                 wakeup(rpipe);
  648                         }
  649 #endif
  650                 } else {
  651                         /*
  652                          * detect EOF condition
  653                          * read returns 0 on EOF, no need to set error
  654                          */
  655                         if (rpipe->pipe_state & PIPE_EOF)
  656                                 break;
  657 
  658                         /*
  659                          * If the "write-side" has been blocked, wake it up now.
  660                          */
  661                         if (rpipe->pipe_state & PIPE_WANTW) {
  662                                 rpipe->pipe_state &= ~PIPE_WANTW;
  663                                 wakeup(rpipe);
  664                         }
  665 
  666                         /*
  667                          * Break if some data was read.
  668                          */
  669                         if (nread > 0)
  670                                 break;
  671 
  672                         /*
  673                          * Unlock the pipe buffer for our remaining processing.
  674                          * We will either break out with an error or we will
  675                          * sleep and relock to loop.
  676                          */
  677                         pipeunlock(rpipe);
  678 
  679                         /*
  680                          * Handle non-blocking mode operation or
  681                          * wait for more data.
  682                          */
  683                         if (fp->f_flag & FNONBLOCK) {
  684                                 error = EAGAIN;
  685                         } else {
  686                                 rpipe->pipe_state |= PIPE_WANTR;
  687                                 if ((error = msleep(rpipe, PIPE_MTX(rpipe),
  688                                     PRIBIO | PCATCH,
  689                                     "piperd", 0)) == 0)
  690                                         error = pipelock(rpipe, 1);
  691                         }
  692                         if (error)
  693                                 goto unlocked_error;
  694                 }
  695         }
  696 #ifdef MAC
  697 locked_error:
  698 #endif
  699         pipeunlock(rpipe);
  700 
  701         /* XXX: should probably do this before getting any locks. */
  702         if (error == 0)
  703                 vfs_timestamp(&rpipe->pipe_atime);
  704 unlocked_error:
  705         --rpipe->pipe_busy;
  706 
  707         /*
  708          * PIPE_WANT processing only makes sense if pipe_busy is 0.
  709          */
  710         if ((rpipe->pipe_busy == 0) && (rpipe->pipe_state & PIPE_WANT)) {
  711                 rpipe->pipe_state &= ~(PIPE_WANT|PIPE_WANTW);
  712                 wakeup(rpipe);
  713         } else if (rpipe->pipe_buffer.cnt < MINPIPESIZE) {
  714                 /*
  715                  * Handle write blocking hysteresis.
  716                  */
  717                 if (rpipe->pipe_state & PIPE_WANTW) {
  718                         rpipe->pipe_state &= ~PIPE_WANTW;
  719                         wakeup(rpipe);
  720                 }
  721         }
  722 
  723         if ((rpipe->pipe_buffer.size - rpipe->pipe_buffer.cnt) >= PIPE_BUF)
  724                 pipeselwakeup(rpipe);
  725 
  726         PIPE_UNLOCK(rpipe);
  727         return (error);
  728 }
  729 
  730 #ifndef PIPE_NODIRECT
  731 /*
  732  * Map the sending processes' buffer into kernel space and wire it.
  733  * This is similar to a physical write operation.
  734  */
  735 static int
  736 pipe_build_write_buffer(wpipe, uio)
  737         struct pipe *wpipe;
  738         struct uio *uio;
  739 {
  740         pmap_t pmap;
  741         u_int size;
  742         int i, j;
  743         vm_offset_t addr, endaddr;
  744 
  745         PIPE_LOCK_ASSERT(wpipe, MA_NOTOWNED);
  746         KASSERT(wpipe->pipe_state & PIPE_DIRECTW,
  747                 ("Clone attempt on non-direct write pipe!"));
  748 
  749         size = (u_int) uio->uio_iov->iov_len;
  750         if (size > wpipe->pipe_buffer.size)
  751                 size = wpipe->pipe_buffer.size;
  752 
  753         pmap = vmspace_pmap(curproc->p_vmspace);
  754         endaddr = round_page((vm_offset_t)uio->uio_iov->iov_base + size);
  755         addr = trunc_page((vm_offset_t)uio->uio_iov->iov_base);
  756         if (endaddr < addr)
  757                 return (EFAULT);
  758         for (i = 0; addr < endaddr; addr += PAGE_SIZE, i++) {
  759                 /*
  760                  * vm_fault_quick() can sleep.  Consequently,
  761                  * vm_page_lock_queue() and vm_page_unlock_queue()
  762                  * should not be performed outside of this loop.
  763                  */
  764         race:
  765                 if (vm_fault_quick((caddr_t)addr, VM_PROT_READ) < 0) {
  766                         vm_page_lock_queues();
  767                         for (j = 0; j < i; j++)
  768                                 vm_page_unhold(wpipe->pipe_map.ms[j]);
  769                         vm_page_unlock_queues();
  770                         return (EFAULT);
  771                 }
  772                 wpipe->pipe_map.ms[i] = pmap_extract_and_hold(pmap, addr,
  773                     VM_PROT_READ);
  774                 if (wpipe->pipe_map.ms[i] == NULL)
  775                         goto race;
  776         }
  777 
  778 /*
  779  * set up the control block
  780  */
  781         wpipe->pipe_map.npages = i;
  782         wpipe->pipe_map.pos =
  783             ((vm_offset_t) uio->uio_iov->iov_base) & PAGE_MASK;
  784         wpipe->pipe_map.cnt = size;
  785 
  786 /*
  787  * and update the uio data
  788  */
  789 
  790         uio->uio_iov->iov_len -= size;
  791         uio->uio_iov->iov_base = (char *)uio->uio_iov->iov_base + size;
  792         if (uio->uio_iov->iov_len == 0)
  793                 uio->uio_iov++;
  794         uio->uio_resid -= size;
  795         uio->uio_offset += size;
  796         return (0);
  797 }
  798 
  799 /*
  800  * unmap and unwire the process buffer
  801  */
  802 static void
  803 pipe_destroy_write_buffer(wpipe)
  804         struct pipe *wpipe;
  805 {
  806         int i;
  807 
  808         PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
  809         vm_page_lock_queues();
  810         for (i = 0; i < wpipe->pipe_map.npages; i++) {
  811                 vm_page_unhold(wpipe->pipe_map.ms[i]);
  812         }
  813         vm_page_unlock_queues();
  814         wpipe->pipe_map.npages = 0;
  815 }
  816 
  817 /*
  818  * In the case of a signal, the writing process might go away.  This
  819  * code copies the data into the circular buffer so that the source
  820  * pages can be freed without loss of data.
  821  */
  822 static void
  823 pipe_clone_write_buffer(wpipe)
  824         struct pipe *wpipe;
  825 {
  826         struct uio uio;
  827         struct iovec iov;
  828         int size;
  829         int pos;
  830 
  831         PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
  832         size = wpipe->pipe_map.cnt;
  833         pos = wpipe->pipe_map.pos;
  834 
  835         wpipe->pipe_buffer.in = size;
  836         wpipe->pipe_buffer.out = 0;
  837         wpipe->pipe_buffer.cnt = size;
  838         wpipe->pipe_state &= ~PIPE_DIRECTW;
  839 
  840         PIPE_UNLOCK(wpipe);
  841         iov.iov_base = wpipe->pipe_buffer.buffer;
  842         iov.iov_len = size;
  843         uio.uio_iov = &iov;
  844         uio.uio_iovcnt = 1;
  845         uio.uio_offset = 0;
  846         uio.uio_resid = size;
  847         uio.uio_segflg = UIO_SYSSPACE;
  848         uio.uio_rw = UIO_READ;
  849         uio.uio_td = curthread;
  850         uiomove_fromphys(wpipe->pipe_map.ms, pos, size, &uio);
  851         PIPE_LOCK(wpipe);
  852         pipe_destroy_write_buffer(wpipe);
  853 }
  854 
  855 /*
  856  * This implements the pipe buffer write mechanism.  Note that only
  857  * a direct write OR a normal pipe write can be pending at any given time.
  858  * If there are any characters in the pipe buffer, the direct write will
  859  * be deferred until the receiving process grabs all of the bytes from
  860  * the pipe buffer.  Then the direct mapping write is set-up.
  861  */
  862 static int
  863 pipe_direct_write(wpipe, uio)
  864         struct pipe *wpipe;
  865         struct uio *uio;
  866 {
  867         int error;
  868 
  869 retry:
  870         PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
  871         error = pipelock(wpipe, 1);
  872         if (wpipe->pipe_state & PIPE_EOF)
  873                 error = EPIPE;
  874         if (error) {
  875                 pipeunlock(wpipe);
  876                 goto error1;
  877         }
  878         while (wpipe->pipe_state & PIPE_DIRECTW) {
  879                 if (wpipe->pipe_state & PIPE_WANTR) {
  880                         wpipe->pipe_state &= ~PIPE_WANTR;
  881                         wakeup(wpipe);
  882                 }
  883                 pipeselwakeup(wpipe);
  884                 wpipe->pipe_state |= PIPE_WANTW;
  885                 pipeunlock(wpipe);
  886                 error = msleep(wpipe, PIPE_MTX(wpipe),
  887                     PRIBIO | PCATCH, "pipdww", 0);
  888                 if (error)
  889                         goto error1;
  890                 else
  891                         goto retry;
  892         }
  893         wpipe->pipe_map.cnt = 0;        /* transfer not ready yet */
  894         if (wpipe->pipe_buffer.cnt > 0) {
  895                 if (wpipe->pipe_state & PIPE_WANTR) {
  896                         wpipe->pipe_state &= ~PIPE_WANTR;
  897                         wakeup(wpipe);
  898                 }
  899                 pipeselwakeup(wpipe);
  900                 wpipe->pipe_state |= PIPE_WANTW;
  901                 pipeunlock(wpipe);
  902                 error = msleep(wpipe, PIPE_MTX(wpipe),
  903                     PRIBIO | PCATCH, "pipdwc", 0);
  904                 if (error)
  905                         goto error1;
  906                 else
  907                         goto retry;
  908         }
  909 
  910         wpipe->pipe_state |= PIPE_DIRECTW;
  911 
  912         PIPE_UNLOCK(wpipe);
  913         error = pipe_build_write_buffer(wpipe, uio);
  914         PIPE_LOCK(wpipe);
  915         if (error) {
  916                 wpipe->pipe_state &= ~PIPE_DIRECTW;
  917                 pipeunlock(wpipe);
  918                 goto error1;
  919         }
  920 
  921         error = 0;
  922         while (!error && (wpipe->pipe_state & PIPE_DIRECTW)) {
  923                 if (wpipe->pipe_state & PIPE_EOF) {
  924                         pipe_destroy_write_buffer(wpipe);
  925                         pipeselwakeup(wpipe);
  926                         pipeunlock(wpipe);
  927                         error = EPIPE;
  928                         goto error1;
  929                 }
  930                 if (wpipe->pipe_state & PIPE_WANTR) {
  931                         wpipe->pipe_state &= ~PIPE_WANTR;
  932                         wakeup(wpipe);
  933                 }
  934                 pipeselwakeup(wpipe);
  935                 pipeunlock(wpipe);
  936                 error = msleep(wpipe, PIPE_MTX(wpipe), PRIBIO | PCATCH,
  937                     "pipdwt", 0);
  938                 pipelock(wpipe, 0);
  939         }
  940 
  941         if (wpipe->pipe_state & PIPE_EOF)
  942                 error = EPIPE;
  943         if (wpipe->pipe_state & PIPE_DIRECTW) {
  944                 /*
  945                  * this bit of trickery substitutes a kernel buffer for
  946                  * the process that might be going away.
  947                  */
  948                 pipe_clone_write_buffer(wpipe);
  949         } else {
  950                 pipe_destroy_write_buffer(wpipe);
  951         }
  952         pipeunlock(wpipe);
  953         return (error);
  954 
  955 error1:
  956         wakeup(wpipe);
  957         return (error);
  958 }
  959 #endif
  960 
  961 static int
  962 pipe_write(fp, uio, active_cred, flags, td)
  963         struct file *fp;
  964         struct uio *uio;
  965         struct ucred *active_cred;
  966         struct thread *td;
  967         int flags;
  968 {
  969         int error = 0;
  970         int desiredsize, orig_resid;
  971         struct pipe *wpipe, *rpipe;
  972 
  973         rpipe = fp->f_data;
  974         wpipe = rpipe->pipe_peer;
  975 
  976         PIPE_LOCK(rpipe);
  977         error = pipelock(wpipe, 1);
  978         if (error) {
  979                 PIPE_UNLOCK(rpipe);
  980                 return (error);
  981         }
  982         /*
  983          * detect loss of pipe read side, issue SIGPIPE if lost.
  984          */
  985         if (wpipe->pipe_present != PIPE_ACTIVE ||
  986             (wpipe->pipe_state & PIPE_EOF)) {
  987                 pipeunlock(wpipe);
  988                 PIPE_UNLOCK(rpipe);
  989                 return (EPIPE);
  990         }
  991 #ifdef MAC
  992         error = mac_check_pipe_write(active_cred, wpipe->pipe_pair);
  993         if (error) {
  994                 pipeunlock(wpipe);
  995                 PIPE_UNLOCK(rpipe);
  996                 return (error);
  997         }
  998 #endif
  999         ++wpipe->pipe_busy;
 1000 
 1001         /* Choose a larger size if it's advantageous */
 1002         desiredsize = max(SMALL_PIPE_SIZE, wpipe->pipe_buffer.size);
 1003         while (desiredsize < wpipe->pipe_buffer.cnt + uio->uio_resid) {
 1004                 if (piperesizeallowed != 1)
 1005                         break;
 1006                 if (amountpipekva > maxpipekva / 2)
 1007                         break;
 1008                 if (desiredsize == BIG_PIPE_SIZE)
 1009                         break;
 1010                 desiredsize = desiredsize * 2;
 1011         }
 1012 
 1013         /* Choose a smaller size if we're in a OOM situation */
 1014         if ((amountpipekva > (3 * maxpipekva) / 4) &&
 1015                 (wpipe->pipe_buffer.size > SMALL_PIPE_SIZE) &&
 1016                 (wpipe->pipe_buffer.cnt <= SMALL_PIPE_SIZE) &&
 1017                 (piperesizeallowed == 1))
 1018                 desiredsize = SMALL_PIPE_SIZE;
 1019 
 1020         /* Resize if the above determined that a new size was necessary */
 1021         if ((desiredsize != wpipe->pipe_buffer.size) &&
 1022                 ((wpipe->pipe_state & PIPE_DIRECTW) == 0)) {
 1023                 PIPE_UNLOCK(wpipe);
 1024                 pipespace(wpipe, desiredsize);
 1025                 PIPE_LOCK(wpipe);
 1026         }
 1027         if (wpipe->pipe_buffer.size == 0) {
 1028                 /*
 1029                  * This can only happen for reverse direction use of pipes
 1030                  * in a complete OOM situation.
 1031                  */
 1032                 error = ENOMEM;
 1033                 --wpipe->pipe_busy;
 1034                 pipeunlock(wpipe);
 1035                 PIPE_UNLOCK(wpipe);
 1036                 return (error);
 1037         }
 1038 
 1039         pipeunlock(wpipe);
 1040 
 1041         orig_resid = uio->uio_resid;
 1042 
 1043         while (uio->uio_resid) {
 1044                 int space;
 1045 
 1046                 pipelock(wpipe, 0);
 1047                 if (wpipe->pipe_state & PIPE_EOF) {
 1048                         pipeunlock(wpipe);
 1049                         error = EPIPE;
 1050                         break;
 1051                 }
 1052 #ifndef PIPE_NODIRECT
 1053                 /*
 1054                  * If the transfer is large, we can gain performance if
 1055                  * we do process-to-process copies directly.
 1056                  * If the write is non-blocking, we don't use the
 1057                  * direct write mechanism.
 1058                  *
 1059                  * The direct write mechanism will detect the reader going
 1060                  * away on us.
 1061                  */
 1062                 if (uio->uio_segflg == UIO_USERSPACE &&
 1063                     uio->uio_iov->iov_len >= PIPE_MINDIRECT &&
 1064                     wpipe->pipe_buffer.size >= PIPE_MINDIRECT &&
 1065                     (fp->f_flag & FNONBLOCK) == 0) {
 1066                         pipeunlock(wpipe);
 1067                         error = pipe_direct_write(wpipe, uio);
 1068                         if (error)
 1069                                 break;
 1070                         continue;
 1071                 }
 1072 #endif
 1073 
 1074                 /*
 1075                  * Pipe buffered writes cannot be coincidental with
 1076                  * direct writes.  We wait until the currently executing
 1077                  * direct write is completed before we start filling the
 1078                  * pipe buffer.  We break out if a signal occurs or the
 1079                  * reader goes away.
 1080                  */
 1081                 if (wpipe->pipe_state & PIPE_DIRECTW) {
 1082                         if (wpipe->pipe_state & PIPE_WANTR) {
 1083                                 wpipe->pipe_state &= ~PIPE_WANTR;
 1084                                 wakeup(wpipe);
 1085                         }
 1086                         pipeselwakeup(wpipe);
 1087                         wpipe->pipe_state |= PIPE_WANTW;
 1088                         pipeunlock(wpipe);
 1089                         error = msleep(wpipe, PIPE_MTX(rpipe), PRIBIO | PCATCH,
 1090                             "pipbww", 0);
 1091                         if (error)
 1092                                 break;
 1093                         else
 1094                                 continue;
 1095                 }
 1096 
 1097                 space = wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt;
 1098 
 1099                 /* Writes of size <= PIPE_BUF must be atomic. */
 1100                 if ((space < uio->uio_resid) && (orig_resid <= PIPE_BUF))
 1101                         space = 0;
 1102 
 1103                 if (space > 0) {
 1104                         int size;       /* Transfer size */
 1105                         int segsize;    /* first segment to transfer */
 1106 
 1107                         /*
 1108                          * Transfer size is minimum of uio transfer
 1109                          * and free space in pipe buffer.
 1110                          */
 1111                         if (space > uio->uio_resid)
 1112                                 size = uio->uio_resid;
 1113                         else
 1114                                 size = space;
 1115                         /*
 1116                          * First segment to transfer is minimum of
 1117                          * transfer size and contiguous space in
 1118                          * pipe buffer.  If first segment to transfer
 1119                          * is less than the transfer size, we've got
 1120                          * a wraparound in the buffer.
 1121                          */
 1122                         segsize = wpipe->pipe_buffer.size -
 1123                                 wpipe->pipe_buffer.in;
 1124                         if (segsize > size)
 1125                                 segsize = size;
 1126 
 1127                         /* Transfer first segment */
 1128 
 1129                         PIPE_UNLOCK(rpipe);
 1130                         error = uiomove(&wpipe->pipe_buffer.buffer[wpipe->pipe_buffer.in],
 1131                                         segsize, uio);
 1132                         PIPE_LOCK(rpipe);
 1133 
 1134                         if (error == 0 && segsize < size) {
 1135                                 KASSERT(wpipe->pipe_buffer.in + segsize ==
 1136                                         wpipe->pipe_buffer.size,
 1137                                         ("Pipe buffer wraparound disappeared"));
 1138                                 /*
 1139                                  * Transfer remaining part now, to
 1140                                  * support atomic writes.  Wraparound
 1141                                  * happened.
 1142                                  */
 1143 
 1144                                 PIPE_UNLOCK(rpipe);
 1145                                 error = uiomove(
 1146                                     &wpipe->pipe_buffer.buffer[0],
 1147                                     size - segsize, uio);
 1148                                 PIPE_LOCK(rpipe);
 1149                         }
 1150                         if (error == 0) {
 1151                                 wpipe->pipe_buffer.in += size;
 1152                                 if (wpipe->pipe_buffer.in >=
 1153                                     wpipe->pipe_buffer.size) {
 1154                                         KASSERT(wpipe->pipe_buffer.in ==
 1155                                                 size - segsize +
 1156                                                 wpipe->pipe_buffer.size,
 1157                                                 ("Expected wraparound bad"));
 1158                                         wpipe->pipe_buffer.in = size - segsize;
 1159                                 }
 1160 
 1161                                 wpipe->pipe_buffer.cnt += size;
 1162                                 KASSERT(wpipe->pipe_buffer.cnt <=
 1163                                         wpipe->pipe_buffer.size,
 1164                                         ("Pipe buffer overflow"));
 1165                         }
 1166                         pipeunlock(wpipe);
 1167                         if (error != 0)
 1168                                 break;
 1169                 } else {
 1170                         /*
 1171                          * If the "read-side" has been blocked, wake it up now.
 1172                          */
 1173                         if (wpipe->pipe_state & PIPE_WANTR) {
 1174                                 wpipe->pipe_state &= ~PIPE_WANTR;
 1175                                 wakeup(wpipe);
 1176                         }
 1177 
 1178                         /*
 1179                          * don't block on non-blocking I/O
 1180                          */
 1181                         if (fp->f_flag & FNONBLOCK) {
 1182                                 error = EAGAIN;
 1183                                 pipeunlock(wpipe);
 1184                                 break;
 1185                         }
 1186 
 1187                         /*
 1188                          * We have no more space and have something to offer,
 1189                          * wake up select/poll.
 1190                          */
 1191                         pipeselwakeup(wpipe);
 1192 
 1193                         wpipe->pipe_state |= PIPE_WANTW;
 1194                         pipeunlock(wpipe);
 1195                         error = msleep(wpipe, PIPE_MTX(rpipe),
 1196                             PRIBIO | PCATCH, "pipewr", 0);
 1197                         if (error != 0)
 1198                                 break;
 1199                 }
 1200         }
 1201 
 1202         pipelock(wpipe, 0);
 1203         --wpipe->pipe_busy;
 1204 
 1205         if ((wpipe->pipe_busy == 0) && (wpipe->pipe_state & PIPE_WANT)) {
 1206                 wpipe->pipe_state &= ~(PIPE_WANT | PIPE_WANTR);
 1207                 wakeup(wpipe);
 1208         } else if (wpipe->pipe_buffer.cnt > 0) {
 1209                 /*
 1210                  * If we have put any characters in the buffer, we wake up
 1211                  * the reader.
 1212                  */
 1213                 if (wpipe->pipe_state & PIPE_WANTR) {
 1214                         wpipe->pipe_state &= ~PIPE_WANTR;
 1215                         wakeup(wpipe);
 1216                 }
 1217         }
 1218 
 1219         /*
 1220          * Don't return EPIPE if I/O was successful
 1221          */
 1222         if ((wpipe->pipe_buffer.cnt == 0) &&
 1223             (uio->uio_resid == 0) &&
 1224             (error == EPIPE)) {
 1225                 error = 0;
 1226         }
 1227 
 1228         if (error == 0)
 1229                 vfs_timestamp(&wpipe->pipe_mtime);
 1230 
 1231         /*
 1232          * We have something to offer,
 1233          * wake up select/poll.
 1234          */
 1235         if (wpipe->pipe_buffer.cnt)
 1236                 pipeselwakeup(wpipe);
 1237 
 1238         pipeunlock(wpipe);
 1239         PIPE_UNLOCK(rpipe);
 1240         return (error);
 1241 }
 1242 
 1243 /*
 1244  * we implement a very minimal set of ioctls for compatibility with sockets.
 1245  */
 1246 static int
 1247 pipe_ioctl(fp, cmd, data, active_cred, td)
 1248         struct file *fp;
 1249         u_long cmd;
 1250         void *data;
 1251         struct ucred *active_cred;
 1252         struct thread *td;
 1253 {
 1254         struct pipe *mpipe = fp->f_data;
 1255         int error;
 1256 
 1257         PIPE_LOCK(mpipe);
 1258 
 1259 #ifdef MAC
 1260         error = mac_check_pipe_ioctl(active_cred, mpipe->pipe_pair, cmd, data);
 1261         if (error) {
 1262                 PIPE_UNLOCK(mpipe);
 1263                 return (error);
 1264         }
 1265 #endif
 1266 
 1267         error = 0;
 1268         switch (cmd) {
 1269 
 1270         case FIONBIO:
 1271                 break;
 1272 
 1273         case FIOASYNC:
 1274                 if (*(int *)data) {
 1275                         mpipe->pipe_state |= PIPE_ASYNC;
 1276                 } else {
 1277                         mpipe->pipe_state &= ~PIPE_ASYNC;
 1278                 }
 1279                 break;
 1280 
 1281         case FIONREAD:
 1282                 if (mpipe->pipe_state & PIPE_DIRECTW)
 1283                         *(int *)data = mpipe->pipe_map.cnt;
 1284                 else
 1285                         *(int *)data = mpipe->pipe_buffer.cnt;
 1286                 break;
 1287 
 1288         case FIOSETOWN:
 1289                 PIPE_UNLOCK(mpipe);
 1290                 error = fsetown(*(int *)data, &mpipe->pipe_sigio);
 1291                 goto out_unlocked;
 1292 
 1293         case FIOGETOWN:
 1294                 *(int *)data = fgetown(&mpipe->pipe_sigio);
 1295                 break;
 1296 
 1297         /* This is deprecated, FIOSETOWN should be used instead. */
 1298         case TIOCSPGRP:
 1299                 PIPE_UNLOCK(mpipe);
 1300                 error = fsetown(-(*(int *)data), &mpipe->pipe_sigio);
 1301                 goto out_unlocked;
 1302 
 1303         /* This is deprecated, FIOGETOWN should be used instead. */
 1304         case TIOCGPGRP:
 1305                 *(int *)data = -fgetown(&mpipe->pipe_sigio);
 1306                 break;
 1307 
 1308         default:
 1309                 error = ENOTTY;
 1310                 break;
 1311         }
 1312         PIPE_UNLOCK(mpipe);
 1313 out_unlocked:
 1314         return (error);
 1315 }
 1316 
 1317 static int
 1318 pipe_poll(fp, events, active_cred, td)
 1319         struct file *fp;
 1320         int events;
 1321         struct ucred *active_cred;
 1322         struct thread *td;
 1323 {
 1324         struct pipe *rpipe = fp->f_data;
 1325         struct pipe *wpipe;
 1326         int revents = 0;
 1327 #ifdef MAC
 1328         int error;
 1329 #endif
 1330 
 1331         wpipe = rpipe->pipe_peer;
 1332         PIPE_LOCK(rpipe);
 1333 #ifdef MAC
 1334         error = mac_check_pipe_poll(active_cred, rpipe->pipe_pair);
 1335         if (error)
 1336                 goto locked_error;
 1337 #endif
 1338         if (events & (POLLIN | POLLRDNORM))
 1339                 if ((rpipe->pipe_state & PIPE_DIRECTW) ||
 1340                     (rpipe->pipe_buffer.cnt > 0) ||
 1341                     (rpipe->pipe_state & PIPE_EOF))
 1342                         revents |= events & (POLLIN | POLLRDNORM);
 1343 
 1344         if (events & (POLLOUT | POLLWRNORM))
 1345                 if (wpipe->pipe_present != PIPE_ACTIVE ||
 1346                     (wpipe->pipe_state & PIPE_EOF) ||
 1347                     (((wpipe->pipe_state & PIPE_DIRECTW) == 0) &&
 1348                      (wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt) >= PIPE_BUF))
 1349                         revents |= events & (POLLOUT | POLLWRNORM);
 1350 
 1351         if ((rpipe->pipe_state & PIPE_EOF) ||
 1352             wpipe->pipe_present != PIPE_ACTIVE ||
 1353             (wpipe->pipe_state & PIPE_EOF))
 1354                 revents |= POLLHUP;
 1355 
 1356         if (revents == 0) {
 1357                 if (events & (POLLIN | POLLRDNORM)) {
 1358                         selrecord(td, &rpipe->pipe_sel);
 1359                         rpipe->pipe_state |= PIPE_SEL;
 1360                 }
 1361 
 1362                 if (events & (POLLOUT | POLLWRNORM)) {
 1363                         selrecord(td, &wpipe->pipe_sel);
 1364                         wpipe->pipe_state |= PIPE_SEL;
 1365                 }
 1366         }
 1367 #ifdef MAC
 1368 locked_error:
 1369 #endif
 1370         PIPE_UNLOCK(rpipe);
 1371 
 1372         return (revents);
 1373 }
 1374 
 1375 /*
 1376  * We shouldn't need locks here as we're doing a read and this should
 1377  * be a natural race.
 1378  */
 1379 static int
 1380 pipe_stat(fp, ub, active_cred, td)
 1381         struct file *fp;
 1382         struct stat *ub;
 1383         struct ucred *active_cred;
 1384         struct thread *td;
 1385 {
 1386         struct pipe *pipe = fp->f_data;
 1387 #ifdef MAC
 1388         int error;
 1389 
 1390         PIPE_LOCK(pipe);
 1391         error = mac_check_pipe_stat(active_cred, pipe->pipe_pair);
 1392         PIPE_UNLOCK(pipe);
 1393         if (error)
 1394                 return (error);
 1395 #endif
 1396         bzero(ub, sizeof(*ub));
 1397         ub->st_mode = S_IFIFO;
 1398         ub->st_blksize = PAGE_SIZE;
 1399         if (pipe->pipe_state & PIPE_DIRECTW)
 1400                 ub->st_size = pipe->pipe_map.cnt;
 1401         else
 1402                 ub->st_size = pipe->pipe_buffer.cnt;
 1403         ub->st_blocks = (ub->st_size + ub->st_blksize - 1) / ub->st_blksize;
 1404         ub->st_atimespec = pipe->pipe_atime;
 1405         ub->st_mtimespec = pipe->pipe_mtime;
 1406         ub->st_ctimespec = pipe->pipe_ctime;
 1407         ub->st_uid = fp->f_cred->cr_uid;
 1408         ub->st_gid = fp->f_cred->cr_gid;
 1409         /*
 1410          * Left as 0: st_dev, st_ino, st_nlink, st_rdev, st_flags, st_gen.
 1411          * XXX (st_dev, st_ino) should be unique.
 1412          */
 1413         return (0);
 1414 }
 1415 
 1416 /* ARGSUSED */
 1417 static int
 1418 pipe_close(fp, td)
 1419         struct file *fp;
 1420         struct thread *td;
 1421 {
 1422         struct pipe *cpipe = fp->f_data;
 1423 
 1424         fp->f_ops = &badfileops;
 1425         fp->f_data = NULL;
 1426         funsetown(&cpipe->pipe_sigio);
 1427         pipeclose(cpipe);
 1428         return (0);
 1429 }
 1430 
 1431 static void
 1432 pipe_free_kmem(cpipe)
 1433         struct pipe *cpipe;
 1434 {
 1435 
 1436         KASSERT(!mtx_owned(PIPE_MTX(cpipe)),
 1437             ("pipe_free_kmem: pipe mutex locked"));
 1438 
 1439         if (cpipe->pipe_buffer.buffer != NULL) {
 1440                 atomic_subtract_long(&amountpipekva, cpipe->pipe_buffer.size);
 1441                 vm_map_remove(pipe_map,
 1442                     (vm_offset_t)cpipe->pipe_buffer.buffer,
 1443                     (vm_offset_t)cpipe->pipe_buffer.buffer + cpipe->pipe_buffer.size);
 1444                 cpipe->pipe_buffer.buffer = NULL;
 1445         }
 1446 #ifndef PIPE_NODIRECT
 1447         {
 1448                 cpipe->pipe_map.cnt = 0;
 1449                 cpipe->pipe_map.pos = 0;
 1450                 cpipe->pipe_map.npages = 0;
 1451         }
 1452 #endif
 1453 }
 1454 
 1455 /*
 1456  * shutdown the pipe
 1457  */
 1458 static void
 1459 pipeclose(cpipe)
 1460         struct pipe *cpipe;
 1461 {
 1462         struct pipepair *pp;
 1463         struct pipe *ppipe;
 1464 
 1465         KASSERT(cpipe != NULL, ("pipeclose: cpipe == NULL"));
 1466 
 1467         PIPE_LOCK(cpipe);
 1468         pipelock(cpipe, 0);
 1469         pp = cpipe->pipe_pair;
 1470 
 1471         pipeselwakeup(cpipe);
 1472 
 1473         /*
 1474          * If the other side is blocked, wake it up saying that
 1475          * we want to close it down.
 1476          */
 1477         cpipe->pipe_state |= PIPE_EOF;
 1478         while (cpipe->pipe_busy) {
 1479                 wakeup(cpipe);
 1480                 cpipe->pipe_state |= PIPE_WANT;
 1481                 pipeunlock(cpipe);
 1482                 msleep(cpipe, PIPE_MTX(cpipe), PRIBIO, "pipecl", 0);
 1483                 pipelock(cpipe, 0);
 1484         }
 1485 
 1486 
 1487         /*
 1488          * Disconnect from peer, if any.
 1489          */
 1490         ppipe = cpipe->pipe_peer;
 1491         if (ppipe->pipe_present == PIPE_ACTIVE) {
 1492                 pipeselwakeup(ppipe);
 1493 
 1494                 ppipe->pipe_state |= PIPE_EOF;
 1495                 wakeup(ppipe);
 1496                 KNOTE_LOCKED(&ppipe->pipe_sel.si_note, 0);
 1497         }
 1498 
 1499         /*
 1500          * Mark this endpoint as free.  Release kmem resources.  We
 1501          * don't mark this endpoint as unused until we've finished
 1502          * doing that, or the pipe might disappear out from under
 1503          * us.
 1504          */
 1505         PIPE_UNLOCK(cpipe);
 1506         pipe_free_kmem(cpipe);
 1507         PIPE_LOCK(cpipe);
 1508         cpipe->pipe_present = PIPE_CLOSING;
 1509         pipeunlock(cpipe);
 1510 
 1511         /*
 1512          * knlist_clear() may sleep dropping the PIPE_MTX. Set the
 1513          * PIPE_FINALIZED, that allows other end to free the
 1514          * pipe_pair, only after the knotes are completely dismantled.
 1515          */
 1516         knlist_clear(&cpipe->pipe_sel.si_note, 1);
 1517         cpipe->pipe_present = PIPE_FINALIZED;
 1518         knlist_destroy(&cpipe->pipe_sel.si_note);
 1519 
 1520         /*
 1521          * If both endpoints are now closed, release the memory for the
 1522          * pipe pair.  If not, unlock.
 1523          */
 1524         if (ppipe->pipe_present == PIPE_FINALIZED) {
 1525                 PIPE_UNLOCK(cpipe);
 1526 #ifdef MAC
 1527                 mac_destroy_pipe(pp);
 1528 #endif
 1529                 uma_zfree(pipe_zone, cpipe->pipe_pair);
 1530         } else
 1531                 PIPE_UNLOCK(cpipe);
 1532 }
 1533 
 1534 /*ARGSUSED*/
 1535 static int
 1536 pipe_kqfilter(struct file *fp, struct knote *kn)
 1537 {
 1538         struct pipe *cpipe;
 1539 
 1540         cpipe = kn->kn_fp->f_data;
 1541         PIPE_LOCK(cpipe);
 1542         switch (kn->kn_filter) {
 1543         case EVFILT_READ:
 1544                 kn->kn_fop = &pipe_rfiltops;
 1545                 break;
 1546         case EVFILT_WRITE:
 1547                 kn->kn_fop = &pipe_wfiltops;
 1548                 if (cpipe->pipe_peer->pipe_present != PIPE_ACTIVE) {
 1549                         /* other end of pipe has been closed */
 1550                         PIPE_UNLOCK(cpipe);
 1551                         return (EPIPE);
 1552                 }
 1553                 cpipe = cpipe->pipe_peer;
 1554                 break;
 1555         default:
 1556                 PIPE_UNLOCK(cpipe);
 1557                 return (EINVAL);
 1558         }
 1559 
 1560         knlist_add(&cpipe->pipe_sel.si_note, kn, 1);
 1561         PIPE_UNLOCK(cpipe);
 1562         return (0);
 1563 }
 1564 
 1565 static void
 1566 filt_pipedetach(struct knote *kn)
 1567 {
 1568         struct pipe *cpipe = (struct pipe *)kn->kn_fp->f_data;
 1569 
 1570         PIPE_LOCK(cpipe);
 1571         if (kn->kn_filter == EVFILT_WRITE)
 1572                 cpipe = cpipe->pipe_peer;
 1573         knlist_remove(&cpipe->pipe_sel.si_note, kn, 1);
 1574         PIPE_UNLOCK(cpipe);
 1575 }
 1576 
 1577 /*ARGSUSED*/
 1578 static int
 1579 filt_piperead(struct knote *kn, long hint)
 1580 {
 1581         struct pipe *rpipe = kn->kn_fp->f_data;
 1582         struct pipe *wpipe = rpipe->pipe_peer;
 1583         int ret;
 1584 
 1585         PIPE_LOCK(rpipe);
 1586         kn->kn_data = rpipe->pipe_buffer.cnt;
 1587         if ((kn->kn_data == 0) && (rpipe->pipe_state & PIPE_DIRECTW))
 1588                 kn->kn_data = rpipe->pipe_map.cnt;
 1589 
 1590         if ((rpipe->pipe_state & PIPE_EOF) ||
 1591             wpipe->pipe_present != PIPE_ACTIVE ||
 1592             (wpipe->pipe_state & PIPE_EOF)) {
 1593                 kn->kn_flags |= EV_EOF;
 1594                 PIPE_UNLOCK(rpipe);
 1595                 return (1);
 1596         }
 1597         ret = kn->kn_data > 0;
 1598         PIPE_UNLOCK(rpipe);
 1599         return ret;
 1600 }
 1601 
 1602 /*ARGSUSED*/
 1603 static int
 1604 filt_pipewrite(struct knote *kn, long hint)
 1605 {
 1606         struct pipe *rpipe = kn->kn_fp->f_data;
 1607         struct pipe *wpipe = rpipe->pipe_peer;
 1608 
 1609         PIPE_LOCK(rpipe);
 1610         if (wpipe->pipe_present != PIPE_ACTIVE ||
 1611             (wpipe->pipe_state & PIPE_EOF)) {
 1612                 kn->kn_data = 0;
 1613                 kn->kn_flags |= EV_EOF;
 1614                 PIPE_UNLOCK(rpipe);
 1615                 return (1);
 1616         }
 1617         kn->kn_data = wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt;
 1618         if (wpipe->pipe_state & PIPE_DIRECTW)
 1619                 kn->kn_data = 0;
 1620 
 1621         PIPE_UNLOCK(rpipe);
 1622         return (kn->kn_data >= PIPE_BUF);
 1623 }

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