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

     /*-
      * Copyright (c) 1996 John S. Dyson
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
      *    notice immediately at the beginning of the file, without modification,
     *    this list of conditions, and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Absolutely no warranty of function or purpose is made by the author
     *    John S. Dyson.
     * 4. Modifications may be freely made to this file if the above conditions
     *    are met.
     */
    
    /*
     * This file contains a high-performance replacement for the socket-based
     * pipes scheme originally used in FreeBSD/4.4Lite.  It does not support
     * all features of sockets, but does do everything that pipes normally
     * do.
     */
    
    /*
     * This code has two modes of operation, a small write mode and a large
     * write mode.  The small write mode acts like conventional pipes with
     * a kernel buffer.  If the buffer is less than PIPE_MINDIRECT, then the
     * "normal" pipe buffering is done.  If the buffer is between PIPE_MINDIRECT
     * and PIPE_SIZE in size, the sending process pins the underlying pages in
     * memory, and the receiving process copies directly from these pinned pages
     * in the sending process.
     *
     * If the sending process receives a signal, it is possible that it will
     * go away, and certainly its address space can change, because control
     * is returned back to the user-mode side.  In that case, the pipe code
     * arranges to copy the buffer supplied by the user process, to a pageable
     * kernel buffer, and the receiving process will grab the data from the
     * pageable kernel buffer.  Since signals don't happen all that often,
     * the copy operation is normally eliminated.
     *
     * The constant PIPE_MINDIRECT is chosen to make sure that buffering will
     * happen for small transfers so that the system will not spend all of
     * its time context switching.
     *
     * In order to limit the resource use of pipes, two sysctls exist:
     *
     * kern.ipc.maxpipekva - This is a hard limit on the amount of pageable
     * address space available to us in pipe_map. This value is normally
     * autotuned, but may also be loader tuned.
     *
     * kern.ipc.pipekva - This read-only sysctl tracks the current amount of
     * memory in use by pipes.
     *
     * Based on how large pipekva is relative to maxpipekva, the following
     * will happen:
     *
     * 0% - 50%:
     *     New pipes are given 16K of memory backing, pipes may dynamically
     *     grow to as large as 64K where needed.
     * 50% - 75%:
     *     New pipes are given 4K (or PAGE_SIZE) of memory backing,
     *     existing pipes may NOT grow.
     * 75% - 100%:
     *     New pipes are given 4K (or PAGE_SIZE) of memory backing,
     *     existing pipes will be shrunk down to 4K whenever possible.
     *
     * Resizing may be disabled by setting kern.ipc.piperesizeallowed=0.  If
     * that is set,  the only resize that will occur is the 0 -> SMALL_PIPE_SIZE
     * resize which MUST occur for reverse-direction pipes when they are
     * first used.
     *
     * Additional information about the current state of pipes may be obtained
     * from kern.ipc.pipes, kern.ipc.pipefragretry, kern.ipc.pipeallocfail,
     * and kern.ipc.piperesizefail.
     *
     * Locking rules:  There are two locks present here:  A mutex, used via
     * PIPE_LOCK, and a flag, used via pipelock().  All locking is done via
     * the flag, as mutexes can not persist over uiomove.  The mutex
     * exists only to guard access to the flag, and is not in itself a
     * locking mechanism.  Also note that there is only a single mutex for
     * both directions of a pipe.
     *
     * As pipelock() may have to sleep before it can acquire the flag, it
     * is important to reread all data after a call to pipelock(); everything
     * in the structure may have changed.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/conf.h>
    #include <sys/fcntl.h>
    #include <sys/file.h>
    #include <sys/filedesc.h>
   #include <sys/filio.h>
   #include <sys/kernel.h>
   #include <sys/lock.h>
   #include <sys/mutex.h>
   #include <sys/ttycom.h>
   #include <sys/stat.h>
   #include <sys/malloc.h>
   #include <sys/poll.h>
   #include <sys/selinfo.h>
   #include <sys/signalvar.h>
   #include <sys/syscallsubr.h>
   #include <sys/sysctl.h>
   #include <sys/sysproto.h>
   #include <sys/pipe.h>
   #include <sys/proc.h>
   #include <sys/vnode.h>
   #include <sys/uio.h>
   #include <sys/event.h>
   
   #include <security/mac/mac_framework.h>
   
   #include <vm/vm.h>
   #include <vm/vm_param.h>
   #include <vm/vm_object.h>
   #include <vm/vm_kern.h>
   #include <vm/vm_extern.h>
   #include <vm/pmap.h>
   #include <vm/vm_map.h>
   #include <vm/vm_page.h>
   #include <vm/uma.h>
   
   /* XXX */
   int     do_pipe(struct thread *td, int fildes[2], int flags);
   
   /*
    * Use this define if you want to disable *fancy* VM things.  Expect an
    * approx 30% decrease in transfer rate.  This could be useful for
    * NetBSD or OpenBSD.
    */
   /* #define PIPE_NODIRECT */
   
   /*
    * interfaces to the outside world
    */
   static fo_rdwr_t        pipe_read;
   static fo_rdwr_t        pipe_write;
   static fo_truncate_t    pipe_truncate;
   static fo_ioctl_t       pipe_ioctl;
   static fo_poll_t        pipe_poll;
   static fo_kqfilter_t    pipe_kqfilter;
   static fo_stat_t        pipe_stat;
   static fo_close_t       pipe_close;
   
   static struct fileops pipeops = {
           .fo_read = pipe_read,
           .fo_write = pipe_write,
           .fo_truncate = pipe_truncate,
           .fo_ioctl = pipe_ioctl,
           .fo_poll = pipe_poll,
           .fo_kqfilter = pipe_kqfilter,
           .fo_stat = pipe_stat,
           .fo_close = pipe_close,
           .fo_chmod = invfo_chmod,
           .fo_chown = invfo_chown,
           .fo_flags = DFLAG_PASSABLE
   };
   
   static void     filt_pipedetach(struct knote *kn);
   static int      filt_piperead(struct knote *kn, long hint);
   static int      filt_pipewrite(struct knote *kn, long hint);
   
   static struct filterops pipe_rfiltops = {
           .f_isfd = 1,
           .f_detach = filt_pipedetach,
           .f_event = filt_piperead
   };
   static struct filterops pipe_wfiltops = {
           .f_isfd = 1,
           .f_detach = filt_pipedetach,
           .f_event = filt_pipewrite
   };
   
   /*
    * Default pipe buffer size(s), this can be kind-of large now because pipe
    * space is pageable.  The pipe code will try to maintain locality of
    * reference for performance reasons, so small amounts of outstanding I/O
    * will not wipe the cache.
    */
   #define MINPIPESIZE (PIPE_SIZE/3)
   #define MAXPIPESIZE (2*PIPE_SIZE/3)
   
   static long amountpipekva;
   static int pipefragretry;
   static int pipeallocfail;
   static int piperesizefail;
   static int piperesizeallowed = 1;
   
   SYSCTL_LONG(_kern_ipc, OID_AUTO, maxpipekva, CTLFLAG_RDTUN,
              &maxpipekva, 0, "Pipe KVA limit");
   SYSCTL_LONG(_kern_ipc, OID_AUTO, pipekva, CTLFLAG_RD,
              &amountpipekva, 0, "Pipe KVA usage");
   SYSCTL_INT(_kern_ipc, OID_AUTO, pipefragretry, CTLFLAG_RD,
             &pipefragretry, 0, "Pipe allocation retries due to fragmentation");
   SYSCTL_INT(_kern_ipc, OID_AUTO, pipeallocfail, CTLFLAG_RD,
             &pipeallocfail, 0, "Pipe allocation failures");
   SYSCTL_INT(_kern_ipc, OID_AUTO, piperesizefail, CTLFLAG_RD,
             &piperesizefail, 0, "Pipe resize failures");
   SYSCTL_INT(_kern_ipc, OID_AUTO, piperesizeallowed, CTLFLAG_RW,
             &piperesizeallowed, 0, "Pipe resizing allowed");
   
   static void pipeinit(void *dummy __unused);
   static void pipeclose(struct pipe *cpipe);
   static void pipe_free_kmem(struct pipe *cpipe);
   static int pipe_create(struct pipe *pipe, int backing);
   static __inline int pipelock(struct pipe *cpipe, int catch);
   static __inline void pipeunlock(struct pipe *cpipe);
   static __inline void pipeselwakeup(struct pipe *cpipe);
   #ifndef PIPE_NODIRECT
   static int pipe_build_write_buffer(struct pipe *wpipe, struct uio *uio);
   static void pipe_destroy_write_buffer(struct pipe *wpipe);
   static int pipe_direct_write(struct pipe *wpipe, struct uio *uio);
   static void pipe_clone_write_buffer(struct pipe *wpipe);
   #endif
   static int pipespace(struct pipe *cpipe, int size);
   static int pipespace_new(struct pipe *cpipe, int size);
   
   static int      pipe_zone_ctor(void *mem, int size, void *arg, int flags);
   static int      pipe_zone_init(void *mem, int size, int flags);
   static void     pipe_zone_fini(void *mem, int size);
   
   static uma_zone_t pipe_zone;
   static struct unrhdr *pipeino_unr;
   static dev_t pipedev_ino;
   
   SYSINIT(vfs, SI_SUB_VFS, SI_ORDER_ANY, pipeinit, NULL);
   
   static void
   pipeinit(void *dummy __unused)
   {
   
           pipe_zone = uma_zcreate("pipe", sizeof(struct pipepair),
               pipe_zone_ctor, NULL, pipe_zone_init, pipe_zone_fini,
               UMA_ALIGN_PTR, 0);
           KASSERT(pipe_zone != NULL, ("pipe_zone not initialized"));
           pipeino_unr = new_unrhdr(1, INT32_MAX, NULL);
           KASSERT(pipeino_unr != NULL, ("pipe fake inodes not initialized"));
           pipedev_ino = devfs_alloc_cdp_inode();
           KASSERT(pipedev_ino > 0, ("pipe dev inode not initialized"));
   }
   
   static int
   pipe_zone_ctor(void *mem, int size, void *arg, int flags)
   {
           struct pipepair *pp;
           struct pipe *rpipe, *wpipe;
   
           KASSERT(size == sizeof(*pp), ("pipe_zone_ctor: wrong size"));
   
           pp = (struct pipepair *)mem;
   
           /*
            * We zero both pipe endpoints to make sure all the kmem pointers
            * are NULL, flag fields are zero'd, etc.  We timestamp both
            * endpoints with the same time.
            */
           rpipe = &pp->pp_rpipe;
           bzero(rpipe, sizeof(*rpipe));
           vfs_timestamp(&rpipe->pipe_ctime);
           rpipe->pipe_atime = rpipe->pipe_mtime = rpipe->pipe_ctime;
   
           wpipe = &pp->pp_wpipe;
           bzero(wpipe, sizeof(*wpipe));
           wpipe->pipe_ctime = rpipe->pipe_ctime;
           wpipe->pipe_atime = wpipe->pipe_mtime = rpipe->pipe_ctime;
   
           rpipe->pipe_peer = wpipe;
           rpipe->pipe_pair = pp;
           wpipe->pipe_peer = rpipe;
           wpipe->pipe_pair = pp;
   
           /*
            * Mark both endpoints as present; they will later get free'd
            * one at a time.  When both are free'd, then the whole pair
            * is released.
            */
           rpipe->pipe_present = PIPE_ACTIVE;
           wpipe->pipe_present = PIPE_ACTIVE;
   
           /*
            * Eventually, the MAC Framework may initialize the label
            * in ctor or init, but for now we do it elswhere to avoid
            * blocking in ctor or init.
            */
           pp->pp_label = NULL;
   
           return (0);
   }
   
   static int
   pipe_zone_init(void *mem, int size, int flags)
   {
           struct pipepair *pp;
   
           KASSERT(size == sizeof(*pp), ("pipe_zone_init: wrong size"));
   
           pp = (struct pipepair *)mem;
   
           mtx_init(&pp->pp_mtx, "pipe mutex", NULL, MTX_DEF | MTX_RECURSE);
           return (0);
   }
   
   static void
   pipe_zone_fini(void *mem, int size)
   {
           struct pipepair *pp;
   
           KASSERT(size == sizeof(*pp), ("pipe_zone_fini: wrong size"));
   
           pp = (struct pipepair *)mem;
   
           mtx_destroy(&pp->pp_mtx);
   }
   
   /*
    * The pipe system call for the DTYPE_PIPE type of pipes.  If we fail, let
    * the zone pick up the pieces via pipeclose().
    */
   int
   kern_pipe(struct thread *td, int fildes[2])
   {
   
           return (do_pipe(td, fildes, 0));
   }
   
   int
   do_pipe(struct thread *td, int fildes[2], int flags)
   {
           struct filedesc *fdp = td->td_proc->p_fd;
           struct file *rf, *wf;
           struct pipepair *pp;
           struct pipe *rpipe, *wpipe;
           int fd, fflags, error;
   
           pp = uma_zalloc(pipe_zone, M_WAITOK);
   #ifdef MAC
           /*
            * The MAC label is shared between the connected endpoints.  As a
            * result mac_pipe_init() and mac_pipe_create() are called once
            * for the pair, and not on the endpoints.
            */
           mac_pipe_init(pp);
           mac_pipe_create(td->td_ucred, pp);
   #endif
           rpipe = &pp->pp_rpipe;
           wpipe = &pp->pp_wpipe;
   
           knlist_init_mtx(&rpipe->pipe_sel.si_note, PIPE_MTX(rpipe));
           knlist_init_mtx(&wpipe->pipe_sel.si_note, PIPE_MTX(wpipe));
   
           /* Only the forward direction pipe is backed by default */
           if ((error = pipe_create(rpipe, 1)) != 0 ||
               (error = pipe_create(wpipe, 0)) != 0) {
                   pipeclose(rpipe);
                   pipeclose(wpipe);
                   return (error);
           }
   
           rpipe->pipe_state |= PIPE_DIRECTOK;
           wpipe->pipe_state |= PIPE_DIRECTOK;
   
           error = falloc(td, &rf, &fd, flags);
           if (error) {
                   pipeclose(rpipe);
                   pipeclose(wpipe);
                   return (error);
           }
           /* An extra reference on `rf' has been held for us by falloc(). */
           fildes[0] = fd;
   
           fflags = FREAD | FWRITE;
           if ((flags & O_NONBLOCK) != 0)
                   fflags |= FNONBLOCK;
   
           /*
            * Warning: once we've gotten past allocation of the fd for the
            * read-side, we can only drop the read side via fdrop() in order
            * to avoid races against processes which manage to dup() the read
            * side while we are blocked trying to allocate the write side.
            */
           finit(rf, fflags, DTYPE_PIPE, rpipe, &pipeops);
           error = falloc(td, &wf, &fd, flags);
           if (error) {
                   fdclose(fdp, rf, fildes[0], td);
                   fdrop(rf, td);
                   /* rpipe has been closed by fdrop(). */
                   pipeclose(wpipe);
                   return (error);
           }
           /* An extra reference on `wf' has been held for us by falloc(). */
           finit(wf, fflags, DTYPE_PIPE, wpipe, &pipeops);
           fdrop(wf, td);
           fildes[1] = fd;
           fdrop(rf, td);
   
           return (0);
   }
   
   /* ARGSUSED */
   int
   sys_pipe(struct thread *td, struct pipe_args *uap)
   {
           int error;
           int fildes[2];
   
           error = kern_pipe(td, fildes);
           if (error)
                   return (error);
           
           td->td_retval[0] = fildes[0];
           td->td_retval[1] = fildes[1];
   
           return (0);
   }
   
   /*
    * Allocate kva for pipe circular buffer, the space is pageable
    * This routine will 'realloc' the size of a pipe safely, if it fails
    * it will retain the old buffer.
    * If it fails it will return ENOMEM.
    */
   static int
   pipespace_new(cpipe, size)
           struct pipe *cpipe;
           int size;
   {
           caddr_t buffer;
           int error, cnt, firstseg;
           static int curfail = 0;
           static struct timeval lastfail;
   
           KASSERT(!mtx_owned(PIPE_MTX(cpipe)), ("pipespace: pipe mutex locked"));
           KASSERT(!(cpipe->pipe_state & PIPE_DIRECTW),
                   ("pipespace: resize of direct writes not allowed"));
   retry:
           cnt = cpipe->pipe_buffer.cnt;
           if (cnt > size)
                   size = cnt;
   
           size = round_page(size);
           buffer = (caddr_t) vm_map_min(pipe_map);
   
           error = vm_map_find(pipe_map, NULL, 0,
                   (vm_offset_t *) &buffer, size, 1,
                   VM_PROT_ALL, VM_PROT_ALL, 0);
           if (error != KERN_SUCCESS) {
                   if ((cpipe->pipe_buffer.buffer == NULL) &&
                           (size > SMALL_PIPE_SIZE)) {
                           size = SMALL_PIPE_SIZE;
                           pipefragretry++;
                           goto retry;
                   }
                   if (cpipe->pipe_buffer.buffer == NULL) {
                           pipeallocfail++;
                           if (ppsratecheck(&lastfail, &curfail, 1))
                                   printf("kern.ipc.maxpipekva exceeded; see tuning(7)\n");
                   } else {
                           piperesizefail++;
                   }
                   return (ENOMEM);
           }
   
           /* copy data, then free old resources if we're resizing */
           if (cnt > 0) {
                   if (cpipe->pipe_buffer.in <= cpipe->pipe_buffer.out) {
                           firstseg = cpipe->pipe_buffer.size - cpipe->pipe_buffer.out;
                           bcopy(&cpipe->pipe_buffer.buffer[cpipe->pipe_buffer.out],
                                   buffer, firstseg);
                           if ((cnt - firstseg) > 0)
                                   bcopy(cpipe->pipe_buffer.buffer, &buffer[firstseg],
                                           cpipe->pipe_buffer.in);
                   } else {
                           bcopy(&cpipe->pipe_buffer.buffer[cpipe->pipe_buffer.out],
                                   buffer, cnt);
                   }
           }
           pipe_free_kmem(cpipe);
           cpipe->pipe_buffer.buffer = buffer;
           cpipe->pipe_buffer.size = size;
           cpipe->pipe_buffer.in = cnt;
           cpipe->pipe_buffer.out = 0;
           cpipe->pipe_buffer.cnt = cnt;
           atomic_add_long(&amountpipekva, cpipe->pipe_buffer.size);
           return (0);
   }
   
   /*
    * Wrapper for pipespace_new() that performs locking assertions.
    */
   static int
   pipespace(cpipe, size)
           struct pipe *cpipe;
           int size;
   {
   
           KASSERT(cpipe->pipe_state & PIPE_LOCKFL,
                   ("Unlocked pipe passed to pipespace"));
           return (pipespace_new(cpipe, size));
   }
   
   /*
    * lock a pipe for I/O, blocking other access
    */
   static __inline int
   pipelock(cpipe, catch)
           struct pipe *cpipe;
           int catch;
   {
           int error;
   
           PIPE_LOCK_ASSERT(cpipe, MA_OWNED);
           while (cpipe->pipe_state & PIPE_LOCKFL) {
                   cpipe->pipe_state |= PIPE_LWANT;
                   error = msleep(cpipe, PIPE_MTX(cpipe),
                       catch ? (PRIBIO | PCATCH) : PRIBIO,
                       "pipelk", 0);
                   if (error != 0)
                           return (error);
           }
           cpipe->pipe_state |= PIPE_LOCKFL;
           return (0);
   }
   
   /*
    * unlock a pipe I/O lock
    */
   static __inline void
   pipeunlock(cpipe)
           struct pipe *cpipe;
   {
   
           PIPE_LOCK_ASSERT(cpipe, MA_OWNED);
           KASSERT(cpipe->pipe_state & PIPE_LOCKFL,
                   ("Unlocked pipe passed to pipeunlock"));
           cpipe->pipe_state &= ~PIPE_LOCKFL;
           if (cpipe->pipe_state & PIPE_LWANT) {
                   cpipe->pipe_state &= ~PIPE_LWANT;
                   wakeup(cpipe);
           }
   }
   
   static __inline void
   pipeselwakeup(cpipe)
           struct pipe *cpipe;
   {
   
           PIPE_LOCK_ASSERT(cpipe, MA_OWNED);
           if (cpipe->pipe_state & PIPE_SEL) {
                   selwakeuppri(&cpipe->pipe_sel, PSOCK);
                   if (!SEL_WAITING(&cpipe->pipe_sel))
                           cpipe->pipe_state &= ~PIPE_SEL;
           }
           if ((cpipe->pipe_state & PIPE_ASYNC) && cpipe->pipe_sigio)
                   pgsigio(&cpipe->pipe_sigio, SIGIO, 0);
           KNOTE_LOCKED(&cpipe->pipe_sel.si_note, 0);
   }
   
   /*
    * Initialize and allocate VM and memory for pipe.  The structure
    * will start out zero'd from the ctor, so we just manage the kmem.
    */
   static int
   pipe_create(pipe, backing)
           struct pipe *pipe;
           int backing;
   {
           int error;
   
           if (backing) {
                   if (amountpipekva > maxpipekva / 2)
                           error = pipespace_new(pipe, SMALL_PIPE_SIZE);
                   else
                           error = pipespace_new(pipe, PIPE_SIZE);
           } else {
                   /* If we're not backing this pipe, no need to do anything. */
                   error = 0;
           }
           pipe->pipe_ino = -1;
           return (error);
   }
   
   /* ARGSUSED */
   static int
   pipe_read(fp, uio, active_cred, flags, td)
           struct file *fp;
           struct uio *uio;
           struct ucred *active_cred;
           struct thread *td;
           int flags;
   {
           struct pipe *rpipe = fp->f_data;
           int error;
           int nread = 0;
           int size;
   
           PIPE_LOCK(rpipe);
           ++rpipe->pipe_busy;
           error = pipelock(rpipe, 1);
           if (error)
                   goto unlocked_error;
   
   #ifdef MAC
           error = mac_pipe_check_read(active_cred, rpipe->pipe_pair);
           if (error)
                   goto locked_error;
   #endif
           if (amountpipekva > (3 * maxpipekva) / 4) {
                   if (!(rpipe->pipe_state & PIPE_DIRECTW) &&
                           (rpipe->pipe_buffer.size > SMALL_PIPE_SIZE) &&
                           (rpipe->pipe_buffer.cnt <= SMALL_PIPE_SIZE) &&
                           (piperesizeallowed == 1)) {
                           PIPE_UNLOCK(rpipe);
                           pipespace(rpipe, SMALL_PIPE_SIZE);
                           PIPE_LOCK(rpipe);
                   }
           }
   
           while (uio->uio_resid) {
                   /*
                    * normal pipe buffer receive
                    */
                   if (rpipe->pipe_buffer.cnt > 0) {
                           size = rpipe->pipe_buffer.size - rpipe->pipe_buffer.out;
                           if (size > rpipe->pipe_buffer.cnt)
                                   size = rpipe->pipe_buffer.cnt;
                           if (size > uio->uio_resid)
                                   size = uio->uio_resid;
   
                           PIPE_UNLOCK(rpipe);
                           error = uiomove(
                               &rpipe->pipe_buffer.buffer[rpipe->pipe_buffer.out],
                               size, uio);
                           PIPE_LOCK(rpipe);
                           if (error)
                                   break;
   
                           rpipe->pipe_buffer.out += size;
                           if (rpipe->pipe_buffer.out >= rpipe->pipe_buffer.size)
                                   rpipe->pipe_buffer.out = 0;
   
                           rpipe->pipe_buffer.cnt -= size;
   
                           /*
                            * If there is no more to read in the pipe, reset
                            * its pointers to the beginning.  This improves
                            * cache hit stats.
                            */
                           if (rpipe->pipe_buffer.cnt == 0) {
                                   rpipe->pipe_buffer.in = 0;
                                   rpipe->pipe_buffer.out = 0;
                           }
                           nread += size;
   #ifndef PIPE_NODIRECT
                   /*
                    * Direct copy, bypassing a kernel buffer.
                    */
                   } else if ((size = rpipe->pipe_map.cnt) &&
                              (rpipe->pipe_state & PIPE_DIRECTW)) {
                           if (size > uio->uio_resid)
                                   size = (u_int) uio->uio_resid;
   
                           PIPE_UNLOCK(rpipe);
                           error = uiomove_fromphys(rpipe->pipe_map.ms,
                               rpipe->pipe_map.pos, size, uio);
                           PIPE_LOCK(rpipe);
                           if (error)
                                   break;
                           nread += size;
                           rpipe->pipe_map.pos += size;
                           rpipe->pipe_map.cnt -= size;
                           if (rpipe->pipe_map.cnt == 0) {
                                   rpipe->pipe_state &= ~PIPE_DIRECTW;
                                   wakeup(rpipe);
                           }
   #endif
                   } else {
                           /*
                            * detect EOF condition
                            * read returns 0 on EOF, no need to set error
                            */
                           if (rpipe->pipe_state & PIPE_EOF)
                                   break;
   
                           /*
                            * If the "write-side" has been blocked, wake it up now.
                            */
                           if (rpipe->pipe_state & PIPE_WANTW) {
                                   rpipe->pipe_state &= ~PIPE_WANTW;
                                   wakeup(rpipe);
                           }
   
                           /*
                            * Break if some data was read.
                            */
                           if (nread > 0)
                                   break;
   
                           /*
                            * Unlock the pipe buffer for our remaining processing.
                            * We will either break out with an error or we will
                            * sleep and relock to loop.
                            */
                           pipeunlock(rpipe);
   
                           /*
                            * Handle non-blocking mode operation or
                            * wait for more data.
                            */
                           if (fp->f_flag & FNONBLOCK) {
                                   error = EAGAIN;
                           } else {
                                   rpipe->pipe_state |= PIPE_WANTR;
                                   if ((error = msleep(rpipe, PIPE_MTX(rpipe),
                                       PRIBIO | PCATCH,
                                       "piperd", 0)) == 0)
                                           error = pipelock(rpipe, 1);
                           }
                           if (error)
                                   goto unlocked_error;
                   }
           }
   #ifdef MAC
   locked_error:
   #endif
           pipeunlock(rpipe);
   
           /* XXX: should probably do this before getting any locks. */
           if (error == 0)
                   vfs_timestamp(&rpipe->pipe_atime);
   unlocked_error:
           --rpipe->pipe_busy;
   
           /*
            * PIPE_WANT processing only makes sense if pipe_busy is 0.
            */
           if ((rpipe->pipe_busy == 0) && (rpipe->pipe_state & PIPE_WANT)) {
                   rpipe->pipe_state &= ~(PIPE_WANT|PIPE_WANTW);
                   wakeup(rpipe);
           } else if (rpipe->pipe_buffer.cnt < MINPIPESIZE) {
                   /*
                    * Handle write blocking hysteresis.
                    */
                   if (rpipe->pipe_state & PIPE_WANTW) {
                           rpipe->pipe_state &= ~PIPE_WANTW;
                           wakeup(rpipe);
                   }
           }
   
           if ((rpipe->pipe_buffer.size - rpipe->pipe_buffer.cnt) >= PIPE_BUF)
                   pipeselwakeup(rpipe);
   
           PIPE_UNLOCK(rpipe);
           return (error);
   }
   
   #ifndef PIPE_NODIRECT
   /*
    * Map the sending processes' buffer into kernel space and wire it.
    * This is similar to a physical write operation.
    */
   static int
   pipe_build_write_buffer(wpipe, uio)
           struct pipe *wpipe;
           struct uio *uio;
   {
           u_int size;
           int i;
   
           PIPE_LOCK_ASSERT(wpipe, MA_NOTOWNED);
           KASSERT(wpipe->pipe_state & PIPE_DIRECTW,
                   ("Clone attempt on non-direct write pipe!"));
   
           if (uio->uio_iov->iov_len > wpipe->pipe_buffer.size)
                   size = wpipe->pipe_buffer.size;
           else
                   size = uio->uio_iov->iov_len;
   
           if ((i = vm_fault_quick_hold_pages(&curproc->p_vmspace->vm_map,
               (vm_offset_t)uio->uio_iov->iov_base, size, VM_PROT_READ,
               wpipe->pipe_map.ms, PIPENPAGES)) < 0)
                   return (EFAULT);
   
   /*
    * set up the control block
    */
           wpipe->pipe_map.npages = i;
           wpipe->pipe_map.pos =
               ((vm_offset_t) uio->uio_iov->iov_base) & PAGE_MASK;
           wpipe->pipe_map.cnt = size;
   
   /*
    * and update the uio data
    */
   
           uio->uio_iov->iov_len -= size;
           uio->uio_iov->iov_base = (char *)uio->uio_iov->iov_base + size;
           if (uio->uio_iov->iov_len == 0)
                   uio->uio_iov++;
           uio->uio_resid -= size;
           uio->uio_offset += size;
           return (0);
   }
   
   /*
    * unmap and unwire the process buffer
    */
   static void
   pipe_destroy_write_buffer(wpipe)
           struct pipe *wpipe;
   {
   
           PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
           vm_page_unhold_pages(wpipe->pipe_map.ms, wpipe->pipe_map.npages);
           wpipe->pipe_map.npages = 0;
   }
   
   /*
    * In the case of a signal, the writing process might go away.  This
    * code copies the data into the circular buffer so that the source
    * pages can be freed without loss of data.
    */
   static void
   pipe_clone_write_buffer(wpipe)
           struct pipe *wpipe;
   {
           struct uio uio;
           struct iovec iov;
           int size;
           int pos;
   
           PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
           size = wpipe->pipe_map.cnt;
           pos = wpipe->pipe_map.pos;
   
           wpipe->pipe_buffer.in = size;
           wpipe->pipe_buffer.out = 0;
           wpipe->pipe_buffer.cnt = size;
           wpipe->pipe_state &= ~PIPE_DIRECTW;
   
           PIPE_UNLOCK(wpipe);
           iov.iov_base = wpipe->pipe_buffer.buffer;
           iov.iov_len = size;
           uio.uio_iov = &iov;
           uio.uio_iovcnt = 1;
           uio.uio_offset = 0;
           uio.uio_resid = size;
           uio.uio_segflg = UIO_SYSSPACE;
           uio.uio_rw = UIO_READ;
           uio.uio_td = curthread;
           uiomove_fromphys(wpipe->pipe_map.ms, pos, size, &uio);
           PIPE_LOCK(wpipe);
           pipe_destroy_write_buffer(wpipe);
   }
   
   /*
    * This implements the pipe buffer write mechanism.  Note that only
    * a direct write OR a normal pipe write can be pending at any given time.
    * If there are any characters in the pipe buffer, the direct write will
    * be deferred until the receiving process grabs all of the bytes from
    * the pipe buffer.  Then the direct mapping write is set-up.
    */
   static int
   pipe_direct_write(wpipe, uio)
           struct pipe *wpipe;
           struct uio *uio;
   {
           int error;
   
   retry:
           PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
           error = pipelock(wpipe, 1);
           if (wpipe->pipe_state & PIPE_EOF)
                   error = EPIPE;
           if (error) {
                   pipeunlock(wpipe);
                   goto error1;
           }
           while (wpipe->pipe_state & PIPE_DIRECTW) {
                   if (wpipe->pipe_state & PIPE_WANTR) {
                           wpipe->pipe_state &= ~PIPE_WANTR;
                           wakeup(wpipe);
                   }
                   pipeselwakeup(wpipe);
                   wpipe->pipe_state |= PIPE_WANTW;
                   pipeunlock(wpipe);
                   error = msleep(wpipe, PIPE_MTX(wpipe),
                       PRIBIO | PCATCH, "pipdww", 0);
                   if (error)
                           goto error1;
                   else
                           goto retry;
           }
           wpipe->pipe_map.cnt = 0;        /* transfer not ready yet */
           if (wpipe->pipe_buffer.cnt > 0) {
                   if (wpipe->pipe_state & PIPE_WANTR) {
                           wpipe->pipe_state &= ~PIPE_WANTR;
                           wakeup(wpipe);
                   }
                   pipeselwakeup(wpipe);
                   wpipe->pipe_state |= PIPE_WANTW;
                   pipeunlock(wpipe);
                   error = msleep(wpipe, PIPE_MTX(wpipe),
                       PRIBIO | PCATCH, "pipdwc", 0);
                   if (error)
                           goto error1;
                   else
                           goto retry;
           }
   
           wpipe->pipe_state |= PIPE_DIRECTW;
   
           PIPE_UNLOCK(wpipe);
           error = pipe_build_write_buffer(wpipe, uio);
           PIPE_LOCK(wpipe);
           if (error) {
                   wpipe->pipe_state &= ~PIPE_DIRECTW;
                   pipeunlock(wpipe);
                   goto error1;
           }
   
           error = 0;
           while (!error && (wpipe->pipe_state & PIPE_DIRECTW)) {
                   if (wpipe->pipe_state & PIPE_EOF) {
                           pipe_destroy_write_buffer(wpipe);
                           pipeselwakeup(wpipe);
                           pipeunlock(wpipe);
                           error = EPIPE;
                           goto error1;
                   }
                   if (wpipe->pipe_state & PIPE_WANTR) {
                           wpipe->pipe_state &= ~PIPE_WANTR;
                           wakeup(wpipe);
                   }
                   pipeselwakeup(wpipe);
                   pipeunlock(wpipe);
                   error = msleep(wpipe, PIPE_MTX(wpipe), PRIBIO | PCATCH,
                       "pipdwt", 0);
                   pipelock(wpipe, 0);
           }
   
           if (wpipe->pipe_state & PIPE_EOF)
                   error = EPIPE;
           if (wpipe->pipe_state & PIPE_DIRECTW) {
                   /*
                    * this bit of trickery substitutes a kernel buffer for
                    * the process that might be going away.
                    */
                   pipe_clone_write_buffer(wpipe);
           } else {
                   pipe_destroy_write_buffer(wpipe);
           }
           pipeunlock(wpipe);
           return (error);
   
   error1:
           wakeup(wpipe);
           return (error);
   }
   #endif
   
   static int
   pipe_write(fp, uio, active_cred, flags, td)
           struct file *fp;
           struct uio *uio;
           struct ucred *active_cred;
           struct thread *td;
           int flags;
   {
           int error = 0;
           int desiredsize;
           ssize_t orig_resid;
           struct pipe *wpipe, *rpipe;
   
           rpipe = fp->f_data;
           wpipe = rpipe->pipe_peer;
   
           PIPE_LOCK(rpipe);
           error = pipelock(wpipe, 1);
           if (error) {
                   PIPE_UNLOCK(rpipe);
                   return (error);
           }
           /*
            * detect loss of pipe read side, issue SIGPIPE if lost.
            */
           if (wpipe->pipe_present != PIPE_ACTIVE ||
               (wpipe->pipe_state & PIPE_EOF)) {
                   pipeunlock(wpipe);
                   PIPE_UNLOCK(rpipe);
                   return (EPIPE);
           }
  #ifdef MAC
          error = mac_pipe_check_write(active_cred, wpipe->pipe_pair);
          if (error) {
                  pipeunlock(wpipe);
                  PIPE_UNLOCK(rpipe);
                  return (error);
          }
  #endif
          ++wpipe->pipe_busy;
  
          /* Choose a larger size if it's advantageous */
          desiredsize = max(SMALL_PIPE_SIZE, wpipe->pipe_buffer.size);
          while (desiredsize < wpipe->pipe_buffer.cnt + uio->uio_resid) {
                  if (piperesizeallowed != 1)
                          break;
                  if (amountpipekva > maxpipekva / 2)
                          break;
                  if (desiredsize == BIG_PIPE_SIZE)
                          break;
                  desiredsize = desiredsize * 2;
          }
  
          /* Choose a smaller size if we're in a OOM situation */
          if ((amountpipekva > (3 * maxpipekva) / 4) &&
                  (wpipe->pipe_buffer.size > SMALL_PIPE_SIZE) &&
                  (wpipe->pipe_buffer.cnt <= SMALL_PIPE_SIZE) &&
                  (piperesizeallowed == 1))
                  desiredsize = SMALL_PIPE_SIZE;
  
          /* Resize if the above determined that a new size was necessary */
          if ((desiredsize != wpipe->pipe_buffer.size) &&
                  ((wpipe->pipe_state & PIPE_DIRECTW) == 0)) {
                  PIPE_UNLOCK(wpipe);
                  pipespace(wpipe, desiredsize);
                  PIPE_LOCK(wpipe);
          }
          if (wpipe->pipe_buffer.size == 0) {
                  /*
                   * This can only happen for reverse direction use of pipes
                   * in a complete OOM situation.
                   */
                  error = ENOMEM;
                  --wpipe->pipe_busy;
                  pipeunlock(wpipe);
                  PIPE_UNLOCK(wpipe);
                  return (error);
          }
  
          pipeunlock(wpipe);
  
          orig_resid = uio->uio_resid;
  
          while (uio->uio_resid) {
                  int space;
  
                  pipelock(wpipe, 0);
                  if (wpipe->pipe_state & PIPE_EOF) {
                          pipeunlock(wpipe);
                          error = EPIPE;
                          break;
                  }
  #ifndef PIPE_NODIRECT
                  /*
                   * If the transfer is large, we can gain performance if
                   * we do process-to-process copies directly.
                   * If the write is non-blocking, we don't use the
                   * direct write mechanism.
                   *
                   * The direct write mechanism will detect the reader going
                   * away on us.
                   */
                  if (uio->uio_segflg == UIO_USERSPACE &&
                      uio->uio_iov->iov_len >= PIPE_MINDIRECT &&
                      wpipe->pipe_buffer.size >= PIPE_MINDIRECT &&
                      (fp->f_flag & FNONBLOCK) == 0) {
                          pipeunlock(wpipe);
                          error = pipe_direct_write(wpipe, uio);
                          if (error)
                                  break;
                          continue;
                  }
  #endif
  
                  /*
                   * Pipe buffered writes cannot be coincidental with
                   * direct writes.  We wait until the currently executing
                   * direct write is completed before we start filling the
                   * pipe buffer.  We break out if a signal occurs or the
                   * reader goes away.
                   */
                  if (wpipe->pipe_state & PIPE_DIRECTW) {
                          if (wpipe->pipe_state & PIPE_WANTR) {
                                  wpipe->pipe_state &= ~PIPE_WANTR;
                                  wakeup(wpipe);
                          }
                          pipeselwakeup(wpipe);
                          wpipe->pipe_state |= PIPE_WANTW;
                          pipeunlock(wpipe);
                          error = msleep(wpipe, PIPE_MTX(rpipe), PRIBIO | PCATCH,
                              "pipbww", 0);
                          if (error)
                                  break;
                          else
                                  continue;
                  }
  
                  space = wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt;
  
                  /* Writes of size <= PIPE_BUF must be atomic. */
                  if ((space < uio->uio_resid) && (orig_resid <= PIPE_BUF))
                          space = 0;
  
                  if (space > 0) {
                          int size;       /* Transfer size */
                          int segsize;    /* first segment to transfer */
  
                          /*
                           * Transfer size is minimum of uio transfer
                           * and free space in pipe buffer.
                           */
                          if (space > uio->uio_resid)
                                  size = uio->uio_resid;
                          else
                                  size = space;
                          /*
                           * First segment to transfer is minimum of
                           * transfer size and contiguous space in
                           * pipe buffer.  If first segment to transfer
                           * is less than the transfer size, we've got
                           * a wraparound in the buffer.
                           */
                          segsize = wpipe->pipe_buffer.size -
                                  wpipe->pipe_buffer.in;
                          if (segsize > size)
                                  segsize = size;
  
                          /* Transfer first segment */
  
                          PIPE_UNLOCK(rpipe);
                          error = uiomove(&wpipe->pipe_buffer.buffer[wpipe->pipe_buffer.in],
                                          segsize, uio);
                          PIPE_LOCK(rpipe);
  
                          if (error == 0 && segsize < size) {
                                  KASSERT(wpipe->pipe_buffer.in + segsize ==
                                          wpipe->pipe_buffer.size,
                                          ("Pipe buffer wraparound disappeared"));
                                  /*
                                   * Transfer remaining part now, to
                                   * support atomic writes.  Wraparound
                                   * happened.
                                   */
  
                                  PIPE_UNLOCK(rpipe);
                                  error = uiomove(
                                      &wpipe->pipe_buffer.buffer[0],
                                      size - segsize, uio);
                                  PIPE_LOCK(rpipe);
                          }
                          if (error == 0) {
                                  wpipe->pipe_buffer.in += size;
                                  if (wpipe->pipe_buffer.in >=
                                      wpipe->pipe_buffer.size) {
                                          KASSERT(wpipe->pipe_buffer.in ==
                                                  size - segsize +
                                                  wpipe->pipe_buffer.size,
                                                  ("Expected wraparound bad"));
                                          wpipe->pipe_buffer.in = size - segsize;
                                  }
  
                                  wpipe->pipe_buffer.cnt += size;
                                  KASSERT(wpipe->pipe_buffer.cnt <=
                                          wpipe->pipe_buffer.size,
                                          ("Pipe buffer overflow"));
                          }
                          pipeunlock(wpipe);
                          if (error != 0)
                                  break;
                  } else {
                          /*
                           * If the "read-side" has been blocked, wake it up now.
                           */
                          if (wpipe->pipe_state & PIPE_WANTR) {
                                  wpipe->pipe_state &= ~PIPE_WANTR;
                                  wakeup(wpipe);
                          }
  
                          /*
                           * don't block on non-blocking I/O
                           */
                          if (fp->f_flag & FNONBLOCK) {
                                  error = EAGAIN;
                                  pipeunlock(wpipe);
                                  break;
                          }
  
                          /*
                           * We have no more space and have something to offer,
                           * wake up select/poll.
                           */
                          pipeselwakeup(wpipe);
  
                          wpipe->pipe_state |= PIPE_WANTW;
                          pipeunlock(wpipe);
                          error = msleep(wpipe, PIPE_MTX(rpipe),
                              PRIBIO | PCATCH, "pipewr", 0);
                          if (error != 0)
                                  break;
                  }
          }
  
          pipelock(wpipe, 0);
          --wpipe->pipe_busy;
  
          if ((wpipe->pipe_busy == 0) && (wpipe->pipe_state & PIPE_WANT)) {
                  wpipe->pipe_state &= ~(PIPE_WANT | PIPE_WANTR);
                  wakeup(wpipe);
          } else if (wpipe->pipe_buffer.cnt > 0) {
                  /*
                   * If we have put any characters in the buffer, we wake up
                   * the reader.
                   */
                  if (wpipe->pipe_state & PIPE_WANTR) {
                          wpipe->pipe_state &= ~PIPE_WANTR;
                          wakeup(wpipe);
                  }
          }
  
          /*
           * Don't return EPIPE if I/O was successful
           */
          if ((wpipe->pipe_buffer.cnt == 0) &&
              (uio->uio_resid == 0) &&
              (error == EPIPE)) {
                  error = 0;
          }
  
          if (error == 0)
                  vfs_timestamp(&wpipe->pipe_mtime);
  
          /*
           * We have something to offer,
           * wake up select/poll.
           */
          if (wpipe->pipe_buffer.cnt)
                  pipeselwakeup(wpipe);
  
          pipeunlock(wpipe);
          PIPE_UNLOCK(rpipe);
          return (error);
  }
  
  /* ARGSUSED */
  static int
  pipe_truncate(fp, length, active_cred, td)
          struct file *fp;
          off_t length;
          struct ucred *active_cred;
          struct thread *td;
  {
  
          return (EINVAL);
  }
  
  /*
   * we implement a very minimal set of ioctls for compatibility with sockets.
   */
  static int
  pipe_ioctl(fp, cmd, data, active_cred, td)
          struct file *fp;
          u_long cmd;
          void *data;
          struct ucred *active_cred;
          struct thread *td;
  {
          struct pipe *mpipe = fp->f_data;
          int error;
  
          PIPE_LOCK(mpipe);
  
  #ifdef MAC
          error = mac_pipe_check_ioctl(active_cred, mpipe->pipe_pair, cmd, data);
          if (error) {
                  PIPE_UNLOCK(mpipe);
                  return (error);
          }
  #endif
  
          error = 0;
          switch (cmd) {
  
          case FIONBIO:
                  break;
  
          case FIOASYNC:
                  if (*(int *)data) {
                          mpipe->pipe_state |= PIPE_ASYNC;
                  } else {
                          mpipe->pipe_state &= ~PIPE_ASYNC;
                  }
                  break;
  
          case FIONREAD:
                  if (mpipe->pipe_state & PIPE_DIRECTW)
                          *(int *)data = mpipe->pipe_map.cnt;
                  else
                          *(int *)data = mpipe->pipe_buffer.cnt;
                  break;
  
          case FIOSETOWN:
                  PIPE_UNLOCK(mpipe);
                  error = fsetown(*(int *)data, &mpipe->pipe_sigio);
                  goto out_unlocked;
  
          case FIOGETOWN:
                  *(int *)data = fgetown(&mpipe->pipe_sigio);
                  break;
  
          /* This is deprecated, FIOSETOWN should be used instead. */
          case TIOCSPGRP:
                  PIPE_UNLOCK(mpipe);
                  error = fsetown(-(*(int *)data), &mpipe->pipe_sigio);
                  goto out_unlocked;
  
          /* This is deprecated, FIOGETOWN should be used instead. */
          case TIOCGPGRP:
                  *(int *)data = -fgetown(&mpipe->pipe_sigio);
                  break;
  
          default:
                  error = ENOTTY;
                  break;
          }
          PIPE_UNLOCK(mpipe);
  out_unlocked:
          return (error);
  }
  
  static int
  pipe_poll(fp, events, active_cred, td)
          struct file *fp;
          int events;
          struct ucred *active_cred;
          struct thread *td;
  {
          struct pipe *rpipe = fp->f_data;
          struct pipe *wpipe;
          int revents = 0;
  #ifdef MAC
          int error;
  #endif
  
          wpipe = rpipe->pipe_peer;
          PIPE_LOCK(rpipe);
  #ifdef MAC
          error = mac_pipe_check_poll(active_cred, rpipe->pipe_pair);
          if (error)
                  goto locked_error;
  #endif
          if (events & (POLLIN | POLLRDNORM))
                  if ((rpipe->pipe_state & PIPE_DIRECTW) ||
                      (rpipe->pipe_buffer.cnt > 0))
                          revents |= events & (POLLIN | POLLRDNORM);
  
          if (events & (POLLOUT | POLLWRNORM))
                  if (wpipe->pipe_present != PIPE_ACTIVE ||
                      (wpipe->pipe_state & PIPE_EOF) ||
                      (((wpipe->pipe_state & PIPE_DIRECTW) == 0) &&
                       ((wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt) >= PIPE_BUF ||
                           wpipe->pipe_buffer.size == 0)))
                          revents |= events & (POLLOUT | POLLWRNORM);
  
          if ((events & POLLINIGNEOF) == 0) {
                  if (rpipe->pipe_state & PIPE_EOF) {
                          revents |= (events & (POLLIN | POLLRDNORM));
                          if (wpipe->pipe_present != PIPE_ACTIVE ||
                              (wpipe->pipe_state & PIPE_EOF))
                                  revents |= POLLHUP;
                  }
          }
  
          if (revents == 0) {
                  if (events & (POLLIN | POLLRDNORM)) {
                          selrecord(td, &rpipe->pipe_sel);
                          if (SEL_WAITING(&rpipe->pipe_sel))
                                  rpipe->pipe_state |= PIPE_SEL;
                  }
  
                  if (events & (POLLOUT | POLLWRNORM)) {
                          selrecord(td, &wpipe->pipe_sel);
                          if (SEL_WAITING(&wpipe->pipe_sel))
                                  wpipe->pipe_state |= PIPE_SEL;
                  }
          }
  #ifdef MAC
  locked_error:
  #endif
          PIPE_UNLOCK(rpipe);
  
          return (revents);
  }
  
  /*
   * We shouldn't need locks here as we're doing a read and this should
   * be a natural race.
   */
  static int
  pipe_stat(fp, ub, active_cred, td)
          struct file *fp;
          struct stat *ub;
          struct ucred *active_cred;
          struct thread *td;
  {
          struct pipe *pipe;
          int new_unr;
  #ifdef MAC
          int error;
  #endif
  
          pipe = fp->f_data;
          PIPE_LOCK(pipe);
  #ifdef MAC
          error = mac_pipe_check_stat(active_cred, pipe->pipe_pair);
          if (error) {
                  PIPE_UNLOCK(pipe);
                  return (error);
          }
  #endif
          /*
           * Lazily allocate an inode number for the pipe.  Most pipe
           * users do not call fstat(2) on the pipe, which means that
           * postponing the inode allocation until it is must be
           * returned to userland is useful.  If alloc_unr failed,
           * assign st_ino zero instead of returning an error.
           * Special pipe_ino values:
           *  -1 - not yet initialized;
           *  0  - alloc_unr failed, return 0 as st_ino forever.
           */
          if (pipe->pipe_ino == (ino_t)-1) {
                  new_unr = alloc_unr(pipeino_unr);
                  if (new_unr != -1)
                          pipe->pipe_ino = new_unr;
                  else
                          pipe->pipe_ino = 0;
          }
          PIPE_UNLOCK(pipe);
  
          bzero(ub, sizeof(*ub));
          ub->st_mode = S_IFIFO;
          ub->st_blksize = PAGE_SIZE;
          if (pipe->pipe_state & PIPE_DIRECTW)
                  ub->st_size = pipe->pipe_map.cnt;
          else
                  ub->st_size = pipe->pipe_buffer.cnt;
          ub->st_blocks = (ub->st_size + ub->st_blksize - 1) / ub->st_blksize;
          ub->st_atim = pipe->pipe_atime;
          ub->st_mtim = pipe->pipe_mtime;
          ub->st_ctim = pipe->pipe_ctime;
          ub->st_uid = fp->f_cred->cr_uid;
          ub->st_gid = fp->f_cred->cr_gid;
          ub->st_dev = pipedev_ino;
          ub->st_ino = pipe->pipe_ino;
          /*
           * Left as 0: st_nlink, st_rdev, st_flags, st_gen.
           */
          return (0);
  }
  
  /* ARGSUSED */
  static int
  pipe_close(fp, td)
          struct file *fp;
          struct thread *td;
  {
          struct pipe *cpipe = fp->f_data;
  
          fp->f_ops = &badfileops;
          fp->f_data = NULL;
          funsetown(&cpipe->pipe_sigio);
          pipeclose(cpipe);
          return (0);
  }
  
  static void
  pipe_free_kmem(cpipe)
          struct pipe *cpipe;
  {
  
          KASSERT(!mtx_owned(PIPE_MTX(cpipe)),
              ("pipe_free_kmem: pipe mutex locked"));
  
          if (cpipe->pipe_buffer.buffer != NULL) {
                  atomic_subtract_long(&amountpipekva, cpipe->pipe_buffer.size);
                  vm_map_remove(pipe_map,
                      (vm_offset_t)cpipe->pipe_buffer.buffer,
                      (vm_offset_t)cpipe->pipe_buffer.buffer + cpipe->pipe_buffer.size);
                  cpipe->pipe_buffer.buffer = NULL;
          }
  #ifndef PIPE_NODIRECT
          {
                  cpipe->pipe_map.cnt = 0;
                  cpipe->pipe_map.pos = 0;
                  cpipe->pipe_map.npages = 0;
          }
  #endif
  }
  
  /*
   * shutdown the pipe
   */
  static void
  pipeclose(cpipe)
          struct pipe *cpipe;
  {
          struct pipepair *pp;
          struct pipe *ppipe;
          ino_t ino;
  
          KASSERT(cpipe != NULL, ("pipeclose: cpipe == NULL"));
  
          PIPE_LOCK(cpipe);
          pipelock(cpipe, 0);
          pp = cpipe->pipe_pair;
  
          pipeselwakeup(cpipe);
  
          /*
           * If the other side is blocked, wake it up saying that
           * we want to close it down.
           */
          cpipe->pipe_state |= PIPE_EOF;
          while (cpipe->pipe_busy) {
                  wakeup(cpipe);
                  cpipe->pipe_state |= PIPE_WANT;
                  pipeunlock(cpipe);
                  msleep(cpipe, PIPE_MTX(cpipe), PRIBIO, "pipecl", 0);
                  pipelock(cpipe, 0);
          }
  
  
          /*
           * Disconnect from peer, if any.
           */
          ppipe = cpipe->pipe_peer;
          if (ppipe->pipe_present == PIPE_ACTIVE) {
                  pipeselwakeup(ppipe);
  
                  ppipe->pipe_state |= PIPE_EOF;
                  wakeup(ppipe);
                  KNOTE_LOCKED(&ppipe->pipe_sel.si_note, 0);
          }
  
          /*
           * Mark this endpoint as free.  Release kmem resources.  We
           * don't mark this endpoint as unused until we've finished
           * doing that, or the pipe might disappear out from under
           * us.
           */
          PIPE_UNLOCK(cpipe);
          pipe_free_kmem(cpipe);
          PIPE_LOCK(cpipe);
          cpipe->pipe_present = PIPE_CLOSING;
          pipeunlock(cpipe);
  
          /*
           * knlist_clear() may sleep dropping the PIPE_MTX. Set the
           * PIPE_FINALIZED, that allows other end to free the
           * pipe_pair, only after the knotes are completely dismantled.
           */
          knlist_clear(&cpipe->pipe_sel.si_note, 1);
          cpipe->pipe_present = PIPE_FINALIZED;
          seldrain(&cpipe->pipe_sel);
          knlist_destroy(&cpipe->pipe_sel.si_note);
  
          /*
           * Postpone the destroy of the fake inode number allocated for
           * our end, until pipe mtx is unlocked.
           */
          ino = cpipe->pipe_ino;
  
          /*
           * If both endpoints are now closed, release the memory for the
           * pipe pair.  If not, unlock.
           */
          if (ppipe->pipe_present == PIPE_FINALIZED) {
                  PIPE_UNLOCK(cpipe);
  #ifdef MAC
                  mac_pipe_destroy(pp);
  #endif
                  uma_zfree(pipe_zone, cpipe->pipe_pair);
          } else
                  PIPE_UNLOCK(cpipe);
  
          if (ino != 0 && ino != (ino_t)-1)
                  free_unr(pipeino_unr, ino);
  }
  
  /*ARGSUSED*/
  static int
  pipe_kqfilter(struct file *fp, struct knote *kn)
  {
          struct pipe *cpipe;
  
          cpipe = kn->kn_fp->f_data;
          PIPE_LOCK(cpipe);
          switch (kn->kn_filter) {
          case EVFILT_READ:
                  kn->kn_fop = &pipe_rfiltops;
                  break;
          case EVFILT_WRITE:
                  kn->kn_fop = &pipe_wfiltops;
                  if (cpipe->pipe_peer->pipe_present != PIPE_ACTIVE) {
                          /* other end of pipe has been closed */
                          PIPE_UNLOCK(cpipe);
                          return (EPIPE);
                  }
                  cpipe = cpipe->pipe_peer;
                  break;
          default:
                  PIPE_UNLOCK(cpipe);
                  return (EINVAL);
          }
  
          knlist_add(&cpipe->pipe_sel.si_note, kn, 1);
          PIPE_UNLOCK(cpipe);
          return (0);
  }
  
  static void
  filt_pipedetach(struct knote *kn)
  {
          struct pipe *cpipe = (struct pipe *)kn->kn_fp->f_data;
  
          PIPE_LOCK(cpipe);
          if (kn->kn_filter == EVFILT_WRITE)
                  cpipe = cpipe->pipe_peer;
          knlist_remove(&cpipe->pipe_sel.si_note, kn, 1);
          PIPE_UNLOCK(cpipe);
  }
  
  /*ARGSUSED*/
  static int
  filt_piperead(struct knote *kn, long hint)
  {
          struct pipe *rpipe = kn->kn_fp->f_data;
          struct pipe *wpipe = rpipe->pipe_peer;
          int ret;
  
          PIPE_LOCK(rpipe);
          kn->kn_data = rpipe->pipe_buffer.cnt;
          if ((kn->kn_data == 0) && (rpipe->pipe_state & PIPE_DIRECTW))
                  kn->kn_data = rpipe->pipe_map.cnt;
  
          if ((rpipe->pipe_state & PIPE_EOF) ||
              wpipe->pipe_present != PIPE_ACTIVE ||
              (wpipe->pipe_state & PIPE_EOF)) {
                  kn->kn_flags |= EV_EOF;
                  PIPE_UNLOCK(rpipe);
                  return (1);
          }
          ret = kn->kn_data > 0;
          PIPE_UNLOCK(rpipe);
          return ret;
  }
  
  /*ARGSUSED*/
  static int
  filt_pipewrite(struct knote *kn, long hint)
  {
          struct pipe *rpipe = kn->kn_fp->f_data;
          struct pipe *wpipe = rpipe->pipe_peer;
  
          PIPE_LOCK(rpipe);
          if (wpipe->pipe_present != PIPE_ACTIVE ||
              (wpipe->pipe_state & PIPE_EOF)) {
                  kn->kn_data = 0;
                  kn->kn_flags |= EV_EOF;
                  PIPE_UNLOCK(rpipe);
                  return (1);
          }
          kn->kn_data = (wpipe->pipe_buffer.size > 0) ?
              (wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt) : PIPE_BUF;
          if (wpipe->pipe_state & PIPE_DIRECTW)
                  kn->kn_data = 0;
  
          PIPE_UNLOCK(rpipe);
          return (kn->kn_data >= PIPE_BUF);
  }

Cache object: 3f11d3562b60b6fb5160aeb1fe05fb25