Ignore machine-check MSRs

[freebsd-src/fkvm-freebsd.git] / 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, it is fully mapped and wired into the kernel, and
 * the receiving process can copy it directly from the 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 "opt_mac.h"

#include <sys/param.h>
#include <sys/systm.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/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>

/*
 * 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_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 =
        { 1, NULL, filt_pipedetach, filt_piperead };
static struct filterops pipe_wfiltops =
        { 1, NULL, filt_pipedetach, 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 int amountpipekva;
static int pipefragretry;
static int pipeallocfail;
static int piperesizefail;
static int piperesizeallowed = 1;

SYSCTL_INT(_kern_ipc, OID_AUTO, maxpipekva, CTLFLAG_RDTUN,
           &maxpipekva, 0, "Pipe KVA limit");
SYSCTL_INT(_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;

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"));
}

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().
 */
/* ARGSUSED */
int
pipe(td, uap)
        struct thread *td;
        struct pipe_args /* {
                int     dummy;
        } */ *uap;
{
        struct filedesc *fdp = td->td_proc->p_fd;
        struct file *rf, *wf;
        struct pipepair *pp;
        struct pipe *rpipe, *wpipe;
        int fd, 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(&rpipe->pipe_sel.si_note, PIPE_MTX(rpipe), NULL, NULL,
            NULL);
        knlist_init(&wpipe->pipe_sel.si_note, PIPE_MTX(wpipe), NULL, NULL,
            NULL);

        /* 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);
        if (error) {
                pipeclose(rpipe);
                pipeclose(wpipe);
                return (error);
        }
        /* An extra reference on `rf' has been held for us by falloc(). */
        td->td_retval[0] = fd;

        /*
         * 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, FREAD | FWRITE, DTYPE_PIPE, rpipe, &pipeops);
        error = falloc(td, &wf, &fd);
        if (error) {
                fdclose(fdp, rf, td->td_retval[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, FREAD | FWRITE, DTYPE_PIPE, wpipe, &pipeops);
        fdrop(wf, td);
        td->td_retval[1] = fd;
        fdrop(rf, td);

        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_int(&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;
        }
        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;
        u_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 > (u_int) uio->uio_resid)
                                size = (u_int) 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 > (u_int) 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;
{
        pmap_t pmap;
        u_int size;
        int i, j;
        vm_offset_t addr, endaddr;

        PIPE_LOCK_ASSERT(wpipe, MA_NOTOWNED);
        KASSERT(wpipe->pipe_state & PIPE_DIRECTW,
                ("Clone attempt on non-direct write pipe!"));

        size = (u_int) uio->uio_iov->iov_len;
        if (size > wpipe->pipe_buffer.size)
                size = wpipe->pipe_buffer.size;

        pmap = vmspace_pmap(curproc->p_vmspace);
        endaddr = round_page((vm_offset_t)uio->uio_iov->iov_base + size);
        addr = trunc_page((vm_offset_t)uio->uio_iov->iov_base);
        for (i = 0; addr < endaddr; addr += PAGE_SIZE, i++) {
                /*
                 * vm_fault_quick() can sleep.  Consequently,
                 * vm_page_lock_queue() and vm_page_unlock_queue()
                 * should not be performed outside of this loop.
                 */
        race:
                if (vm_fault_quick((caddr_t)addr, VM_PROT_READ) < 0) {
                        vm_page_lock_queues();
                        for (j = 0; j < i; j++)
                                vm_page_unhold(wpipe->pipe_map.ms[j]);
                        vm_page_unlock_queues();
                        return (EFAULT);
                }
                wpipe->pipe_map.ms[i] = pmap_extract_and_hold(pmap, addr,
                    VM_PROT_READ);
                if (wpipe->pipe_map.ms[i] == NULL)
                        goto race;
        }

/*
 * 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;
{
        int i;

        PIPE_LOCK_ASSERT(wpipe, MA_OWNED);
        vm_page_lock_queues();
        for (i = 0; i < wpipe->pipe_map.npages; i++) {
                vm_page_unhold(wpipe->pipe_map.ms[i]);
        }
        vm_page_unlock_queues();
        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, 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) ||
                    (rpipe->pipe_state & PIPE_EOF))
                        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))
                        revents |= events & (POLLOUT | POLLWRNORM);

        if ((rpipe->pipe_state & PIPE_EOF) ||
            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 = fp->f_data;
#ifdef MAC
        int error;

        PIPE_LOCK(pipe);
        error = mac_pipe_check_stat(active_cred, pipe->pipe_pair);
        PIPE_UNLOCK(pipe);
        if (error)
                return (error);
#endif
        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_atimespec = pipe->pipe_atime;
        ub->st_mtimespec = pipe->pipe_mtime;
        ub->st_ctimespec = pipe->pipe_ctime;
        ub->st_uid = fp->f_cred->cr_uid;
        ub->st_gid = fp->f_cred->cr_gid;
        /*
         * Left as 0: st_dev, st_ino, st_nlink, st_rdev, st_flags, st_gen.
         * XXX (st_dev, st_ino) should be unique.
         */
        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_int(&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;

        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;
        knlist_destroy(&cpipe->pipe_sel.si_note);

        /*
         * 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);
}

/*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 - wpipe->pipe_buffer.cnt;
        if (wpipe->pipe_state & PIPE_DIRECTW)
                kn->kn_data = 0;

        PIPE_UNLOCK(rpipe);
        return (kn->kn_data >= PIPE_BUF);
}