/*      $OpenBSD: sys_pipe.c,v 1.149 2025/08/04 04:59:31 guenther Exp $ */

/*
 * 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.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/fcntl.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/pool.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/signalvar.h>
#include <sys/mount.h>
#include <sys/syscallargs.h>
#include <sys/event.h>
#ifdef KTRACE
#include <sys/ktrace.h>
#endif

#include <uvm/uvm_extern.h>

#include <sys/pipe.h>

struct pipe_pair {
        struct pipe pp_wpipe;
        struct pipe pp_rpipe;
        struct rwlock pp_lock;
};

/*
 * interfaces to the outside world
 */
int     pipe_read(struct file *, struct uio *, int);
int     pipe_write(struct file *, struct uio *, int);
int     pipe_close(struct file *, struct proc *);
int     pipe_kqfilter(struct file *fp, struct knote *kn);
int     pipe_ioctl(struct file *, u_long, caddr_t, struct proc *);
int     pipe_stat(struct file *fp, struct stat *ub, struct proc *p);

static const struct fileops pipeops = {
        .fo_read        = pipe_read,
        .fo_write       = pipe_write,
        .fo_ioctl       = pipe_ioctl,
        .fo_kqfilter    = pipe_kqfilter,
        .fo_stat        = pipe_stat,
        .fo_close       = pipe_close
};

void    filt_pipedetach(struct knote *kn);
int     filt_piperead(struct knote *kn, long hint);
int     filt_pipewrite(struct knote *kn, long hint);
int     filt_pipeexcept(struct knote *kn, long hint);
int     filt_pipemodify(struct kevent *kev, struct knote *kn);
int     filt_pipeprocess(struct knote *kn, struct kevent *kev);

const struct filterops pipe_rfiltops = {
        .f_flags        = FILTEROP_ISFD | FILTEROP_MPSAFE,
        .f_attach       = NULL,
        .f_detach       = filt_pipedetach,
        .f_event        = filt_piperead,
        .f_modify       = filt_pipemodify,
        .f_process      = filt_pipeprocess,
};

const struct filterops pipe_wfiltops = {
        .f_flags        = FILTEROP_ISFD | FILTEROP_MPSAFE,
        .f_attach       = NULL,
        .f_detach       = filt_pipedetach,
        .f_event        = filt_pipewrite,
        .f_modify       = filt_pipemodify,
        .f_process      = filt_pipeprocess,
};

const struct filterops pipe_efiltops = {
        .f_flags        = FILTEROP_ISFD | FILTEROP_MPSAFE,
        .f_attach       = NULL,
        .f_detach       = filt_pipedetach,
        .f_event        = filt_pipeexcept,
        .f_modify       = filt_pipemodify,
        .f_process      = filt_pipeprocess,
};

/*
 * 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)

/*
 * Limit the number of "big" pipes
 */
#define LIMITBIGPIPES   32
unsigned int nbigpipe;
static unsigned int amountpipekva;

struct pool pipe_pair_pool;

int     dopipe(struct proc *, int *, int);
void    pipe_wakeup(struct pipe *);

int     pipe_create(struct pipe *);
void    pipe_destroy(struct pipe *);
int     pipe_rundown(struct pipe *);
struct pipe *pipe_peer(struct pipe *);
int     pipe_buffer_realloc(struct pipe *, u_int);
void    pipe_buffer_free(struct pipe *);

int     pipe_iolock(struct pipe *);
void    pipe_iounlock(struct pipe *);
int     pipe_iosleep(struct pipe *, const char *);

struct pipe_pair *pipe_pair_create(void);
void    pipe_pair_destroy(struct pipe_pair *);

/*
 * The pipe system call for the DTYPE_PIPE type of pipes
 */

int
sys_pipe(struct proc *p, void *v, register_t *retval)
{
        struct sys_pipe_args /* {
                syscallarg(int *) fdp;
        } */ *uap = v;

        return (dopipe(p, SCARG(uap, fdp), 0));
}

int
sys_pipe2(struct proc *p, void *v, register_t *retval)
{
        struct sys_pipe2_args /* {
                syscallarg(int *) fdp;
                syscallarg(int) flags;
        } */ *uap = v;

        if (SCARG(uap, flags) & ~(O_CLOEXEC | O_CLOFORK | FNONBLOCK))
                return (EINVAL);

        return (dopipe(p, SCARG(uap, fdp), SCARG(uap, flags)));
}

int
dopipe(struct proc *p, int *ufds, int flags)
{
        struct filedesc *fdp = p->p_fd;
        struct file *rf, *wf;
        struct pipe_pair *pp;
        struct pipe *rpipe, *wpipe = NULL;
        int fds[2], fdflags, error;

        fdflags = ((flags & O_CLOEXEC) ? UF_EXCLOSE : 0)
            | ((flags & O_CLOFORK) ? UF_FORKCLOSE : 0);

        pp = pipe_pair_create();
        if (pp == NULL)
                return (ENOMEM);
        wpipe = &pp->pp_wpipe;
        rpipe = &pp->pp_rpipe;

        fdplock(fdp);

        error = falloc(p, &rf, &fds[0]);
        if (error != 0)
                goto free2;
        rf->f_flag = FREAD | FWRITE | (flags & FNONBLOCK);
        rf->f_type = DTYPE_PIPE;
        rf->f_data = rpipe;
        rf->f_ops = &pipeops;

        error = falloc(p, &wf, &fds[1]);
        if (error != 0)
                goto free3;
        wf->f_flag = FREAD | FWRITE | (flags & FNONBLOCK);
        wf->f_type = DTYPE_PIPE;
        wf->f_data = wpipe;
        wf->f_ops = &pipeops;

        fdinsert(fdp, fds[0], fdflags, rf);
        fdinsert(fdp, fds[1], fdflags, wf);

        error = copyout(fds, ufds, sizeof(fds));
        if (error == 0) {
                fdpunlock(fdp);
#ifdef KTRACE
                if (KTRPOINT(p, KTR_STRUCT))
                        ktrfds(p, fds, 2);
#endif
        } else {
                /* fdrelease() unlocks fdp. */
                fdrelease(p, fds[0]);
                fdplock(fdp);
                fdrelease(p, fds[1]);
        }

        FRELE(rf, p);
        FRELE(wf, p);
        return (error);

free3:
        fdremove(fdp, fds[0]);
        closef(rf, p);
        rpipe = NULL;
free2:
        fdpunlock(fdp);
        pipe_destroy(wpipe);
        pipe_destroy(rpipe);
        return (error);
}

/*
 * 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.
 */
int
pipe_buffer_realloc(struct pipe *cpipe, u_int size)
{
        caddr_t buffer;

        /* buffer uninitialized or pipe locked */
        KASSERT((cpipe->pipe_buffer.buffer == NULL) ||
            (cpipe->pipe_state & PIPE_LOCK));

        /* buffer should be empty */
        KASSERT(cpipe->pipe_buffer.cnt == 0);

        buffer = km_alloc(size, &kv_any, &kp_pageable, &kd_waitok);
        if (buffer == NULL)
                return (ENOMEM);

        /* free old resources if we are resizing */
        pipe_buffer_free(cpipe);

        cpipe->pipe_buffer.buffer = buffer;
        cpipe->pipe_buffer.size = size;
        cpipe->pipe_buffer.in = 0;
        cpipe->pipe_buffer.out = 0;

        atomic_add_int(&amountpipekva, cpipe->pipe_buffer.size);

        return (0);
}

/*
 * initialize and allocate VM and memory for pipe
 */
int
pipe_create(struct pipe *cpipe)
{
        int error;

        error = pipe_buffer_realloc(cpipe, PIPE_SIZE);
        if (error != 0)
                return (error);

        sigio_init(&cpipe->pipe_sigio);

        getnanotime(&cpipe->pipe_ctime);
        cpipe->pipe_atime = cpipe->pipe_ctime;
        cpipe->pipe_mtime = cpipe->pipe_ctime;

        return (0);
}

struct pipe *
pipe_peer(struct pipe *cpipe)
{
        struct pipe *peer;

        rw_assert_anylock(cpipe->pipe_lock);

        peer = cpipe->pipe_peer;
        if (peer == NULL || (peer->pipe_state & PIPE_EOF))
                return (NULL);
        return (peer);
}

/*
 * Lock a pipe for exclusive I/O access.
 */
int
pipe_iolock(struct pipe *cpipe)
{
        int error;

        rw_assert_wrlock(cpipe->pipe_lock);

        while (cpipe->pipe_state & PIPE_LOCK) {
                cpipe->pipe_state |= PIPE_LWANT;
                error = rwsleep_nsec(cpipe, cpipe->pipe_lock, PRIBIO | PCATCH,
                    "pipeiolk", INFSLP);
                if (error)
                        return (error);
        }
        cpipe->pipe_state |= PIPE_LOCK;
        return (0);
}

/*
 * Unlock a pipe I/O lock.
 */
void
pipe_iounlock(struct pipe *cpipe)
{
        rw_assert_wrlock(cpipe->pipe_lock);
        KASSERT(cpipe->pipe_state & PIPE_LOCK);

        cpipe->pipe_state &= ~PIPE_LOCK;
        if (cpipe->pipe_state & PIPE_LWANT) {
                cpipe->pipe_state &= ~PIPE_LWANT;
                wakeup(cpipe);
        }
}

/*
 * Unlock the pipe I/O lock and go to sleep. Returns 0 on success and the I/O
 * lock is relocked. Otherwise if a signal was caught, non-zero is returned and
 * the I/O lock is not locked.
 *
 * Any caller must obtain a reference to the pipe by incrementing `pipe_busy'
 * before calling this function in order ensure that the same pipe is not
 * destroyed while sleeping.
 */
int
pipe_iosleep(struct pipe *cpipe, const char *wmesg)
{
        int error;

        pipe_iounlock(cpipe);
        error = rwsleep_nsec(cpipe, cpipe->pipe_lock, PRIBIO | PCATCH, wmesg,
            INFSLP);
        if (error)
                return (error);
        return (pipe_iolock(cpipe));
}

void
pipe_wakeup(struct pipe *cpipe)
{
        rw_assert_wrlock(cpipe->pipe_lock);

        knote_locked(&cpipe->pipe_klist, 0);

        if (cpipe->pipe_state & PIPE_ASYNC)
                pgsigio(&cpipe->pipe_sigio, SIGIO, 0);
}

int
pipe_read(struct file *fp, struct uio *uio, int fflags)
{
        struct pipe *rpipe = fp->f_data;
        size_t nread = 0, size;
        int error;

        rw_enter_write(rpipe->pipe_lock);
        ++rpipe->pipe_busy;
        error = pipe_iolock(rpipe);
        if (error) {
                --rpipe->pipe_busy;
                pipe_rundown(rpipe);
                rw_exit_write(rpipe->pipe_lock);
                return (error);
        }

        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;
                        rw_exit_write(rpipe->pipe_lock);
                        error = uiomove(&rpipe->pipe_buffer.buffer[rpipe->pipe_buffer.out],
                                        size, uio);
                        rw_enter_write(rpipe->pipe_lock);
                        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;
                } 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. */
                        if (rpipe->pipe_state & PIPE_WANTW) {
                                rpipe->pipe_state &= ~PIPE_WANTW;
                                wakeup(rpipe);
                        }

                        /* Break if some data was read. */
                        if (nread > 0)
                                break;

                        /* Handle non-blocking mode operation. */
                        if (fp->f_flag & FNONBLOCK) {
                                error = EAGAIN;
                                break;
                        }

                        /* Wait for more data. */
                        rpipe->pipe_state |= PIPE_WANTR;
                        error = pipe_iosleep(rpipe, "piperd");
                        if (error)
                                goto unlocked_error;
                }
        }
        pipe_iounlock(rpipe);

        if (error == 0)
                getnanotime(&rpipe->pipe_atime);
unlocked_error:
        --rpipe->pipe_busy;

        if (pipe_rundown(rpipe) == 0 && 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)
                pipe_wakeup(rpipe);

        rw_exit_write(rpipe->pipe_lock);
        return (error);
}

int
pipe_write(struct file *fp, struct uio *uio, int fflags)
{
        struct pipe *rpipe = fp->f_data, *wpipe;
        struct rwlock *lock = rpipe->pipe_lock;
        size_t orig_resid;
        int error;

        rw_enter_write(lock);
        wpipe = pipe_peer(rpipe);

        /* Detect loss of pipe read side, issue SIGPIPE if lost. */
        if (wpipe == NULL) {
                rw_exit_write(lock);
                return (EPIPE);
        }

        ++wpipe->pipe_busy;
        error = pipe_iolock(wpipe);
        if (error) {
                --wpipe->pipe_busy;
                pipe_rundown(wpipe);
                rw_exit_write(lock);
                return (error);
        }


        /* If it is advantageous to resize the pipe buffer, do so. */
        if (uio->uio_resid > PIPE_SIZE &&
            wpipe->pipe_buffer.size <= PIPE_SIZE &&
            wpipe->pipe_buffer.cnt == 0) {
                unsigned int npipe;

                npipe = atomic_inc_int_nv(&nbigpipe);
                if (npipe > LIMITBIGPIPES ||
                    pipe_buffer_realloc(wpipe, BIG_PIPE_SIZE) != 0)
                        atomic_dec_int(&nbigpipe);
        }

        orig_resid = uio->uio_resid;

        while (uio->uio_resid) {
                size_t space;

                if (wpipe->pipe_state & PIPE_EOF) {
                        error = EPIPE;
                        break;
                }

                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) {
                        size_t size;    /* Transfer size */
                        size_t 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 */

                        rw_exit_write(lock);
                        error = uiomove(&wpipe->pipe_buffer.buffer[wpipe->pipe_buffer.in],
                                        segsize, uio);
                        rw_enter_write(lock);

                        if (error == 0 && segsize < size) {
                                /*
                                 * Transfer remaining part now, to
                                 * support atomic writes.  Wraparound
                                 * happened.
                                 */
#ifdef DIAGNOSTIC
                                if (wpipe->pipe_buffer.in + segsize !=
                                    wpipe->pipe_buffer.size)
                                        panic("Expected pipe buffer wraparound disappeared");
#endif

                                rw_exit_write(lock);
                                error = uiomove(&wpipe->pipe_buffer.buffer[0],
                                                size - segsize, uio);
                                rw_enter_write(lock);
                        }
                        if (error == 0) {
                                wpipe->pipe_buffer.in += size;
                                if (wpipe->pipe_buffer.in >=
                                    wpipe->pipe_buffer.size) {
#ifdef DIAGNOSTIC
                                        if (wpipe->pipe_buffer.in != size - segsize + wpipe->pipe_buffer.size)
                                                panic("Expected wraparound bad");
#endif
                                        wpipe->pipe_buffer.in = size - segsize;
                                }

                                wpipe->pipe_buffer.cnt += size;
#ifdef DIAGNOSTIC
                                if (wpipe->pipe_buffer.cnt > wpipe->pipe_buffer.size)
                                        panic("Pipe buffer overflow");
#endif
                        }
                        if (error)
                                break;
                } else {
                        /* If the "read-side" has been blocked, wake it up. */
                        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;
                                break;
                        }

                        /*
                         * We have no more space and have something to offer,
                         * wake up select/poll.
                         */
                        pipe_wakeup(wpipe);

                        wpipe->pipe_state |= PIPE_WANTW;
                        error = pipe_iosleep(wpipe, "pipewr");
                        if (error)
                                goto unlocked_error;

                        /*
                         * If read side wants to go away, we just issue a
                         * signal to ourselves.
                         */
                        if (wpipe->pipe_state & PIPE_EOF) {
                                error = EPIPE;
                                break;
                        }
                }
        }
        pipe_iounlock(wpipe);

unlocked_error:
        --wpipe->pipe_busy;

        if (pipe_rundown(wpipe) == 0 && 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)
                getnanotime(&wpipe->pipe_mtime);
        /* We have something to offer, wake up select/poll. */
        if (wpipe->pipe_buffer.cnt)
                pipe_wakeup(wpipe);

        rw_exit_write(lock);
        return (error);
}

/*
 * we implement a very minimal set of ioctls for compatibility with sockets.
 */
int
pipe_ioctl(struct file *fp, u_long cmd, caddr_t data, struct proc *p)
{
        struct pipe *mpipe = fp->f_data;
        int error = 0;

        switch (cmd) {

        case FIOASYNC:
                rw_enter_write(mpipe->pipe_lock);
                if (*(int *)data) {
                        mpipe->pipe_state |= PIPE_ASYNC;
                } else {
                        mpipe->pipe_state &= ~PIPE_ASYNC;
                }
                rw_exit_write(mpipe->pipe_lock);
                break;

        case FIONREAD:
                rw_enter_read(mpipe->pipe_lock);
                *(int *)data = mpipe->pipe_buffer.cnt;
                rw_exit_read(mpipe->pipe_lock);
                break;

        case FIOSETOWN:
        case SIOCSPGRP:
        case TIOCSPGRP:
                error = sigio_setown(&mpipe->pipe_sigio, cmd, data);
                break;

        case FIOGETOWN:
        case SIOCGPGRP:
        case TIOCGPGRP:
                sigio_getown(&mpipe->pipe_sigio, cmd, data);
                break;

        default:
                error = ENOTTY;
        }

        return (error);
}

int
pipe_stat(struct file *fp, struct stat *ub, struct proc *p)
{
        struct pipe *pipe = fp->f_data;

        memset(ub, 0, sizeof(*ub));

        rw_enter_read(pipe->pipe_lock);
        ub->st_mode = S_IFIFO;
        ub->st_blksize = pipe->pipe_buffer.size;
        ub->st_size = pipe->pipe_buffer.cnt;
        ub->st_blocks = (ub->st_size + ub->st_blksize - 1) / ub->st_blksize;
        ub->st_atim.tv_sec  = pipe->pipe_atime.tv_sec;
        ub->st_atim.tv_nsec = pipe->pipe_atime.tv_nsec;
        ub->st_mtim.tv_sec  = pipe->pipe_mtime.tv_sec;
        ub->st_mtim.tv_nsec = pipe->pipe_mtime.tv_nsec;
        ub->st_ctim.tv_sec  = pipe->pipe_ctime.tv_sec;
        ub->st_ctim.tv_nsec = pipe->pipe_ctime.tv_nsec;
        ub->st_uid = fp->f_cred->cr_uid;
        ub->st_gid = fp->f_cred->cr_gid;
        rw_exit_read(pipe->pipe_lock);
        /*
         * 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);
}

int
pipe_close(struct file *fp, struct proc *p)
{
        struct pipe *cpipe = fp->f_data;

        fp->f_ops = NULL;
        fp->f_data = NULL;
        pipe_destroy(cpipe);
        return (0);
}

/*
 * Free kva for pipe circular buffer.
 * No pipe lock check as only called from pipe_buffer_realloc() and pipeclose()
 */
void
pipe_buffer_free(struct pipe *cpipe)
{
        u_int size;

        if (cpipe->pipe_buffer.buffer == NULL)
                return;

        size = cpipe->pipe_buffer.size;

        km_free(cpipe->pipe_buffer.buffer, size, &kv_any, &kp_pageable);

        cpipe->pipe_buffer.buffer = NULL;

        atomic_sub_int(&amountpipekva, size);
        if (size > PIPE_SIZE)
                atomic_dec_int(&nbigpipe);
}

/*
 * shutdown the pipe, and free resources.
 */
void
pipe_destroy(struct pipe *cpipe)
{
        struct pipe *ppipe;

        if (cpipe == NULL)
                return;

        rw_enter_write(cpipe->pipe_lock);

        pipe_wakeup(cpipe);
        sigio_free(&cpipe->pipe_sigio);

        /*
         * 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_WANTD;
                rwsleep_nsec(cpipe, cpipe->pipe_lock, PRIBIO, "pipecl", INFSLP);
        }

        /* Disconnect from peer. */
        if ((ppipe = cpipe->pipe_peer) != NULL) {
                pipe_wakeup(ppipe);

                ppipe->pipe_state |= PIPE_EOF;
                wakeup(ppipe);
                ppipe->pipe_peer = NULL;
        }

        pipe_buffer_free(cpipe);

        rw_exit_write(cpipe->pipe_lock);

        if (ppipe == NULL)
                pipe_pair_destroy(cpipe->pipe_pair);
}

/*
 * Returns non-zero if a rundown is currently ongoing.
 */
int
pipe_rundown(struct pipe *cpipe)
{
        rw_assert_wrlock(cpipe->pipe_lock);

        if (cpipe->pipe_busy > 0 || (cpipe->pipe_state & PIPE_WANTD) == 0)
                return (0);

        /* Only wakeup pipe_destroy() once the pipe is no longer busy. */
        cpipe->pipe_state &= ~(PIPE_WANTD | PIPE_WANTR | PIPE_WANTW);
        wakeup(cpipe);
        return (1);
}

int
pipe_kqfilter(struct file *fp, struct knote *kn)
{
        struct pipe *rpipe = kn->kn_fp->f_data, *wpipe;
        struct rwlock *lock = rpipe->pipe_lock;
        int error = 0;

        rw_enter_write(lock);
        wpipe = pipe_peer(rpipe);

        switch (kn->kn_filter) {
        case EVFILT_READ:
                kn->kn_fop = &pipe_rfiltops;
                kn->kn_hook = rpipe;
                klist_insert_locked(&rpipe->pipe_klist, kn);
                break;
        case EVFILT_WRITE:
                if (wpipe == NULL) {
                        /*
                         * The other end of the pipe has been closed.
                         * Since the filter now always indicates a pending
                         * event, attach the knote to the current side
                         * to proceed with the registration.
                         */
                        wpipe = rpipe;
                }
                kn->kn_fop = &pipe_wfiltops;
                kn->kn_hook = wpipe;
                klist_insert_locked(&wpipe->pipe_klist, kn);
                break;
        case EVFILT_EXCEPT:
                if (kn->kn_flags & __EV_SELECT) {
                        /* Prevent triggering exceptfds. */
                        error = EPERM;
                        break;
                }
                if ((kn->kn_flags & __EV_POLL) == 0) {
                        /* Disallow usage through kevent(2). */
                        error = EINVAL;
                        break;
                }
                kn->kn_fop = &pipe_efiltops;
                kn->kn_hook = rpipe;
                klist_insert_locked(&rpipe->pipe_klist, kn);
                break;
        default:
                error = EINVAL;
        }

        rw_exit_write(lock);

        return (error);
}

void
filt_pipedetach(struct knote *kn)
{
        struct pipe *cpipe = kn->kn_hook;

        klist_remove(&cpipe->pipe_klist, kn);
}

int
filt_piperead(struct knote *kn, long hint)
{
        struct pipe *rpipe = kn->kn_fp->f_data, *wpipe;

        rw_assert_wrlock(rpipe->pipe_lock);

        wpipe = pipe_peer(rpipe);

        kn->kn_data = rpipe->pipe_buffer.cnt;

        if ((rpipe->pipe_state & PIPE_EOF) || wpipe == NULL) {
                kn->kn_flags |= EV_EOF; 
                if (kn->kn_flags & __EV_POLL)
                        kn->kn_flags |= __EV_HUP;
                return (1);
        }

        return (kn->kn_data > 0);
}

int
filt_pipewrite(struct knote *kn, long hint)
{
        struct pipe *rpipe = kn->kn_fp->f_data, *wpipe;

        rw_assert_wrlock(rpipe->pipe_lock);

        wpipe = pipe_peer(rpipe);

        if (wpipe == NULL) {
                kn->kn_data = 0;
                kn->kn_flags |= EV_EOF; 
                if (kn->kn_flags & __EV_POLL)
                        kn->kn_flags |= __EV_HUP;
                return (1);
        }
        kn->kn_data = wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt;

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

int
filt_pipeexcept(struct knote *kn, long hint)
{
        struct pipe *rpipe = kn->kn_fp->f_data, *wpipe;
        int active = 0;

        rw_assert_wrlock(rpipe->pipe_lock);

        wpipe = pipe_peer(rpipe);

        if (kn->kn_flags & __EV_POLL) {
                if ((rpipe->pipe_state & PIPE_EOF) || wpipe == NULL) {
                        kn->kn_flags |= __EV_HUP;
                        active = 1;
                }
        }

        return (active);
}

int
filt_pipemodify(struct kevent *kev, struct knote *kn)
{
        struct pipe *rpipe = kn->kn_fp->f_data;
        int active;

        rw_enter_write(rpipe->pipe_lock);
        active = knote_modify(kev, kn);
        rw_exit_write(rpipe->pipe_lock);

        return (active);
}

int
filt_pipeprocess(struct knote *kn, struct kevent *kev)
{
        struct pipe *rpipe = kn->kn_fp->f_data;
        int active;

        rw_enter_write(rpipe->pipe_lock);
        active = knote_process(kn, kev);
        rw_exit_write(rpipe->pipe_lock);

        return (active);
}

void
pipe_init(void)
{
        pool_init(&pipe_pair_pool, sizeof(struct pipe_pair), 0, IPL_MPFLOOR,
            PR_WAITOK, "pipepl", NULL);
}

struct pipe_pair *
pipe_pair_create(void)
{
        struct pipe_pair *pp;

        pp = pool_get(&pipe_pair_pool, PR_WAITOK | PR_ZERO);
        pp->pp_wpipe.pipe_pair = pp;
        pp->pp_rpipe.pipe_pair = pp;
        pp->pp_wpipe.pipe_peer = &pp->pp_rpipe;
        pp->pp_rpipe.pipe_peer = &pp->pp_wpipe;
        /*
         * One lock is used per pipe pair in order to obtain exclusive access to
         * the pipe pair.
         */
        rw_init(&pp->pp_lock, "pipelk");
        pp->pp_wpipe.pipe_lock = &pp->pp_lock;
        pp->pp_rpipe.pipe_lock = &pp->pp_lock;

        klist_init_rwlock(&pp->pp_wpipe.pipe_klist, &pp->pp_lock);
        klist_init_rwlock(&pp->pp_rpipe.pipe_klist, &pp->pp_lock);

        if (pipe_create(&pp->pp_wpipe) || pipe_create(&pp->pp_rpipe))
                goto err;
        return (pp);
err:
        pipe_destroy(&pp->pp_wpipe);
        pipe_destroy(&pp->pp_rpipe);
        return (NULL);
}

void
pipe_pair_destroy(struct pipe_pair *pp)
{
        klist_free(&pp->pp_wpipe.pipe_klist);
        klist_free(&pp->pp_rpipe.pipe_klist);
        pool_put(&pipe_pair_pool, pp);
}