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[netbsd-mini2440.git] / sys / kern / sys_pipe.c

/*      $NetBSD: sys_pipe.c,v 1.126 2009/12/15 18:35:18 dsl Exp $       */

/*-
 * Copyright (c) 2003, 2007, 2008, 2009 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Paul Kranenburg, and by Andrew Doran.
 *
 * 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, 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * 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.  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 mapped read-only into the kernel address space
 * using the UVM page loan facility from where the receiving process can copy
 * the data directly from the pages in the sending process.
 *
 * 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.  PIPE_SIZE is constrained by the
 * amount of kernel virtual memory.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: sys_pipe.c,v 1.126 2009/12/15 18:35:18 dsl Exp $");

#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/filio.h>
#include <sys/kernel.h>
#include <sys/ttycom.h>
#include <sys/stat.h>
#include <sys/poll.h>
#include <sys/signalvar.h>
#include <sys/vnode.h>
#include <sys/uio.h>
#include <sys/select.h>
#include <sys/mount.h>
#include <sys/syscallargs.h>
#include <sys/sysctl.h>
#include <sys/kauth.h>
#include <sys/atomic.h>
#include <sys/pipe.h>

#include <uvm/uvm.h>

/*
 * Use this to disable direct I/O and decrease the code size:
 * #define PIPE_NODIRECT
 */

/* XXX Disabled for now; rare hangs switching between direct/buffered */        
#define PIPE_NODIRECT

static int      pipe_read(file_t *, off_t *, struct uio *, kauth_cred_t, int);
static int      pipe_write(file_t *, off_t *, struct uio *, kauth_cred_t, int);
static int      pipe_close(file_t *);
static int      pipe_poll(file_t *, int);
static int      pipe_kqfilter(file_t *, struct knote *);
static int      pipe_stat(file_t *, struct stat *);
static int      pipe_ioctl(file_t *, u_long, void *);
static void     pipe_restart(file_t *);

static const struct fileops pipeops = {
        .fo_read = pipe_read,
        .fo_write = pipe_write,
        .fo_ioctl = pipe_ioctl,
        .fo_fcntl = fnullop_fcntl,
        .fo_poll = pipe_poll,
        .fo_stat = pipe_stat,
        .fo_close = pipe_close,
        .fo_kqfilter = pipe_kqfilter,
        .fo_restart = pipe_restart,
};

/*
 * 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)

/*
 * Maximum amount of kva for pipes -- this is kind-of a soft limit, but
 * is there so that on large systems, we don't exhaust it.
 */
#define MAXPIPEKVA      (8 * 1024 * 1024)
static u_int    maxpipekva = MAXPIPEKVA;

/*
 * Limit for direct transfers, we cannot, of course limit
 * the amount of kva for pipes in general though.
 */
#define LIMITPIPEKVA    (16 * 1024 * 1024)
static u_int    limitpipekva = LIMITPIPEKVA;

/*
 * Limit the number of "big" pipes
 */
#define LIMITBIGPIPES   32
static u_int    maxbigpipes = LIMITBIGPIPES;
static u_int    nbigpipe = 0;

/*
 * Amount of KVA consumed by pipe buffers.
 */
static u_int    amountpipekva = 0;

static void     pipeclose(struct pipe *);
static void     pipe_free_kmem(struct pipe *);
static int      pipe_create(struct pipe **, pool_cache_t);
static int      pipelock(struct pipe *, int);
static inline void pipeunlock(struct pipe *);
static void     pipeselwakeup(struct pipe *, struct pipe *, int);
#ifndef PIPE_NODIRECT
static int      pipe_direct_write(file_t *, struct pipe *, struct uio *);
#endif
static int      pipespace(struct pipe *, int);
static int      pipe_ctor(void *, void *, int);
static void     pipe_dtor(void *, void *);

#ifndef PIPE_NODIRECT
static int      pipe_loan_alloc(struct pipe *, int);
static void     pipe_loan_free(struct pipe *);
#endif /* PIPE_NODIRECT */

static pool_cache_t     pipe_wr_cache;
static pool_cache_t     pipe_rd_cache;

void
pipe_init(void)
{

        /* Writer side is not automatically allocated KVA. */
        pipe_wr_cache = pool_cache_init(sizeof(struct pipe), 0, 0, 0, "pipewr",
            NULL, IPL_NONE, pipe_ctor, pipe_dtor, NULL);
        KASSERT(pipe_wr_cache != NULL);

        /* Reader side gets preallocated KVA. */
        pipe_rd_cache = pool_cache_init(sizeof(struct pipe), 0, 0, 0, "piperd",
            NULL, IPL_NONE, pipe_ctor, pipe_dtor, (void *)1);
        KASSERT(pipe_rd_cache != NULL);
}

static int
pipe_ctor(void *arg, void *obj, int flags)
{
        struct pipe *pipe;
        vaddr_t va;

        pipe = obj;

        memset(pipe, 0, sizeof(struct pipe));
        if (arg != NULL) {
                /* Preallocate space. */
                va = uvm_km_alloc(kernel_map, PIPE_SIZE, 0,
                    UVM_KMF_PAGEABLE | UVM_KMF_WAITVA);
                KASSERT(va != 0);
                pipe->pipe_kmem = va;
                atomic_add_int(&amountpipekva, PIPE_SIZE);
        }
        cv_init(&pipe->pipe_rcv, "piperd");
        cv_init(&pipe->pipe_wcv, "pipewr");
        cv_init(&pipe->pipe_draincv, "pipedrain");
        cv_init(&pipe->pipe_lkcv, "pipelk");
        selinit(&pipe->pipe_sel);
        pipe->pipe_state = PIPE_SIGNALR;

        return 0;
}

static void
pipe_dtor(void *arg, void *obj)
{
        struct pipe *pipe;

        pipe = obj;

        cv_destroy(&pipe->pipe_rcv);
        cv_destroy(&pipe->pipe_wcv);
        cv_destroy(&pipe->pipe_draincv);
        cv_destroy(&pipe->pipe_lkcv);
        seldestroy(&pipe->pipe_sel);
        if (pipe->pipe_kmem != 0) {
                uvm_km_free(kernel_map, pipe->pipe_kmem, PIPE_SIZE,
                    UVM_KMF_PAGEABLE);
                atomic_add_int(&amountpipekva, -PIPE_SIZE);
        }
}

/*
 * The pipe system call for the DTYPE_PIPE type of pipes
 */
int
sys_pipe(struct lwp *l, const void *v, register_t *retval)
{
        struct pipe *rpipe, *wpipe;
        file_t *rf, *wf;
        int fd, error;
        proc_t *p;

        p = curproc;
        rpipe = wpipe = NULL;
        if (pipe_create(&rpipe, pipe_rd_cache) ||
            pipe_create(&wpipe, pipe_wr_cache)) {
                error = ENOMEM;
                goto free2;
        }
        rpipe->pipe_lock = mutex_obj_alloc(MUTEX_DEFAULT, IPL_NONE);
        wpipe->pipe_lock = rpipe->pipe_lock;
        mutex_obj_hold(wpipe->pipe_lock);

        error = fd_allocfile(&rf, &fd);
        if (error)
                goto free2;
        retval[0] = fd;
        rf->f_flag = FREAD;
        rf->f_type = DTYPE_PIPE;
        rf->f_data = (void *)rpipe;
        rf->f_ops = &pipeops;

        error = fd_allocfile(&wf, &fd);
        if (error)
                goto free3;
        retval[1] = fd;
        wf->f_flag = FWRITE;
        wf->f_type = DTYPE_PIPE;
        wf->f_data = (void *)wpipe;
        wf->f_ops = &pipeops;

        rpipe->pipe_peer = wpipe;
        wpipe->pipe_peer = rpipe;

        fd_affix(p, rf, (int)retval[0]);
        fd_affix(p, wf, (int)retval[1]);
        return (0);
free3:
        fd_abort(p, rf, (int)retval[0]);
free2:
        pipeclose(wpipe);
        pipeclose(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.
 */
static int
pipespace(struct pipe *pipe, int size)
{
        void *buffer;

        /*
         * Allocate pageable virtual address space.  Physical memory is
         * allocated on demand.
         */
        if (size == PIPE_SIZE && pipe->pipe_kmem != 0) {
                buffer = (void *)pipe->pipe_kmem;
        } else {
                buffer = (void *)uvm_km_alloc(kernel_map, round_page(size),
                    0, UVM_KMF_PAGEABLE);
                if (buffer == NULL)
                        return (ENOMEM);
                atomic_add_int(&amountpipekva, size);
        }

        /* free old resources if we're resizing */
        pipe_free_kmem(pipe);
        pipe->pipe_buffer.buffer = buffer;
        pipe->pipe_buffer.size = size;
        pipe->pipe_buffer.in = 0;
        pipe->pipe_buffer.out = 0;
        pipe->pipe_buffer.cnt = 0;
        return (0);
}

/*
 * Initialize and allocate VM and memory for pipe.
 */
static int
pipe_create(struct pipe **pipep, pool_cache_t cache)
{
        struct pipe *pipe;
        int error;

        pipe = pool_cache_get(cache, PR_WAITOK);
        KASSERT(pipe != NULL);
        *pipep = pipe;
        error = 0;
        getnanotime(&pipe->pipe_btime);
        pipe->pipe_atime = pipe->pipe_mtime = pipe->pipe_btime;
        pipe->pipe_lock = NULL;
        if (cache == pipe_rd_cache) {
                error = pipespace(pipe, PIPE_SIZE);
        } else {
                pipe->pipe_buffer.buffer = NULL;
                pipe->pipe_buffer.size = 0;
                pipe->pipe_buffer.in = 0;
                pipe->pipe_buffer.out = 0;
                pipe->pipe_buffer.cnt = 0;
        }
        return error;
}

/*
 * Lock a pipe for I/O, blocking other access
 * Called with pipe spin lock held.
 */
static int
pipelock(struct pipe *pipe, int catch)
{
        int error;

        KASSERT(mutex_owned(pipe->pipe_lock));

        while (pipe->pipe_state & PIPE_LOCKFL) {
                pipe->pipe_state |= PIPE_LWANT;
                if (catch) {
                        error = cv_wait_sig(&pipe->pipe_lkcv, pipe->pipe_lock);
                        if (error != 0)
                                return error;
                } else
                        cv_wait(&pipe->pipe_lkcv, pipe->pipe_lock);
        }

        pipe->pipe_state |= PIPE_LOCKFL;

        return 0;
}

/*
 * unlock a pipe I/O lock
 */
static inline void
pipeunlock(struct pipe *pipe)
{

        KASSERT(pipe->pipe_state & PIPE_LOCKFL);

        pipe->pipe_state &= ~PIPE_LOCKFL;
        if (pipe->pipe_state & PIPE_LWANT) {
                pipe->pipe_state &= ~PIPE_LWANT;
                cv_broadcast(&pipe->pipe_lkcv);
        }
}

/*
 * Select/poll wakup. This also sends SIGIO to peer connected to
 * 'sigpipe' side of pipe.
 */
static void
pipeselwakeup(struct pipe *selp, struct pipe *sigp, int code)
{
        int band;

        switch (code) {
        case POLL_IN:
                band = POLLIN|POLLRDNORM;
                break;
        case POLL_OUT:
                band = POLLOUT|POLLWRNORM;
                break;
        case POLL_HUP:
                band = POLLHUP;
                break;
        case POLL_ERR:
                band = POLLERR;
                break;
        default:
                band = 0;
#ifdef DIAGNOSTIC
                printf("bad siginfo code %d in pipe notification.\n", code);
#endif
                break;
        }

        selnotify(&selp->pipe_sel, band, NOTE_SUBMIT);

        if (sigp == NULL || (sigp->pipe_state & PIPE_ASYNC) == 0)
                return;

        fownsignal(sigp->pipe_pgid, SIGIO, code, band, selp);
}

static int
pipe_read(file_t *fp, off_t *offset, struct uio *uio, kauth_cred_t cred,
    int flags)
{
        struct pipe *rpipe = (struct pipe *) fp->f_data;
        struct pipebuf *bp = &rpipe->pipe_buffer;
        kmutex_t *lock = rpipe->pipe_lock;
        int error;
        size_t nread = 0;
        size_t size;
        size_t ocnt;
        unsigned int wakeup_state = 0;

        mutex_enter(lock);
        ++rpipe->pipe_busy;
        ocnt = bp->cnt;

again:
        error = pipelock(rpipe, 1);
        if (error)
                goto unlocked_error;

        while (uio->uio_resid) {
                /*
                 * Normal pipe buffer receive.
                 */
                if (bp->cnt > 0) {
                        size = bp->size - bp->out;
                        if (size > bp->cnt)
                                size = bp->cnt;
                        if (size > uio->uio_resid)
                                size = uio->uio_resid;

                        mutex_exit(lock);
                        error = uiomove((char *)bp->buffer + bp->out, size, uio);
                        mutex_enter(lock);
                        if (error)
                                break;

                        bp->out += size;
                        if (bp->out >= bp->size)
                                bp->out = 0;

                        bp->cnt -= size;

                        /*
                         * If there is no more to read in the pipe, reset
                         * its pointers to the beginning.  This improves
                         * cache hit stats.
                         */
                        if (bp->cnt == 0) {
                                bp->in = 0;
                                bp->out = 0;
                        }
                        nread += size;
                        continue;
                }

#ifndef PIPE_NODIRECT
                if ((rpipe->pipe_state & PIPE_DIRECTR) != 0) {
                        /*
                         * Direct copy, bypassing a kernel buffer.
                         */
                        void *va;
                        u_int gen;

                        KASSERT(rpipe->pipe_state & PIPE_DIRECTW);

                        size = rpipe->pipe_map.cnt;
                        if (size > uio->uio_resid)
                                size = uio->uio_resid;

                        va = (char *)rpipe->pipe_map.kva + rpipe->pipe_map.pos;
                        gen = rpipe->pipe_map.egen;
                        mutex_exit(lock);

                        /*
                         * Consume emap and read the data from loaned pages.
                         */
                        uvm_emap_consume(gen);
                        error = uiomove(va, size, uio);

                        mutex_enter(lock);
                        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_DIRECTR;
                                cv_broadcast(&rpipe->pipe_wcv);
                        }
                        continue;
                }
#endif
                /*
                 * Break if some data was read.
                 */
                if (nread > 0)
                        break;

                /*
                 * Detect EOF condition.
                 * Read returns 0 on EOF, no need to set error.
                 */
                if (rpipe->pipe_state & PIPE_EOF)
                        break;

                /*
                 * Don't block on non-blocking I/O.
                 */
                if (fp->f_flag & FNONBLOCK) {
                        error = EAGAIN;
                        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);

                /*
                 * Re-check to see if more direct writes are pending.
                 */
                if ((rpipe->pipe_state & PIPE_DIRECTR) != 0)
                        goto again;

#if 1   /* XXX (dsl) I'm sure these aren't needed here ... */
                /*
                 * We want to read more, wake up select/poll.
                 */
                pipeselwakeup(rpipe, rpipe->pipe_peer, POLL_OUT);

                /*
                 * If the "write-side" is blocked, wake it up now.
                 */
                cv_broadcast(&rpipe->pipe_wcv);
#endif

                if (wakeup_state & PIPE_RESTART) {
                        error = ERESTART;
                        goto unlocked_error;
                }

                /* Now wait until the pipe is filled */
                error = cv_wait_sig(&rpipe->pipe_rcv, lock);
                if (error != 0)
                        goto unlocked_error;
                wakeup_state = rpipe->pipe_state;
                goto again;
        }

        if (error == 0)
                getnanotime(&rpipe->pipe_atime);
        pipeunlock(rpipe);

unlocked_error:
        --rpipe->pipe_busy;
        if (rpipe->pipe_busy == 0) {
                rpipe->pipe_state &= ~PIPE_RESTART;
                cv_broadcast(&rpipe->pipe_draincv);
        }
        if (bp->cnt < MINPIPESIZE) {
                cv_broadcast(&rpipe->pipe_wcv);
        }

        /*
         * If anything was read off the buffer, signal to the writer it's
         * possible to write more data. Also send signal if we are here for the
         * first time after last write.
         */
        if ((bp->size - bp->cnt) >= PIPE_BUF
            && (ocnt != bp->cnt || (rpipe->pipe_state & PIPE_SIGNALR))) {
                pipeselwakeup(rpipe, rpipe->pipe_peer, POLL_OUT);
                rpipe->pipe_state &= ~PIPE_SIGNALR;
        }

        mutex_exit(lock);
        return (error);
}

#ifndef PIPE_NODIRECT
/*
 * Allocate structure for loan transfer.
 */
static int
pipe_loan_alloc(struct pipe *wpipe, int npages)
{
        vsize_t len;

        len = (vsize_t)npages << PAGE_SHIFT;
        atomic_add_int(&amountpipekva, len);
        wpipe->pipe_map.kva = uvm_km_alloc(kernel_map, len, 0,
            UVM_KMF_VAONLY | UVM_KMF_WAITVA);
        if (wpipe->pipe_map.kva == 0) {
                atomic_add_int(&amountpipekva, -len);
                return (ENOMEM);
        }

        wpipe->pipe_map.npages = npages;
        wpipe->pipe_map.pgs = kmem_alloc(npages * sizeof(struct vm_page *),
            KM_SLEEP);
        return (0);
}

/*
 * Free resources allocated for loan transfer.
 */
static void
pipe_loan_free(struct pipe *wpipe)
{
        vsize_t len;

        len = (vsize_t)wpipe->pipe_map.npages << PAGE_SHIFT;
        uvm_emap_remove(wpipe->pipe_map.kva, len);      /* XXX */
        uvm_km_free(kernel_map, wpipe->pipe_map.kva, len, UVM_KMF_VAONLY);
        wpipe->pipe_map.kva = 0;
        atomic_add_int(&amountpipekva, -len);
        kmem_free(wpipe->pipe_map.pgs,
            wpipe->pipe_map.npages * sizeof(struct vm_page *));
        wpipe->pipe_map.pgs = NULL;
}

/*
 * NetBSD direct write, using uvm_loan() mechanism.
 * 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.
 *
 * Called with the long-term pipe lock held.
 */
static int
pipe_direct_write(file_t *fp, struct pipe *wpipe, struct uio *uio)
{
        struct vm_page **pgs;
        vaddr_t bbase, base, bend;
        vsize_t blen, bcnt;
        int error, npages;
        voff_t bpos;
        kmutex_t *lock = wpipe->pipe_lock;

        KASSERT(mutex_owned(wpipe->pipe_lock));
        KASSERT(wpipe->pipe_map.cnt == 0);

        mutex_exit(lock);

        /*
         * Handle first PIPE_CHUNK_SIZE bytes of buffer. Deal with buffers
         * not aligned to PAGE_SIZE.
         */
        bbase = (vaddr_t)uio->uio_iov->iov_base;
        base = trunc_page(bbase);
        bend = round_page(bbase + uio->uio_iov->iov_len);
        blen = bend - base;
        bpos = bbase - base;

        if (blen > PIPE_DIRECT_CHUNK) {
                blen = PIPE_DIRECT_CHUNK;
                bend = base + blen;
                bcnt = PIPE_DIRECT_CHUNK - bpos;
        } else {
                bcnt = uio->uio_iov->iov_len;
        }
        npages = blen >> PAGE_SHIFT;

        /*
         * Free the old kva if we need more pages than we have
         * allocated.
         */
        if (wpipe->pipe_map.kva != 0 && npages > wpipe->pipe_map.npages)
                pipe_loan_free(wpipe);

        /* Allocate new kva. */
        if (wpipe->pipe_map.kva == 0) {
                error = pipe_loan_alloc(wpipe, npages);
                if (error) {
                        mutex_enter(lock);
                        return (error);
                }
        }

        /* Loan the write buffer memory from writer process */
        pgs = wpipe->pipe_map.pgs;
        error = uvm_loan(&uio->uio_vmspace->vm_map, base, blen,
                         pgs, UVM_LOAN_TOPAGE);
        if (error) {
                pipe_loan_free(wpipe);
                mutex_enter(lock);
                return (ENOMEM); /* so that caller fallback to ordinary write */
        }

        /* Enter the loaned pages to KVA, produce new emap generation number. */
        uvm_emap_enter(wpipe->pipe_map.kva, pgs, npages);
        wpipe->pipe_map.egen = uvm_emap_produce();

        /* Now we can put the pipe in direct write mode */
        wpipe->pipe_map.pos = bpos;
        wpipe->pipe_map.cnt = bcnt;

        /*
         * But before we can let someone do a direct read, we
         * have to wait until the pipe is drained.  Release the
         * pipe lock while we wait.
         */
        mutex_enter(lock);
        wpipe->pipe_state |= PIPE_DIRECTW;
        pipeunlock(wpipe);

        while (error == 0 && wpipe->pipe_buffer.cnt > 0) {
                cv_broadcast(&wpipe->pipe_rcv);
                error = cv_wait_sig(&wpipe->pipe_wcv, lock);
                if (error == 0 && wpipe->pipe_state & PIPE_EOF)
                        error = EPIPE;
        }

        /* Pipe is drained; next read will off the direct buffer */
        wpipe->pipe_state |= PIPE_DIRECTR;

        /* Wait until the reader is done */
        while (error == 0 && (wpipe->pipe_state & PIPE_DIRECTR)) {
                cv_broadcast(&wpipe->pipe_rcv);
                pipeselwakeup(wpipe, wpipe, POLL_IN);
                error = cv_wait_sig(&wpipe->pipe_wcv, lock);
                if (error == 0 && wpipe->pipe_state & PIPE_EOF)
                        error = EPIPE;
        }

        /* Take pipe out of direct write mode */
        wpipe->pipe_state &= ~(PIPE_DIRECTW | PIPE_DIRECTR);

        /* Acquire the pipe lock and cleanup */
        (void)pipelock(wpipe, 0);
        mutex_exit(lock);

        if (pgs != NULL) {
                /* XXX: uvm_emap_remove */
                uvm_unloan(pgs, npages, UVM_LOAN_TOPAGE);
        }
        if (error || amountpipekva > maxpipekva)
                pipe_loan_free(wpipe);

        mutex_enter(lock);
        if (error) {
                pipeselwakeup(wpipe, wpipe, POLL_ERR);

                /*
                 * If nothing was read from what we offered, return error
                 * straight on. Otherwise update uio resid first. Caller
                 * will deal with the error condition, returning short
                 * write, error, or restarting the write(2) as appropriate.
                 */
                if (wpipe->pipe_map.cnt == bcnt) {
                        wpipe->pipe_map.cnt = 0;
                        cv_broadcast(&wpipe->pipe_wcv);
                        return (error);
                }

                bcnt -= wpipe->pipe_map.cnt;
        }

        uio->uio_resid -= bcnt;
        /* uio_offset not updated, not set/used for write(2) */
        uio->uio_iov->iov_base = (char *)uio->uio_iov->iov_base + bcnt;
        uio->uio_iov->iov_len -= bcnt;
        if (uio->uio_iov->iov_len == 0) {
                uio->uio_iov++;
                uio->uio_iovcnt--;
        }

        wpipe->pipe_map.cnt = 0;
        return (error);
}
#endif /* !PIPE_NODIRECT */

static int
pipe_write(file_t *fp, off_t *offset, struct uio *uio, kauth_cred_t cred,
    int flags)
{
        struct pipe *wpipe, *rpipe;
        struct pipebuf *bp;
        kmutex_t *lock;
        int error;
        unsigned int wakeup_state = 0;

        /* We want to write to our peer */
        rpipe = (struct pipe *) fp->f_data;
        lock = rpipe->pipe_lock;
        error = 0;

        mutex_enter(lock);
        wpipe = rpipe->pipe_peer;

        /*
         * Detect loss of pipe read side, issue SIGPIPE if lost.
         */
        if (wpipe == NULL || (wpipe->pipe_state & PIPE_EOF) != 0) {
                mutex_exit(lock);
                return EPIPE;
        }
        ++wpipe->pipe_busy;

        /* Aquire the long-term pipe lock */
        if ((error = pipelock(wpipe, 1)) != 0) {
                --wpipe->pipe_busy;
                if (wpipe->pipe_busy == 0) {
                        wpipe->pipe_state &= ~PIPE_RESTART;
                        cv_broadcast(&wpipe->pipe_draincv);
                }
                mutex_exit(lock);
                return (error);
        }

        bp = &wpipe->pipe_buffer;

        /*
         * If it is advantageous to resize the pipe buffer, do so.
         */
        if ((uio->uio_resid > PIPE_SIZE) &&
            (nbigpipe < maxbigpipes) &&
#ifndef PIPE_NODIRECT
            (wpipe->pipe_state & PIPE_DIRECTW) == 0 &&
#endif
            (bp->size <= PIPE_SIZE) && (bp->cnt == 0)) {

                if (pipespace(wpipe, BIG_PIPE_SIZE) == 0)
                        atomic_inc_uint(&nbigpipe);
        }

        while (uio->uio_resid) {
                size_t space;

#ifndef PIPE_NODIRECT
                /*
                 * Pipe buffered writes cannot be coincidental with
                 * direct writes.  Also, only one direct write can be
                 * in progress at any one time.  We wait until the currently
                 * executing direct write is completed before continuing.
                 *
                 * We break out if a signal occurs or the reader goes away.
                 */
                while (error == 0 && wpipe->pipe_state & PIPE_DIRECTW) {
                        cv_broadcast(&wpipe->pipe_rcv);
                        pipeunlock(wpipe);
                        error = cv_wait_sig(&wpipe->pipe_wcv, lock);
                        (void)pipelock(wpipe, 0);
                        if (wpipe->pipe_state & PIPE_EOF)
                                error = EPIPE;
                }
                if (error)
                        break;

                /*
                 * 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_iov->iov_len >= PIPE_MINDIRECT) &&
                    (fp->f_flag & FNONBLOCK) == 0 &&
                    (wpipe->pipe_map.kva || (amountpipekva < limitpipekva))) {
                        error = pipe_direct_write(fp, wpipe, uio);

                        /*
                         * Break out if error occurred, unless it's ENOMEM.
                         * ENOMEM means we failed to allocate some resources
                         * for direct write, so we just fallback to ordinary
                         * write. If the direct write was successful,
                         * process rest of data via ordinary write.
                         */
                        if (error == 0)
                                continue;

                        if (error != ENOMEM)
                                break;
                }
#endif /* PIPE_NODIRECT */

                space = bp->size - bp->cnt;

                /* Writes of size <= PIPE_BUF must be atomic. */
                if ((space < uio->uio_resid) && (uio->uio_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 = bp->size - bp->in;
                        if (segsize > size)
                                segsize = size;

                        /* Transfer first segment */
                        mutex_exit(lock);
                        error = uiomove((char *)bp->buffer + bp->in, segsize,
                            uio);

                        if (error == 0 && segsize < size) {
                                /*
                                 * Transfer remaining part now, to
                                 * support atomic writes.  Wraparound
                                 * happened.
                                 */
                                KASSERT(bp->in + segsize == bp->size);
                                error = uiomove(bp->buffer,
                                    size - segsize, uio);
                        }
                        mutex_enter(lock);
                        if (error)
                                break;

                        bp->in += size;
                        if (bp->in >= bp->size) {
                                KASSERT(bp->in == size - segsize + bp->size);
                                bp->in = size - segsize;
                        }

                        bp->cnt += size;
                        KASSERT(bp->cnt <= bp->size);
                        wakeup_state = 0;
                } else {
                        /*
                         * If the "read-side" has been blocked, wake it up now.
                         */
                        cv_broadcast(&wpipe->pipe_rcv);

                        /*
                         * 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.
                         */
                        if (bp->cnt)
                                pipeselwakeup(wpipe, wpipe, POLL_IN);

                        if (wakeup_state & PIPE_RESTART) {
                                error = ERESTART;
                                break;
                        }

                        pipeunlock(wpipe);
                        error = cv_wait_sig(&wpipe->pipe_wcv, lock);
                        (void)pipelock(wpipe, 0);
                        if (error != 0)
                                break;
                        /*
                         * If read side wants to go away, we just issue a signal
                         * to ourselves.
                         */
                        if (wpipe->pipe_state & PIPE_EOF) {
                                error = EPIPE;
                                break;
                        }
                        wakeup_state = wpipe->pipe_state;
                }
        }

        --wpipe->pipe_busy;
        if (wpipe->pipe_busy == 0) {
                wpipe->pipe_state &= ~PIPE_RESTART;
                cv_broadcast(&wpipe->pipe_draincv);
        }
        if (bp->cnt > 0) {
                cv_broadcast(&wpipe->pipe_rcv);
        }

        /*
         * Don't return EPIPE if I/O was successful
         */
        if (error == EPIPE && bp->cnt == 0 && uio->uio_resid == 0)
                error = 0;

        if (error == 0)
                getnanotime(&wpipe->pipe_mtime);

        /*
         * We have something to offer, wake up select/poll.
         * wpipe->pipe_map.cnt is always 0 in this point (direct write
         * is only done synchronously), so check only wpipe->pipe_buffer.cnt
         */
        if (bp->cnt)
                pipeselwakeup(wpipe, wpipe, POLL_IN);

        /*
         * Arrange for next read(2) to do a signal.
         */
        wpipe->pipe_state |= PIPE_SIGNALR;

        pipeunlock(wpipe);
        mutex_exit(lock);
        return (error);
}

/*
 * We implement a very minimal set of ioctls for compatibility with sockets.
 */
int
pipe_ioctl(file_t *fp, u_long cmd, void *data)
{
        struct pipe *pipe = fp->f_data;
        kmutex_t *lock = pipe->pipe_lock;

        switch (cmd) {

        case FIONBIO:
                return (0);

        case FIOASYNC:
                mutex_enter(lock);
                if (*(int *)data) {
                        pipe->pipe_state |= PIPE_ASYNC;
                } else {
                        pipe->pipe_state &= ~PIPE_ASYNC;
                }
                mutex_exit(lock);
                return (0);

        case FIONREAD:
                mutex_enter(lock);
#ifndef PIPE_NODIRECT
                if (pipe->pipe_state & PIPE_DIRECTW)
                        *(int *)data = pipe->pipe_map.cnt;
                else
#endif
                        *(int *)data = pipe->pipe_buffer.cnt;
                mutex_exit(lock);
                return (0);

        case FIONWRITE:
                /* Look at other side */
                pipe = pipe->pipe_peer;
                mutex_enter(lock);
#ifndef PIPE_NODIRECT
                if (pipe->pipe_state & PIPE_DIRECTW)
                        *(int *)data = pipe->pipe_map.cnt;
                else
#endif
                        *(int *)data = pipe->pipe_buffer.cnt;
                mutex_exit(lock);
                return (0);

        case FIONSPACE:
                /* Look at other side */
                pipe = pipe->pipe_peer;
                mutex_enter(lock);
#ifndef PIPE_NODIRECT
                /*
                 * If we're in direct-mode, we don't really have a
                 * send queue, and any other write will block. Thus
                 * zero seems like the best answer.
                 */
                if (pipe->pipe_state & PIPE_DIRECTW)
                        *(int *)data = 0;
                else
#endif
                        *(int *)data = pipe->pipe_buffer.size -
                            pipe->pipe_buffer.cnt;
                mutex_exit(lock);
                return (0);

        case TIOCSPGRP:
        case FIOSETOWN:
                return fsetown(&pipe->pipe_pgid, cmd, data);

        case TIOCGPGRP:
        case FIOGETOWN:
                return fgetown(pipe->pipe_pgid, cmd, data);

        }
        return (EPASSTHROUGH);
}

int
pipe_poll(file_t *fp, int events)
{
        struct pipe *rpipe = fp->f_data;
        struct pipe *wpipe;
        int eof = 0;
        int revents = 0;

        mutex_enter(rpipe->pipe_lock);
        wpipe = rpipe->pipe_peer;

        if (events & (POLLIN | POLLRDNORM))
                if ((rpipe->pipe_buffer.cnt > 0) ||
#ifndef PIPE_NODIRECT
                    (rpipe->pipe_state & PIPE_DIRECTR) ||
#endif
                    (rpipe->pipe_state & PIPE_EOF))
                        revents |= events & (POLLIN | POLLRDNORM);

        eof |= (rpipe->pipe_state & PIPE_EOF);

        if (wpipe == NULL)
                revents |= events & (POLLOUT | POLLWRNORM);
        else {
                if (events & (POLLOUT | POLLWRNORM))
                        if ((wpipe->pipe_state & PIPE_EOF) || (
#ifndef PIPE_NODIRECT
                             (wpipe->pipe_state & PIPE_DIRECTW) == 0 &&
#endif
                             (wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt) >= PIPE_BUF))
                                revents |= events & (POLLOUT | POLLWRNORM);

                eof |= (wpipe->pipe_state & PIPE_EOF);
        }

        if (wpipe == NULL || eof)
                revents |= POLLHUP;

        if (revents == 0) {
                if (events & (POLLIN | POLLRDNORM))
                        selrecord(curlwp, &rpipe->pipe_sel);

                if (events & (POLLOUT | POLLWRNORM))
                        selrecord(curlwp, &wpipe->pipe_sel);
        }
        mutex_exit(rpipe->pipe_lock);

        return (revents);
}

static int
pipe_stat(file_t *fp, struct stat *ub)
{
        struct pipe *pipe = fp->f_data;

        mutex_enter(pipe->pipe_lock);
        memset(ub, 0, sizeof(*ub));
        ub->st_mode = S_IFIFO | S_IRUSR | S_IWUSR;
        ub->st_blksize = pipe->pipe_buffer.size;
        if (ub->st_blksize == 0 && pipe->pipe_peer)
                ub->st_blksize = pipe->pipe_peer->pipe_buffer.size;
        ub->st_size = pipe->pipe_buffer.cnt;
        ub->st_blocks = (ub->st_size) ? 1 : 0;
        ub->st_atimespec = pipe->pipe_atime;
        ub->st_mtimespec = pipe->pipe_mtime;
        ub->st_ctimespec = ub->st_birthtimespec = pipe->pipe_btime;
        ub->st_uid = kauth_cred_geteuid(fp->f_cred);
        ub->st_gid = kauth_cred_getegid(fp->f_cred);

        /*
         * Left as 0: st_dev, st_ino, st_nlink, st_rdev, st_flags, st_gen.
         * XXX (st_dev, st_ino) should be unique.
         */
        mutex_exit(pipe->pipe_lock);
        return 0;
}

static int
pipe_close(file_t *fp)
{
        struct pipe *pipe = fp->f_data;

        fp->f_data = NULL;
        pipeclose(pipe);
        return (0);
}

static void
pipe_restart(file_t *fp)
{
        struct pipe *pipe = fp->f_data;

        /*
         * Unblock blocked reads/writes in order to allow close() to complete.
         * System calls return ERESTART so that the fd is revalidated.
         * (Partial writes return the transfer length.)
         */
        mutex_enter(pipe->pipe_lock);
        pipe->pipe_state |= PIPE_RESTART;
        /* Wakeup both cvs, maybe we only need one, but maybe there are some
         * other paths where wakeup is needed, and it saves deciding which! */
        cv_broadcast(&pipe->pipe_rcv);
        cv_broadcast(&pipe->pipe_wcv);
        mutex_exit(pipe->pipe_lock);
}

static void
pipe_free_kmem(struct pipe *pipe)
{

        if (pipe->pipe_buffer.buffer != NULL) {
                if (pipe->pipe_buffer.size > PIPE_SIZE) {
                        atomic_dec_uint(&nbigpipe);
                }
                if (pipe->pipe_buffer.buffer != (void *)pipe->pipe_kmem) {
                        uvm_km_free(kernel_map,
                            (vaddr_t)pipe->pipe_buffer.buffer,
                            pipe->pipe_buffer.size, UVM_KMF_PAGEABLE);
                        atomic_add_int(&amountpipekva,
                            -pipe->pipe_buffer.size);
                }
                pipe->pipe_buffer.buffer = NULL;
        }
#ifndef PIPE_NODIRECT
        if (pipe->pipe_map.kva != 0) {
                pipe_loan_free(pipe);
                pipe->pipe_map.cnt = 0;
                pipe->pipe_map.kva = 0;
                pipe->pipe_map.pos = 0;
                pipe->pipe_map.npages = 0;
        }
#endif /* !PIPE_NODIRECT */
}

/*
 * Shutdown the pipe.
 */
static void
pipeclose(struct pipe *pipe)
{
        kmutex_t *lock;
        struct pipe *ppipe;

        if (pipe == NULL)
                return;

        KASSERT(cv_is_valid(&pipe->pipe_rcv));
        KASSERT(cv_is_valid(&pipe->pipe_wcv));
        KASSERT(cv_is_valid(&pipe->pipe_draincv));
        KASSERT(cv_is_valid(&pipe->pipe_lkcv));

        lock = pipe->pipe_lock;
        if (lock == NULL)
                /* Must have failed during create */
                goto free_resources;

        mutex_enter(lock);
        pipeselwakeup(pipe, pipe, POLL_HUP);

        /*
         * If the other side is blocked, wake it up saying that
         * we want to close it down.
         */
        pipe->pipe_state |= PIPE_EOF;
        if (pipe->pipe_busy) {
                while (pipe->pipe_busy) {
                        cv_broadcast(&pipe->pipe_wcv);
                        cv_wait_sig(&pipe->pipe_draincv, lock);
                }
        }

        /*
         * Disconnect from peer.
         */
        if ((ppipe = pipe->pipe_peer) != NULL) {
                pipeselwakeup(ppipe, ppipe, POLL_HUP);
                ppipe->pipe_state |= PIPE_EOF;
                cv_broadcast(&ppipe->pipe_rcv);
                ppipe->pipe_peer = NULL;
        }

        /*
         * Any knote objects still left in the list are
         * the one attached by peer.  Since no one will
         * traverse this list, we just clear it.
         */
        SLIST_INIT(&pipe->pipe_sel.sel_klist);

        KASSERT((pipe->pipe_state & PIPE_LOCKFL) == 0);
        mutex_exit(lock);
        mutex_obj_free(lock);

        /*
         * Free resources.
         */
    free_resources:
        pipe->pipe_pgid = 0;
        pipe->pipe_state = PIPE_SIGNALR;
        pipe_free_kmem(pipe);
        if (pipe->pipe_kmem != 0) {
                pool_cache_put(pipe_rd_cache, pipe);
        } else {
                pool_cache_put(pipe_wr_cache, pipe);
        }
}

static void
filt_pipedetach(struct knote *kn)
{
        struct pipe *pipe;
        kmutex_t *lock;

        pipe = ((file_t *)kn->kn_obj)->f_data;
        lock = pipe->pipe_lock;

        mutex_enter(lock);

        switch(kn->kn_filter) {
        case EVFILT_WRITE:
                /* Need the peer structure, not our own. */
                pipe = pipe->pipe_peer;

                /* If reader end already closed, just return. */
                if (pipe == NULL) {
                        mutex_exit(lock);
                        return;
                }

                break;
        default:
                /* Nothing to do. */
                break;
        }

        KASSERT(kn->kn_hook == pipe);
        SLIST_REMOVE(&pipe->pipe_sel.sel_klist, kn, knote, kn_selnext);
        mutex_exit(lock);
}

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

        if ((hint & NOTE_SUBMIT) == 0) {
                mutex_enter(rpipe->pipe_lock);
        }
        wpipe = rpipe->pipe_peer;
        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 == NULL) || (wpipe->pipe_state & PIPE_EOF)) {
                kn->kn_flags |= EV_EOF;
                if ((hint & NOTE_SUBMIT) == 0) {
                        mutex_exit(rpipe->pipe_lock);
                }
                return (1);
        }

        if ((hint & NOTE_SUBMIT) == 0) {
                mutex_exit(rpipe->pipe_lock);
        }
        return (kn->kn_data > 0);
}

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

        if ((hint & NOTE_SUBMIT) == 0) {
                mutex_enter(rpipe->pipe_lock);
        }
        wpipe = rpipe->pipe_peer;

        if ((wpipe == NULL) || (wpipe->pipe_state & PIPE_EOF)) {
                kn->kn_data = 0;
                kn->kn_flags |= EV_EOF;
                if ((hint & NOTE_SUBMIT) == 0) {
                        mutex_exit(rpipe->pipe_lock);
                }
                return (1);
        }
        kn->kn_data = wpipe->pipe_buffer.size - wpipe->pipe_buffer.cnt;
        if (wpipe->pipe_state & PIPE_DIRECTW)
                kn->kn_data = 0;

        if ((hint & NOTE_SUBMIT) == 0) {
                mutex_exit(rpipe->pipe_lock);
        }
        return (kn->kn_data >= PIPE_BUF);
}

static const struct filterops pipe_rfiltops =
        { 1, NULL, filt_pipedetach, filt_piperead };
static const struct filterops pipe_wfiltops =
        { 1, NULL, filt_pipedetach, filt_pipewrite };

static int
pipe_kqfilter(file_t *fp, struct knote *kn)
{
        struct pipe *pipe;
        kmutex_t *lock;

        pipe = ((file_t *)kn->kn_obj)->f_data;
        lock = pipe->pipe_lock;

        mutex_enter(lock);

        switch (kn->kn_filter) {
        case EVFILT_READ:
                kn->kn_fop = &pipe_rfiltops;
                break;
        case EVFILT_WRITE:
                kn->kn_fop = &pipe_wfiltops;
                pipe = pipe->pipe_peer;
                if (pipe == NULL) {
                        /* Other end of pipe has been closed. */
                        mutex_exit(lock);
                        return (EBADF);
                }
                break;
        default:
                mutex_exit(lock);
                return (EINVAL);
        }

        kn->kn_hook = pipe;
        SLIST_INSERT_HEAD(&pipe->pipe_sel.sel_klist, kn, kn_selnext);
        mutex_exit(lock);

        return (0);
}

/*
 * Handle pipe sysctls.
 */
SYSCTL_SETUP(sysctl_kern_pipe_setup, "sysctl kern.pipe subtree setup")
{

        sysctl_createv(clog, 0, NULL, NULL,
                       CTLFLAG_PERMANENT,
                       CTLTYPE_NODE, "kern", NULL,
                       NULL, 0, NULL, 0,
                       CTL_KERN, CTL_EOL);
        sysctl_createv(clog, 0, NULL, NULL,
                       CTLFLAG_PERMANENT,
                       CTLTYPE_NODE, "pipe",
                       SYSCTL_DESCR("Pipe settings"),
                       NULL, 0, NULL, 0,
                       CTL_KERN, KERN_PIPE, CTL_EOL);

        sysctl_createv(clog, 0, NULL, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "maxkvasz",
                       SYSCTL_DESCR("Maximum amount of kernel memory to be "
                                    "used for pipes"),
                       NULL, 0, &maxpipekva, 0,
                       CTL_KERN, KERN_PIPE, KERN_PIPE_MAXKVASZ, CTL_EOL);
        sysctl_createv(clog, 0, NULL, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "maxloankvasz",
                       SYSCTL_DESCR("Limit for direct transfers via page loan"),
                       NULL, 0, &limitpipekva, 0,
                       CTL_KERN, KERN_PIPE, KERN_PIPE_LIMITKVA, CTL_EOL);
        sysctl_createv(clog, 0, NULL, NULL,
                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
                       CTLTYPE_INT, "maxbigpipes",
                       SYSCTL_DESCR("Maximum number of \"big\" pipes"),
                       NULL, 0, &maxbigpipes, 0,
                       CTL_KERN, KERN_PIPE, KERN_PIPE_MAXBIGPIPES, CTL_EOL);
        sysctl_createv(clog, 0, NULL, NULL,
                       CTLFLAG_PERMANENT,
                       CTLTYPE_INT, "nbigpipes",
                       SYSCTL_DESCR("Number of \"big\" pipes"),
                       NULL, 0, &nbigpipe, 0,
                       CTL_KERN, KERN_PIPE, KERN_PIPE_NBIGPIPES, CTL_EOL);
        sysctl_createv(clog, 0, NULL, NULL,
                       CTLFLAG_PERMANENT,
                       CTLTYPE_INT, "kvasize",
                       SYSCTL_DESCR("Amount of kernel memory consumed by pipe "
                                    "buffers"),
                       NULL, 0, &amountpipekva, 0,
                       CTL_KERN, KERN_PIPE, KERN_PIPE_KVASIZE, CTL_EOL);
}