kernel - Fix excessive call stack depth on stuck interrupt

[dragonfly.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.
 *
 * $FreeBSD: src/sys/kern/sys_pipe.c,v 1.60.2.13 2002/08/05 15:05:15 des Exp $
 */

/*
 * 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/kernel.h>
#include <sys/proc.h>
#include <sys/fcntl.h>
#include <sys/file.h>
#include <sys/filedesc.h>
#include <sys/filio.h>
#include <sys/ttycom.h>
#include <sys/stat.h>
#include <sys/signalvar.h>
#include <sys/sysproto.h>
#include <sys/pipe.h>
#include <sys/vnode.h>
#include <sys/uio.h>
#include <sys/event.h>
#include <sys/globaldata.h>
#include <sys/module.h>
#include <sys/malloc.h>
#include <sys/sysctl.h>
#include <sys/socket.h>
#include <sys/kern_syscall.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <sys/lock.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/vm_zone.h>

#include <sys/file2.h>
#include <sys/signal2.h>

#include <machine/cpufunc.h>

/*
 * interfaces to the outside world
 */
static int pipe_read (struct file *fp, struct uio *uio, 
                struct ucred *cred, int flags);
static int pipe_write (struct file *fp, struct uio *uio, 
                struct ucred *cred, int flags);
static int pipe_close (struct file *fp);
static int pipe_shutdown (struct file *fp, int how);
static int pipe_kqfilter (struct file *fp, struct knote *kn);
static int pipe_stat (struct file *fp, struct stat *sb, struct ucred *cred);
static int pipe_ioctl (struct file *fp, u_long cmd, caddr_t data,
                struct ucred *cred, struct sysmsg *msg);

static 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,
        .fo_shutdown = pipe_shutdown
};

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 =
        { FILTEROP_ISFD|FILTEROP_MPSAFE, NULL, filt_pipedetach, filt_piperead };
static struct filterops pipe_wfiltops =
        { FILTEROP_ISFD|FILTEROP_MPSAFE, NULL, filt_pipedetach, filt_pipewrite };

MALLOC_DEFINE(M_PIPE, "pipe", "pipe structures");

/*
 * 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)

/*
 * Limit the number of "big" pipes
 */
#define LIMITBIGPIPES   64
#define PIPEQ_MAX_CACHE 16      /* per-cpu pipe structure cache */

static int pipe_maxbig = LIMITBIGPIPES;
static int pipe_maxcache = PIPEQ_MAX_CACHE;
static int pipe_bigcount;
static int pipe_nbig;
static int pipe_bcache_alloc;
static int pipe_bkmem_alloc;
static int pipe_rblocked_count;
static int pipe_wblocked_count;

SYSCTL_NODE(_kern, OID_AUTO, pipe, CTLFLAG_RW, 0, "Pipe operation");
SYSCTL_INT(_kern_pipe, OID_AUTO, nbig,
        CTLFLAG_RD, &pipe_nbig, 0, "number of big pipes allocated");
SYSCTL_INT(_kern_pipe, OID_AUTO, bigcount,
        CTLFLAG_RW, &pipe_bigcount, 0, "number of times pipe expanded");
SYSCTL_INT(_kern_pipe, OID_AUTO, rblocked,
        CTLFLAG_RW, &pipe_rblocked_count, 0, "number of times pipe expanded");
SYSCTL_INT(_kern_pipe, OID_AUTO, wblocked,
        CTLFLAG_RW, &pipe_wblocked_count, 0, "number of times pipe expanded");
SYSCTL_INT(_kern_pipe, OID_AUTO, maxcache,
        CTLFLAG_RW, &pipe_maxcache, 0, "max pipes cached per-cpu");
SYSCTL_INT(_kern_pipe, OID_AUTO, maxbig,
        CTLFLAG_RW, &pipe_maxbig, 0, "max number of big pipes");
static int pipe_delay = 5000;   /* 5uS default */
SYSCTL_INT(_kern_pipe, OID_AUTO, delay,
        CTLFLAG_RW, &pipe_delay, 0, "SMP delay optimization in ns");
#if !defined(NO_PIPE_SYSCTL_STATS)
SYSCTL_INT(_kern_pipe, OID_AUTO, bcache_alloc,
        CTLFLAG_RW, &pipe_bcache_alloc, 0, "pipe buffer from pcpu cache");
SYSCTL_INT(_kern_pipe, OID_AUTO, bkmem_alloc,
        CTLFLAG_RW, &pipe_bkmem_alloc, 0, "pipe buffer from kmem");
#endif

/*
 * Auto-size pipe cache to reduce kmem allocations and frees.
 */
static
void
pipeinit(void *dummy)
{
        size_t mbytes = kmem_lim_size();

        if (pipe_maxbig == LIMITBIGPIPES) {
                if (mbytes >= 7 * 1024)
                        pipe_maxbig *= 2;
                if (mbytes >= 15 * 1024)
                        pipe_maxbig *= 2;
        }
        if (pipe_maxcache == PIPEQ_MAX_CACHE) {
                if (mbytes >= 7 * 1024)
                        pipe_maxcache *= 2;
                if (mbytes >= 15 * 1024)
                        pipe_maxcache *= 2;
        }
}
SYSINIT(kmem, SI_BOOT2_MACHDEP, SI_ORDER_ANY, pipeinit, NULL);

static void pipeclose (struct pipe *cpipe);
static void pipe_free_kmem (struct pipe *cpipe);
static int pipe_create (struct pipe **cpipep);
static int pipespace (struct pipe *cpipe, int size);

static __inline void
pipewakeup(struct pipe *cpipe, int dosigio)
{
        if (dosigio && (cpipe->pipe_state & PIPE_ASYNC) && cpipe->pipe_sigio) {
                lwkt_gettoken(&sigio_token);
                pgsigio(cpipe->pipe_sigio, SIGIO, 0);
                lwkt_reltoken(&sigio_token);
        }
        KNOTE(&cpipe->pipe_kq.ki_note, 0);
}

/*
 * These routines are called before and after a UIO.  The UIO
 * may block, causing our held tokens to be lost temporarily.
 *
 * We use these routines to serialize reads against other reads
 * and writes against other writes.
 *
 * The read token is held on entry so *ipp does not race.
 */
static __inline int
pipe_start_uio(struct pipe *cpipe, int *ipp)
{
        int error;

        while (*ipp) {
                *ipp = -1;
                error = tsleep(ipp, PCATCH, "pipexx", 0);
                if (error)
                        return (error);
        }
        *ipp = 1;
        return (0);
}

static __inline void
pipe_end_uio(struct pipe *cpipe, int *ipp)
{
        if (*ipp < 0) {
                *ipp = 0;
                wakeup(ipp);
        } else {
                KKASSERT(*ipp > 0);
                *ipp = 0;
        }
}

/*
 * The pipe system call for the DTYPE_PIPE type of pipes
 *
 * pipe_args(int dummy)
 *
 * MPSAFE
 */
int
sys_pipe(struct pipe_args *uap)
{
        return kern_pipe(uap->sysmsg_fds, 0);
}

int
sys_pipe2(struct pipe2_args *uap)
{
        return kern_pipe(uap->sysmsg_fds, uap->flags);
}

int
kern_pipe(long *fds, int flags)
{
        struct thread *td = curthread;
        struct filedesc *fdp = td->td_proc->p_fd;
        struct file *rf, *wf;
        struct pipe *rpipe, *wpipe;
        int fd1, fd2, error;

        rpipe = wpipe = NULL;
        if (pipe_create(&rpipe) || pipe_create(&wpipe)) {
                pipeclose(rpipe); 
                pipeclose(wpipe); 
                return (ENFILE);
        }
        
        error = falloc(td->td_lwp, &rf, &fd1);
        if (error) {
                pipeclose(rpipe);
                pipeclose(wpipe);
                return (error);
        }
        fds[0] = fd1;

        /*
         * 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.
         */
        rf->f_type = DTYPE_PIPE;
        rf->f_flag = FREAD | FWRITE;
        rf->f_ops = &pipeops;
        rf->f_data = rpipe;
        if (flags & O_NONBLOCK)
                rf->f_flag |= O_NONBLOCK;
        if (flags & O_CLOEXEC)
                fdp->fd_files[fd1].fileflags |= UF_EXCLOSE;

        error = falloc(td->td_lwp, &wf, &fd2);
        if (error) {
                fsetfd(fdp, NULL, fd1);
                fdrop(rf);
                /* rpipe has been closed by fdrop(). */
                pipeclose(wpipe);
                return (error);
        }
        wf->f_type = DTYPE_PIPE;
        wf->f_flag = FREAD | FWRITE;
        wf->f_ops = &pipeops;
        wf->f_data = wpipe;
        if (flags & O_NONBLOCK)
                wf->f_flag |= O_NONBLOCK;
        if (flags & O_CLOEXEC)
                fdp->fd_files[fd2].fileflags |= UF_EXCLOSE;

        fds[1] = fd2;

        rpipe->pipe_slock = kmalloc(sizeof(struct lock),
                                    M_PIPE, M_WAITOK|M_ZERO);
        wpipe->pipe_slock = rpipe->pipe_slock;
        rpipe->pipe_peer = wpipe;
        wpipe->pipe_peer = rpipe;
        lockinit(rpipe->pipe_slock, "pipecl", 0, 0);

        /*
         * Once activated the peer relationship remains valid until
         * both sides are closed.
         */
        fsetfd(fdp, rf, fd1);
        fsetfd(fdp, wf, fd2);
        fdrop(rf);
        fdrop(wf);

        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(struct pipe *cpipe, int size)
{
        struct vm_object *object;
        caddr_t buffer;
        int npages, error;

        npages = round_page(size) / PAGE_SIZE;
        object = cpipe->pipe_buffer.object;

        /*
         * [re]create the object if necessary and reserve space for it
         * in the kernel_map.  The object and memory are pageable.  On
         * success, free the old resources before assigning the new
         * ones.
         */
        if (object == NULL || object->size != npages) {
                object = vm_object_allocate(OBJT_DEFAULT, npages);
                buffer = (caddr_t)vm_map_min(&kernel_map);

                error = vm_map_find(&kernel_map, object, NULL,
                                    0, (vm_offset_t *)&buffer, size,
                                    PAGE_SIZE, TRUE,
                                    VM_MAPTYPE_NORMAL, VM_SUBSYS_PIPE,
                                    VM_PROT_ALL, VM_PROT_ALL, 0);

                if (error != KERN_SUCCESS) {
                        vm_object_deallocate(object);
                        return (ENOMEM);
                }
                pipe_free_kmem(cpipe);
                cpipe->pipe_buffer.object = object;
                cpipe->pipe_buffer.buffer = buffer;
                cpipe->pipe_buffer.size = size;
                ++pipe_bkmem_alloc;
        } else {
                ++pipe_bcache_alloc;
        }
        cpipe->pipe_buffer.rindex = 0;
        cpipe->pipe_buffer.windex = 0;
        return (0);
}

/*
 * Initialize and allocate VM and memory for pipe, pulling the pipe from
 * our per-cpu cache if possible.  For now make sure it is sized for the
 * smaller PIPE_SIZE default.
 */
static int
pipe_create(struct pipe **cpipep)
{
        globaldata_t gd = mycpu;
        struct pipe *cpipe;
        int error;

        if ((cpipe = gd->gd_pipeq) != NULL) {
                gd->gd_pipeq = cpipe->pipe_peer;
                --gd->gd_pipeqcount;
                cpipe->pipe_peer = NULL;
                cpipe->pipe_wantwcnt = 0;
        } else {
                cpipe = kmalloc(sizeof(struct pipe), M_PIPE, M_WAITOK|M_ZERO);
        }
        *cpipep = cpipe;
        if ((error = pipespace(cpipe, PIPE_SIZE)) != 0)
                return (error);
        vfs_timestamp(&cpipe->pipe_ctime);
        cpipe->pipe_atime = cpipe->pipe_ctime;
        cpipe->pipe_mtime = cpipe->pipe_ctime;
        lwkt_token_init(&cpipe->pipe_rlock, "piper");
        lwkt_token_init(&cpipe->pipe_wlock, "pipew");
        return (0);
}

static int
pipe_read(struct file *fp, struct uio *uio, struct ucred *cred, int fflags)
{
        struct pipe *rpipe;
        struct pipe *wpipe;
        int error;
        size_t nread = 0;
        int nbio;
        u_int size;     /* total bytes available */
        u_int nsize;    /* total bytes to read */
        u_int rindex;   /* contiguous bytes available */
        int notify_writer;
        int bigread;
        int bigcount;

        atomic_set_int(&curthread->td_mpflags, TDF_MP_BATCH_DEMARC);

        if (uio->uio_resid == 0)
                return(0);

        /*
         * Setup locks, calculate nbio
         */
        rpipe = (struct pipe *)fp->f_data;
        wpipe = rpipe->pipe_peer;
        lwkt_gettoken(&rpipe->pipe_rlock);

        if (fflags & O_FBLOCKING)
                nbio = 0;
        else if (fflags & O_FNONBLOCKING)
                nbio = 1;
        else if (fp->f_flag & O_NONBLOCK)
                nbio = 1;
        else
                nbio = 0;

        /*
         * Reads are serialized.  Note however that pipe_buffer.buffer and
         * pipe_buffer.size can change out from under us when the number
         * of bytes in the buffer are zero due to the write-side doing a
         * pipespace().
         */
        error = pipe_start_uio(rpipe, &rpipe->pipe_rip);
        if (error) {
                lwkt_reltoken(&rpipe->pipe_rlock);
                return (error);
        }
        notify_writer = 0;

        bigread = (uio->uio_resid > 10 * 1024 * 1024);
        bigcount = 10;

        while (uio->uio_resid) {
                /*
                 * Don't hog the cpu.
                 */
                if (bigread && --bigcount == 0) {
                        lwkt_user_yield();
                        bigcount = 10;
                        if (CURSIG(curthread->td_lwp)) {
                                error = EINTR;
                                break;
                        }
                }

                size = rpipe->pipe_buffer.windex - rpipe->pipe_buffer.rindex;
                cpu_lfence();
                if (size) {
                        rindex = rpipe->pipe_buffer.rindex &
                                 (rpipe->pipe_buffer.size - 1);
                        nsize = size;
                        if (nsize > rpipe->pipe_buffer.size - rindex)
                                nsize = rpipe->pipe_buffer.size - rindex;
                        nsize = szmin(nsize, uio->uio_resid);

                        error = uiomove(&rpipe->pipe_buffer.buffer[rindex],
                                        nsize, uio);
                        if (error)
                                break;
                        cpu_mfence();
                        rpipe->pipe_buffer.rindex += nsize;
                        nread += nsize;

                        /*
                         * If the FIFO is still over half full just continue
                         * and do not try to notify the writer yet.
                         */
                        if (size - nsize >= (rpipe->pipe_buffer.size >> 1)) {
                                notify_writer = 0;
                                continue;
                        }

                        /*
                         * When the FIFO is less then half full notify any
                         * waiting writer.  WANTW can be checked while
                         * holding just the rlock.
                         */
                        notify_writer = 1;
                        if ((rpipe->pipe_state & PIPE_WANTW) == 0)
                                continue;
                }

                /*
                 * If the "write-side" was blocked we wake it up.  This code
                 * is reached either when the buffer is completely emptied
                 * or if it becomes more then half-empty.
                 *
                 * Pipe_state can only be modified if both the rlock and
                 * wlock are held.
                 */
                if (rpipe->pipe_state & PIPE_WANTW) {
                        lwkt_gettoken(&rpipe->pipe_wlock);
                        if (rpipe->pipe_state & PIPE_WANTW) {
                                rpipe->pipe_state &= ~PIPE_WANTW;
                                lwkt_reltoken(&rpipe->pipe_wlock);
                                wakeup(rpipe);
                        } else {
                                lwkt_reltoken(&rpipe->pipe_wlock);
                        }
                }

                /*
                 * Pick up our copy loop again if the writer sent data to
                 * us while we were messing around.
                 *
                 * On a SMP box poll up to pipe_delay nanoseconds for new
                 * data.  Typically a value of 2000 to 4000 is sufficient
                 * to eradicate most IPIs/tsleeps/wakeups when a pipe
                 * is used for synchronous communications with small packets,
                 * and 8000 or so (8uS) will pipeline large buffer xfers
                 * between cpus over a pipe.
                 *
                 * For synchronous communications a hit means doing a
                 * full Awrite-Bread-Bwrite-Aread cycle in less then 2uS,
                 * where as miss requiring a tsleep/wakeup sequence
                 * will take 7uS or more.
                 */
                if (rpipe->pipe_buffer.windex != rpipe->pipe_buffer.rindex)
                        continue;

#ifdef _RDTSC_SUPPORTED_
                if (pipe_delay) {
                        int64_t tsc_target;
                        int good = 0;

                        tsc_target = tsc_get_target(pipe_delay);
                        while (tsc_test_target(tsc_target) == 0) {
                                if (rpipe->pipe_buffer.windex !=
                                    rpipe->pipe_buffer.rindex) {
                                        good = 1;
                                        break;
                                }
                        }
                        if (good)
                                continue;
                }
#endif

                /*
                 * Detect EOF condition, do not set error.
                 */
                if (rpipe->pipe_state & PIPE_REOF)
                        break;

                /*
                 * Break if some data was read, or if this was a non-blocking
                 * read.
                 */
                if (nread > 0)
                        break;

                if (nbio) {
                        error = EAGAIN;
                        break;
                }

                /*
                 * Last chance, interlock with WANTR.
                 */
                lwkt_gettoken(&rpipe->pipe_wlock);
                size = rpipe->pipe_buffer.windex - rpipe->pipe_buffer.rindex;
                if (size) {
                        lwkt_reltoken(&rpipe->pipe_wlock);
                        continue;
                }

                /*
                 * Retest EOF - acquiring a new token can temporarily release
                 * tokens already held.
                 */
                if (rpipe->pipe_state & PIPE_REOF) {
                        lwkt_reltoken(&rpipe->pipe_wlock);
                        break;
                }

                /*
                 * If there is no more to read in the pipe, reset its
                 * pointers to the beginning.  This improves cache hit
                 * stats.
                 *
                 * We need both locks to modify both pointers, and there
                 * must also not be a write in progress or the uiomove()
                 * in the write might block and temporarily release
                 * its wlock, then reacquire and update windex.  We are
                 * only serialized against reads, not writes.
                 *
                 * XXX should we even bother resetting the indices?  It
                 *     might actually be more cache efficient not to.
                 */
                if (rpipe->pipe_buffer.rindex == rpipe->pipe_buffer.windex &&
                    rpipe->pipe_wip == 0) {
                        rpipe->pipe_buffer.rindex = 0;
                        rpipe->pipe_buffer.windex = 0;
                }

                /*
                 * Wait for more data.
                 *
                 * Pipe_state can only be set if both the rlock and wlock
                 * are held.
                 */
                rpipe->pipe_state |= PIPE_WANTR;
                tsleep_interlock(rpipe, PCATCH);
                lwkt_reltoken(&rpipe->pipe_wlock);
                error = tsleep(rpipe, PCATCH | PINTERLOCKED, "piperd", 0);
                ++pipe_rblocked_count;
                if (error)
                        break;
        }
        pipe_end_uio(rpipe, &rpipe->pipe_rip);

        /*
         * Uptime last access time
         */
        if (error == 0 && nread)
                vfs_timestamp(&rpipe->pipe_atime);

        /*
         * If we drained the FIFO more then half way then handle
         * write blocking hysteresis.
         *
         * Note that PIPE_WANTW cannot be set by the writer without
         * it holding both rlock and wlock, so we can test it
         * while holding just rlock.
         */
        if (notify_writer) {
                /*
                 * Synchronous blocking is done on the pipe involved
                 */
                if (rpipe->pipe_state & PIPE_WANTW) {
                        lwkt_gettoken(&rpipe->pipe_wlock);
                        if (rpipe->pipe_state & PIPE_WANTW) {
                                rpipe->pipe_state &= ~PIPE_WANTW;
                                lwkt_reltoken(&rpipe->pipe_wlock);
                                wakeup(rpipe);
                        } else {
                                lwkt_reltoken(&rpipe->pipe_wlock);
                        }
                }

                /*
                 * But we may also have to deal with a kqueue which is
                 * stored on the same pipe as its descriptor, so a
                 * EVFILT_WRITE event waiting for our side to drain will
                 * be on the other side.
                 */
                lwkt_gettoken(&wpipe->pipe_wlock);
                pipewakeup(wpipe, 0);
                lwkt_reltoken(&wpipe->pipe_wlock);
        }
        /*size = rpipe->pipe_buffer.windex - rpipe->pipe_buffer.rindex;*/
        lwkt_reltoken(&rpipe->pipe_rlock);

        return (error);
}

static int
pipe_write(struct file *fp, struct uio *uio, struct ucred *cred, int fflags)
{
        int error;
        int orig_resid;
        int nbio;
        struct pipe *wpipe;
        struct pipe *rpipe;
        u_int windex;
        u_int space;
        u_int wcount;
        int bigwrite;
        int bigcount;

        /*
         * Writes go to the peer.  The peer will always exist.
         */
        rpipe = (struct pipe *) fp->f_data;
        wpipe = rpipe->pipe_peer;
        lwkt_gettoken(&wpipe->pipe_wlock);
        if (wpipe->pipe_state & PIPE_WEOF) {
                lwkt_reltoken(&wpipe->pipe_wlock);
                return (EPIPE);
        }

        /*
         * Degenerate case (EPIPE takes prec)
         */
        if (uio->uio_resid == 0) {
                lwkt_reltoken(&wpipe->pipe_wlock);
                return(0);
        }

        /*
         * Writes are serialized (start_uio must be called with wlock)
         */
        error = pipe_start_uio(wpipe, &wpipe->pipe_wip);
        if (error) {
                lwkt_reltoken(&wpipe->pipe_wlock);
                return (error);
        }

        if (fflags & O_FBLOCKING)
                nbio = 0;
        else if (fflags & O_FNONBLOCKING)
                nbio = 1;
        else if (fp->f_flag & O_NONBLOCK)
                nbio = 1;
        else
                nbio = 0;

        /*
         * If it is advantageous to resize the pipe buffer, do
         * so.  We are write-serialized so we can block safely.
         */
        if ((wpipe->pipe_buffer.size <= PIPE_SIZE) &&
            (pipe_nbig < pipe_maxbig) &&
            wpipe->pipe_wantwcnt > 4 &&
            (wpipe->pipe_buffer.rindex == wpipe->pipe_buffer.windex)) {
                /* 
                 * Recheck after lock.
                 */
                lwkt_gettoken(&wpipe->pipe_rlock);
                if ((wpipe->pipe_buffer.size <= PIPE_SIZE) &&
                    (pipe_nbig < pipe_maxbig) &&
                    (wpipe->pipe_buffer.rindex == wpipe->pipe_buffer.windex)) {
                        atomic_add_int(&pipe_nbig, 1);
                        if (pipespace(wpipe, BIG_PIPE_SIZE) == 0)
                                ++pipe_bigcount;
                        else
                                atomic_subtract_int(&pipe_nbig, 1);
                }
                lwkt_reltoken(&wpipe->pipe_rlock);
        }

        orig_resid = uio->uio_resid;
        wcount = 0;

        bigwrite = (uio->uio_resid > 10 * 1024 * 1024);
        bigcount = 10;

        while (uio->uio_resid) {
                if (wpipe->pipe_state & PIPE_WEOF) {
                        error = EPIPE;
                        break;
                }

                /*
                 * Don't hog the cpu.
                 */
                if (bigwrite && --bigcount == 0) {
                        lwkt_user_yield();
                        bigcount = 10;
                        if (CURSIG(curthread->td_lwp)) {
                                error = EINTR;
                                break;
                        }
                }

                windex = wpipe->pipe_buffer.windex &
                         (wpipe->pipe_buffer.size - 1);
                space = wpipe->pipe_buffer.size -
                        (wpipe->pipe_buffer.windex - wpipe->pipe_buffer.rindex);
                cpu_lfence();

                /* Writes of size <= PIPE_BUF must be atomic. */
                if ((space < uio->uio_resid) && (orig_resid <= PIPE_BUF))
                        space = 0;

                /* 
                 * Write to fill, read size handles write hysteresis.  Also
                 * additional restrictions can cause select-based non-blocking
                 * writes to spin.
                 */
                if (space > 0) {
                        u_int segsize;

                        /*
                         * Transfer size is minimum of uio transfer
                         * and free space in pipe buffer.
                         *
                         * Limit each uiocopy to no more then PIPE_SIZE
                         * so we can keep the gravy train going on a
                         * SMP box.  This doubles the performance for
                         * write sizes > 16K.  Otherwise large writes
                         * wind up doing an inefficient synchronous
                         * ping-pong.
                         */
                        space = szmin(space, uio->uio_resid);
                        if (space > PIPE_SIZE)
                                space = PIPE_SIZE;

                        /*
                         * 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 - windex;
                        if (segsize > space)
                                segsize = space;

                        /*
                         * If this is the first loop and the reader is
                         * blocked, do a preemptive wakeup of the reader.
                         *
                         * On SMP the IPI latency plus the wlock interlock
                         * on the reader side is the fastest way to get the
                         * reader going.  (The scheduler will hard loop on
                         * lock tokens).
                         *
                         * NOTE: We can't clear WANTR here without acquiring
                         * the rlock, which we don't want to do here!
                         */
                        if ((wpipe->pipe_state & PIPE_WANTR))
                                wakeup(wpipe);

                        /*
                         * Transfer segment, which may include a wrap-around.
                         * Update windex to account for both all in one go
                         * so the reader can read() the data atomically.
                         */
                        error = uiomove(&wpipe->pipe_buffer.buffer[windex],
                                        segsize, uio);
                        if (error == 0 && segsize < space) {
                                segsize = space - segsize;
                                error = uiomove(&wpipe->pipe_buffer.buffer[0],
                                                segsize, uio);
                        }
                        if (error)
                                break;
                        cpu_mfence();
                        wpipe->pipe_buffer.windex += space;
                        wcount += space;
                        continue;
                }

                /*
                 * We need both the rlock and the wlock to interlock against
                 * the EOF, WANTW, and size checks, and to modify pipe_state.
                 *
                 * These are token locks so we do not have to worry about
                 * deadlocks.
                 */
                lwkt_gettoken(&wpipe->pipe_rlock);

                /*
                 * If the "read-side" has been blocked, wake it up now
                 * and yield to let it drain synchronously rather
                 * then block.
                 */
                if (wpipe->pipe_state & PIPE_WANTR) {
                        wpipe->pipe_state &= ~PIPE_WANTR;
                        wakeup(wpipe);
                }

                /*
                 * don't block on non-blocking I/O
                 */
                if (nbio) {
                        lwkt_reltoken(&wpipe->pipe_rlock);
                        error = EAGAIN;
                        break;
                }

                /*
                 * re-test whether we have to block in the writer after
                 * acquiring both locks, in case the reader opened up
                 * some space.
                 */
                space = wpipe->pipe_buffer.size -
                        (wpipe->pipe_buffer.windex - wpipe->pipe_buffer.rindex);
                cpu_lfence();
                if ((space < uio->uio_resid) && (orig_resid <= PIPE_BUF))
                        space = 0;

                /*
                 * Retest EOF - acquiring a new token can temporarily release
                 * tokens already held.
                 */
                if (wpipe->pipe_state & PIPE_WEOF) {
                        lwkt_reltoken(&wpipe->pipe_rlock);
                        error = EPIPE;
                        break;
                }

                /*
                 * We have no more space and have something to offer,
                 * wake up select/poll/kq.
                 */
                if (space == 0) {
                        wpipe->pipe_state |= PIPE_WANTW;
                        ++wpipe->pipe_wantwcnt;
                        pipewakeup(wpipe, 1);
                        if (wpipe->pipe_state & PIPE_WANTW)
                                error = tsleep(wpipe, PCATCH, "pipewr", 0);
                        ++pipe_wblocked_count;
                }
                lwkt_reltoken(&wpipe->pipe_rlock);

                /*
                 * Break out if we errored or the read side wants us to go
                 * away.
                 */
                if (error)
                        break;
                if (wpipe->pipe_state & PIPE_WEOF) {
                        error = EPIPE;
                        break;
                }
        }
        pipe_end_uio(wpipe, &wpipe->pipe_wip);

        /*
         * If we have put any characters in the buffer, we wake up
         * the reader.
         *
         * Both rlock and wlock are required to be able to modify pipe_state.
         */
        if (wpipe->pipe_buffer.windex != wpipe->pipe_buffer.rindex) {
                if (wpipe->pipe_state & PIPE_WANTR) {
                        lwkt_gettoken(&wpipe->pipe_rlock);
                        if (wpipe->pipe_state & PIPE_WANTR) {
                                wpipe->pipe_state &= ~PIPE_WANTR;
                                lwkt_reltoken(&wpipe->pipe_rlock);
                                wakeup(wpipe);
                        } else {
                                lwkt_reltoken(&wpipe->pipe_rlock);
                        }
                }
                lwkt_gettoken(&wpipe->pipe_rlock);
                pipewakeup(wpipe, 1);
                lwkt_reltoken(&wpipe->pipe_rlock);
        }

        /*
         * Don't return EPIPE if I/O was successful
         */
        if ((wpipe->pipe_buffer.rindex == wpipe->pipe_buffer.windex) &&
            (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/kq.
         */
        /*space = wpipe->pipe_buffer.windex - wpipe->pipe_buffer.rindex;*/
        lwkt_reltoken(&wpipe->pipe_wlock);
        return (error);
}

/*
 * we implement a very minimal set of ioctls for compatibility with sockets.
 */
static int
pipe_ioctl(struct file *fp, u_long cmd, caddr_t data,
           struct ucred *cred, struct sysmsg *msg)
{
        struct pipe *mpipe;
        int error;

        mpipe = (struct pipe *)fp->f_data;

        lwkt_gettoken(&mpipe->pipe_rlock);
        lwkt_gettoken(&mpipe->pipe_wlock);

        switch (cmd) {
        case FIOASYNC:
                if (*(int *)data) {
                        mpipe->pipe_state |= PIPE_ASYNC;
                } else {
                        mpipe->pipe_state &= ~PIPE_ASYNC;
                }
                error = 0;
                break;
        case FIONREAD:
                *(int *)data = mpipe->pipe_buffer.windex -
                                mpipe->pipe_buffer.rindex;
                error = 0;
                break;
        case FIOSETOWN:
                error = fsetown(*(int *)data, &mpipe->pipe_sigio);
                break;
        case FIOGETOWN:
                *(int *)data = fgetown(&mpipe->pipe_sigio);
                error = 0;
                break;
        case TIOCSPGRP:
                /* This is deprecated, FIOSETOWN should be used instead. */
                error = fsetown(-(*(int *)data), &mpipe->pipe_sigio);
                break;

        case TIOCGPGRP:
                /* This is deprecated, FIOGETOWN should be used instead. */
                *(int *)data = -fgetown(&mpipe->pipe_sigio);
                error = 0;
                break;
        default:
                error = ENOTTY;
                break;
        }
        lwkt_reltoken(&mpipe->pipe_wlock);
        lwkt_reltoken(&mpipe->pipe_rlock);

        return (error);
}

/*
 * MPSAFE
 */
static int
pipe_stat(struct file *fp, struct stat *ub, struct ucred *cred)
{
        struct pipe *pipe;

        pipe = (struct pipe *)fp->f_data;

        bzero((caddr_t)ub, sizeof(*ub));
        ub->st_mode = S_IFIFO;
        ub->st_blksize = pipe->pipe_buffer.size;
        ub->st_size = pipe->pipe_buffer.windex - pipe->pipe_buffer.rindex;
        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;
        /*
         * Left as 0: st_dev, st_ino, st_nlink, st_uid, st_gid, st_rdev,
         * st_flags, st_gen.
         * XXX (st_dev, st_ino) should be unique.
         */
        return (0);
}

static int
pipe_close(struct file *fp)
{
        struct pipe *cpipe;

        cpipe = (struct pipe *)fp->f_data;
        fp->f_ops = &badfileops;
        fp->f_data = NULL;
        funsetown(&cpipe->pipe_sigio);
        pipeclose(cpipe);
        return (0);
}

/*
 * Shutdown one or both directions of a full-duplex pipe.
 */
static int
pipe_shutdown(struct file *fp, int how)
{
        struct pipe *rpipe;
        struct pipe *wpipe;
        int error = EPIPE;

        rpipe = (struct pipe *)fp->f_data;
        wpipe = rpipe->pipe_peer;

        /*
         * We modify pipe_state on both pipes, which means we need
         * all four tokens!
         */
        lwkt_gettoken(&rpipe->pipe_rlock);
        lwkt_gettoken(&rpipe->pipe_wlock);
        lwkt_gettoken(&wpipe->pipe_rlock);
        lwkt_gettoken(&wpipe->pipe_wlock);

        switch(how) {
        case SHUT_RDWR:
        case SHUT_RD:
                rpipe->pipe_state |= PIPE_REOF;         /* my reads */
                rpipe->pipe_state |= PIPE_WEOF;         /* peer writes */
                if (rpipe->pipe_state & PIPE_WANTR) {
                        rpipe->pipe_state &= ~PIPE_WANTR;
                        wakeup(rpipe);
                }
                if (rpipe->pipe_state & PIPE_WANTW) {
                        rpipe->pipe_state &= ~PIPE_WANTW;
                        wakeup(rpipe);
                }
                error = 0;
                if (how == SHUT_RD)
                        break;
                /* fall through */
        case SHUT_WR:
                wpipe->pipe_state |= PIPE_REOF;         /* peer reads */
                wpipe->pipe_state |= PIPE_WEOF;         /* my writes */
                if (wpipe->pipe_state & PIPE_WANTR) {
                        wpipe->pipe_state &= ~PIPE_WANTR;
                        wakeup(wpipe);
                }
                if (wpipe->pipe_state & PIPE_WANTW) {
                        wpipe->pipe_state &= ~PIPE_WANTW;
                        wakeup(wpipe);
                }
                error = 0;
                break;
        }
        pipewakeup(rpipe, 1);
        pipewakeup(wpipe, 1);

        lwkt_reltoken(&wpipe->pipe_wlock);
        lwkt_reltoken(&wpipe->pipe_rlock);
        lwkt_reltoken(&rpipe->pipe_wlock);
        lwkt_reltoken(&rpipe->pipe_rlock);

        return (error);
}

static void
pipe_free_kmem(struct pipe *cpipe)
{
        if (cpipe->pipe_buffer.buffer != NULL) {
                if (cpipe->pipe_buffer.size > PIPE_SIZE)
                        atomic_subtract_int(&pipe_nbig, 1);
                kmem_free(&kernel_map,
                        (vm_offset_t)cpipe->pipe_buffer.buffer,
                        cpipe->pipe_buffer.size);
                cpipe->pipe_buffer.buffer = NULL;
                cpipe->pipe_buffer.object = NULL;
        }
}

/*
 * Close the pipe.  The slock must be held to interlock against simultanious
 * closes.  The rlock and wlock must be held to adjust the pipe_state.
 */
static void
pipeclose(struct pipe *cpipe)
{
        globaldata_t gd;
        struct pipe *ppipe;

        if (cpipe == NULL)
                return;

        /*
         * The slock may not have been allocated yet (close during
         * initialization)
         *
         * We need both the read and write tokens to modify pipe_state.
         */
        if (cpipe->pipe_slock)
                lockmgr(cpipe->pipe_slock, LK_EXCLUSIVE);
        lwkt_gettoken(&cpipe->pipe_rlock);
        lwkt_gettoken(&cpipe->pipe_wlock);

        /*
         * Set our state, wakeup anyone waiting in select/poll/kq, and
         * wakeup anyone blocked on our pipe.
         */
        cpipe->pipe_state |= PIPE_CLOSED | PIPE_REOF | PIPE_WEOF;
        pipewakeup(cpipe, 1);
        if (cpipe->pipe_state & (PIPE_WANTR | PIPE_WANTW)) {
                cpipe->pipe_state &= ~(PIPE_WANTR | PIPE_WANTW);
                wakeup(cpipe);
        }

        /*
         * Disconnect from peer.
         */
        if ((ppipe = cpipe->pipe_peer) != NULL) {
                lwkt_gettoken(&ppipe->pipe_rlock);
                lwkt_gettoken(&ppipe->pipe_wlock);
                ppipe->pipe_state |= PIPE_REOF | PIPE_WEOF;
                pipewakeup(ppipe, 1);
                if (ppipe->pipe_state & (PIPE_WANTR | PIPE_WANTW)) {
                        ppipe->pipe_state &= ~(PIPE_WANTR | PIPE_WANTW);
                        wakeup(ppipe);
                }
                if (SLIST_FIRST(&ppipe->pipe_kq.ki_note))
                        KNOTE(&ppipe->pipe_kq.ki_note, 0);
                lwkt_reltoken(&ppipe->pipe_wlock);
                lwkt_reltoken(&ppipe->pipe_rlock);
        }

        /*
         * If the peer is also closed we can free resources for both
         * sides, otherwise we leave our side intact to deal with any
         * races (since we only have the slock).
         */
        if (ppipe && (ppipe->pipe_state & PIPE_CLOSED)) {
                cpipe->pipe_peer = NULL;
                ppipe->pipe_peer = NULL;
                ppipe->pipe_slock = NULL;       /* we will free the slock */
                pipeclose(ppipe);
                ppipe = NULL;
        }

        lwkt_reltoken(&cpipe->pipe_wlock);
        lwkt_reltoken(&cpipe->pipe_rlock);
        if (cpipe->pipe_slock)
                lockmgr(cpipe->pipe_slock, LK_RELEASE);

        /*
         * If we disassociated from our peer we can free resources
         */
        if (ppipe == NULL) {
                gd = mycpu;
                if (cpipe->pipe_slock) {
                        kfree(cpipe->pipe_slock, M_PIPE);
                        cpipe->pipe_slock = NULL;
                }
                if (gd->gd_pipeqcount >= pipe_maxcache ||
                    cpipe->pipe_buffer.size != PIPE_SIZE
                ) {
                        pipe_free_kmem(cpipe);
                        kfree(cpipe, M_PIPE);
                } else {
                        cpipe->pipe_state = 0;
                        cpipe->pipe_peer = gd->gd_pipeq;
                        gd->gd_pipeq = cpipe;
                        ++gd->gd_pipeqcount;
                }
        }
}

static int
pipe_kqfilter(struct file *fp, struct knote *kn)
{
        struct pipe *cpipe;

        cpipe = (struct pipe *)kn->kn_fp->f_data;

        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 == NULL) {
                        /* other end of pipe has been closed */
                        return (EPIPE);
                }
                break;
        default:
                return (EOPNOTSUPP);
        }
        kn->kn_hook = (caddr_t)cpipe;

        knote_insert(&cpipe->pipe_kq.ki_note, kn);

        return (0);
}

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

        knote_remove(&cpipe->pipe_kq.ki_note, kn);
}

/*ARGSUSED*/
static int
filt_piperead(struct knote *kn, long hint)
{
        struct pipe *rpipe = (struct pipe *)kn->kn_fp->f_data;
        int ready = 0;

        lwkt_gettoken(&rpipe->pipe_rlock);
        lwkt_gettoken(&rpipe->pipe_wlock);

        kn->kn_data = rpipe->pipe_buffer.windex - rpipe->pipe_buffer.rindex;

        if (rpipe->pipe_state & PIPE_REOF) {
                /*
                 * Only set NODATA if all data has been exhausted
                 */
                if (kn->kn_data == 0)
                        kn->kn_flags |= EV_NODATA;
                kn->kn_flags |= EV_EOF; 
                ready = 1;
        }

        lwkt_reltoken(&rpipe->pipe_wlock);
        lwkt_reltoken(&rpipe->pipe_rlock);

        if (!ready)
                ready = kn->kn_data > 0;

        return (ready);
}

/*ARGSUSED*/
static int
filt_pipewrite(struct knote *kn, long hint)
{
        struct pipe *rpipe = (struct pipe *)kn->kn_fp->f_data;
        struct pipe *wpipe = rpipe->pipe_peer;
        int ready = 0;

        kn->kn_data = 0;
        if (wpipe == NULL) {
                kn->kn_flags |= (EV_EOF | EV_NODATA);
                return (1);
        }

        lwkt_gettoken(&wpipe->pipe_rlock);
        lwkt_gettoken(&wpipe->pipe_wlock);

        if (wpipe->pipe_state & PIPE_WEOF) {
                kn->kn_flags |= (EV_EOF | EV_NODATA);
                ready = 1;
        }

        if (!ready)
                kn->kn_data = wpipe->pipe_buffer.size -
                              (wpipe->pipe_buffer.windex -
                               wpipe->pipe_buffer.rindex);

        lwkt_reltoken(&wpipe->pipe_wlock);
        lwkt_reltoken(&wpipe->pipe_rlock);

        if (!ready)
                ready = kn->kn_data >= PIPE_BUF;

        return (ready);
}