/*
 * Copyright (c) 1996 John S. Dyson
 * All rights reserved.
 * Copyright (c) 2003-2017 The DragonFly Project.  All rights reserved.
 *
 * This code is derived from software contributed to The DragonFly Project
 * by Matthew Dillon <dillon@backplane.com>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice immediately at the beginning of the file, without modification,
 *    this list of conditions, and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Absolutely no warranty of function or purpose is made by the author
 *    John S. Dyson.
 * 4. Modifications may be freely made to this file if the above conditions
 *    are met.
 */

/*
 * This file contains a high-performance replacement for the socket-based
 * pipes scheme originally used in FreeBSD/4.4Lite.  It does not support
 * all features of sockets, but does do everything that pipes normally
 * do.
 */
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/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/sysmsg.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 <sys/lock.h>
#include <sys/mutex.h>

#include <vm/vm.h>
#include <vm/vm_param.h>
#include <vm/vm_object.h>
#include <vm/vm_kern.h>
#include <vm/vm_extern.h>
#include <vm/pmap.h>
#include <vm/vm_map.h>
#include <vm/vm_page.h>
#include <vm/vm_zone.h>

#include <sys/file2.h>
#include <sys/signal2.h>
#include <sys/mutex2.h>

#include <machine/cpufunc.h>

struct pipegdlock {
        struct mtx      mtx;
} __cachealign;

/*
 * 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);

__read_mostly 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,
        .fo_seek = badfo_seek
};

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);

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

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

#define PIPEQ_MAX_CACHE 16      /* per-cpu pipe structure cache */

__read_mostly static int pipe_maxcache = PIPEQ_MAX_CACHE;
__read_mostly static struct pipegdlock *pipe_gdlocks;

SYSCTL_NODE(_kern, OID_AUTO, pipe, CTLFLAG_RW, 0, "Pipe operation");
SYSCTL_INT(_kern_pipe, OID_AUTO, maxcache,
        CTLFLAG_RW, &pipe_maxcache, 0, "max pipes cached per-cpu");

/*
 * The pipe buffer size can be changed at any time.  Only new pipe()s
 * are affected.  Note that due to cpu cache effects, you do not want
 * to make this value too large.
 */
__read_mostly static int pipe_size = 32768;
SYSCTL_INT(_kern_pipe, OID_AUTO, size,
        CTLFLAG_RW, &pipe_size, 0, "Pipe buffer size (16384 minimum)");

/*
 * Reader/writer delay loop.  When the reader exhausts the pipe buffer
 * or the write completely fills the pipe buffer and would otherwise sleep,
 * it first busy-loops for a few microseconds waiting for data or buffer
 * space.  This eliminates IPIs for most high-bandwidth writer/reader pipes
 * and also helps when the user program uses a large data buffer in its
 * UIOs.
 *
 * This defaults to 4uS.
 */
#ifdef _RDTSC_SUPPORTED_
__read_mostly static int pipe_delay = 4000;     /* 4uS default */
SYSCTL_INT(_kern_pipe, OID_AUTO, delay,
        CTLFLAG_RW, &pipe_delay, 0, "SMP delay optimization in ns");
#endif

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

        if (pipe_maxcache == PIPEQ_MAX_CACHE) {
                if (mbytes >= 7 * 1024)
                        pipe_maxcache *= 2;
                if (mbytes >= 15 * 1024)
                        pipe_maxcache *= 2;
        }

        /*
         * Detune the pcpu caching a bit on systems with an insane number
         * of cpu threads to reduce memory waste.
         */
        if (ncpus > 64) {
                pipe_maxcache = pipe_maxcache * 64 / ncpus;
                if (pipe_maxcache < PIPEQ_MAX_CACHE)
                        pipe_maxcache = PIPEQ_MAX_CACHE;
        }

        pipe_gdlocks = kmalloc(sizeof(*pipe_gdlocks) * ncpus,
                             M_PIPE, M_WAITOK | M_ZERO);
        for (n = 0; n < ncpus; ++n)
                mtx_init(&pipe_gdlocks[n].mtx, "pipekm");
}
SYSINIT(kmem, SI_BOOT2_MACHDEP, SI_ORDER_ANY, pipeinit, NULL);

static void pipeclose (struct pipe *pipe,
                struct pipebuf *pbr, struct pipebuf *pbw);
static void pipe_free_kmem (struct pipebuf *buf);
static int pipe_create (struct pipe **pipep);

/*
 * Test and clear the specified flag, wakeup(pb) if it was set.
 * This function must also act as a memory barrier.
 */
static __inline void
pipesignal(struct pipebuf *pb, uint32_t flags)
{
        uint32_t oflags;
        uint32_t nflags;

        for (;;) {
                oflags = pb->state;
                cpu_ccfence();
                nflags = oflags & ~flags;
                if (atomic_cmpset_int(&pb->state, oflags, nflags))
                        break;
        }
        if (oflags & flags)
                wakeup(pb);
}

/*
 *
 */
static __inline void
pipewakeup(struct pipebuf *pb, int dosigio)
{
        if (dosigio && (pb->state & PIPE_ASYNC) && pb->sigio) {
                lwkt_gettoken(&sigio_token);
                pgsigio(pb->sigio, SIGIO, 0);
                lwkt_reltoken(&sigio_token);
        }
        KNOTE(&pb->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 appropriate token is held on entry so *ipp does not race.
 */
static __inline int
pipe_start_uio(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(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 sysmsg *sysmsg, const struct pipe_args *uap)
{
        return kern_pipe(sysmsg->sysmsg_fds, 0);
}

int
sys_pipe2(struct sysmsg *sysmsg, const struct pipe2_args *uap)
{
        if ((uap->flags & ~(O_CLOEXEC | O_CLOFORK | O_NONBLOCK)) != 0)
                return (EINVAL);
        return kern_pipe(sysmsg->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 *pipe;
        int fd1, fd2, error;

        pipe = NULL;
        if (pipe_create(&pipe)) {
                pipeclose(pipe, &pipe->bufferA, &pipe->bufferB);
                pipeclose(pipe, &pipe->bufferB, &pipe->bufferA);
                return (ENFILE);
        }
        
        error = falloc(td->td_lwp, &rf, &fd1);
        if (error) {
                pipeclose(pipe, &pipe->bufferA, &pipe->bufferB);
                pipeclose(pipe, &pipe->bufferB, &pipe->bufferA);
                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 = (void *)((intptr_t)pipe | 0);
        if (flags & O_NONBLOCK)
                rf->f_flag |= O_NONBLOCK;
        if (flags & O_CLOEXEC)
                fdp->fd_files[fd1].fileflags |= UF_EXCLOSE;
        if (flags & O_CLOFORK)
                fdp->fd_files[fd1].fileflags |= UF_FOCLOSE;

        error = falloc(td->td_lwp, &wf, &fd2);
        if (error) {
                fsetfd(fdp, NULL, fd1);
                fdrop(rf);
                /* pipeA has been closed by fdrop() */
                /* close pipeB here */
                pipeclose(pipe, &pipe->bufferB, &pipe->bufferA);
                return (error);
        }
        wf->f_type = DTYPE_PIPE;
        wf->f_flag = FREAD | FWRITE;
        wf->f_ops = &pipeops;
        wf->f_data = (void *)((intptr_t)pipe | 1);
        if (flags & O_NONBLOCK)
                wf->f_flag |= O_NONBLOCK;
        if (flags & O_CLOEXEC)
                fdp->fd_files[fd2].fileflags |= UF_EXCLOSE;
        if (flags & O_CLOFORK)
                fdp->fd_files[fd2].fileflags |= UF_FOCLOSE;

        fds[1] = fd2;

        /*
         * 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);
}

/*
 * [re]allocates KVA for the pipe's circular buffer.  The space is
 * pageable.  Called twice to setup full-duplex communications.
 *
 * NOTE: Independent vm_object's are used to improve performance.
 *
 * Returns 0 on success, ENOMEM on failure.
 */
static int
pipespace(struct pipe *pipe, struct pipebuf *pb, size_t size)
{
        struct vm_object *object;
        caddr_t buffer;
        vm_pindex_t npages;
        int error;

        size = (size + PAGE_MASK) & ~(size_t)PAGE_MASK;
        if (size < 16384)
                size = 16384;
        if (size > 1024*1024)
                size = 1024*1024;

        npages = round_page(size) / PAGE_SIZE;
        object = pb->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(pb);
                pb->object = object;
                pb->buffer = buffer;
                pb->size = size;
        }
        pb->rindex = 0;
        pb->windex = 0;

        return (0);
}

/*
 * Initialize and allocate VM and memory for pipe, pulling the pipe from
 * our per-cpu cache if possible.
 *
 * Returns 0 on success, else an error code (typically ENOMEM).  Caller
 * must still deallocate the pipe on failure.
 */
static int
pipe_create(struct pipe **pipep)
{
        globaldata_t gd = mycpu;
        struct pipe *pipe;
        int error;

        if ((pipe = gd->gd_pipeq) != NULL) {
                gd->gd_pipeq = pipe->next;
                --gd->gd_pipeqcount;
                pipe->next = NULL;
        } else {
                pipe = kmalloc(sizeof(*pipe), M_PIPE, M_WAITOK | M_ZERO);
                pipe->inum = gd->gd_anoninum++ * ncpus + gd->gd_cpuid + 2;
                lwkt_token_init(&pipe->bufferA.rlock, "piper");
                lwkt_token_init(&pipe->bufferA.wlock, "pipew");
                lwkt_token_init(&pipe->bufferB.rlock, "piper");
                lwkt_token_init(&pipe->bufferB.wlock, "pipew");
        }
        *pipep = pipe;
        if ((error = pipespace(pipe, &pipe->bufferA, pipe_size)) != 0) {
                return (error);
        }
        if ((error = pipespace(pipe, &pipe->bufferB, pipe_size)) != 0) {
                return (error);
        }
        vfs_timestamp(&pipe->ctime);
        pipe->bufferA.atime = pipe->ctime;
        pipe->bufferA.mtime = pipe->ctime;
        pipe->bufferB.atime = pipe->ctime;
        pipe->bufferB.mtime = pipe->ctime;
        pipe->open_count = 2;

        return (0);
}

/*
 * Read data from a pipe
 */
static int
pipe_read(struct file *fp, struct uio *uio, struct ucred *cred, int fflags)
{
        struct pipebuf *rpb;
        struct pipebuf *wpb;
        struct pipe *pipe;
        size_t nread = 0;
        size_t size;    /* total bytes available */
        size_t nsize;   /* total bytes to read */
        size_t rindex;  /* contiguous bytes available */
        int notify_writer;
        int bigread;
        int bigcount;
        int error;
        int nbio;

        pipe = (struct pipe *)((intptr_t)fp->f_data & ~(intptr_t)1);
        if ((intptr_t)fp->f_data & 1) {
                rpb = &pipe->bufferB;
                wpb = &pipe->bufferA;
        } else {
                rpb = &pipe->bufferA;
                wpb = &pipe->bufferB;
        }
        atomic_set_int(&curthread->td_mpflags, TDF_MP_BATCH_DEMARC);

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

        /*
         * Calculate nbio
         */
        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;

        /*
         * 'quick' NBIO test before things get expensive.
         */
        if (nbio && rpb->rindex == rpb->windex &&
            (rpb->state & PIPE_REOF) == 0) {
                return EAGAIN;
        }

        /*
         * Reads are serialized.  Note however that buffer.buffer and
         * 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().
         */
        lwkt_gettoken(&rpb->rlock);
        error = pipe_start_uio(&rpb->rip);
        if (error) {
                lwkt_reltoken(&rpb->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;
                        }
                }

                /*
                 * lfence required to avoid read-reordering of buffer
                 * contents prior to validation of size.
                 */
                size = rpb->windex - rpb->rindex;
                cpu_lfence();
                if (size) {
                        rindex = rpb->rindex & (rpb->size - 1);
                        nsize = size;
                        if (nsize > rpb->size - rindex)
                                nsize = rpb->size - rindex;
                        nsize = szmin(nsize, uio->uio_resid);

                        /*
                         * Limit how much we move in one go so we have a
                         * chance to kick the writer while data is still
                         * available in the pipe.  This avoids getting into
                         * a ping-pong with the writer.
                         */
                        if (nsize > (rpb->size >> 1))
                                nsize = rpb->size >> 1;

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

                        /*
                         * If the FIFO is still over half full just continue
                         * and do not try to notify the writer yet.  If
                         * less than half full notify any waiting writer.
                         */
                        if (size - nsize > (rpb->size >> 1)) {
                                notify_writer = 0;
                        } else {
                                notify_writer = 1;
                                pipesignal(rpb, PIPE_WANTW);
                        }
                        continue;
                }

                /*
                 * If the "write-side" was blocked we wake it up.  This code
                 * is reached when the buffer is completely emptied.
                 */
                pipesignal(rpb, PIPE_WANTW);

                /*
                 * 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 (rpb->windex != rpb->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) {
                                cpu_lfence();
                                if (rpb->windex != rpb->rindex) {
                                        good = 1;
                                        break;
                                }
                                cpu_pause();
                        }
                        if (good)
                                continue;
                }
#endif

                /*
                 * Detect EOF condition, do not set error.
                 */
                if (rpb->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
                 */
                tsleep_interlock(rpb, PCATCH);
                atomic_set_int(&rpb->state, PIPE_WANTR);

                /*
                 * Retest bytes available after memory barrier above.
                 */
                size = rpb->windex - rpb->rindex;
                if (size)
                        continue;

                /*
                 * Retest EOF after memory barrier above.
                 */
                if (rpb->state & PIPE_REOF)
                        break;

                /*
                 * Wait for more data or state change
                 */
                error = tsleep(rpb, PCATCH | PINTERLOCKED, "piperd", 0);
                if (error)
                        break;
        }
        pipe_end_uio(&rpb->rip);

        /*
         * Uptime last access time
         */
        if (error == 0 && nread && rpb->lticks != ticks) {
                vfs_timestamp(&rpb->atime);
                rpb->lticks = ticks;
        }

        /*
         * 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
                 */
                pipesignal(rpb, PIPE_WANTW);

                /*
                 * 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.
                 */
                pipewakeup(wpb, 0);
        }
        /*size = rpb->windex - rpb->rindex;*/
        lwkt_reltoken(&rpb->rlock);

        return (error);
}

static int
pipe_write(struct file *fp, struct uio *uio, struct ucred *cred, int fflags)
{
        struct pipebuf *rpb;
        struct pipebuf *wpb;
        struct pipe *pipe;
        size_t windex;
        size_t space;
        size_t wcount;
        size_t orig_resid;
        int bigwrite;
        int bigcount;
        int error;
        int nbio;

        pipe = (struct pipe *)((intptr_t)fp->f_data & ~(intptr_t)1);
        if ((intptr_t)fp->f_data & 1) {
                rpb = &pipe->bufferB;
                wpb = &pipe->bufferA;
        } else {
                rpb = &pipe->bufferA;
                wpb = &pipe->bufferB;
        }

        /*
         * Calculate nbio
         */
        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;

        /*
         * 'quick' NBIO test before things get expensive.
         */
        if (nbio && wpb->size == (wpb->windex - wpb->rindex) &&
            uio->uio_resid && (wpb->state & PIPE_WEOF) == 0) {
                return EAGAIN;
        }

        /*
         * Writes go to the peer.  The peer will always exist.
         */
        lwkt_gettoken(&wpb->wlock);
        if (wpb->state & PIPE_WEOF) {
                lwkt_reltoken(&wpb->wlock);
                return (EPIPE);
        }

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

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

        orig_resid = uio->uio_resid;
        wcount = 0;

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

        while (uio->uio_resid) {
                if (wpb->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 = wpb->windex & (wpb->size - 1);
                space = wpb->size - (wpb->windex - wpb->rindex);

                /*
                 * 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) {
                        size_t segsize;

                        /*
                         * We want to notify a potentially waiting reader
                         * before we exhaust the write buffer for SMP
                         * pipelining.  Otherwise the write/read will begin
                         * to ping-pong.
                         */
                        space = szmin(space, uio->uio_resid);
                        if (space > (wpb->size >> 1))
                                space = (wpb->size >> 1);

                        /*
                         * 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 = wpb->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).
                         */
                        if (wcount == 0)
                                pipesignal(wpb, PIPE_WANTR);

                        /*
                         * 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(&wpb->buffer[windex], segsize, uio);
                        if (error == 0 && segsize < space) {
                                segsize = space - segsize;
                                error = uiomove(&wpb->buffer[0], segsize, uio);
                        }
                        if (error)
                                break;

                        /*
                         * Memory fence prior to windex updating (note: not
                         * needed so this is a NOP on Intel).
                         */
                        cpu_sfence();
                        wpb->windex += space;

                        /*
                         * Signal reader
                         */
                        if (wcount != 0)
                                pipesignal(wpb, PIPE_WANTR);
                        wcount += space;
                        continue;
                }

                /*
                 * Wakeup any pending reader
                 */
                pipesignal(wpb, PIPE_WANTR);

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

#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) {
                                cpu_lfence();
                                space = wpb->size - (wpb->windex - wpb->rindex);
                                if ((space < uio->uio_resid) &&
                                    (orig_resid <= PIPE_BUF)) {
                                        space = 0;
                                }
                                if (space) {
                                        good = 1;
                                        break;
                                }
                                cpu_pause();
                        }
                        if (good)
                                continue;
                }
#endif

                /*
                 * Interlocked test.   Atomic op enforces the memory barrier.
                 */
                tsleep_interlock(wpb, PCATCH);
                atomic_set_int(&wpb->state, PIPE_WANTW);

                /*
                 * Retest space available after memory barrier above.
                 * Writes of size <= PIPE_BUF must be atomic.
                 */
                space = wpb->size - (wpb->windex - wpb->rindex);
                if ((space < uio->uio_resid) && (orig_resid <= PIPE_BUF))
                        space = 0;

                /*
                 * Retest EOF after memory barrier above.
                 */
                if (wpb->state & PIPE_WEOF) {
                        error = EPIPE;
                        break;
                }

                /*
                 * We have no more space and have something to offer,
                 * wake up select/poll/kq.
                 */
                if (space == 0) {
                        pipewakeup(wpb, 1);
                        error = tsleep(wpb, PCATCH | PINTERLOCKED, "pipewr", 0);
                }

                /*
                 * Break out if we errored or the read side wants us to go
                 * away.
                 */
                if (error)
                        break;
                if (wpb->state & PIPE_WEOF) {
                        error = EPIPE;
                        break;
                }
        }
        pipe_end_uio(&wpb->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 (wpb->windex != wpb->rindex) {
                pipesignal(wpb, PIPE_WANTR);
                pipewakeup(wpb, 1);
        }

        /*
         * Don't return EPIPE if I/O was successful
         */
        if ((wpb->rindex == wpb->windex) &&
            (uio->uio_resid == 0) &&
            (error == EPIPE)) {
                error = 0;
        }

        if (error == 0 && wpb->lticks != ticks) {
                vfs_timestamp(&wpb->mtime);
                wpb->lticks = ticks;
        }

        /*
         * We have something to offer,
         * wake up select/poll/kq.
         */
        /*space = wpb->windex - wpb->rindex;*/
        lwkt_reltoken(&wpb->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 pipebuf *rpb;
        struct pipe *pipe;
        int error;

        pipe = (struct pipe *)((intptr_t)fp->f_data & ~(intptr_t)1);
        if ((intptr_t)fp->f_data & 1) {
                rpb = &pipe->bufferB;
        } else {
                rpb = &pipe->bufferA;
        }

        lwkt_gettoken(&rpb->rlock);
        lwkt_gettoken(&rpb->wlock);

        switch (cmd) {
        case FIOASYNC:
                if (*(int *)data) {
                        atomic_set_int(&rpb->state, PIPE_ASYNC);
                } else {
                        atomic_clear_int(&rpb->state, PIPE_ASYNC);
                }
                error = 0;
                break;
        case FIONREAD:
                *(int *)data = (int)(rpb->windex - rpb->rindex);
                error = 0;
                break;
        case FIOSETOWN:
                error = fsetown(*(int *)data, &rpb->sigio);
                break;
        case FIOGETOWN:
                *(int *)data = fgetown(&rpb->sigio);
                error = 0;
                break;
        case TIOCSPGRP:
                /* This is deprecated, FIOSETOWN should be used instead. */
                error = fsetown(-(*(int *)data), &rpb->sigio);
                break;

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

        return (error);
}

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

        pipe = (struct pipe *)((intptr_t)fp->f_data & ~(intptr_t)1);
        if ((intptr_t)fp->f_data & 1) {
                rpb = &pipe->bufferB;
        } else {
                rpb = &pipe->bufferA;
        }

        bzero((caddr_t)ub, sizeof(*ub));
        ub->st_mode = S_IFIFO;
        ub->st_blksize = rpb->size;
        ub->st_size = rpb->windex - rpb->rindex;
        ub->st_blocks = howmany(ub->st_size, ub->st_blksize);
        ub->st_atimespec = rpb->atime;
        ub->st_mtimespec = rpb->mtime;
        ub->st_ctimespec = pipe->ctime;
        ub->st_uid = fp->f_cred->cr_uid;
        ub->st_gid = fp->f_cred->cr_gid;
        ub->st_ino = pipe->inum;
        /*
         * Left as 0: st_dev, st_nlink, st_rdev,
         * st_flags, st_gen.
         * XXX (st_dev, st_ino) should be unique.
         */

        return (0);
}

static int
pipe_close(struct file *fp)
{
        struct pipebuf *rpb;
        struct pipebuf *wpb;
        struct pipe *pipe;

        pipe = (struct pipe *)((intptr_t)fp->f_data & ~(intptr_t)1);
        if ((intptr_t)fp->f_data & 1) {
                rpb = &pipe->bufferB;
                wpb = &pipe->bufferA;
        } else {
                rpb = &pipe->bufferA;
                wpb = &pipe->bufferB;
        }

        fp->f_ops = &badfileops;
        fp->f_data = NULL;
        funsetown(&rpb->sigio);
        pipeclose(pipe, rpb, wpb);

        return (0);
}

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

        pipe = (struct pipe *)((intptr_t)fp->f_data & ~(intptr_t)1);
        if ((intptr_t)fp->f_data & 1) {
                rpb = &pipe->bufferB;
                wpb = &pipe->bufferA;
        } else {
                rpb = &pipe->bufferA;
                wpb = &pipe->bufferB;
        }

        /*
         * We modify pipe_state on both pipes, which means we need
         * all four tokens!
         */
        lwkt_gettoken(&rpb->rlock);
        lwkt_gettoken(&rpb->wlock);
        lwkt_gettoken(&wpb->rlock);
        lwkt_gettoken(&wpb->wlock);

        switch(how) {
        case SHUT_RDWR:
        case SHUT_RD:
                /*
                 * EOF on my reads and peer writes
                 */
                atomic_set_int(&rpb->state, PIPE_REOF | PIPE_WEOF);
                if (rpb->state & PIPE_WANTR) {
                        rpb->state &= ~PIPE_WANTR;
                        wakeup(rpb);
                }
                if (rpb->state & PIPE_WANTW) {
                        rpb->state &= ~PIPE_WANTW;
                        wakeup(rpb);
                }
                error = 0;
                if (how == SHUT_RD)
                        break;
                /* fall through */
        case SHUT_WR:
                /*
                 * EOF on peer reads and my writes
                 */
                atomic_set_int(&wpb->state, PIPE_REOF | PIPE_WEOF);
                if (wpb->state & PIPE_WANTR) {
                        wpb->state &= ~PIPE_WANTR;
                        wakeup(wpb);
                }
                if (wpb->state & PIPE_WANTW) {
                        wpb->state &= ~PIPE_WANTW;
                        wakeup(wpb);
                }
                error = 0;
                break;
        }
        pipewakeup(rpb, 1);
        pipewakeup(wpb, 1);

        lwkt_reltoken(&wpb->wlock);
        lwkt_reltoken(&wpb->rlock);
        lwkt_reltoken(&rpb->wlock);
        lwkt_reltoken(&rpb->rlock);

        return (error);
}

/*
 * Destroy the pipe buffer.
 */
static void
pipe_free_kmem(struct pipebuf *pb)
{
        if (pb->buffer != NULL) {
                kmem_free(kernel_map, (vm_offset_t)pb->buffer, pb->size);
                pb->buffer = NULL;
                pb->object = NULL;
        }
}

/*
 * Close one half of the pipe.  We are closing the pipe for reading on rpb
 * and writing on wpb.  This routine must be called twice with the pipebufs
 * reversed to close both directions.
 */
static void
pipeclose(struct pipe *pipe, struct pipebuf *rpb, struct pipebuf *wpb)
{
        globaldata_t gd;

        if (pipe == NULL)
                return;

        /*
         * We need both the read and write tokens to modify pipe_state.
         */
        lwkt_gettoken(&rpb->rlock);
        lwkt_gettoken(&rpb->wlock);

        /*
         * Set our state, wakeup anyone waiting in select/poll/kq, and
         * wakeup anyone blocked on our pipe.  No action if our side
         * is already closed.
         */
        if (rpb->state & PIPE_CLOSED) {
                lwkt_reltoken(&rpb->wlock);
                lwkt_reltoken(&rpb->rlock);
                return;
        }

        atomic_set_int(&rpb->state, PIPE_CLOSED | PIPE_REOF | PIPE_WEOF);
        pipewakeup(rpb, 1);
        if (rpb->state & (PIPE_WANTR | PIPE_WANTW)) {
                rpb->state &= ~(PIPE_WANTR | PIPE_WANTW);
                wakeup(rpb);
        }
        lwkt_reltoken(&rpb->wlock);
        lwkt_reltoken(&rpb->rlock);

        /*
         * Disconnect from peer.
         */
        lwkt_gettoken(&wpb->rlock);
        lwkt_gettoken(&wpb->wlock);

        atomic_set_int(&wpb->state, PIPE_REOF | PIPE_WEOF);
        pipewakeup(wpb, 1);
        if (wpb->state & (PIPE_WANTR | PIPE_WANTW)) {
                wpb->state &= ~(PIPE_WANTR | PIPE_WANTW);
                wakeup(wpb);
        }
        if (SLIST_FIRST(&wpb->kq.ki_note))
                KNOTE(&wpb->kq.ki_note, 0);
        lwkt_reltoken(&wpb->wlock);
        lwkt_reltoken(&wpb->rlock);

        /*
         * Free resources once both sides are closed.  We maintain a pcpu
         * cache to improve performance, so the actual tear-down case is
         * limited to bulk situations.
         *
         * However, the bulk tear-down case can cause intense contention
         * on the kernel_map when, e.g. hundreds to hundreds of thousands
         * of processes are killed at the same time.  To deal with this we
         * use a pcpu mutex to maintain concurrency but also limit the
         * number of threads banging on the map and pmap.
         *
         * We use the mtx mechanism instead of the lockmgr mechanism because
         * the mtx mechanism utilizes a queued design which will not break
         * down in the face of thousands to hundreds of thousands of
         * processes trying to free pipes simultaneously.  The lockmgr
         * mechanism will wind up waking them all up each time a lock
         * cycles.
         */
        if (atomic_fetchadd_int(&pipe->open_count, -1) == 1) {
                gd = mycpu;
                if (gd->gd_pipeqcount >= pipe_maxcache) {
                        mtx_lock(&pipe_gdlocks[gd->gd_cpuid].mtx);
                        pipe_free_kmem(rpb);
                        pipe_free_kmem(wpb);
                        mtx_unlock(&pipe_gdlocks[gd->gd_cpuid].mtx);
                        kfree(pipe, M_PIPE);
                } else {
                        rpb->state = 0;
                        wpb->state = 0;
                        pipe->next = gd->gd_pipeq;
                        gd->gd_pipeq = pipe;
                        ++gd->gd_pipeqcount;
                }
        }
}

static int
pipe_kqfilter(struct file *fp, struct knote *kn)
{
        struct pipebuf *rpb;
        struct pipebuf *wpb;
        struct pipe *pipe;

        pipe = (struct pipe *)((intptr_t)fp->f_data & ~(intptr_t)1);
        if ((intptr_t)fp->f_data & 1) {
                rpb = &pipe->bufferB;
                wpb = &pipe->bufferA;
        } else {
                rpb = &pipe->bufferA;
                wpb = &pipe->bufferB;
        }

        switch (kn->kn_filter) {
        case EVFILT_READ:
                kn->kn_fop = &pipe_rfiltops;
                break;
        case EVFILT_WRITE:
                kn->kn_fop = &pipe_wfiltops;
                break;
        default:
                return (EOPNOTSUPP);
        }

        if (rpb == &pipe->bufferA)
                kn->kn_hook = (caddr_t)(void *)((intptr_t)pipe | 0);
        else
                kn->kn_hook = (caddr_t)(void *)((intptr_t)pipe | 1);

        knote_insert(&rpb->kq.ki_note, kn);

        return (0);
}

static void
filt_pipedetach(struct knote *kn)
{
        struct pipebuf *rpb;
        struct pipebuf *wpb;
        struct pipe *pipe;

        pipe = (struct pipe *)((intptr_t)kn->kn_hook & ~(intptr_t)1);
        if ((intptr_t)kn->kn_hook & 1) {
                rpb = &pipe->bufferB;
                wpb = &pipe->bufferA;
        } else {
                rpb = &pipe->bufferA;
                wpb = &pipe->bufferB;
        }
        knote_remove(&rpb->kq.ki_note, kn);
}

/*ARGSUSED*/
static int
filt_piperead(struct knote *kn, long hint)
{
        struct pipebuf *rpb;
        struct pipebuf *wpb;
        struct pipe *pipe;
        int ready = 0;

        pipe = (struct pipe *)((intptr_t)kn->kn_fp->f_data & ~(intptr_t)1);
        if ((intptr_t)kn->kn_fp->f_data & 1) {
                rpb = &pipe->bufferB;
                wpb = &pipe->bufferA;
        } else {
                rpb = &pipe->bufferA;
                wpb = &pipe->bufferB;
        }

        /*
         * We shouldn't need the pipe locks because the knote itself is
         * locked via KN_PROCESSING.  If we lose a race against the writer,
         * the writer will just issue a KNOTE() after us.
         */
#if 0
        lwkt_gettoken(&rpb->rlock);
        lwkt_gettoken(&rpb->wlock);
#endif

        kn->kn_data = rpb->windex - rpb->rindex;
        if (kn->kn_data < 0)
                kn->kn_data = 0;

        if (rpb->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;

                /*
                 * Only set HUP if the pipe is completely closed.
                 * half-closed does not count (to make the behavior
                 * the same as linux).
                 */
                if (wpb->state & PIPE_CLOSED) {
                        kn->kn_flags |= EV_HUP;
                        ready = 1;
                }
        }

#if 0
        lwkt_reltoken(&rpb->wlock);
        lwkt_reltoken(&rpb->rlock);
#endif

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

        return (ready);
}

/*ARGSUSED*/
static int
filt_pipewrite(struct knote *kn, long hint)
{
        struct pipebuf *rpb;
        struct pipebuf *wpb;
        struct pipe *pipe;
        int ready = 0;

        pipe = (struct pipe *)((intptr_t)kn->kn_fp->f_data & ~(intptr_t)1);
        if ((intptr_t)kn->kn_fp->f_data & 1) {
                rpb = &pipe->bufferB;
                wpb = &pipe->bufferA;
        } else {
                rpb = &pipe->bufferA;
                wpb = &pipe->bufferB;
        }

        kn->kn_data = 0;
        if (wpb->state & PIPE_CLOSED) {
                kn->kn_flags |= EV_EOF | EV_HUP | EV_NODATA;
                return (1);
        }

        /*
         * We shouldn't need the pipe locks because the knote itself is
         * locked via KN_PROCESSING.  If we lose a race against the reader,
         * the writer will just issue a KNOTE() after us.
         */
#if 0
        lwkt_gettoken(&wpb->rlock);
        lwkt_gettoken(&wpb->wlock);
#endif

        if (wpb->state & PIPE_WEOF) {
                kn->kn_flags |= EV_EOF | EV_HUP | EV_NODATA;
                ready = 1;
        }

        if (!ready) {
                kn->kn_data = wpb->size - (wpb->windex - wpb->rindex);
                if (kn->kn_data < 0)
                        kn->kn_data = 0;
        }

#if 0
        lwkt_reltoken(&wpb->wlock);
        lwkt_reltoken(&wpb->rlock);
#endif

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

        return (ready);
}