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

/*      $NetBSD: kern_descrip.c,v 1.201 2009/12/09 21:32:59 dsl Exp $   */

/*-
 * Copyright (c) 2008, 2009 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Andrew Doran.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * Copyright (c) 1982, 1986, 1989, 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)kern_descrip.c      8.8 (Berkeley) 2/14/95
 */

/*
 * File descriptor management.
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: kern_descrip.c,v 1.201 2009/12/09 21:32:59 dsl Exp $");

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/file.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/fcntl.h>
#include <sys/pool.h>
#include <sys/unistd.h>
#include <sys/resourcevar.h>
#include <sys/conf.h>
#include <sys/event.h>
#include <sys/kauth.h>
#include <sys/atomic.h>
#include <sys/syscallargs.h>
#include <sys/cpu.h>
#include <sys/kmem.h>
#include <sys/vnode.h>

static int      file_ctor(void *, void *, int);
static void     file_dtor(void *, void *);
static int      fdfile_ctor(void *, void *, int);
static void     fdfile_dtor(void *, void *);
static int      filedesc_ctor(void *, void *, int);
static void     filedesc_dtor(void *, void *);
static int      filedescopen(dev_t, int, int, lwp_t *);

kmutex_t        filelist_lock;  /* lock on filehead */
struct filelist filehead;       /* head of list of open files */
u_int           nfiles;         /* actual number of open files */

static pool_cache_t filedesc_cache;
static pool_cache_t file_cache;
static pool_cache_t fdfile_cache;

const struct cdevsw filedesc_cdevsw = {
        filedescopen, noclose, noread, nowrite, noioctl,
        nostop, notty, nopoll, nommap, nokqfilter, D_OTHER | D_MPSAFE,
};

/* For ease of reading. */
__strong_alias(fd_putvnode,fd_putfile)
__strong_alias(fd_putsock,fd_putfile)

/*
 * Initialize the descriptor system.
 */
void
fd_sys_init(void)
{

        mutex_init(&filelist_lock, MUTEX_DEFAULT, IPL_NONE);

        file_cache = pool_cache_init(sizeof(file_t), coherency_unit, 0,
            0, "file", NULL, IPL_NONE, file_ctor, file_dtor, NULL);
        KASSERT(file_cache != NULL);

        fdfile_cache = pool_cache_init(sizeof(fdfile_t), coherency_unit, 0,
            PR_LARGECACHE, "fdfile", NULL, IPL_NONE, fdfile_ctor, fdfile_dtor,
            NULL);
        KASSERT(fdfile_cache != NULL);

        filedesc_cache = pool_cache_init(sizeof(filedesc_t), coherency_unit,
            0, 0, "filedesc", NULL, IPL_NONE, filedesc_ctor, filedesc_dtor,
            NULL);
        KASSERT(filedesc_cache != NULL);
}

static bool
fd_isused(filedesc_t *fdp, unsigned fd)
{
        u_int off = fd >> NDENTRYSHIFT;

        KASSERT(fd < fdp->fd_dt->dt_nfiles);

        return (fdp->fd_lomap[off] & (1 << (fd & NDENTRYMASK))) != 0;
}

/*
 * Verify that the bitmaps match the descriptor table.
 */
static inline void
fd_checkmaps(filedesc_t *fdp)
{
#ifdef DEBUG
        fdtab_t *dt;
        u_int fd;

        dt = fdp->fd_dt;
        if (fdp->fd_refcnt == -1) {
                /*
                 * fd_free tears down the table without maintaining its bitmap.
                 */
                return;
        }
        for (fd = 0; fd < dt->dt_nfiles; fd++) {
                if (fd < NDFDFILE) {
                        KASSERT(dt->dt_ff[fd] ==
                            (fdfile_t *)fdp->fd_dfdfile[fd]);
                }
                if (dt->dt_ff[fd] == NULL) {
                        KASSERT(!fd_isused(fdp, fd));
                } else if (dt->dt_ff[fd]->ff_file != NULL) {
                        KASSERT(fd_isused(fdp, fd));
                }
        }
#else   /* DEBUG */
        /* nothing */
#endif  /* DEBUG */
}

static int
fd_next_zero(filedesc_t *fdp, uint32_t *bitmap, int want, u_int bits)
{
        int i, off, maxoff;
        uint32_t sub;

        KASSERT(mutex_owned(&fdp->fd_lock));

        fd_checkmaps(fdp);

        if (want > bits)
                return -1;

        off = want >> NDENTRYSHIFT;
        i = want & NDENTRYMASK;
        if (i) {
                sub = bitmap[off] | ((u_int)~0 >> (NDENTRIES - i));
                if (sub != ~0)
                        goto found;
                off++;
        }

        maxoff = NDLOSLOTS(bits);
        while (off < maxoff) {
                if ((sub = bitmap[off]) != ~0)
                        goto found;
                off++;
        }

        return (-1);

 found:
        return (off << NDENTRYSHIFT) + ffs(~sub) - 1;
}

static int
fd_last_set(filedesc_t *fd, int last)
{
        int off, i;
        fdfile_t **ff = fd->fd_dt->dt_ff;
        uint32_t *bitmap = fd->fd_lomap;

        KASSERT(mutex_owned(&fd->fd_lock));

        fd_checkmaps(fd);

        off = (last - 1) >> NDENTRYSHIFT;

        while (off >= 0 && !bitmap[off])
                off--;

        if (off < 0)
                return (-1);

        i = ((off + 1) << NDENTRYSHIFT) - 1;
        if (i >= last)
                i = last - 1;

        /* XXX should use bitmap */
        while (i > 0 && (ff[i] == NULL || !ff[i]->ff_allocated))
                i--;

        return (i);
}

static inline void
fd_used(filedesc_t *fdp, unsigned fd)
{
        u_int off = fd >> NDENTRYSHIFT;
        fdfile_t *ff;

        ff = fdp->fd_dt->dt_ff[fd];

        KASSERT(mutex_owned(&fdp->fd_lock));
        KASSERT((fdp->fd_lomap[off] & (1 << (fd & NDENTRYMASK))) == 0);
        KASSERT(ff != NULL);
        KASSERT(ff->ff_file == NULL);
        KASSERT(!ff->ff_allocated);

        ff->ff_allocated = 1;
        fdp->fd_lomap[off] |= 1 << (fd & NDENTRYMASK);
        if (__predict_false(fdp->fd_lomap[off] == ~0)) {
                KASSERT((fdp->fd_himap[off >> NDENTRYSHIFT] &
                    (1 << (off & NDENTRYMASK))) == 0);
                fdp->fd_himap[off >> NDENTRYSHIFT] |= 1 << (off & NDENTRYMASK);
        }

        if ((int)fd > fdp->fd_lastfile) {
                fdp->fd_lastfile = fd;
        }

        fd_checkmaps(fdp);
}

static inline void
fd_unused(filedesc_t *fdp, unsigned fd)
{
        u_int off = fd >> NDENTRYSHIFT;
        fdfile_t *ff;

        ff = fdp->fd_dt->dt_ff[fd];

        /*
         * Don't assert the lock is held here, as we may be copying
         * the table during exec() and it is not needed there.
         * procfs and sysctl are locked out by proc::p_reflock.
         *
         * KASSERT(mutex_owned(&fdp->fd_lock));
         */
        KASSERT(ff != NULL);
        KASSERT(ff->ff_file == NULL);
        KASSERT(ff->ff_allocated);

        if (fd < fdp->fd_freefile) {
                fdp->fd_freefile = fd;
        }

        if (fdp->fd_lomap[off] == ~0) {
                KASSERT((fdp->fd_himap[off >> NDENTRYSHIFT] &
                    (1 << (off & NDENTRYMASK))) != 0);
                fdp->fd_himap[off >> NDENTRYSHIFT] &=
                    ~(1 << (off & NDENTRYMASK));
        }
        KASSERT((fdp->fd_lomap[off] & (1 << (fd & NDENTRYMASK))) != 0);
        fdp->fd_lomap[off] &= ~(1 << (fd & NDENTRYMASK));
        ff->ff_allocated = 0;

        KASSERT(fd <= fdp->fd_lastfile);
        if (fd == fdp->fd_lastfile) {
                fdp->fd_lastfile = fd_last_set(fdp, fd);
        }
        fd_checkmaps(fdp);
}

/*
 * Look up the file structure corresponding to a file descriptor
 * and return the file, holding a reference on the descriptor.
 */
inline file_t *
fd_getfile(unsigned fd)
{
        filedesc_t *fdp;
        fdfile_t *ff;
        file_t *fp;
        fdtab_t *dt;

        /*
         * Look up the fdfile structure representing this descriptor.
         * We are doing this unlocked.  See fd_tryexpand().
         */
        fdp = curlwp->l_fd;
        dt = fdp->fd_dt;
        if (__predict_false(fd >= dt->dt_nfiles)) {
                return NULL;
        }
        ff = dt->dt_ff[fd];
        KASSERT(fd >= NDFDFILE || ff == (fdfile_t *)fdp->fd_dfdfile[fd]);
        if (__predict_false(ff == NULL)) {
                return NULL;
        }

        /* Now get a reference to the descriptor. */
        if (fdp->fd_refcnt == 1) {
                /*
                 * Single threaded: don't need to worry about concurrent
                 * access (other than earlier calls to kqueue, which may
                 * hold a reference to the descriptor).
                 */
                ff->ff_refcnt++;
        } else {
                /*
                 * Multi threaded: issue a memory barrier to ensure that we
                 * acquire the file pointer _after_ adding a reference.  If
                 * no memory barrier, we could fetch a stale pointer.
                 */
                atomic_inc_uint(&ff->ff_refcnt);
#ifndef __HAVE_ATOMIC_AS_MEMBAR
                membar_enter();
#endif
        }

        /*
         * If the file is not open or is being closed then put the
         * reference back.
         */
        fp = ff->ff_file;
        if (__predict_true(fp != NULL)) {
                return fp;
        }
        fd_putfile(fd);
        return NULL;
}

/*
 * Release a reference to a file descriptor acquired with fd_getfile().
 */
void
fd_putfile(unsigned fd)
{
        filedesc_t *fdp;
        fdfile_t *ff;
        u_int u, v;

        fdp = curlwp->l_fd;
        ff = fdp->fd_dt->dt_ff[fd];

        KASSERT(fd < fdp->fd_dt->dt_nfiles);
        KASSERT(ff != NULL);
        KASSERT((ff->ff_refcnt & FR_MASK) > 0);
        KASSERT(fd >= NDFDFILE || ff == (fdfile_t *)fdp->fd_dfdfile[fd]);

        if (fdp->fd_refcnt == 1) {
                /*
                 * Single threaded: don't need to worry about concurrent
                 * access (other than earlier calls to kqueue, which may
                 * hold a reference to the descriptor).
                 */
                if (__predict_false((ff->ff_refcnt & FR_CLOSING) != 0)) {
                        fd_close(fd);
                        return;
                }
                ff->ff_refcnt--;
                return;
        }

        /*
         * Ensure that any use of the file is complete and globally
         * visible before dropping the final reference.  If no membar,
         * the current CPU could still access memory associated with
         * the file after it has been freed or recycled by another
         * CPU.
         */
#ifndef __HAVE_ATOMIC_AS_MEMBAR
        membar_exit();
#endif

        /*
         * Be optimistic and start out with the assumption that no other
         * threads are trying to close the descriptor.  If the CAS fails,
         * we lost a race and/or it's being closed.
         */
        for (u = ff->ff_refcnt & FR_MASK;; u = v) {
                v = atomic_cas_uint(&ff->ff_refcnt, u, u - 1);
                if (__predict_true(u == v)) {
                        return;
                }
                if (__predict_false((v & FR_CLOSING) != 0)) {
                        break;
                }
        }

        /* Another thread is waiting to close the file: join it. */
        (void)fd_close(fd);
}

/*
 * Convenience wrapper around fd_getfile() that returns reference
 * to a vnode.
 */
int
fd_getvnode(unsigned fd, file_t **fpp)
{
        vnode_t *vp;
        file_t *fp;

        fp = fd_getfile(fd);
        if (__predict_false(fp == NULL)) {
                return EBADF;
        }
        if (__predict_false(fp->f_type != DTYPE_VNODE)) {
                fd_putfile(fd);
                return EINVAL;
        }
        vp = fp->f_data;
        if (__predict_false(vp->v_type == VBAD)) {
                /* XXX Is this case really necessary? */
                fd_putfile(fd);
                return EBADF;
        }
        *fpp = fp;
        return 0;
}

/*
 * Convenience wrapper around fd_getfile() that returns reference
 * to a socket.
 */
int
fd_getsock(unsigned fd, struct socket **sop)
{
        file_t *fp;

        fp = fd_getfile(fd);
        if (__predict_false(fp == NULL)) {
                return EBADF;
        }
        if (__predict_false(fp->f_type != DTYPE_SOCKET)) {
                fd_putfile(fd);
                return ENOTSOCK;
        }
        *sop = fp->f_data;
        return 0;
}

/*
 * Look up the file structure corresponding to a file descriptor
 * and return it with a reference held on the file, not the
 * descriptor.
 *
 * This is heavyweight and only used when accessing descriptors
 * from a foreign process.  The caller must ensure that `p' does
 * not exit or fork across this call.
 *
 * To release the file (not descriptor) reference, use closef().
 */
file_t *
fd_getfile2(proc_t *p, unsigned fd)
{
        filedesc_t *fdp;
        fdfile_t *ff;
        file_t *fp;
        fdtab_t *dt;

        fdp = p->p_fd;
        mutex_enter(&fdp->fd_lock);
        dt = fdp->fd_dt;
        if (fd >= dt->dt_nfiles) {
                mutex_exit(&fdp->fd_lock);
                return NULL;
        }
        if ((ff = dt->dt_ff[fd]) == NULL) {
                mutex_exit(&fdp->fd_lock);
                return NULL;
        }
        if ((fp = ff->ff_file) == NULL) {
                mutex_exit(&fdp->fd_lock);
                return NULL;
        }
        mutex_enter(&fp->f_lock);
        fp->f_count++;
        mutex_exit(&fp->f_lock);
        mutex_exit(&fdp->fd_lock);

        return fp;
}

/*
 * Internal form of close.  Must be called with a reference to the
 * descriptor, and will drop the reference.  When all descriptor
 * references are dropped, releases the descriptor slot and a single
 * reference to the file structure.
 */
int
fd_close(unsigned fd)
{
        struct flock lf;
        filedesc_t *fdp;
        fdfile_t *ff;
        file_t *fp;
        proc_t *p;
        lwp_t *l;
        u_int refcnt;

        l = curlwp;
        p = l->l_proc;
        fdp = l->l_fd;
        ff = fdp->fd_dt->dt_ff[fd];

        KASSERT(fd >= NDFDFILE || ff == (fdfile_t *)fdp->fd_dfdfile[fd]);

        mutex_enter(&fdp->fd_lock);
        KASSERT((ff->ff_refcnt & FR_MASK) > 0);
        if (__predict_false(ff->ff_file == NULL)) {
                /*
                 * Another user of the file is already closing, and is
                 * waiting for other users of the file to drain.  Release
                 * our reference, and wake up the closer.
                 */
                atomic_dec_uint(&ff->ff_refcnt);
                cv_broadcast(&ff->ff_closing);
                mutex_exit(&fdp->fd_lock);

                /*
                 * An application error, so pretend that the descriptor
                 * was already closed.  We can't safely wait for it to
                 * be closed without potentially deadlocking.
                 */
                return (EBADF);
        }
        KASSERT((ff->ff_refcnt & FR_CLOSING) == 0);

        /*
         * There may be multiple users of this file within the process.
         * Notify existing and new users that the file is closing.  This
         * will prevent them from adding additional uses to this file
         * while we are closing it.
         */
        fp = ff->ff_file;
        ff->ff_file = NULL;
        ff->ff_exclose = false;

        /*
         * We expect the caller to hold a descriptor reference - drop it.
         * The reference count may increase beyond zero at this point due
         * to an erroneous descriptor reference by an application, but
         * fd_getfile() will notice that the file is being closed and drop
         * the reference again.
         */
        if (fdp->fd_refcnt == 1) {
                /* Single threaded. */
                refcnt = --(ff->ff_refcnt);
        } else {
                /* Multi threaded. */
#ifndef __HAVE_ATOMIC_AS_MEMBAR
                membar_producer();
#endif
                refcnt = atomic_dec_uint_nv(&ff->ff_refcnt);
        }
        if (__predict_false(refcnt != 0)) {
                /*
                 * Wait for other references to drain.  This is typically
                 * an application error - the descriptor is being closed
                 * while still in use.
                 * (Or just a threaded application trying to unblock its
                 * thread that sleeps in (say) accept()).
                 */
                atomic_or_uint(&ff->ff_refcnt, FR_CLOSING);

                /*
                 * Remove any knotes attached to the file.  A knote
                 * attached to the descriptor can hold references on it.
                 */
                mutex_exit(&fdp->fd_lock);
                if (!SLIST_EMPTY(&ff->ff_knlist)) {
                        knote_fdclose(fd);
                }

                /*
                 * Since the file system code doesn't know which fd
                 * each request came from (think dup()), we have to
                 * ask it to return ERESTART for any long-term blocks.
                 * The re-entry through read/write/etc will detect the
                 * closed fd and return EBAFD.
                 * Blocked partial writes may return a short length.
                 */
                (*fp->f_ops->fo_restart)(fp);
                mutex_enter(&fdp->fd_lock);

                /*
                 * We need to see the count drop to zero at least once,
                 * in order to ensure that all pre-existing references
                 * have been drained.  New references past this point are
                 * of no interest.
                 * XXX (dsl) this may need to call fo_restart() after a
                 * timeout to guarantee that all the system calls exit.
                 */
                while ((ff->ff_refcnt & FR_MASK) != 0) {
                        cv_wait(&ff->ff_closing, &fdp->fd_lock);
                }
                atomic_and_uint(&ff->ff_refcnt, ~FR_CLOSING);
        } else {
                /* If no references, there must be no knotes. */
                KASSERT(SLIST_EMPTY(&ff->ff_knlist));
        }

        /*
         * POSIX record locking dictates that any close releases ALL
         * locks owned by this process.  This is handled by setting
         * a flag in the unlock to free ONLY locks obeying POSIX
         * semantics, and not to free BSD-style file locks.
         * If the descriptor was in a message, POSIX-style locks
         * aren't passed with the descriptor.
         */
        if (__predict_false((p->p_flag & PK_ADVLOCK) != 0 &&
            fp->f_type == DTYPE_VNODE)) {
                lf.l_whence = SEEK_SET;
                lf.l_start = 0;
                lf.l_len = 0;
                lf.l_type = F_UNLCK;
                mutex_exit(&fdp->fd_lock);
                (void)VOP_ADVLOCK(fp->f_data, p, F_UNLCK, &lf, F_POSIX);
                mutex_enter(&fdp->fd_lock);
        }

        /* Free descriptor slot. */
        fd_unused(fdp, fd);
        mutex_exit(&fdp->fd_lock);

        /* Now drop reference to the file itself. */
        return closef(fp);
}

/*
 * Duplicate a file descriptor.
 */
int
fd_dup(file_t *fp, int minfd, int *newp, bool exclose)
{
        proc_t *p;
        int error;

        p = curproc;

        while ((error = fd_alloc(p, minfd, newp)) != 0) {
                if (error != ENOSPC) {
                        return error;
                }
                fd_tryexpand(p);
        }

        curlwp->l_fd->fd_dt->dt_ff[*newp]->ff_exclose = exclose;
        fd_affix(p, fp, *newp);
        return 0;
}

/*
 * dup2 operation.
 */
int
fd_dup2(file_t *fp, unsigned new)
{
        filedesc_t *fdp;
        fdfile_t *ff;
        fdtab_t *dt;

        fdp = curlwp->l_fd;

        /*
         * Ensure there are enough slots in the descriptor table,
         * and allocate an fdfile_t up front in case we need it.
         */
        while (new >= fdp->fd_dt->dt_nfiles) {
                fd_tryexpand(curproc);
        }
        ff = pool_cache_get(fdfile_cache, PR_WAITOK);

        /*
         * If there is already a file open, close it.  If the file is
         * half open, wait for it to be constructed before closing it.
         * XXX Potential for deadlock here?
         */
        mutex_enter(&fdp->fd_lock);
        while (fd_isused(fdp, new)) {
                mutex_exit(&fdp->fd_lock);
                if (fd_getfile(new) != NULL) {
                        (void)fd_close(new);
                } else {
                        /*
                         * Crummy, but unlikely to happen.
                         * Can occur if we interrupt another
                         * thread while it is opening a file.
                         */
                        kpause("dup2", false, 1, NULL);
                }
                mutex_enter(&fdp->fd_lock);
        }
        dt = fdp->fd_dt;
        if (dt->dt_ff[new] == NULL) {
                KASSERT(new >= NDFDFILE);
                dt->dt_ff[new] = ff;
                ff = NULL;
        }               
        fd_used(fdp, new);
        mutex_exit(&fdp->fd_lock);

        /* Slot is now allocated.  Insert copy of the file. */
        fd_affix(curproc, fp, new);
        if (ff != NULL) {
                pool_cache_put(fdfile_cache, ff);
        }
        return 0;
}

/*
 * Drop reference to a file structure.
 */
int
closef(file_t *fp)
{
        struct flock lf;
        int error;

        /*
         * Drop reference.  If referenced elsewhere it's still open
         * and we have nothing more to do.
         */
        mutex_enter(&fp->f_lock);
        KASSERT(fp->f_count > 0);
        if (--fp->f_count > 0) {
                mutex_exit(&fp->f_lock);
                return 0;
        }
        KASSERT(fp->f_count == 0);
        mutex_exit(&fp->f_lock);

        /* We held the last reference - release locks, close and free. */
        if ((fp->f_flag & FHASLOCK) && fp->f_type == DTYPE_VNODE) {
                lf.l_whence = SEEK_SET;
                lf.l_start = 0;
                lf.l_len = 0;
                lf.l_type = F_UNLCK;
                (void)VOP_ADVLOCK(fp->f_data, fp, F_UNLCK, &lf, F_FLOCK);
        }
        if (fp->f_ops != NULL) {
                error = (*fp->f_ops->fo_close)(fp);
        } else {
                error = 0;
        }
        KASSERT(fp->f_count == 0);
        KASSERT(fp->f_cred != NULL);
        pool_cache_put(file_cache, fp);

        return error;
}

/*
 * Allocate a file descriptor for the process.
 */
int
fd_alloc(proc_t *p, int want, int *result)
{
        filedesc_t *fdp;
        int i, lim, last, error;
        u_int off, new;
        fdtab_t *dt;

        KASSERT(p == curproc || p == &proc0);

        fdp = p->p_fd;

        /*
         * Search for a free descriptor starting at the higher
         * of want or fd_freefile.
         */
        mutex_enter(&fdp->fd_lock);
        fd_checkmaps(fdp);
        dt = fdp->fd_dt;
        KASSERT(dt->dt_ff[0] == (fdfile_t *)fdp->fd_dfdfile[0]);
        lim = min((int)p->p_rlimit[RLIMIT_NOFILE].rlim_cur, maxfiles);
        last = min(dt->dt_nfiles, lim);
        for (;;) {
                if ((i = want) < fdp->fd_freefile)
                        i = fdp->fd_freefile;
                off = i >> NDENTRYSHIFT;
                new = fd_next_zero(fdp, fdp->fd_himap, off,
                    (last + NDENTRIES - 1) >> NDENTRYSHIFT);
                if (new == -1)
                        break;
                i = fd_next_zero(fdp, &fdp->fd_lomap[new],
                    new > off ? 0 : i & NDENTRYMASK, NDENTRIES);
                if (i == -1) {
                        /*
                         * Free file descriptor in this block was
                         * below want, try again with higher want.
                         */
                        want = (new + 1) << NDENTRYSHIFT;
                        continue;
                }
                i += (new << NDENTRYSHIFT);
                if (i >= last) {
                        break;
                }
                if (dt->dt_ff[i] == NULL) {
                        KASSERT(i >= NDFDFILE);
                        dt->dt_ff[i] = pool_cache_get(fdfile_cache, PR_WAITOK);
                }
                KASSERT(dt->dt_ff[i]->ff_refcnt == 0);
                KASSERT(dt->dt_ff[i]->ff_file == NULL);
                fd_used(fdp, i);
                if (want <= fdp->fd_freefile) {
                        fdp->fd_freefile = i;
                }
                *result = i;
                KASSERT(i >= NDFDFILE ||
                    dt->dt_ff[i] == (fdfile_t *)fdp->fd_dfdfile[i]);
                fd_checkmaps(fdp);
                mutex_exit(&fdp->fd_lock);
                return 0;
        }

        /* No space in current array.  Let the caller expand and retry. */
        error = (dt->dt_nfiles >= lim) ? EMFILE : ENOSPC;
        mutex_exit(&fdp->fd_lock);
        return error;
}

/*
 * Allocate memory for a descriptor table.
 */
static fdtab_t *
fd_dtab_alloc(int n)
{
        fdtab_t *dt;
        size_t sz;

        KASSERT(n > NDFILE);

        sz = sizeof(*dt) + (n - NDFILE) * sizeof(dt->dt_ff[0]);
        dt = kmem_alloc(sz, KM_SLEEP);
#ifdef DIAGNOSTIC
        memset(dt, 0xff, sz);
#endif
        dt->dt_nfiles = n;
        dt->dt_link = NULL;
        return dt;
}

/*
 * Free a descriptor table, and all tables linked for deferred free.
 */
static void
fd_dtab_free(fdtab_t *dt)
{
        fdtab_t *next;
        size_t sz;

        do {
                next = dt->dt_link;
                KASSERT(dt->dt_nfiles > NDFILE);
                sz = sizeof(*dt) +
                    (dt->dt_nfiles - NDFILE) * sizeof(dt->dt_ff[0]);
#ifdef DIAGNOSTIC
                memset(dt, 0xff, sz);
#endif
                kmem_free(dt, sz);
                dt = next;
        } while (dt != NULL);
}

/*
 * Allocate descriptor bitmap.
 */
static void
fd_map_alloc(int n, uint32_t **lo, uint32_t **hi)
{
        uint8_t *ptr;
        size_t szlo, szhi;

        KASSERT(n > NDENTRIES);

        szlo = NDLOSLOTS(n) * sizeof(uint32_t);
        szhi = NDHISLOTS(n) * sizeof(uint32_t);
        ptr = kmem_alloc(szlo + szhi, KM_SLEEP);
        *lo = (uint32_t *)ptr;
        *hi = (uint32_t *)(ptr + szlo);
}

/*
 * Free descriptor bitmap.
 */
static void
fd_map_free(int n, uint32_t *lo, uint32_t *hi)
{
        size_t szlo, szhi;

        KASSERT(n > NDENTRIES);

        szlo = NDLOSLOTS(n) * sizeof(uint32_t);
        szhi = NDHISLOTS(n) * sizeof(uint32_t);
        KASSERT(hi == (uint32_t *)((uint8_t *)lo + szlo));
        kmem_free(lo, szlo + szhi);
}

/*
 * Expand a process' descriptor table.
 */
void
fd_tryexpand(proc_t *p)
{
        filedesc_t *fdp;
        int i, numfiles, oldnfiles;
        fdtab_t *newdt, *dt;
        uint32_t *newhimap, *newlomap;

        KASSERT(p == curproc || p == &proc0);

        fdp = p->p_fd;
        newhimap = NULL;
        newlomap = NULL;
        oldnfiles = fdp->fd_dt->dt_nfiles;

        if (oldnfiles < NDEXTENT)
                numfiles = NDEXTENT;
        else
                numfiles = 2 * oldnfiles;

        newdt = fd_dtab_alloc(numfiles);
        if (NDHISLOTS(numfiles) > NDHISLOTS(oldnfiles)) {
                fd_map_alloc(numfiles, &newlomap, &newhimap);
        }

        mutex_enter(&fdp->fd_lock);
        dt = fdp->fd_dt;
        KASSERT(dt->dt_ff[0] == (fdfile_t *)fdp->fd_dfdfile[0]);
        if (dt->dt_nfiles != oldnfiles) {
                /* fdp changed; caller must retry */
                mutex_exit(&fdp->fd_lock);
                fd_dtab_free(newdt);
                if (NDHISLOTS(numfiles) > NDHISLOTS(oldnfiles)) {
                        fd_map_free(numfiles, newlomap, newhimap);
                }
                return;
        }

        /* Copy the existing descriptor table and zero the new portion. */
        i = sizeof(fdfile_t *) * oldnfiles;
        memcpy(newdt->dt_ff, dt->dt_ff, i);
        memset((uint8_t *)newdt->dt_ff + i, 0,
            numfiles * sizeof(fdfile_t *) - i);

        /*
         * Link old descriptor array into list to be discarded.  We defer
         * freeing until the last reference to the descriptor table goes
         * away (usually process exit).  This allows us to do lockless
         * lookups in fd_getfile().
         */
        if (oldnfiles > NDFILE) {
                if (fdp->fd_refcnt > 1) {
                        newdt->dt_link = dt;
                } else {
                        fd_dtab_free(dt);
                }
        }

        if (NDHISLOTS(numfiles) > NDHISLOTS(oldnfiles)) {
                i = NDHISLOTS(oldnfiles) * sizeof(uint32_t);
                memcpy(newhimap, fdp->fd_himap, i);
                memset((uint8_t *)newhimap + i, 0,
                    NDHISLOTS(numfiles) * sizeof(uint32_t) - i);

                i = NDLOSLOTS(oldnfiles) * sizeof(uint32_t);
                memcpy(newlomap, fdp->fd_lomap, i);
                memset((uint8_t *)newlomap + i, 0,
                    NDLOSLOTS(numfiles) * sizeof(uint32_t) - i);

                if (NDHISLOTS(oldnfiles) > NDHISLOTS(NDFILE)) {
                        fd_map_free(oldnfiles, fdp->fd_lomap, fdp->fd_himap);
                }
                fdp->fd_himap = newhimap;
                fdp->fd_lomap = newlomap;
        }

        /*
         * All other modifications must become globally visible before
         * the change to fd_dt.  See fd_getfile().
         */
        membar_producer();
        fdp->fd_dt = newdt;
        KASSERT(newdt->dt_ff[0] == (fdfile_t *)fdp->fd_dfdfile[0]);
        fd_checkmaps(fdp);
        mutex_exit(&fdp->fd_lock);
}

/*
 * Create a new open file structure and allocate a file descriptor
 * for the current process.
 */
int
fd_allocfile(file_t **resultfp, int *resultfd)
{
        kauth_cred_t cred;
        file_t *fp;
        proc_t *p;
        int error;

        p = curproc;

        while ((error = fd_alloc(p, 0, resultfd)) != 0) {
                if (error != ENOSPC) {
                        return error;
                }
                fd_tryexpand(p);
        }

        fp = pool_cache_get(file_cache, PR_WAITOK);
        if (fp == NULL) {
                return ENFILE;
        }
        KASSERT(fp->f_count == 0);
        KASSERT(fp->f_msgcount == 0);
        KASSERT(fp->f_unpcount == 0);

        /* Replace cached credentials if not what we need. */
        cred = curlwp->l_cred;
        if (__predict_false(cred != fp->f_cred)) {
                kauth_cred_free(fp->f_cred);
                kauth_cred_hold(cred);
                fp->f_cred = cred;
        }

        /*
         * Don't allow recycled files to be scanned.
         * See uipc_usrreq.c.
         */
        if (__predict_false((fp->f_flag & FSCAN) != 0)) {
                mutex_enter(&fp->f_lock);
                atomic_and_uint(&fp->f_flag, ~FSCAN);
                mutex_exit(&fp->f_lock);
        }

        fp->f_advice = 0;
        fp->f_offset = 0;
        *resultfp = fp;

        return 0;
}

/*
 * Successful creation of a new descriptor: make visible to the process.
 */
void
fd_affix(proc_t *p, file_t *fp, unsigned fd)
{
        fdfile_t *ff;
        filedesc_t *fdp;

        KASSERT(p == curproc || p == &proc0);

        /* Add a reference to the file structure. */
        mutex_enter(&fp->f_lock);
        fp->f_count++;
        mutex_exit(&fp->f_lock);

        /*
         * Insert the new file into the descriptor slot.
         *
         * The memory barriers provided by lock activity in this routine
         * ensure that any updates to the file structure become globally
         * visible before the file becomes visible to other LWPs in the
         * current process.
         */
        fdp = p->p_fd;
        ff = fdp->fd_dt->dt_ff[fd];

        KASSERT(ff != NULL);
        KASSERT(ff->ff_file == NULL);
        KASSERT(ff->ff_allocated);
        KASSERT(fd_isused(fdp, fd));
        KASSERT(fd >= NDFDFILE || ff == (fdfile_t *)fdp->fd_dfdfile[fd]);

        /* No need to lock in order to make file initially visible. */
        ff->ff_file = fp;
}

/*
 * Abort creation of a new descriptor: free descriptor slot and file.
 */
void
fd_abort(proc_t *p, file_t *fp, unsigned fd)
{
        filedesc_t *fdp;
        fdfile_t *ff;

        KASSERT(p == curproc || p == &proc0);

        fdp = p->p_fd;
        ff = fdp->fd_dt->dt_ff[fd];

        KASSERT(fd >= NDFDFILE || ff == (fdfile_t *)fdp->fd_dfdfile[fd]);

        mutex_enter(&fdp->fd_lock);
        KASSERT(fd_isused(fdp, fd));
        fd_unused(fdp, fd);
        mutex_exit(&fdp->fd_lock);

        if (fp != NULL) {
                KASSERT(fp->f_count == 0);
                KASSERT(fp->f_cred != NULL);
                pool_cache_put(file_cache, fp);
        }
}

static int
file_ctor(void *arg, void *obj, int flags)
{
        file_t *fp = obj;

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

        mutex_enter(&filelist_lock);
        if (__predict_false(nfiles >= maxfiles)) {
                mutex_exit(&filelist_lock);
                tablefull("file", "increase kern.maxfiles or MAXFILES");
                return ENFILE;
        }
        nfiles++;
        LIST_INSERT_HEAD(&filehead, fp, f_list);
        mutex_init(&fp->f_lock, MUTEX_DEFAULT, IPL_NONE);
        fp->f_cred = curlwp->l_cred;
        kauth_cred_hold(fp->f_cred);
        mutex_exit(&filelist_lock);

        return 0;
}

static void
file_dtor(void *arg, void *obj)
{
        file_t *fp = obj;

        mutex_enter(&filelist_lock);
        nfiles--;
        LIST_REMOVE(fp, f_list);
        mutex_exit(&filelist_lock);

        kauth_cred_free(fp->f_cred);
        mutex_destroy(&fp->f_lock);
}

static int
fdfile_ctor(void *arg, void *obj, int flags)
{
        fdfile_t *ff = obj;

        memset(ff, 0, sizeof(*ff));
        cv_init(&ff->ff_closing, "fdclose");

        return 0;
}

static void
fdfile_dtor(void *arg, void *obj)
{
        fdfile_t *ff = obj;

        cv_destroy(&ff->ff_closing);
}

file_t *
fgetdummy(void)
{
        file_t *fp;

        fp = kmem_alloc(sizeof(*fp), KM_SLEEP);
        if (fp != NULL) {
                memset(fp, 0, sizeof(*fp));
                mutex_init(&fp->f_lock, MUTEX_DEFAULT, IPL_NONE);
        }
        return fp;
}

void
fputdummy(file_t *fp)
{

        mutex_destroy(&fp->f_lock);
        kmem_free(fp, sizeof(*fp));
}

/*
 * Create an initial filedesc structure.
 */
filedesc_t *
fd_init(filedesc_t *fdp)
{
#ifdef DIAGNOSTIC
        unsigned fd;
#endif

        if (__predict_true(fdp == NULL)) {
                fdp = pool_cache_get(filedesc_cache, PR_WAITOK);
        } else {
                /* XXXRUMP KASSERT(fdp == &filedesc0); */
                filedesc_ctor(NULL, fdp, PR_WAITOK);
        }

#ifdef DIAGNOSTIC
        KASSERT(fdp->fd_lastfile == -1);
        KASSERT(fdp->fd_lastkqfile == -1);
        KASSERT(fdp->fd_knhash == NULL);
        KASSERT(fdp->fd_freefile == 0);
        KASSERT(fdp->fd_exclose == false);
        KASSERT(fdp->fd_dt == &fdp->fd_dtbuiltin);
        KASSERT(fdp->fd_dtbuiltin.dt_nfiles == NDFILE);
        for (fd = 0; fd < NDFDFILE; fd++) {
                KASSERT(fdp->fd_dtbuiltin.dt_ff[fd] ==
                    (fdfile_t *)fdp->fd_dfdfile[fd]);
        }
        for (fd = NDFDFILE; fd < NDFILE; fd++) {
                KASSERT(fdp->fd_dtbuiltin.dt_ff[fd] == NULL);
        }
        KASSERT(fdp->fd_himap == fdp->fd_dhimap);
        KASSERT(fdp->fd_lomap == fdp->fd_dlomap);
#endif  /* DIAGNOSTIC */

        fdp->fd_refcnt = 1;
        fd_checkmaps(fdp);

        return fdp;
}

/*
 * Initialize a file descriptor table.
 */
static int
filedesc_ctor(void *arg, void *obj, int flag)
{
        filedesc_t *fdp = obj;
        fdfile_t **ffp;
        int i;

        memset(fdp, 0, sizeof(*fdp));
        mutex_init(&fdp->fd_lock, MUTEX_DEFAULT, IPL_NONE);
        fdp->fd_lastfile = -1;
        fdp->fd_lastkqfile = -1;
        fdp->fd_dt = &fdp->fd_dtbuiltin;
        fdp->fd_dtbuiltin.dt_nfiles = NDFILE;
        fdp->fd_himap = fdp->fd_dhimap;
        fdp->fd_lomap = fdp->fd_dlomap;

        CTASSERT(sizeof(fdp->fd_dfdfile[0]) >= sizeof(fdfile_t));
        for (i = 0, ffp = fdp->fd_dt->dt_ff; i < NDFDFILE; i++, ffp++) {
                *ffp = (fdfile_t *)fdp->fd_dfdfile[i];
                (void)fdfile_ctor(NULL, fdp->fd_dfdfile[i], PR_WAITOK);
        }

        return 0;
}

static void
filedesc_dtor(void *arg, void *obj)
{
        filedesc_t *fdp = obj;
        int i;

        for (i = 0; i < NDFDFILE; i++) {
                fdfile_dtor(NULL, fdp->fd_dfdfile[i]);
        }

        mutex_destroy(&fdp->fd_lock);
}

/*
 * Make p2 share p1's filedesc structure.
 */
void
fd_share(struct proc *p2)
{
        filedesc_t *fdp;

        fdp = curlwp->l_fd;
        p2->p_fd = fdp;
        atomic_inc_uint(&fdp->fd_refcnt);
}

/*
 * Acquire a hold on a filedesc structure.
 */
void
fd_hold(lwp_t *l)
{
        filedesc_t *fdp = l->l_fd;

        KASSERT(fdp == curlwp->l_fd || fdp == lwp0.l_fd);
        atomic_inc_uint(&fdp->fd_refcnt);
}

/*
 * Copy a filedesc structure.
 */
filedesc_t *
fd_copy(void)
{
        filedesc_t *newfdp, *fdp;
        fdfile_t *ff, **ffp, **nffp, *ff2;
        int i, j, numfiles, lastfile, newlast;
        file_t *fp;
        fdtab_t *newdt;

        fdp = curproc->p_fd;
        newfdp = pool_cache_get(filedesc_cache, PR_WAITOK);
        newfdp->fd_refcnt = 1;

#ifdef DIAGNOSTIC
        KASSERT(newfdp->fd_lastfile == -1);
        KASSERT(newfdp->fd_lastkqfile == -1);
        KASSERT(newfdp->fd_knhash == NULL);
        KASSERT(newfdp->fd_freefile == 0);
        KASSERT(newfdp->fd_exclose == false);
        KASSERT(newfdp->fd_dt == &newfdp->fd_dtbuiltin);
        KASSERT(newfdp->fd_dtbuiltin.dt_nfiles == NDFILE);
        for (i = 0; i < NDFDFILE; i++) {
                KASSERT(newfdp->fd_dtbuiltin.dt_ff[i] ==
                    (fdfile_t *)&newfdp->fd_dfdfile[i]);
        }
        for (i = NDFDFILE; i < NDFILE; i++) {
                KASSERT(newfdp->fd_dtbuiltin.dt_ff[i] == NULL);
        }
#endif  /* DIAGNOSTIC */

        mutex_enter(&fdp->fd_lock);
        fd_checkmaps(fdp);
        numfiles = fdp->fd_dt->dt_nfiles;
        lastfile = fdp->fd_lastfile;

        /*
         * If the number of open files fits in the internal arrays
         * of the open file structure, use them, otherwise allocate
         * additional memory for the number of descriptors currently
         * in use.
         */
        if (lastfile < NDFILE) {
                i = NDFILE;
                newdt = newfdp->fd_dt;
                KASSERT(newfdp->fd_dt == &newfdp->fd_dtbuiltin);
        } else {
                /*
                 * Compute the smallest multiple of NDEXTENT needed
                 * for the file descriptors currently in use,
                 * allowing the table to shrink.
                 */
                i = numfiles;
                while (i >= 2 * NDEXTENT && i > lastfile * 2) {
                        i /= 2;
                }
                KASSERT(i > NDFILE);
                newdt = fd_dtab_alloc(i);
                newfdp->fd_dt = newdt;
                memcpy(newdt->dt_ff, newfdp->fd_dtbuiltin.dt_ff,
                    NDFDFILE * sizeof(fdfile_t **));
                memset(newdt->dt_ff + NDFDFILE, 0,
                    (i - NDFDFILE) * sizeof(fdfile_t **));
        }
        if (NDHISLOTS(i) <= NDHISLOTS(NDFILE)) {
                newfdp->fd_himap = newfdp->fd_dhimap;
                newfdp->fd_lomap = newfdp->fd_dlomap;
        } else {
                fd_map_alloc(i, &newfdp->fd_lomap, &newfdp->fd_himap);
                KASSERT(i >= NDENTRIES * NDENTRIES);
                memset(newfdp->fd_himap, 0, NDHISLOTS(i)*sizeof(uint32_t));
                memset(newfdp->fd_lomap, 0, NDLOSLOTS(i)*sizeof(uint32_t));
        }
        newfdp->fd_freefile = fdp->fd_freefile;
        newfdp->fd_exclose = fdp->fd_exclose;

        ffp = fdp->fd_dt->dt_ff;
        nffp = newdt->dt_ff;
        newlast = -1;
        for (i = 0; i <= (int)lastfile; i++, ffp++, nffp++) {
                KASSERT(i >= NDFDFILE ||
                    *nffp == (fdfile_t *)newfdp->fd_dfdfile[i]);
                ff = *ffp;
                if (ff == NULL || (fp = ff->ff_file) == NULL) {
                        /* Descriptor unused, or descriptor half open. */
                        KASSERT(!fd_isused(newfdp, i));
                        continue;
                }
                if (__predict_false(fp->f_type == DTYPE_KQUEUE)) {
                        /* kqueue descriptors cannot be copied. */
                       if (i < newfdp->fd_freefile)
                               newfdp->fd_freefile = i;
                        continue;
                }
                /* It's active: add a reference to the file. */
                mutex_enter(&fp->f_lock);
                fp->f_count++;
                mutex_exit(&fp->f_lock);

                /* Allocate an fdfile_t to represent it. */
                if (i >= NDFDFILE) {
                        ff2 = pool_cache_get(fdfile_cache, PR_WAITOK);
                        *nffp = ff2;
                } else {
                        ff2 = newdt->dt_ff[i];
                }
                ff2->ff_file = fp;
                ff2->ff_exclose = ff->ff_exclose;
                ff2->ff_allocated = true;

                /* Fix up bitmaps. */
                j = i >> NDENTRYSHIFT;
                KASSERT((newfdp->fd_lomap[j] & (1 << (i & NDENTRYMASK))) == 0);
                newfdp->fd_lomap[j] |= 1 << (i & NDENTRYMASK);
                if (__predict_false(newfdp->fd_lomap[j] == ~0)) {
                        KASSERT((newfdp->fd_himap[j >> NDENTRYSHIFT] &
                            (1 << (j & NDENTRYMASK))) == 0);
                        newfdp->fd_himap[j >> NDENTRYSHIFT] |=
                            1 << (j & NDENTRYMASK);
                }
                newlast = i;
        }
        KASSERT(newdt->dt_ff[0] == (fdfile_t *)newfdp->fd_dfdfile[0]);
        newfdp->fd_lastfile = newlast;
        fd_checkmaps(newfdp);
        mutex_exit(&fdp->fd_lock);
        
        return (newfdp);
}

/*
 * Release a filedesc structure.
 */
void
fd_free(void)
{
        fdfile_t *ff;
        file_t *fp;
        int fd, nf;
        fdtab_t *dt;
        lwp_t * const l = curlwp;
        filedesc_t * const fdp = l->l_fd;
        const bool noadvlock = (l->l_proc->p_flag & PK_ADVLOCK) == 0;

        KASSERT(fdp->fd_dt->dt_ff[0] == (fdfile_t *)fdp->fd_dfdfile[0]);
        KASSERT(fdp->fd_dtbuiltin.dt_nfiles == NDFILE);
        KASSERT(fdp->fd_dtbuiltin.dt_link == NULL);

#ifndef __HAVE_ATOMIC_AS_MEMBAR
        membar_exit();
#endif
        if (atomic_dec_uint_nv(&fdp->fd_refcnt) > 0)
                return;

        /*
         * Close any files that the process holds open.
         */
        dt = fdp->fd_dt;
        fd_checkmaps(fdp);
#ifdef DEBUG
        fdp->fd_refcnt = -1; /* see fd_checkmaps */
#endif
        for (fd = 0, nf = dt->dt_nfiles; fd < nf; fd++) {
                ff = dt->dt_ff[fd];
                KASSERT(fd >= NDFDFILE ||
                    ff == (fdfile_t *)fdp->fd_dfdfile[fd]);
                if (ff == NULL)
                        continue;
                if ((fp = ff->ff_file) != NULL) {
                        /*
                         * Must use fd_close() here if there is
                         * a reference from kqueue or we might have posix
                         * advisory locks.
                         */
                        if (__predict_true(ff->ff_refcnt == 0) &&
                            (noadvlock || fp->f_type != DTYPE_VNODE)) {
                                ff->ff_file = NULL;
                                ff->ff_exclose = false;
                                ff->ff_allocated = false;
                                closef(fp);
                        } else {
                                ff->ff_refcnt++;
                                fd_close(fd);
                        }
                }
                KASSERT(ff->ff_refcnt == 0);
                KASSERT(ff->ff_file == NULL);
                KASSERT(!ff->ff_exclose);
                KASSERT(!ff->ff_allocated);
                if (fd >= NDFDFILE) {
                        pool_cache_put(fdfile_cache, ff);
                        dt->dt_ff[fd] = NULL;
                }
        }

        /*
         * Clean out the descriptor table for the next user and return
         * to the cache.
         */
        if (__predict_false(dt != &fdp->fd_dtbuiltin)) {
                fd_dtab_free(fdp->fd_dt);
                /* Otherwise, done above. */
                memset(&fdp->fd_dtbuiltin.dt_ff[NDFDFILE], 0,
                    (NDFILE - NDFDFILE) * sizeof(fdp->fd_dtbuiltin.dt_ff[0]));
                fdp->fd_dt = &fdp->fd_dtbuiltin;
        }
        if (__predict_false(NDHISLOTS(nf) > NDHISLOTS(NDFILE))) {
                KASSERT(fdp->fd_himap != fdp->fd_dhimap);
                KASSERT(fdp->fd_lomap != fdp->fd_dlomap);
                fd_map_free(nf, fdp->fd_lomap, fdp->fd_himap);
        }
        if (__predict_false(fdp->fd_knhash != NULL)) {
                hashdone(fdp->fd_knhash, HASH_LIST, fdp->fd_knhashmask);
                fdp->fd_knhash = NULL;
                fdp->fd_knhashmask = 0;
        } else {
                KASSERT(fdp->fd_knhashmask == 0);
        }
        fdp->fd_dt = &fdp->fd_dtbuiltin;
        fdp->fd_lastkqfile = -1;
        fdp->fd_lastfile = -1;
        fdp->fd_freefile = 0;
        fdp->fd_exclose = false;
        memset(&fdp->fd_startzero, 0, sizeof(*fdp) -
            offsetof(filedesc_t, fd_startzero));
        fdp->fd_himap = fdp->fd_dhimap;
        fdp->fd_lomap = fdp->fd_dlomap;
        KASSERT(fdp->fd_dtbuiltin.dt_nfiles == NDFILE);
        KASSERT(fdp->fd_dtbuiltin.dt_link == NULL);
        KASSERT(fdp->fd_dt == &fdp->fd_dtbuiltin);
#ifdef DEBUG
        fdp->fd_refcnt = 0; /* see fd_checkmaps */
#endif
        fd_checkmaps(fdp);
        pool_cache_put(filedesc_cache, fdp);
}

/*
 * File Descriptor pseudo-device driver (/dev/fd/).
 *
 * Opening minor device N dup()s the file (if any) connected to file
 * descriptor N belonging to the calling process.  Note that this driver
 * consists of only the ``open()'' routine, because all subsequent
 * references to this file will be direct to the other driver.
 */
static int
filedescopen(dev_t dev, int mode, int type, lwp_t *l)
{

        /*
         * XXX Kludge: set dupfd to contain the value of the
         * the file descriptor being sought for duplication. The error
         * return ensures that the vnode for this device will be released
         * by vn_open. Open will detect this special error and take the
         * actions in dupfdopen below. Other callers of vn_open or VOP_OPEN
         * will simply report the error.
         */
        l->l_dupfd = minor(dev);        /* XXX */
        return EDUPFD;
}

/*
 * Duplicate the specified descriptor to a free descriptor.
 */
int
fd_dupopen(int old, int *new, int mode, int error)
{
        filedesc_t *fdp;
        fdfile_t *ff;
        file_t *fp;
        fdtab_t *dt;

        if ((fp = fd_getfile(old)) == NULL) {
                return EBADF;
        }
        fdp = curlwp->l_fd;
        dt = fdp->fd_dt;
        ff = dt->dt_ff[old];

        /*
         * There are two cases of interest here.
         *
         * For EDUPFD simply dup (dfd) to file descriptor
         * (indx) and return.
         *
         * For EMOVEFD steal away the file structure from (dfd) and
         * store it in (indx).  (dfd) is effectively closed by
         * this operation.
         *
         * Any other error code is just returned.
         */
        switch (error) {
        case EDUPFD:
                /*
                 * Check that the mode the file is being opened for is a
                 * subset of the mode of the existing descriptor.
                 */
                if (((mode & (FREAD|FWRITE)) | fp->f_flag) != fp->f_flag) {
                        error = EACCES;
                        break;
                }

                /* Copy it. */
                error = fd_dup(fp, 0, new, ff->ff_exclose);
                break;

        case EMOVEFD:
                /* Copy it. */
                error = fd_dup(fp, 0, new, ff->ff_exclose);
                if (error != 0) {
                        break;
                }

                /* Steal away the file pointer from 'old'. */
                (void)fd_close(old);
                return 0;
        }

        fd_putfile(old);
        return error;
}

/*
 * Sets descriptor owner. If the owner is a process, 'pgid'
 * is set to positive value, process ID. If the owner is process group,
 * 'pgid' is set to -pg_id.
 */
int
fsetown(pid_t *pgid, u_long cmd, const void *data)
{
        int id = *(const int *)data;
        int error;

        switch (cmd) {
        case TIOCSPGRP:
                if (id < 0)
                        return (EINVAL);
                id = -id;
                break;
        default:
                break;
        }

        if (id > 0 && !pfind(id))
                return (ESRCH);
        else if (id < 0 && (error = pgid_in_session(curproc, -id)))
                return (error);

        *pgid = id;
        return (0);
}

/*
 * Return descriptor owner information. If the value is positive,
 * it's process ID. If it's negative, it's process group ID and
 * needs the sign removed before use.
 */
int
fgetown(pid_t pgid, u_long cmd, void *data)
{

        switch (cmd) {
        case TIOCGPGRP:
                *(int *)data = -pgid;
                break;
        default:
                *(int *)data = pgid;
                break;
        }
        return (0);
}

/*
 * Send signal to descriptor owner, either process or process group.
 */
void
fownsignal(pid_t pgid, int signo, int code, int band, void *fdescdata)
{
        ksiginfo_t ksi;

        KASSERT(!cpu_intr_p());

        if (pgid == 0) {
                return;
        }

        KSI_INIT(&ksi);
        ksi.ksi_signo = signo;
        ksi.ksi_code = code;
        ksi.ksi_band = band;

        mutex_enter(proc_lock);
        if (pgid > 0) {
                struct proc *p1;

                p1 = p_find(pgid, PFIND_LOCKED);
                if (p1 != NULL) {
                        kpsignal(p1, &ksi, fdescdata);
                }
        } else {
                struct pgrp *pgrp;

                KASSERT(pgid < 0);
                pgrp = pg_find(-pgid, PFIND_LOCKED);
                if (pgrp != NULL) {
                        kpgsignal(pgrp, &ksi, fdescdata, 0);
                }
        }
        mutex_exit(proc_lock);
}

int
fd_clone(file_t *fp, unsigned fd, int flag, const struct fileops *fops,
         void *data)
{

        fp->f_flag = flag;
        fp->f_type = DTYPE_MISC;
        fp->f_ops = fops;
        fp->f_data = data;
        curlwp->l_dupfd = fd;
        fd_affix(curproc, fp, fd);

        return EMOVEFD;
}

int
fnullop_fcntl(file_t *fp, u_int cmd, void *data)
{

        if (cmd == F_SETFL)
                return 0;

        return EOPNOTSUPP;
}

int
fnullop_poll(file_t *fp, int which)
{

        return 0;
}

int
fnullop_kqfilter(file_t *fp, struct knote *kn)
{

        return 0;
}

void
fnullop_restart(file_t *fp)
{

}

int
fbadop_read(file_t *fp, off_t *offset, struct uio *uio,
            kauth_cred_t cred, int flags)
{

        return EOPNOTSUPP;
}

int
fbadop_write(file_t *fp, off_t *offset, struct uio *uio,
             kauth_cred_t cred, int flags)
{

        return EOPNOTSUPP;
}

int
fbadop_ioctl(file_t *fp, u_long com, void *data)
{

        return EOPNOTSUPP;
}

int
fbadop_stat(file_t *fp, struct stat *sb)
{

        return EOPNOTSUPP;
}

int
fbadop_close(file_t *fp)
{

        return EOPNOTSUPP;
}