[dragonfly.git] / sys / kern / kern_descrip.c

/*
 * Copyright (c) 2005 The DragonFly Project.  All rights reserved.
 * 
 * This code is derived from software contributed to The DragonFly Project
 * by Jeffrey Hsu.
 * 
 * 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 DragonFly Project 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 COPYRIGHT HOLDERS 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
 * COPYRIGHT HOLDERS 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. 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      8.6 (Berkeley) 4/19/94
 * $FreeBSD: src/sys/kern/kern_descrip.c,v 1.81.2.19 2004/02/28 00:43:31 tegge Exp $
 * $DragonFly: src/sys/kern/kern_descrip.c,v 1.79 2008/08/31 13:18:28 aggelos Exp $
 */

#include "opt_compat.h"
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/sysproto.h>
#include <sys/conf.h>
#include <sys/device.h>
#include <sys/filedesc.h>
#include <sys/kernel.h>
#include <sys/sysctl.h>
#include <sys/vnode.h>
#include <sys/proc.h>
#include <sys/nlookup.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <sys/filio.h>
#include <sys/fcntl.h>
#include <sys/unistd.h>
#include <sys/resourcevar.h>
#include <sys/event.h>
#include <sys/kern_syscall.h>
#include <sys/kcore.h>
#include <sys/kinfo.h>
#include <sys/un.h>

#include <vm/vm.h>
#include <vm/vm_extern.h>

#include <sys/thread2.h>
#include <sys/file2.h>
#include <sys/spinlock2.h>

static void fsetfd_locked(struct filedesc *fdp, struct file *fp, int fd);
static void fdreserve_locked (struct filedesc *fdp, int fd0, int incr);
static struct file *funsetfd_locked (struct filedesc *fdp, int fd);
static int checkfpclosed(struct filedesc *fdp, int fd, struct file *fp);
static void ffree(struct file *fp);

static MALLOC_DEFINE(M_FILEDESC, "file desc", "Open file descriptor table");
static MALLOC_DEFINE(M_FILEDESC_TO_LEADER, "file desc to leader",
                     "file desc to leader structures");
MALLOC_DEFINE(M_FILE, "file", "Open file structure");
static MALLOC_DEFINE(M_SIGIO, "sigio", "sigio structures");

static   d_open_t  fdopen;
#define NUMFDESC 64

#define CDEV_MAJOR 22
static struct dev_ops fildesc_ops = {
        { "FD", CDEV_MAJOR, 0 },
        .d_open =       fdopen,
};

static int badfo_readwrite (struct file *fp, struct uio *uio,
    struct ucred *cred, int flags);
static int badfo_ioctl (struct file *fp, u_long com, caddr_t data,
    struct ucred *cred);
static int badfo_poll (struct file *fp, int events, struct ucred *cred);
static int badfo_kqfilter (struct file *fp, struct knote *kn);
static int badfo_stat (struct file *fp, struct stat *sb, struct ucred *cred);
static int badfo_close (struct file *fp);
static int badfo_shutdown (struct file *fp, int how);

/*
 * Descriptor management.
 */
static struct filelist filehead = LIST_HEAD_INITIALIZER(&filehead);
static struct spinlock filehead_spin = SPINLOCK_INITIALIZER(&filehead_spin);
static int nfiles;              /* actual number of open files */
extern int cmask;       

/*
 * Fixup fd_freefile and fd_lastfile after a descriptor has been cleared.
 *
 * MPSAFE - must be called with fdp->fd_spin exclusively held
 */
static __inline
void
fdfixup_locked(struct filedesc *fdp, int fd)
{
        if (fd < fdp->fd_freefile) {
               fdp->fd_freefile = fd;
        }
        while (fdp->fd_lastfile >= 0 &&
               fdp->fd_files[fdp->fd_lastfile].fp == NULL &&
               fdp->fd_files[fdp->fd_lastfile].reserved == 0
        ) {
                --fdp->fd_lastfile;
        }
}

/*
 * System calls on descriptors.
 *
 * MPSAFE
 */
int
sys_getdtablesize(struct getdtablesize_args *uap) 
{
        struct proc *p = curproc;
        struct plimit *limit = p->p_limit;

        spin_lock_rd(&limit->p_spin);
        uap->sysmsg_result = 
            min((int)limit->pl_rlimit[RLIMIT_NOFILE].rlim_cur, maxfilesperproc);
        spin_unlock_rd(&limit->p_spin);
        return (0);
}

/*
 * Duplicate a file descriptor to a particular value.
 *
 * note: keep in mind that a potential race condition exists when closing
 * descriptors from a shared descriptor table (via rfork).
 *
 * MPSAFE
 */
int
sys_dup2(struct dup2_args *uap)
{
        int error;

        error = kern_dup(DUP_FIXED, uap->from, uap->to, uap->sysmsg_fds);

        return (error);
}

/*
 * Duplicate a file descriptor.
 *
 * MPSAFE
 */
int
sys_dup(struct dup_args *uap)
{
        int error;

        error = kern_dup(DUP_VARIABLE, uap->fd, 0, uap->sysmsg_fds);

        return (error);
}

/*
 * MPALMOSTSAFE - acquires mplock for fp operations
 */
int
kern_fcntl(int fd, int cmd, union fcntl_dat *dat, struct ucred *cred)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        struct file *fp;
        struct vnode *vp;
        u_int newmin;
        u_int oflags;
        int tmp, error, flg = F_POSIX;

        KKASSERT(p);

        /*
         * Operations on file descriptors that do not require a file pointer.
         */
        switch (cmd) {
        case F_GETFD:
                error = fgetfdflags(p->p_fd, fd, &tmp);
                if (error == 0)
                        dat->fc_cloexec = (tmp & UF_EXCLOSE) ? FD_CLOEXEC : 0;
                return (error);

        case F_SETFD:
                if (dat->fc_cloexec & FD_CLOEXEC)
                        error = fsetfdflags(p->p_fd, fd, UF_EXCLOSE);
                else
                        error = fclrfdflags(p->p_fd, fd, UF_EXCLOSE);
                return (error);
        case F_DUPFD:
                newmin = dat->fc_fd;
                error = kern_dup(DUP_VARIABLE, fd, newmin, &dat->fc_fd);
                return (error);
        default:
                break;
        }

        /*
         * Operations on file pointers
         */
        if ((fp = holdfp(p->p_fd, fd, -1)) == NULL)
                return (EBADF);

        get_mplock();
        switch (cmd) {
        case F_GETFL:
                dat->fc_flags = OFLAGS(fp->f_flag);
                error = 0;
                break;

        case F_SETFL:
                oflags = fp->f_flag & FCNTLFLAGS;
                fp->f_flag &= ~FCNTLFLAGS;
                fp->f_flag |= FFLAGS(dat->fc_flags & ~O_ACCMODE) & FCNTLFLAGS;
                error = 0;
                if ((fp->f_flag ^ oflags) & FASYNC) {
                        tmp = fp->f_flag & FASYNC;
                        error = fo_ioctl(fp, FIOASYNC, (caddr_t)&tmp, cred);
                }
                if (error)
                        fp->f_flag = (fp->f_flag & ~FCNTLFLAGS) | oflags;
                break;

        case F_GETOWN:
                error = fo_ioctl(fp, FIOGETOWN, (caddr_t)&dat->fc_owner, cred);
                break;

        case F_SETOWN:
                error = fo_ioctl(fp, FIOSETOWN, (caddr_t)&dat->fc_owner, cred);
                break;

        case F_SETLKW:
                flg |= F_WAIT;
                /* Fall into F_SETLK */

        case F_SETLK:
                if (fp->f_type != DTYPE_VNODE) {
                        error = EBADF;
                        break;
                }
                vp = (struct vnode *)fp->f_data;

                /*
                 * copyin/lockop may block
                 */
                if (dat->fc_flock.l_whence == SEEK_CUR)
                        dat->fc_flock.l_start += fp->f_offset;

                switch (dat->fc_flock.l_type) {
                case F_RDLCK:
                        if ((fp->f_flag & FREAD) == 0) {
                                error = EBADF;
                                break;
                        }
                        p->p_leader->p_flag |= P_ADVLOCK;
                        error = VOP_ADVLOCK(vp, (caddr_t)p->p_leader, F_SETLK,
                            &dat->fc_flock, flg);
                        break;
                case F_WRLCK:
                        if ((fp->f_flag & FWRITE) == 0) {
                                error = EBADF;
                                break;
                        }
                        p->p_leader->p_flag |= P_ADVLOCK;
                        error = VOP_ADVLOCK(vp, (caddr_t)p->p_leader, F_SETLK,
                            &dat->fc_flock, flg);
                        break;
                case F_UNLCK:
                        error = VOP_ADVLOCK(vp, (caddr_t)p->p_leader, F_UNLCK,
                                &dat->fc_flock, F_POSIX);
                        break;
                default:
                        error = EINVAL;
                        break;
                }

                /*
                 * It is possible to race a close() on the descriptor while
                 * we were blocked getting the lock.  If this occurs the
                 * close might not have caught the lock.
                 */
                if (checkfpclosed(p->p_fd, fd, fp)) {
                        dat->fc_flock.l_whence = SEEK_SET;
                        dat->fc_flock.l_start = 0;
                        dat->fc_flock.l_len = 0;
                        dat->fc_flock.l_type = F_UNLCK;
                        (void) VOP_ADVLOCK(vp, (caddr_t)p->p_leader,
                                           F_UNLCK, &dat->fc_flock, F_POSIX);
                }
                break;

        case F_GETLK:
                if (fp->f_type != DTYPE_VNODE) {
                        error = EBADF;
                        break;
                }
                vp = (struct vnode *)fp->f_data;
                /*
                 * copyin/lockop may block
                 */
                if (dat->fc_flock.l_type != F_RDLCK &&
                    dat->fc_flock.l_type != F_WRLCK &&
                    dat->fc_flock.l_type != F_UNLCK) {
                        error = EINVAL;
                        break;
                }
                if (dat->fc_flock.l_whence == SEEK_CUR)
                        dat->fc_flock.l_start += fp->f_offset;
                error = VOP_ADVLOCK(vp, (caddr_t)p->p_leader, F_GETLK,
                            &dat->fc_flock, F_POSIX);
                break;
        default:
                error = EINVAL;
                break;
        }
        rel_mplock();

        fdrop(fp);
        return (error);
}

/*
 * The file control system call.
 *
 * MPSAFE
 */
int
sys_fcntl(struct fcntl_args *uap)
{
        union fcntl_dat dat;
        int error;

        switch (uap->cmd) {
        case F_DUPFD:
                dat.fc_fd = uap->arg;
                break;
        case F_SETFD:
                dat.fc_cloexec = uap->arg;
                break;
        case F_SETFL:
                dat.fc_flags = uap->arg;
                break;
        case F_SETOWN:
                dat.fc_owner = uap->arg;
                break;
        case F_SETLKW:
        case F_SETLK:
        case F_GETLK:
                error = copyin((caddr_t)uap->arg, &dat.fc_flock,
                               sizeof(struct flock));
                if (error)
                        return (error);
                break;
        }

        error = kern_fcntl(uap->fd, uap->cmd, &dat, curproc->p_ucred);

        if (error == 0) {
                switch (uap->cmd) {
                case F_DUPFD:
                        uap->sysmsg_result = dat.fc_fd;
                        break;
                case F_GETFD:
                        uap->sysmsg_result = dat.fc_cloexec;
                        break;
                case F_GETFL:
                        uap->sysmsg_result = dat.fc_flags;
                        break;
                case F_GETOWN:
                        uap->sysmsg_result = dat.fc_owner;
                case F_GETLK:
                        error = copyout(&dat.fc_flock, (caddr_t)uap->arg,
                            sizeof(struct flock));
                        break;
                }
        }

        return (error);
}

/*
 * Common code for dup, dup2, and fcntl(F_DUPFD).
 *
 * The type flag can be either DUP_FIXED or DUP_VARIABLE.  DUP_FIXED tells
 * kern_dup() to destructively dup over an existing file descriptor if new
 * is already open.  DUP_VARIABLE tells kern_dup() to find the lowest
 * unused file descriptor that is greater than or equal to new.
 *
 * MPSAFE
 */
int
kern_dup(enum dup_type type, int old, int new, int *res)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        struct filedesc *fdp = p->p_fd;
        struct file *fp;
        struct file *delfp;
        int oldflags;
        int holdleaders;
        int error, newfd;

        /*
         * Verify that we have a valid descriptor to dup from and
         * possibly to dup to.
         */
retry:
        spin_lock_wr(&fdp->fd_spin);
        if (new < 0 || new > p->p_rlimit[RLIMIT_NOFILE].rlim_cur ||
            new >= maxfilesperproc) {
                spin_unlock_wr(&fdp->fd_spin);
                return (EINVAL);
        }
        if ((unsigned)old >= fdp->fd_nfiles || fdp->fd_files[old].fp == NULL) {
                spin_unlock_wr(&fdp->fd_spin);
                return (EBADF);
        }
        if (type == DUP_FIXED && old == new) {
                *res = new;
                spin_unlock_wr(&fdp->fd_spin);
                return (0);
        }
        fp = fdp->fd_files[old].fp;
        oldflags = fdp->fd_files[old].fileflags;
        fhold(fp);      /* MPSAFE - can be called with a spinlock held */

        /*
         * Allocate a new descriptor if DUP_VARIABLE, or expand the table
         * if the requested descriptor is beyond the current table size.
         *
         * This can block.  Retry if the source descriptor no longer matches
         * or if our expectation in the expansion case races.
         *
         * If we are not expanding or allocating a new decriptor, then reset
         * the target descriptor to a reserved state so we have a uniform
         * setup for the next code block.
         */
        if (type == DUP_VARIABLE || new >= fdp->fd_nfiles) {
                spin_unlock_wr(&fdp->fd_spin);
                error = fdalloc(p, new, &newfd);
                spin_lock_wr(&fdp->fd_spin);
                if (error) {
                        spin_unlock_wr(&fdp->fd_spin);
                        fdrop(fp);
                        return (error);
                }
                /*
                 * Check for ripout
                 */
                if (old >= fdp->fd_nfiles || fdp->fd_files[old].fp != fp) {
                        fsetfd_locked(fdp, NULL, newfd);
                        spin_unlock_wr(&fdp->fd_spin);
                        fdrop(fp);
                        goto retry;
                }
                /*
                 * Check for expansion race
                 */
                if (type != DUP_VARIABLE && new != newfd) {
                        fsetfd_locked(fdp, NULL, newfd);
                        spin_unlock_wr(&fdp->fd_spin);
                        fdrop(fp);
                        goto retry;
                }
                /*
                 * Check for ripout, newfd reused old (this case probably
                 * can't occur).
                 */
                if (old == newfd) {
                        fsetfd_locked(fdp, NULL, newfd);
                        spin_unlock_wr(&fdp->fd_spin);
                        fdrop(fp);
                        goto retry;
                }
                new = newfd;
                delfp = NULL;
        } else {
                if (fdp->fd_files[new].reserved) {
                        spin_unlock_wr(&fdp->fd_spin);
                        fdrop(fp);
                        kprintf("Warning: dup(): target descriptor %d is reserved, waiting for it to be resolved\n", new);
                        tsleep(fdp, 0, "fdres", hz);
                        goto retry;
                }

                /*
                 * If the target descriptor was never allocated we have
                 * to allocate it.  If it was we have to clean out the
                 * old descriptor.  delfp inherits the ref from the 
                 * descriptor table.
                 */
                delfp = fdp->fd_files[new].fp;
                fdp->fd_files[new].fp = NULL;
                fdp->fd_files[new].reserved = 1;
                if (delfp == NULL) {
                        fdreserve_locked(fdp, new, 1);
                        if (new > fdp->fd_lastfile)
                                fdp->fd_lastfile = new;
                }

        }

        /*
         * NOTE: still holding an exclusive spinlock
         */

        /*
         * If a descriptor is being overwritten we may hve to tell 
         * fdfree() to sleep to ensure that all relevant process
         * leaders can be traversed in closef().
         */
        if (delfp != NULL && p->p_fdtol != NULL) {
                fdp->fd_holdleaderscount++;
                holdleaders = 1;
        } else {
                holdleaders = 0;
        }
        KASSERT(delfp == NULL || type == DUP_FIXED,
                ("dup() picked an open file"));

        /*
         * Duplicate the source descriptor, update lastfile.  If the new
         * descriptor was not allocated and we aren't replacing an existing
         * descriptor we have to mark the descriptor as being in use.
         *
         * The fd_files[] array inherits fp's hold reference.
         */
        fsetfd_locked(fdp, fp, new);
        fdp->fd_files[new].fileflags = oldflags & ~UF_EXCLOSE;
        spin_unlock_wr(&fdp->fd_spin);
        fdrop(fp);
        *res = new;

        /*
         * If we dup'd over a valid file, we now own the reference to it
         * and must dispose of it using closef() semantics (as if a
         * close() were performed on it).
         */
        if (delfp) {
                closef(delfp, p);
                if (holdleaders) {
                        spin_lock_wr(&fdp->fd_spin);
                        fdp->fd_holdleaderscount--;
                        if (fdp->fd_holdleaderscount == 0 &&
                            fdp->fd_holdleaderswakeup != 0) {
                                fdp->fd_holdleaderswakeup = 0;
                                spin_unlock_wr(&fdp->fd_spin);
                                wakeup(&fdp->fd_holdleaderscount);
                        } else {
                                spin_unlock_wr(&fdp->fd_spin);
                        }
                }
        }
        return (0);
}

/*
 * If sigio is on the list associated with a process or process group,
 * disable signalling from the device, remove sigio from the list and
 * free sigio.
 */
void
funsetown(struct sigio *sigio)
{
        if (sigio == NULL)
                return;
        crit_enter();
        *(sigio->sio_myref) = NULL;
        crit_exit();
        if (sigio->sio_pgid < 0) {
                SLIST_REMOVE(&sigio->sio_pgrp->pg_sigiolst, sigio,
                             sigio, sio_pgsigio);
        } else /* if ((*sigiop)->sio_pgid > 0) */ {
                SLIST_REMOVE(&sigio->sio_proc->p_sigiolst, sigio,
                             sigio, sio_pgsigio);
        }
        crfree(sigio->sio_ucred);
        kfree(sigio, M_SIGIO);
}

/* Free a list of sigio structures. */
void
funsetownlst(struct sigiolst *sigiolst)
{
        struct sigio *sigio;

        while ((sigio = SLIST_FIRST(sigiolst)) != NULL)
                funsetown(sigio);
}

/*
 * This is common code for FIOSETOWN ioctl called by fcntl(fd, F_SETOWN, arg).
 *
 * After permission checking, add a sigio structure to the sigio list for
 * the process or process group.
 */
int
fsetown(pid_t pgid, struct sigio **sigiop)
{
        struct proc *proc;
        struct pgrp *pgrp;
        struct sigio *sigio;

        if (pgid == 0) {
                funsetown(*sigiop);
                return (0);
        }
        if (pgid > 0) {
                proc = pfind(pgid);
                if (proc == NULL)
                        return (ESRCH);

                /*
                 * Policy - Don't allow a process to FSETOWN a process
                 * in another session.
                 *
                 * Remove this test to allow maximum flexibility or
                 * restrict FSETOWN to the current process or process
                 * group for maximum safety.
                 */
                if (proc->p_session != curproc->p_session)
                        return (EPERM);

                pgrp = NULL;
        } else /* if (pgid < 0) */ {
                pgrp = pgfind(-pgid);
                if (pgrp == NULL)
                        return (ESRCH);

                /*
                 * Policy - Don't allow a process to FSETOWN a process
                 * in another session.
                 *
                 * Remove this test to allow maximum flexibility or
                 * restrict FSETOWN to the current process or process
                 * group for maximum safety.
                 */
                if (pgrp->pg_session != curproc->p_session)
                        return (EPERM);

                proc = NULL;
        }
        funsetown(*sigiop);
        sigio = kmalloc(sizeof(struct sigio), M_SIGIO, M_WAITOK);
        if (pgid > 0) {
                SLIST_INSERT_HEAD(&proc->p_sigiolst, sigio, sio_pgsigio);
                sigio->sio_proc = proc;
        } else {
                SLIST_INSERT_HEAD(&pgrp->pg_sigiolst, sigio, sio_pgsigio);
                sigio->sio_pgrp = pgrp;
        }
        sigio->sio_pgid = pgid;
        sigio->sio_ucred = crhold(curproc->p_ucred);
        /* It would be convenient if p_ruid was in ucred. */
        sigio->sio_ruid = curproc->p_ucred->cr_ruid;
        sigio->sio_myref = sigiop;
        crit_enter();
        *sigiop = sigio;
        crit_exit();
        return (0);
}

/*
 * This is common code for FIOGETOWN ioctl called by fcntl(fd, F_GETOWN, arg).
 */
pid_t
fgetown(struct sigio *sigio)
{
        return (sigio != NULL ? sigio->sio_pgid : 0);
}

/*
 * Close many file descriptors.
 *
 * MPSAFE
 */
int
sys_closefrom(struct closefrom_args *uap)
{
        return(kern_closefrom(uap->fd));
}

/*
 * Close all file descriptors greater then or equal to fd
 *
 * MPSAFE
 */
int
kern_closefrom(int fd)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        struct filedesc *fdp;

        KKASSERT(p);
        fdp = p->p_fd;

        if (fd < 0)
                return (EINVAL);

        /*
         * NOTE: This function will skip unassociated descriptors and
         * reserved descriptors that have not yet been assigned.  
         * fd_lastfile can change as a side effect of kern_close().
         */
        spin_lock_wr(&fdp->fd_spin);
        while (fd <= fdp->fd_lastfile) {
                if (fdp->fd_files[fd].fp != NULL) {
                        spin_unlock_wr(&fdp->fd_spin);
                        /* ok if this races another close */
                        if (kern_close(fd) == EINTR)
                                return (EINTR);
                        spin_lock_wr(&fdp->fd_spin);
                }
                ++fd;
        }
        spin_unlock_wr(&fdp->fd_spin);
        return (0);
}

/*
 * Close a file descriptor.
 *
 * MPSAFE
 */
int
sys_close(struct close_args *uap)
{
        return(kern_close(uap->fd));
}

/*
 * MPALMOSTSAFE - acquires mplock around knote_fdclose() calls
 */
int
kern_close(int fd)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        struct filedesc *fdp;
        struct file *fp;
        int error;
        int holdleaders;

        KKASSERT(p);
        fdp = p->p_fd;

        spin_lock_wr(&fdp->fd_spin);
        if ((fp = funsetfd_locked(fdp, fd)) == NULL) {
                spin_unlock_wr(&fdp->fd_spin);
                return (EBADF);
        }
        holdleaders = 0;
        if (p->p_fdtol != NULL) {
                /*
                 * Ask fdfree() to sleep to ensure that all relevant
                 * process leaders can be traversed in closef().
                 */
                fdp->fd_holdleaderscount++;
                holdleaders = 1;
        }

        /*
         * we now hold the fp reference that used to be owned by the descriptor
         * array.
         */
        spin_unlock_wr(&fdp->fd_spin);
        if (fd < fdp->fd_knlistsize) {
                get_mplock();
                if (fd < fdp->fd_knlistsize)
                        knote_fdclose(p, fd);
                rel_mplock();
        }
        error = closef(fp, p);
        if (holdleaders) {
                spin_lock_wr(&fdp->fd_spin);
                fdp->fd_holdleaderscount--;
                if (fdp->fd_holdleaderscount == 0 &&
                    fdp->fd_holdleaderswakeup != 0) {
                        fdp->fd_holdleaderswakeup = 0;
                        spin_unlock_wr(&fdp->fd_spin);
                        wakeup(&fdp->fd_holdleaderscount);
                } else {
                        spin_unlock_wr(&fdp->fd_spin);
                }
        }
        return (error);
}

/*
 * shutdown_args(int fd, int how)
 */
int
kern_shutdown(int fd, int how)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        struct file *fp;
        int error;

        KKASSERT(p);

        if ((fp = holdfp(p->p_fd, fd, -1)) == NULL)
                return (EBADF);
        error = fo_shutdown(fp, how);
        fdrop(fp);

        return (error);
}

int
sys_shutdown(struct shutdown_args *uap)
{
        int error;

        error = kern_shutdown(uap->s, uap->how);

        return (error);
}

int
kern_fstat(int fd, struct stat *ub)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        struct file *fp;
        int error;

        KKASSERT(p);

        if ((fp = holdfp(p->p_fd, fd, -1)) == NULL)
                return (EBADF);
        error = fo_stat(fp, ub, p->p_ucred);
        fdrop(fp);

        return (error);
}

/*
 * Return status information about a file descriptor.
 */
int
sys_fstat(struct fstat_args *uap)
{
        struct stat st;
        int error;

        error = kern_fstat(uap->fd, &st);

        if (error == 0)
                error = copyout(&st, uap->sb, sizeof(st));
        return (error);
}

/*
 * Return pathconf information about a file descriptor.
 */
/* ARGSUSED */
int
sys_fpathconf(struct fpathconf_args *uap)
{
        struct thread *td = curthread;
        struct proc *p = td->td_proc;
        struct file *fp;
        struct vnode *vp;
        int error = 0;

        KKASSERT(p);

        if ((fp = holdfp(p->p_fd, uap->fd, -1)) == NULL)
                return (EBADF);

        switch (fp->f_type) {
        case DTYPE_PIPE:
        case DTYPE_SOCKET:
                if (uap->name != _PC_PIPE_BUF) {
                        error = EINVAL;
                } else {
                        uap->sysmsg_result = PIPE_BUF;
                        error = 0;
                }
                break;
        case DTYPE_FIFO:
        case DTYPE_VNODE:
                vp = (struct vnode *)fp->f_data;
                error = VOP_PATHCONF(vp, uap->name, uap->sysmsg_fds);
                break;
        default:
                error = EOPNOTSUPP;
                break;
        }
        fdrop(fp);
        return(error);
}

static int fdexpand;
SYSCTL_INT(_debug, OID_AUTO, fdexpand, CTLFLAG_RD, &fdexpand, 0, "");

/*
 * Grow the file table so it can hold through descriptor (want).
 *
 * The fdp's spinlock must be held exclusively on entry and may be held
 * exclusively on return.  The spinlock may be cycled by the routine.
 *
 * MPSAFE
 */
static void
fdgrow_locked(struct filedesc *fdp, int want)
{
        struct fdnode *newfiles;
        struct fdnode *oldfiles;
        int nf, extra;

        nf = fdp->fd_nfiles;
        do {
                /* nf has to be of the form 2^n - 1 */
                nf = 2 * nf + 1;
        } while (nf <= want);

        spin_unlock_wr(&fdp->fd_spin);
        newfiles = kmalloc(nf * sizeof(struct fdnode), M_FILEDESC, M_WAITOK);
        spin_lock_wr(&fdp->fd_spin);

        /*
         * We could have raced another extend while we were not holding
         * the spinlock.
         */
        if (fdp->fd_nfiles >= nf) {
                spin_unlock_wr(&fdp->fd_spin);
                kfree(newfiles, M_FILEDESC);
                spin_lock_wr(&fdp->fd_spin);
                return;
        }
        /*
         * Copy the existing ofile and ofileflags arrays
         * and zero the new portion of each array.
         */
        extra = nf - fdp->fd_nfiles;
        bcopy(fdp->fd_files, newfiles, fdp->fd_nfiles * sizeof(struct fdnode));
        bzero(&newfiles[fdp->fd_nfiles], extra * sizeof(struct fdnode));

        oldfiles = fdp->fd_files;
        fdp->fd_files = newfiles;
        fdp->fd_nfiles = nf;

        if (oldfiles != fdp->fd_builtin_files) {
                spin_unlock_wr(&fdp->fd_spin);
                kfree(oldfiles, M_FILEDESC);
                spin_lock_wr(&fdp->fd_spin);
        }
        fdexpand++;
}

/*
 * Number of nodes in right subtree, including the root.
 */
static __inline int
right_subtree_size(int n)
{
        return (n ^ (n | (n + 1)));
}

/*
 * Bigger ancestor.
 */
static __inline int
right_ancestor(int n)
{
        return (n | (n + 1));
}

/*
 * Smaller ancestor.
 */
static __inline int
left_ancestor(int n)
{
        return ((n & (n + 1)) - 1);
}

/*
 * Traverse the in-place binary tree buttom-up adjusting the allocation
 * count so scans can determine where free descriptors are located.
 *
 * MPSAFE - caller must be holding an exclusive spinlock on fdp
 */
static
void
fdreserve_locked(struct filedesc *fdp, int fd, int incr)
{
        while (fd >= 0) {
                fdp->fd_files[fd].allocated += incr;
                KKASSERT(fdp->fd_files[fd].allocated >= 0);
                fd = left_ancestor(fd);
        }
}

/*
 * Reserve a file descriptor for the process.  If no error occurs, the
 * caller MUST at some point call fsetfd() or assign a file pointer
 * or dispose of the reservation.
 *
 * MPSAFE
 */
int
fdalloc(struct proc *p, int want, int *result)
{
        struct filedesc *fdp = p->p_fd;
        int fd, rsize, rsum, node, lim;

        spin_lock_rd(&p->p_limit->p_spin);
        lim = min((int)p->p_rlimit[RLIMIT_NOFILE].rlim_cur, maxfilesperproc);
        spin_unlock_rd(&p->p_limit->p_spin);
        if (want >= lim)
                return (EMFILE);
        spin_lock_wr(&fdp->fd_spin);
        if (want >= fdp->fd_nfiles)
                fdgrow_locked(fdp, want);

        /*
         * Search for a free descriptor starting at the higher
         * of want or fd_freefile.  If that fails, consider
         * expanding the ofile array.
         *
         * NOTE! the 'allocated' field is a cumulative recursive allocation
         * count.  If we happen to see a value of 0 then we can shortcut
         * our search.  Otherwise we run through through the tree going
         * down branches we know have free descriptor(s) until we hit a
         * leaf node.  The leaf node will be free but will not necessarily
         * have an allocated field of 0.
         */
retry:
        /* move up the tree looking for a subtree with a free node */
        for (fd = max(want, fdp->fd_freefile); fd < min(fdp->fd_nfiles, lim);
             fd = right_ancestor(fd)) {
                if (fdp->fd_files[fd].allocated == 0)
                        goto found;

                rsize = right_subtree_size(fd);
                if (fdp->fd_files[fd].allocated == rsize)
                        continue;       /* right subtree full */

                /*
                 * Free fd is in the right subtree of the tree rooted at fd.
                 * Call that subtree R.  Look for the smallest (leftmost)
                 * subtree of R with an unallocated fd: continue moving
                 * down the left branch until encountering a full left
                 * subtree, then move to the right.
                 */
                for (rsum = 0, rsize /= 2; rsize > 0; rsize /= 2) {
                        node = fd + rsize;
                        rsum += fdp->fd_files[node].allocated;
                        if (fdp->fd_files[fd].allocated == rsum + rsize) {
                                fd = node;      /* move to the right */
                                if (fdp->fd_files[node].allocated == 0)
                                        goto found;
                                rsum = 0;
                        }
                }
                goto found;
        }

        /*
         * No space in current array.  Expand?
         */
        if (fdp->fd_nfiles >= lim) {
                spin_unlock_wr(&fdp->fd_spin);
                return (EMFILE);
        }
        fdgrow_locked(fdp, want);
        goto retry;

found:
        KKASSERT(fd < fdp->fd_nfiles);
        if (fd > fdp->fd_lastfile)
                fdp->fd_lastfile = fd;
        if (want <= fdp->fd_freefile)
                fdp->fd_freefile = fd;
        *result = fd;
        KKASSERT(fdp->fd_files[fd].fp == NULL);
        KKASSERT(fdp->fd_files[fd].reserved == 0);
        fdp->fd_files[fd].fileflags = 0;
        fdp->fd_files[fd].reserved = 1;
        fdreserve_locked(fdp, fd, 1);
        spin_unlock_wr(&fdp->fd_spin);
        return (0);
}

/*
 * Check to see whether n user file descriptors
 * are available to the process p.
 *
 * MPSAFE
 */
int
fdavail(struct proc *p, int n)
{
        struct filedesc *fdp = p->p_fd;
        struct fdnode *fdnode;
        int i, lim, last;

        spin_lock_rd(&p->p_limit->p_spin);
        lim = min((int)p->p_rlimit[RLIMIT_NOFILE].rlim_cur, maxfilesperproc);
        spin_unlock_rd(&p->p_limit->p_spin);

        spin_lock_rd(&fdp->fd_spin);
        if ((i = lim - fdp->fd_nfiles) > 0 && (n -= i) <= 0) {
                spin_unlock_rd(&fdp->fd_spin);
                return (1);
        }
        last = min(fdp->fd_nfiles, lim);
        fdnode = &fdp->fd_files[fdp->fd_freefile];
        for (i = last - fdp->fd_freefile; --i >= 0; ++fdnode) {
                if (fdnode->fp == NULL && --n <= 0) {
                        spin_unlock_rd(&fdp->fd_spin);
                        return (1);
                }
        }
        spin_unlock_rd(&fdp->fd_spin);
        return (0);
}

/*
 * Revoke open descriptors referencing (f_data, f_type)
 *
 * Any revoke executed within a prison is only able to
 * revoke descriptors for processes within that prison.
 *
 * Returns 0 on success or an error code.
 */
struct fdrevoke_info {
        void *data;
        short type;
        short unused;
        int count;
        int intransit;
        struct ucred *cred;
        struct file *nfp;
};

static int fdrevoke_check_callback(struct file *fp, void *vinfo);
static int fdrevoke_proc_callback(struct proc *p, void *vinfo);

int
fdrevoke(void *f_data, short f_type, struct ucred *cred)
{
        struct fdrevoke_info info;
        int error;

        bzero(&info, sizeof(info));
        info.data = f_data;
        info.type = f_type;
        info.cred = cred;
        error = falloc(NULL, &info.nfp, NULL);
        if (error)
                return (error);

        /*
         * Scan the file pointer table once.  dups do not dup file pointers,
         * only descriptors, so there is no leak.  Set FREVOKED on the fps
         * being revoked.
         */
        allfiles_scan_exclusive(fdrevoke_check_callback, &info);

        /*
         * If any fps were marked track down the related descriptors
         * and close them.  Any dup()s at this point will notice
         * the FREVOKED already set in the fp and do the right thing.
         *
         * Any fps with non-zero msgcounts (aka sent over a unix-domain
         * socket) bumped the intransit counter and will require a
         * scan.  Races against fps leaving the socket are closed by
         * the socket code checking for FREVOKED.
         */
        if (info.count)
                allproc_scan(fdrevoke_proc_callback, &info);
        if (info.intransit)
                unp_revoke_gc(info.nfp);
        fdrop(info.nfp);
        return(0);
}

/*
 * Locate matching file pointers directly.
 */
static int
fdrevoke_check_callback(struct file *fp, void *vinfo)
{
        struct fdrevoke_info *info = vinfo;

        /*
         * File pointers already flagged for revokation are skipped.
         */
        if (fp->f_flag & FREVOKED)
                return(0);

        /*
         * If revoking from a prison file pointers created outside of
         * that prison, or file pointers without creds, cannot be revoked.
         */
        if (info->cred->cr_prison &&
            (fp->f_cred == NULL ||
             info->cred->cr_prison != fp->f_cred->cr_prison)) {
                return(0);
        }

        /*
         * If the file pointer matches then mark it for revocation.  The
         * flag is currently only used by unp_revoke_gc().
         *
         * info->count is a heuristic and can race in a SMP environment.
         */
        if (info->data == fp->f_data && info->type == fp->f_type) {
                atomic_set_int(&fp->f_flag, FREVOKED);
                info->count += fp->f_count;
                if (fp->f_msgcount)
                        ++info->intransit;
        }
        return(0);
}

/*
 * Locate matching file pointers via process descriptor tables.
 */
static int
fdrevoke_proc_callback(struct proc *p, void *vinfo)
{
        struct fdrevoke_info *info = vinfo;
        struct filedesc *fdp;
        struct file *fp;
        int n;

        if (p->p_stat == SIDL || p->p_stat == SZOMB)
                return(0);
        if (info->cred->cr_prison &&
            info->cred->cr_prison != p->p_ucred->cr_prison) {
                return(0);
        }

        /*
         * If the controlling terminal of the process matches the
         * vnode being revoked we clear the controlling terminal.
         *
         * The normal spec_close() may not catch this because it
         * uses curproc instead of p.
         */
        if (p->p_session && info->type == DTYPE_VNODE &&
            info->data == p->p_session->s_ttyvp) {
                p->p_session->s_ttyvp = NULL;
                vrele(info->data);
        }

        /*
         * Locate and close any matching file descriptors.
         */
        if ((fdp = p->p_fd) == NULL)
                return(0);
        spin_lock_wr(&fdp->fd_spin);
        for (n = 0; n < fdp->fd_nfiles; ++n) {
                if ((fp = fdp->fd_files[n].fp) == NULL)
                        continue;
                if (fp->f_flag & FREVOKED) {
                        fhold(info->nfp);
                        fdp->fd_files[n].fp = info->nfp;
                        spin_unlock_wr(&fdp->fd_spin);
                        closef(fp, p);
                        spin_lock_wr(&fdp->fd_spin);
                        --info->count;
                }
        }
        spin_unlock_wr(&fdp->fd_spin);
        return(0);
}

/*
 * falloc:
 *      Create a new open file structure and reserve a file decriptor
 *      for the process that refers to it.
 *
 *      Root creds are checked using p, or assumed if p is NULL.  If
 *      resultfd is non-NULL then p must also be non-NULL.  No file
 *      descriptor is reserved if resultfd is NULL.
 *
 *      A file pointer with a refcount of 1 is returned.  Note that the
 *      file pointer is NOT associated with the descriptor.  If falloc
 *      returns success, fsetfd() MUST be called to either associate the
 *      file pointer or clear the reservation.
 *
 * MPSAFE
 */
int
falloc(struct proc *p, struct file **resultfp, int *resultfd)
{
        static struct timeval lastfail;
        static int curfail;
        struct file *fp;
        int error;

        fp = NULL;

        /*
         * Handle filetable full issues and root overfill.
         */
        if (nfiles >= maxfiles - maxfilesrootres &&
            ((p && p->p_ucred->cr_ruid != 0) || nfiles >= maxfiles)) {
                if (ppsratecheck(&lastfail, &curfail, 1)) {
                        kprintf("kern.maxfiles limit exceeded by uid %d, please see tuning(7).\n",
                                (p ? p->p_ucred->cr_ruid : -1));
                }
                error = ENFILE;
                goto done;
        }

        /*
         * Allocate a new file descriptor.
         */
        fp = kmalloc(sizeof(struct file), M_FILE, M_WAITOK | M_ZERO);
        spin_init(&fp->f_spin);
        fp->f_count = 1;
        fp->f_ops = &badfileops;
        fp->f_seqcount = 1;
        if (p)
                fp->f_cred = crhold(p->p_ucred);
        else
                fp->f_cred = crhold(proc0.p_ucred);
        spin_lock_wr(&filehead_spin);
        nfiles++;
        LIST_INSERT_HEAD(&filehead, fp, f_list);
        spin_unlock_wr(&filehead_spin);
        if (resultfd) {
                if ((error = fdalloc(p, 0, resultfd)) != 0) {
                        fdrop(fp);
                        fp = NULL;
                }
        } else {
                error = 0;
        }
done:
        *resultfp = fp;
        return (error);
}

/*
 * MPSAFE
 */
static
int
checkfpclosed(struct filedesc *fdp, int fd, struct file *fp)
{
        int error;

        spin_lock_rd(&fdp->fd_spin);
        if ((unsigned) fd >= fdp->fd_nfiles || fp != fdp->fd_files[fd].fp)
                error = EBADF;
        else
                error = 0;
        spin_unlock_rd(&fdp->fd_spin);
        return (error);
}

/*
 * Associate a file pointer with a previously reserved file descriptor.
 * This function always succeeds.
 *
 * If fp is NULL, the file descriptor is returned to the pool.
 */

/*
 * MPSAFE (exclusive spinlock must be held on call)
 */
static void
fsetfd_locked(struct filedesc *fdp, struct file *fp, int fd)
{
        KKASSERT((unsigned)fd < fdp->fd_nfiles);
        KKASSERT(fdp->fd_files[fd].reserved != 0);
        if (fp) {
                fhold(fp);
                fdp->fd_files[fd].fp = fp;
                fdp->fd_files[fd].reserved = 0;
                if (fp->f_type == DTYPE_KQUEUE) {
                        if (fdp->fd_knlistsize < 0)
                                fdp->fd_knlistsize = 0;
                }
        } else {
                fdp->fd_files[fd].reserved = 0;
                fdreserve_locked(fdp, fd, -1);
                fdfixup_locked(fdp, fd);
        }
}

/*
 * MPSAFE
 */
void
fsetfd(struct proc *p, struct file *fp, int fd)
{
        struct filedesc *fdp = p->p_fd;

        spin_lock_wr(&fdp->fd_spin);
        fsetfd_locked(fdp, fp, fd);
        spin_unlock_wr(&fdp->fd_spin);
}

/*
 * MPSAFE (exclusive spinlock must be held on call)
 */
static 
struct file *
funsetfd_locked(struct filedesc *fdp, int fd)
{
        struct file *fp;

        if ((unsigned)fd >= fdp->fd_nfiles)
                return (NULL);
        if ((fp = fdp->fd_files[fd].fp) == NULL)
                return (NULL);
        fdp->fd_files[fd].fp = NULL;
        fdp->fd_files[fd].fileflags = 0;

        fdreserve_locked(fdp, fd, -1);
        fdfixup_locked(fdp, fd);
        return(fp);
}

/*
 * MPSAFE
 */
int
fgetfdflags(struct filedesc *fdp, int fd, int *flagsp)
{
        int error;

        spin_lock_rd(&fdp->fd_spin);
        if (((u_int)fd) >= fdp->fd_nfiles) {
                error = EBADF;
        } else if (fdp->fd_files[fd].fp == NULL) {
                error = EBADF;
        } else {
                *flagsp = fdp->fd_files[fd].fileflags;
                error = 0;
        }
        spin_unlock_rd(&fdp->fd_spin);
        return (error);
}

/*
 * MPSAFE
 */
int
fsetfdflags(struct filedesc *fdp, int fd, int add_flags)
{
        int error;

        spin_lock_wr(&fdp->fd_spin);
        if (((u_int)fd) >= fdp->fd_nfiles) {
                error = EBADF;
        } else if (fdp->fd_files[fd].fp == NULL) {
                error = EBADF;
        } else {
                fdp->fd_files[fd].fileflags |= add_flags;
                error = 0;
        }
        spin_unlock_wr(&fdp->fd_spin);
        return (error);
}

/*
 * MPSAFE
 */
int
fclrfdflags(struct filedesc *fdp, int fd, int rem_flags)
{
        int error;

        spin_lock_wr(&fdp->fd_spin);
        if (((u_int)fd) >= fdp->fd_nfiles) {
                error = EBADF;
        } else if (fdp->fd_files[fd].fp == NULL) {
                error = EBADF;
        } else {
                fdp->fd_files[fd].fileflags &= ~rem_flags;
                error = 0;
        }
        spin_unlock_wr(&fdp->fd_spin);
        return (error);
}

void
fsetcred(struct file *fp, struct ucred *cr)
{
        crhold(cr);
        crfree(fp->f_cred);
        fp->f_cred = cr;
}

/*
 * Free a file descriptor.
 */
static
void
ffree(struct file *fp)
{
        KASSERT((fp->f_count == 0), ("ffree: fp_fcount not 0!"));
        spin_lock_wr(&filehead_spin);
        LIST_REMOVE(fp, f_list);
        nfiles--;
        spin_unlock_wr(&filehead_spin);
        crfree(fp->f_cred);
        if (fp->f_nchandle.ncp)
            cache_drop(&fp->f_nchandle);
        kfree(fp, M_FILE);
}

/*
 * called from init_main, initialize filedesc0 for proc0.
 */
void
fdinit_bootstrap(struct proc *p0, struct filedesc *fdp0, int cmask)
{
        p0->p_fd = fdp0;
        p0->p_fdtol = NULL;
        fdp0->fd_refcnt = 1;
        fdp0->fd_cmask = cmask;
        fdp0->fd_files = fdp0->fd_builtin_files;
        fdp0->fd_nfiles = NDFILE;
        fdp0->fd_lastfile = -1;
        spin_init(&fdp0->fd_spin);
}

/*
 * Build a new filedesc structure.
 *
 * NOT MPSAFE (vref)
 */
struct filedesc *
fdinit(struct proc *p)
{
        struct filedesc *newfdp;
        struct filedesc *fdp = p->p_fd;

        newfdp = kmalloc(sizeof(struct filedesc), M_FILEDESC, M_WAITOK|M_ZERO);
        spin_lock_rd(&fdp->fd_spin);
        if (fdp->fd_cdir) {
                newfdp->fd_cdir = fdp->fd_cdir;
                vref(newfdp->fd_cdir);
                cache_copy(&fdp->fd_ncdir, &newfdp->fd_ncdir);
        }

        /*
         * rdir may not be set in e.g. proc0 or anything vm_fork'd off of
         * proc0, but should unconditionally exist in other processes.
         */
        if (fdp->fd_rdir) {
                newfdp->fd_rdir = fdp->fd_rdir;
                vref(newfdp->fd_rdir);
                cache_copy(&fdp->fd_nrdir, &newfdp->fd_nrdir);
        }
        if (fdp->fd_jdir) {
                newfdp->fd_jdir = fdp->fd_jdir;
                vref(newfdp->fd_jdir);
                cache_copy(&fdp->fd_njdir, &newfdp->fd_njdir);
        }
        spin_unlock_rd(&fdp->fd_spin);

        /* Create the file descriptor table. */
        newfdp->fd_refcnt = 1;
        newfdp->fd_cmask = cmask;
        newfdp->fd_files = newfdp->fd_builtin_files;
        newfdp->fd_nfiles = NDFILE;
        newfdp->fd_knlistsize = -1;
        newfdp->fd_lastfile = -1;
        spin_init(&newfdp->fd_spin);

        return (newfdp);
}

/*
 * Share a filedesc structure.
 *
 * MPSAFE
 */
struct filedesc *
fdshare(struct proc *p)
{
        struct filedesc *fdp;

        fdp = p->p_fd;
        spin_lock_wr(&fdp->fd_spin);
        fdp->fd_refcnt++;
        spin_unlock_wr(&fdp->fd_spin);
        return (fdp);
}

/*
 * Copy a filedesc structure.
 *
 * MPSAFE
 */
struct filedesc *
fdcopy(struct proc *p)
{
        struct filedesc *fdp = p->p_fd;
        struct filedesc *newfdp;
        struct fdnode *fdnode;
        int i;
        int ni;

        /*
         * Certain daemons might not have file descriptors. 
         */
        if (fdp == NULL)
                return (NULL);

        /*
         * Allocate the new filedesc and fd_files[] array.  This can race
         * with operations by other threads on the fdp so we have to be
         * careful.
         */
        newfdp = kmalloc(sizeof(struct filedesc), M_FILEDESC, M_WAITOK | M_ZERO);
again:
        spin_lock_rd(&fdp->fd_spin);
        if (fdp->fd_lastfile < NDFILE) {
                newfdp->fd_files = newfdp->fd_builtin_files;
                i = NDFILE;
        } else {
                /*
                 * We have to allocate (N^2-1) entries for our in-place
                 * binary tree.  Allow the table to shrink.
                 */
                i = fdp->fd_nfiles;
                ni = (i - 1) / 2;
                while (ni > fdp->fd_lastfile && ni > NDFILE) {
                        i = ni;
                        ni = (i - 1) / 2;
                }
                spin_unlock_rd(&fdp->fd_spin);
                newfdp->fd_files = kmalloc(i * sizeof(struct fdnode),
                                          M_FILEDESC, M_WAITOK | M_ZERO);

                /*
                 * Check for race, retry
                 */
                spin_lock_rd(&fdp->fd_spin);
                if (i <= fdp->fd_lastfile) {
                        spin_unlock_rd(&fdp->fd_spin);
                        kfree(newfdp->fd_files, M_FILEDESC);
                        goto again;
                }
        }

        /*
         * Dup the remaining fields. vref() and cache_hold() can be
         * safely called while holding the read spinlock on fdp.
         *
         * The read spinlock on fdp is still being held.
         *
         * NOTE: vref and cache_hold calls for the case where the vnode
         * or cache entry already has at least one ref may be called
         * while holding spin locks.
         */
        if ((newfdp->fd_cdir = fdp->fd_cdir) != NULL) {
                vref(newfdp->fd_cdir);
                cache_copy(&fdp->fd_ncdir, &newfdp->fd_ncdir);
        }
        /*
         * We must check for fd_rdir here, at least for now because
         * the init process is created before we have access to the
         * rootvode to take a reference to it.
         */
        if ((newfdp->fd_rdir = fdp->fd_rdir) != NULL) {
                vref(newfdp->fd_rdir);
                cache_copy(&fdp->fd_nrdir, &newfdp->fd_nrdir);
        }
        if ((newfdp->fd_jdir = fdp->fd_jdir) != NULL) {
                vref(newfdp->fd_jdir);
                cache_copy(&fdp->fd_njdir, &newfdp->fd_njdir);
        }
        newfdp->fd_refcnt = 1;
        newfdp->fd_nfiles = i;
        newfdp->fd_lastfile = fdp->fd_lastfile;
        newfdp->fd_freefile = fdp->fd_freefile;
        newfdp->fd_cmask = fdp->fd_cmask;
        newfdp->fd_knlist = NULL;
        newfdp->fd_knlistsize = -1;
        newfdp->fd_knhash = NULL;
        newfdp->fd_knhashmask = 0;
        spin_init(&newfdp->fd_spin);

        /*
         * Copy the descriptor table through (i).  This also copies the
         * allocation state.   Then go through and ref the file pointers
         * and clean up any KQ descriptors.
         *
         * kq descriptors cannot be copied.  Since we haven't ref'd the
         * copied files yet we can ignore the return value from funsetfd().
         *
         * The read spinlock on fdp is still being held.
         */
        bcopy(fdp->fd_files, newfdp->fd_files, i * sizeof(struct fdnode));
        for (i = 0 ; i < newfdp->fd_nfiles; ++i) {
                fdnode = &newfdp->fd_files[i];
                if (fdnode->reserved) {
                        fdreserve_locked(newfdp, i, -1);
                        fdnode->reserved = 0;
                        fdfixup_locked(newfdp, i);
                } else if (fdnode->fp) {
                        if (fdnode->fp->f_type == DTYPE_KQUEUE) {
                                (void)funsetfd_locked(newfdp, i);
                        } else {
                                fhold(fdnode->fp);
                        }
                }
        }
        spin_unlock_rd(&fdp->fd_spin);
        return (newfdp);
}

/*
 * Release a filedesc structure.
 *
 * NOT MPSAFE (MPSAFE for refs > 1, but the final cleanup code is not MPSAFE)
 */
void
fdfree(struct proc *p)
{
        struct filedesc *fdp = p->p_fd;
        struct fdnode *fdnode;
        int i;
        struct filedesc_to_leader *fdtol;
        struct file *fp;
        struct vnode *vp;
        struct flock lf;

        /* Certain daemons might not have file descriptors. */
        if (fdp == NULL)
                return;

        /*
         * Severe messing around to follow
         */
        spin_lock_wr(&fdp->fd_spin);

        /* Check for special need to clear POSIX style locks */
        fdtol = p->p_fdtol;
        if (fdtol != NULL) {
                KASSERT(fdtol->fdl_refcount > 0,
                        ("filedesc_to_refcount botch: fdl_refcount=%d",
                         fdtol->fdl_refcount));
                if (fdtol->fdl_refcount == 1 &&
                    (p->p_leader->p_flag & P_ADVLOCK) != 0) {
                        for (i = 0; i <= fdp->fd_lastfile; ++i) {
                                fdnode = &fdp->fd_files[i];
                                if (fdnode->fp == NULL ||
                                    fdnode->fp->f_type != DTYPE_VNODE) {
                                        continue;
                                }
                                fp = fdnode->fp;
                                fhold(fp);
                                spin_unlock_wr(&fdp->fd_spin);

                                lf.l_whence = SEEK_SET;
                                lf.l_start = 0;
                                lf.l_len = 0;
                                lf.l_type = F_UNLCK;
                                vp = (struct vnode *)fp->f_data;
                                (void) VOP_ADVLOCK(vp,
                                                   (caddr_t)p->p_leader,
                                                   F_UNLCK,
                                                   &lf,
                                                   F_POSIX);
                                fdrop(fp);
                                spin_lock_wr(&fdp->fd_spin);
                        }
                }
        retry:
                if (fdtol->fdl_refcount == 1) {
                        if (fdp->fd_holdleaderscount > 0 &&
                            (p->p_leader->p_flag & P_ADVLOCK) != 0) {
                                /*
                                 * close() or do_dup() has cleared a reference
                                 * in a shared file descriptor table.
                                 */
                                fdp->fd_holdleaderswakeup = 1;
                                msleep(&fdp->fd_holdleaderscount, 
                                       &fdp->fd_spin, 0, "fdlhold", 0);
                                goto retry;
                        }
                        if (fdtol->fdl_holdcount > 0) {
                                /* 
                                 * Ensure that fdtol->fdl_leader
                                 * remains valid in closef().
                                 */
                                fdtol->fdl_wakeup = 1;
                                msleep(fdtol, &fdp->fd_spin, 0, "fdlhold", 0);
                                goto retry;
                        }
                }
                fdtol->fdl_refcount--;
                if (fdtol->fdl_refcount == 0 &&
                    fdtol->fdl_holdcount == 0) {
                        fdtol->fdl_next->fdl_prev = fdtol->fdl_prev;
                        fdtol->fdl_prev->fdl_next = fdtol->fdl_next;
                } else {
                        fdtol = NULL;
                }
                p->p_fdtol = NULL;
                if (fdtol != NULL) {
                        spin_unlock_wr(&fdp->fd_spin);
                        kfree(fdtol, M_FILEDESC_TO_LEADER);
                        spin_lock_wr(&fdp->fd_spin);
                }
        }
        if (--fdp->fd_refcnt > 0) {
                spin_unlock_wr(&fdp->fd_spin);
                return;
        }
        spin_unlock_wr(&fdp->fd_spin);

        /*
         * we are the last reference to the structure, we can
         * safely assume it will not change out from under us.
         */
        for (i = 0; i <= fdp->fd_lastfile; ++i) {
                if (fdp->fd_files[i].fp)
                        closef(fdp->fd_files[i].fp, p);
        }
        if (fdp->fd_files != fdp->fd_builtin_files)
                kfree(fdp->fd_files, M_FILEDESC);
        if (fdp->fd_cdir) {
                cache_drop(&fdp->fd_ncdir);
                vrele(fdp->fd_cdir);
        }
        if (fdp->fd_rdir) {
                cache_drop(&fdp->fd_nrdir);
                vrele(fdp->fd_rdir);
        }
        if (fdp->fd_jdir) {
                cache_drop(&fdp->fd_njdir);
                vrele(fdp->fd_jdir);
        }
        if (fdp->fd_knlist)
                kfree(fdp->fd_knlist, M_KQUEUE);
        if (fdp->fd_knhash)
                kfree(fdp->fd_knhash, M_KQUEUE);
        kfree(fdp, M_FILEDESC);
}

/*
 * Retrieve and reference the file pointer associated with a descriptor.
 *
 * MPSAFE
 */
struct file *
holdfp(struct filedesc *fdp, int fd, int flag)
{
        struct file* fp;

        spin_lock_rd(&fdp->fd_spin);
        if (((u_int)fd) >= fdp->fd_nfiles) {
                fp = NULL;
                goto done;
        }
        if ((fp = fdp->fd_files[fd].fp) == NULL)
                goto done;
        if ((fp->f_flag & flag) == 0 && flag != -1) {
                fp = NULL;
                goto done;
        }
        fhold(fp);
done:
        spin_unlock_rd(&fdp->fd_spin);
        return (fp);
}

/*
 * holdsock() - load the struct file pointer associated
 * with a socket into *fpp.  If an error occurs, non-zero
 * will be returned and *fpp will be set to NULL.
 *
 * MPSAFE
 */
int
holdsock(struct filedesc *fdp, int fd, struct file **fpp)
{
        struct file *fp;
        int error;

        spin_lock_rd(&fdp->fd_spin);
        if ((unsigned)fd >= fdp->fd_nfiles) {
                error = EBADF;
                fp = NULL;
                goto done;
        }
        if ((fp = fdp->fd_files[fd].fp) == NULL) {
                error = EBADF;
                goto done;
        }
        if (fp->f_type != DTYPE_SOCKET) {
                error = ENOTSOCK;
                goto done;
        }
        fhold(fp);
        error = 0;
done:
        spin_unlock_rd(&fdp->fd_spin);
        *fpp = fp;
        return (error);
}

/*
 * Convert a user file descriptor to a held file pointer.
 *
 * MPSAFE
 */
int
holdvnode(struct filedesc *fdp, int fd, struct file **fpp)
{
        struct file *fp;
        int error;

        spin_lock_rd(&fdp->fd_spin);
        if ((unsigned)fd >= fdp->fd_nfiles) {
                error = EBADF;
                fp = NULL;
                goto done;
        }
        if ((fp = fdp->fd_files[fd].fp) == NULL) {
                error = EBADF;
                goto done;
        }
        if (fp->f_type != DTYPE_VNODE && fp->f_type != DTYPE_FIFO) {
                fp = NULL;
                error = EINVAL;
                goto done;
        }
        fhold(fp);
        error = 0;
done:
        spin_unlock_rd(&fdp->fd_spin);
        *fpp = fp;
        return (error);
}

/*
 * For setugid programs, we don't want to people to use that setugidness
 * to generate error messages which write to a file which otherwise would
 * otherwise be off-limits to the process.
 *
 * This is a gross hack to plug the hole.  A better solution would involve
 * a special vop or other form of generalized access control mechanism.  We
 * go ahead and just reject all procfs file systems accesses as dangerous.
 *
 * Since setugidsafety calls this only for fd 0, 1 and 2, this check is
 * sufficient.  We also don't for check setugidness since we know we are.
 */
static int
is_unsafe(struct file *fp)
{
        if (fp->f_type == DTYPE_VNODE && 
            ((struct vnode *)(fp->f_data))->v_tag == VT_PROCFS)
                return (1);
        return (0);
}

/*
 * Make this setguid thing safe, if at all possible.
 *
 * NOT MPSAFE - scans fdp without spinlocks, calls knote_fdclose()
 */
void
setugidsafety(struct proc *p)
{
        struct filedesc *fdp = p->p_fd;
        int i;

        /* Certain daemons might not have file descriptors. */
        if (fdp == NULL)
                return;

        /*
         * note: fdp->fd_files may be reallocated out from under us while
         * we are blocked in a close.  Be careful!
         */
        for (i = 0; i <= fdp->fd_lastfile; i++) {
                if (i > 2)
                        break;
                if (fdp->fd_files[i].fp && is_unsafe(fdp->fd_files[i].fp)) {
                        struct file *fp;

                        if (i < fdp->fd_knlistsize)
                                knote_fdclose(p, i);
                        /*
                         * NULL-out descriptor prior to close to avoid
                         * a race while close blocks.
                         */
                        if ((fp = funsetfd_locked(fdp, i)) != NULL)
                                closef(fp, p);
                }
        }
}

/*
 * Close any files on exec?
 *
 * NOT MPSAFE - scans fdp without spinlocks, calls knote_fdclose()
 */
void
fdcloseexec(struct proc *p)
{
        struct filedesc *fdp = p->p_fd;
        int i;

        /* Certain daemons might not have file descriptors. */
        if (fdp == NULL)
                return;

        /*
         * We cannot cache fd_files since operations may block and rip
         * them out from under us.
         */
        for (i = 0; i <= fdp->fd_lastfile; i++) {
                if (fdp->fd_files[i].fp != NULL &&
                    (fdp->fd_files[i].fileflags & UF_EXCLOSE)) {
                        struct file *fp;

                        if (i < fdp->fd_knlistsize)
                                knote_fdclose(p, i);
                        /*
                         * NULL-out descriptor prior to close to avoid
                         * a race while close blocks.
                         */
                        if ((fp = funsetfd_locked(fdp, i)) != NULL)
                                closef(fp, p);
                }
        }
}

/*
 * It is unsafe for set[ug]id processes to be started with file
 * descriptors 0..2 closed, as these descriptors are given implicit
 * significance in the Standard C library.  fdcheckstd() will create a
 * descriptor referencing /dev/null for each of stdin, stdout, and
 * stderr that is not already open.
 *
 * NOT MPSAFE - calls falloc, vn_open, etc
 */
int
fdcheckstd(struct proc *p)
{
        struct nlookupdata nd;
        struct filedesc *fdp;
        struct file *fp;
        register_t retval;
        int i, error, flags, devnull;

        fdp = p->p_fd;
        if (fdp == NULL)
                return (0);
        devnull = -1;
        error = 0;
        for (i = 0; i < 3; i++) {
                if (fdp->fd_files[i].fp != NULL)
                        continue;
                if (devnull < 0) {
                        if ((error = falloc(p, &fp, &devnull)) != 0)
                                break;

                        error = nlookup_init(&nd, "/dev/null", UIO_SYSSPACE,
                                                NLC_FOLLOW|NLC_LOCKVP);
                        flags = FREAD | FWRITE;
                        if (error == 0)
                                error = vn_open(&nd, fp, flags, 0);
                        if (error == 0)
                                fsetfd(p, fp, devnull);
                        else
                                fsetfd(p, NULL, devnull);
                        fdrop(fp);
                        nlookup_done(&nd);
                        if (error)
                                break;
                        KKASSERT(i == devnull);
                } else {
                        error = kern_dup(DUP_FIXED, devnull, i, &retval);
                        if (error != 0)
                                break;
                }
        }
        return (error);
}

/*
 * Internal form of close.
 * Decrement reference count on file structure.
 * Note: td and/or p may be NULL when closing a file
 * that was being passed in a message.
 *
 * MPALMOSTSAFE - acquires mplock for VOP operations
 */
int
closef(struct file *fp, struct proc *p)
{
        struct vnode *vp;
        struct flock lf;
        struct filedesc_to_leader *fdtol;

        if (fp == NULL)
                return (0);

        /*
         * 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 (p != NULL && fp->f_type == DTYPE_VNODE &&
            (((struct vnode *)fp->f_data)->v_flag & VMAYHAVELOCKS)
        ) {
                get_mplock();
                if ((p->p_leader->p_flag & P_ADVLOCK) != 0) {
                        lf.l_whence = SEEK_SET;
                        lf.l_start = 0;
                        lf.l_len = 0;
                        lf.l_type = F_UNLCK;
                        vp = (struct vnode *)fp->f_data;
                        (void) VOP_ADVLOCK(vp, (caddr_t)p->p_leader, F_UNLCK,
                                           &lf, F_POSIX);
                }
                fdtol = p->p_fdtol;
                if (fdtol != NULL) {
                        /*
                         * Handle special case where file descriptor table
                         * is shared between multiple process leaders.
                         */
                        for (fdtol = fdtol->fdl_next;
                             fdtol != p->p_fdtol;
                             fdtol = fdtol->fdl_next) {
                                if ((fdtol->fdl_leader->p_flag &
                                     P_ADVLOCK) == 0)
                                        continue;
                                fdtol->fdl_holdcount++;
                                lf.l_whence = SEEK_SET;
                                lf.l_start = 0;
                                lf.l_len = 0;
                                lf.l_type = F_UNLCK;
                                vp = (struct vnode *)fp->f_data;
                                (void) VOP_ADVLOCK(vp,
                                                   (caddr_t)fdtol->fdl_leader,
                                                   F_UNLCK, &lf, F_POSIX);
                                fdtol->fdl_holdcount--;
                                if (fdtol->fdl_holdcount == 0 &&
                                    fdtol->fdl_wakeup != 0) {
                                        fdtol->fdl_wakeup = 0;
                                        wakeup(fdtol);
                                }
                        }
                }
                rel_mplock();
        }
        return (fdrop(fp));
}

/*
 * MPSAFE
 *
 * fhold() can only be called if f_count is already at least 1 (i.e. the
 * caller of fhold() already has a reference to the file pointer in some
 * manner or other). 
 *
 * f_count is not spin-locked.  Instead, atomic ops are used for
 * incrementing, decrementing, and handling the 1->0 transition.
 */
void
fhold(struct file *fp)
{
        atomic_add_int(&fp->f_count, 1);
}

/*
 * fdrop() - drop a reference to a descriptor
 *
 * MPALMOSTSAFE - acquires mplock for final close sequence
 */
int
fdrop(struct file *fp)
{
        struct flock lf;
        struct vnode *vp;
        int error;

        /*
         * A combined fetch and subtract is needed to properly detect
         * 1->0 transitions, otherwise two cpus dropping from a ref
         * count of 2 might both try to run the 1->0 code.
         */
        if (atomic_fetchadd_int(&fp->f_count, -1) > 1)
                return (0);

        get_mplock();

        /*
         * The last reference has gone away, we own the fp structure free
         * and clear.
         */
        if (fp->f_count < 0)
                panic("fdrop: count < 0");
        if ((fp->f_flag & FHASLOCK) && fp->f_type == DTYPE_VNODE &&
            (((struct vnode *)fp->f_data)->v_flag & VMAYHAVELOCKS)
        ) {
                lf.l_whence = SEEK_SET;
                lf.l_start = 0;
                lf.l_len = 0;
                lf.l_type = F_UNLCK;
                vp = (struct vnode *)fp->f_data;
                (void) VOP_ADVLOCK(vp, (caddr_t)fp, F_UNLCK, &lf, 0);
        }
        if (fp->f_ops != &badfileops)
                error = fo_close(fp);
        else
                error = 0;
        ffree(fp);
        rel_mplock();
        return (error);
}

/*
 * Apply an advisory lock on a file descriptor.
 *
 * Just attempt to get a record lock of the requested type on
 * the entire file (l_whence = SEEK_SET, l_start = 0, l_len = 0).
 */
int
sys_flock(struct flock_args *uap)
{
        struct proc *p = curproc;
        struct file *fp;
        struct vnode *vp;
        struct flock lf;
        int error;

        if ((fp = holdfp(p->p_fd, uap->fd, -1)) == NULL)
                return (EBADF);
        if (fp->f_type != DTYPE_VNODE) {
                error = EOPNOTSUPP;
                goto done;
        }
        vp = (struct vnode *)fp->f_data;
        lf.l_whence = SEEK_SET;
        lf.l_start = 0;
        lf.l_len = 0;
        if (uap->how & LOCK_UN) {
                lf.l_type = F_UNLCK;
                fp->f_flag &= ~FHASLOCK;
                error = VOP_ADVLOCK(vp, (caddr_t)fp, F_UNLCK, &lf, 0);
                goto done;
        }
        if (uap->how & LOCK_EX)
                lf.l_type = F_WRLCK;
        else if (uap->how & LOCK_SH)
                lf.l_type = F_RDLCK;
        else {
                error = EBADF;
                goto done;
        }
        fp->f_flag |= FHASLOCK;
        if (uap->how & LOCK_NB)
                error = VOP_ADVLOCK(vp, (caddr_t)fp, F_SETLK, &lf, 0);
        else
                error = VOP_ADVLOCK(vp, (caddr_t)fp, F_SETLK, &lf, F_WAIT);
done:
        fdrop(fp);
        return (error);
}

/*
 * 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.
 */
/* ARGSUSED */
static int
fdopen(struct dev_open_args *ap)
{
        thread_t td = curthread;

        KKASSERT(td->td_lwp != NULL);

        /*
         * XXX Kludge: set curlwp->lwp_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.
         */
        td->td_lwp->lwp_dupfd = minor(ap->a_head.a_dev);
        return (ENODEV);
}

/*
 * The caller has reserved the file descriptor dfd for us.  On success we
 * must fsetfd() it.  On failure the caller will clean it up.
 *
 * NOT MPSAFE - isn't getting spinlocks, possibly other things
 */
int
dupfdopen(struct proc *p, int dfd, int sfd, int mode, int error)
{
        struct filedesc *fdp = p->p_fd;
        struct file *wfp;
        struct file *xfp;
        int werror;

        if ((wfp = holdfp(fdp, sfd, -1)) == NULL)
                return (EBADF);

        /*
         * Close a revoke/dup race.  Duping a descriptor marked as revoked
         * will dup a dummy descriptor instead of the real one.
         */
        if (wfp->f_flag & FREVOKED) {
                kprintf("Warning: attempt to dup() a revoked descriptor\n");
                fdrop(wfp);
                wfp = NULL;
                werror = falloc(NULL, &wfp, NULL);
                if (werror)
                        return (werror);
        }

        /*
         * There are two cases of interest here.
         *
         * For ENODEV simply dup sfd to file descriptor dfd and return.
         *
         * For ENXIO steal away the file structure from sfd and store it
         * dfd.  sfd is effectively closed by this operation.
         *
         * Any other error code is just returned.
         */
        switch (error) {
        case ENODEV:
                /*
                 * Check that the mode the file is being opened for is a
                 * subset of the mode of the existing descriptor.
                 */
                if (((mode & (FREAD|FWRITE)) | wfp->f_flag) != wfp->f_flag) {
                        error = EACCES;
                        break;
                }
                fdp->fd_files[dfd].fileflags = fdp->fd_files[sfd].fileflags;
                fsetfd(p, wfp, dfd);
                error = 0;
                break;
        case ENXIO:
                /*
                 * Steal away the file pointer from dfd, and stuff it into indx.
                 */
                fdp->fd_files[dfd].fileflags = fdp->fd_files[sfd].fileflags;
                fsetfd(p, wfp, dfd);
                if ((xfp = funsetfd_locked(fdp, sfd)) != NULL)
                        fdrop(xfp);
                error = 0;
                break;
        default:
                break;
        }
        fdrop(wfp);
        return (error);
}

/*
 * NOT MPSAFE - I think these refer to a common file descriptor table
 * and we need to spinlock that to link fdtol in.
 */
struct filedesc_to_leader *
filedesc_to_leader_alloc(struct filedesc_to_leader *old,
                         struct proc *leader)
{
        struct filedesc_to_leader *fdtol;
        
        fdtol = kmalloc(sizeof(struct filedesc_to_leader), 
                        M_FILEDESC_TO_LEADER, M_WAITOK);
        fdtol->fdl_refcount = 1;
        fdtol->fdl_holdcount = 0;
        fdtol->fdl_wakeup = 0;
        fdtol->fdl_leader = leader;
        if (old != NULL) {
                fdtol->fdl_next = old->fdl_next;
                fdtol->fdl_prev = old;
                old->fdl_next = fdtol;
                fdtol->fdl_next->fdl_prev = fdtol;
        } else {
                fdtol->fdl_next = fdtol;
                fdtol->fdl_prev = fdtol;
        }
        return fdtol;
}

/*
 * Scan all file pointers in the system.  The callback is made with
 * the master list spinlock held exclusively.
 *
 * MPSAFE
 */
void
allfiles_scan_exclusive(int (*callback)(struct file *, void *), void *data)
{
        struct file *fp;
        int res;

        spin_lock_wr(&filehead_spin);
        LIST_FOREACH(fp, &filehead, f_list) {
                res = callback(fp, data);
                if (res < 0)
                        break;
        }
        spin_unlock_wr(&filehead_spin);
}

/*
 * Get file structures.
 *
 * NOT MPSAFE - process list scan, SYSCTL_OUT (probably not mpsafe)
 */

struct sysctl_kern_file_info {
        int count;
        int error;
        struct sysctl_req *req;
};

static int sysctl_kern_file_callback(struct proc *p, void *data);

static int
sysctl_kern_file(SYSCTL_HANDLER_ARGS)
{
        struct sysctl_kern_file_info info;

        /*
         * Note: because the number of file descriptors is calculated
         * in different ways for sizing vs returning the data,
         * there is information leakage from the first loop.  However,
         * it is of a similar order of magnitude to the leakage from
         * global system statistics such as kern.openfiles.
         *
         * When just doing a count, note that we cannot just count
         * the elements and add f_count via the filehead list because 
         * threaded processes share their descriptor table and f_count might
         * still be '1' in that case.
         *
         * Since the SYSCTL op can block, we must hold the process to
         * prevent it being ripped out from under us either in the 
         * file descriptor loop or in the greater LIST_FOREACH.  The
         * process may be in varying states of disrepair.  If the process
         * is in SZOMB we may have caught it just as it is being removed
         * from the allproc list, we must skip it in that case to maintain
         * an unbroken chain through the allproc list.
         */
        info.count = 0;
        info.error = 0;
        info.req = req;
        allproc_scan(sysctl_kern_file_callback, &info);

        /*
         * When just calculating the size, overestimate a bit to try to
         * prevent system activity from causing the buffer-fill call 
         * to fail later on.
         */
        if (req->oldptr == NULL) {
                info.count = (info.count + 16) + (info.count / 10);
                info.error = SYSCTL_OUT(req, NULL,
                                        info.count * sizeof(struct kinfo_file));
        }
        return (info.error);
}

static int
sysctl_kern_file_callback(struct proc *p, void *data)
{
        struct sysctl_kern_file_info *info = data;
        struct kinfo_file kf;
        struct filedesc *fdp;
        struct file *fp;
        uid_t uid;
        int n;

        if (p->p_stat == SIDL || p->p_stat == SZOMB)
                return(0);
        if (!PRISON_CHECK(info->req->td->td_proc->p_ucred, p->p_ucred) != 0)
                return(0);
        if ((fdp = p->p_fd) == NULL)
                return(0);
        spin_lock_rd(&fdp->fd_spin);
        for (n = 0; n < fdp->fd_nfiles; ++n) {
                if ((fp = fdp->fd_files[n].fp) == NULL)
                        continue;
                if (info->req->oldptr == NULL) {
                        ++info->count;
                } else {
                        uid = p->p_ucred ? p->p_ucred->cr_uid : -1;
                        kcore_make_file(&kf, fp, p->p_pid, uid, n);
                        spin_unlock_rd(&fdp->fd_spin);
                        info->error = SYSCTL_OUT(info->req, &kf, sizeof(kf));
                        spin_lock_rd(&fdp->fd_spin);
                        if (info->error)
                                break;
                }
        }
        spin_unlock_rd(&fdp->fd_spin);
        if (info->error)
                return(-1);
        return(0);
}

SYSCTL_PROC(_kern, KERN_FILE, file, CTLTYPE_OPAQUE|CTLFLAG_RD,
    0, 0, sysctl_kern_file, "S,file", "Entire file table");

SYSCTL_INT(_kern, KERN_MAXFILESPERPROC, maxfilesperproc, CTLFLAG_RW, 
    &maxfilesperproc, 0, "Maximum files allowed open per process");

SYSCTL_INT(_kern, KERN_MAXFILES, maxfiles, CTLFLAG_RW, 
    &maxfiles, 0, "Maximum number of files");

SYSCTL_INT(_kern, OID_AUTO, maxfilesrootres, CTLFLAG_RW, 
    &maxfilesrootres, 0, "Descriptors reserved for root use");

SYSCTL_INT(_kern, OID_AUTO, openfiles, CTLFLAG_RD, 
        &nfiles, 0, "System-wide number of open files");

static void
fildesc_drvinit(void *unused)
{
        int fd;

        dev_ops_add(&fildesc_ops, 0, 0);
        for (fd = 0; fd < NUMFDESC; fd++) {
                make_dev(&fildesc_ops, fd,
                    UID_BIN, GID_BIN, 0666, "fd/%d", fd);
        }
        make_dev(&fildesc_ops, 0, UID_ROOT, GID_WHEEL, 0666, "stdin");
        make_dev(&fildesc_ops, 1, UID_ROOT, GID_WHEEL, 0666, "stdout");
        make_dev(&fildesc_ops, 2, UID_ROOT, GID_WHEEL, 0666, "stderr");
}

/*
 * MPSAFE
 */
struct fileops badfileops = {
        .fo_read = badfo_readwrite,
        .fo_write = badfo_readwrite,
        .fo_ioctl = badfo_ioctl,
        .fo_poll = badfo_poll,
        .fo_kqfilter = badfo_kqfilter,
        .fo_stat = badfo_stat,
        .fo_close = badfo_close,
        .fo_shutdown = badfo_shutdown
};

/*
 * MPSAFE
 */
static int
badfo_readwrite(
        struct file *fp,
        struct uio *uio,
        struct ucred *cred,
        int flags
) {
        return (EBADF);
}

/*
 * MPSAFE
 */
static int
badfo_ioctl(struct file *fp, u_long com, caddr_t data, struct ucred *cred)
{
        return (EBADF);
}

/*
 * MPSAFE
 */
static int
badfo_poll(struct file *fp, int events, struct ucred *cred)
{
        return (0);
}

/*
 * MPSAFE
 */
static int
badfo_kqfilter(struct file *fp, struct knote *kn)
{
        return (0);
}

static int
badfo_stat(struct file *fp, struct stat *sb, struct ucred *cred)
{
        return (EBADF);
}

/*
 * MPSAFE
 */
static int
badfo_close(struct file *fp)
{
        return (EBADF);
}

/*
 * MPSAFE
 */
static int
badfo_shutdown(struct file *fp, int how)
{
        return (EBADF);
}

/*
 * MPSAFE
 */
int
nofo_shutdown(struct file *fp, int how)
{
        return (EOPNOTSUPP);
}

SYSINIT(fildescdev,SI_SUB_DRIVERS,SI_ORDER_MIDDLE+CDEV_MAJOR,
                                        fildesc_drvinit,NULL)