FreeBSD/Linux Kernel Cross Reference
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. 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 $
     */
    
    #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/file.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/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 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 struct krate krate_uidinfo = { .freq = 1 };
   
   static   d_open_t  fdopen;
   #define NUMFDESC 64
   
   #define CDEV_MAJOR 22
   static struct dev_ops fildesc_ops = {
           { "FD", 0, 0 },
           .d_open =       fdopen,
   };
   
   /*
    * 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;
           int dtsize;
   
           spin_lock(&limit->p_spin);
           if (limit->pl_rlimit[RLIMIT_NOFILE].rlim_cur > INT_MAX)
                   dtsize = INT_MAX;
           else
                   dtsize = (int)limit->pl_rlimit[RLIMIT_NOFILE].rlim_cur;
           spin_unlock(&limit->p_spin);
   
           if (dtsize > maxfilesperproc)
                   dtsize = maxfilesperproc;
           if (dtsize < minfilesperproc)
                   dtsize = minfilesperproc;
           if (p->p_ucred->cr_uid && dtsize > maxfilesperuser)
                   dtsize = maxfilesperuser;
           uap->sysmsg_result = dtsize;
           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;
           int fd = 0;
   
           error = kern_dup(DUP_FIXED, uap->from, uap->to, &fd);
           uap->sysmsg_fds[0] = fd;
   
           return (error);
   }
   
   /*
    * Duplicate a file descriptor.
    *
    * MPSAFE
    */
   int
   sys_dup(struct dup_args *uap)
   {
           int error;
           int fd = 0;
   
           error = kern_dup(DUP_VARIABLE, uap->fd, 0, &fd);
           uap->sysmsg_fds[0] = fd;
   
           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;
           u_int nflags;
           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);
           case F_DUP2FD:
                   newmin = dat->fc_fd;
                   error = kern_dup(DUP_FIXED, fd, newmin, &dat->fc_fd);
                   return (error);
           case F_DUPFD_CLOEXEC:
                   newmin = dat->fc_fd;
                   error = kern_dup(DUP_VARIABLE | DUP_CLOEXEC, fd, newmin,
                                    &dat->fc_fd);
                   return (error);
           case F_DUP2FD_CLOEXEC:
                   newmin = dat->fc_fd;
                   error = kern_dup(DUP_FIXED | DUP_CLOEXEC, fd, newmin,
                                    &dat->fc_fd);
                   return (error);
           default:
                   break;
           }
   
           /*
            * Operations on file pointers
            */
           if ((fp = holdfp(p->p_fd, fd, -1)) == NULL)
                   return (EBADF);
   
           switch (cmd) {
           case F_GETFL:
                   dat->fc_flags = OFLAGS(fp->f_flag);
                   error = 0;
                   break;
   
           case F_SETFL:
                   oflags = fp->f_flag;
                   nflags = FFLAGS(dat->fc_flags & ~O_ACCMODE) & FCNTLFLAGS;
                   nflags |= oflags & ~FCNTLFLAGS;
   
                   error = 0;
                   if (((nflags ^ oflags) & O_APPEND) && (oflags & FAPPENDONLY))
                           error = EINVAL;
                   if (error == 0 && ((nflags ^ oflags) & FASYNC)) {
                           tmp = nflags & FASYNC;
                           error = fo_ioctl(fp, FIOASYNC, (caddr_t)&tmp,
                                            cred, NULL);
                   }
                   if (error == 0)
                           fp->f_flag = nflags;
                   break;
   
           case F_GETOWN:
                   error = fo_ioctl(fp, FIOGETOWN, (caddr_t)&dat->fc_owner,
                                    cred, NULL);
                   break;
   
           case F_SETOWN:
                   error = fo_ioctl(fp, FIOSETOWN, (caddr_t)&dat->fc_owner,
                                    cred, NULL);
                   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;
                           }
                           if ((p->p_leader->p_flags & P_ADVLOCK) == 0) {
                                   lwkt_gettoken(&p->p_leader->p_token);
                                   p->p_leader->p_flags |= P_ADVLOCK;
                                   lwkt_reltoken(&p->p_leader->p_token);
                           }
                           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;
                           }
                           if ((p->p_leader->p_flags & P_ADVLOCK) == 0) {
                                   lwkt_gettoken(&p->p_leader->p_token);
                                   p->p_leader->p_flags |= P_ADVLOCK;
                                   lwkt_reltoken(&p->p_leader->p_token);
                           }
                           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 (checkfdclosed(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;
           }
   
           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:
           case F_DUP2FD:
           case F_DUPFD_CLOEXEC:
           case F_DUP2FD_CLOEXEC:
                   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, curthread->td_ucred);
   
           if (error == 0) {
                   switch (uap->cmd) {
                   case F_DUPFD:
                   case F_DUP2FD:
                   case F_DUPFD_CLOEXEC:
                   case F_DUP2FD_CLOEXEC:
                           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;
                           break;
                   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).
    *
    * There are three type flags: DUP_FIXED, DUP_VARIABLE, and DUP_CLOEXEC.
    * The first two flags are mutually exclusive, and the third is optional.
    * 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".  DUP_CLOEXEC, which works with either of the first
    * two flags, sets the close-on-exec flag on the "new" file descriptor.
    *
    * MPSAFE
    */
   int
   kern_dup(int flags, 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 dtsize;
           int error, newfd;
   
           /*
            * Verify that we have a valid descriptor to dup from and
            * possibly to dup to.
            *
            * NOTE: maxfilesperuser is not applicable to dup()
            */
   retry:
           if (p->p_rlimit[RLIMIT_NOFILE].rlim_cur > INT_MAX)
                   dtsize = INT_MAX;
           else
                   dtsize = (int)p->p_rlimit[RLIMIT_NOFILE].rlim_cur;
           if (dtsize > maxfilesperproc)
                   dtsize = maxfilesperproc;
           if (dtsize < minfilesperproc)
                   dtsize = minfilesperproc;
   
           if (new < 0 || new > dtsize)
                   return (EINVAL);
   
           spin_lock(&fdp->fd_spin);
           if ((unsigned)old >= fdp->fd_nfiles || fdp->fd_files[old].fp == NULL) {
                   spin_unlock(&fdp->fd_spin);
                   return (EBADF);
           }
           if ((flags & DUP_FIXED) && old == new) {
                   *res = new;
                   if (flags & DUP_CLOEXEC)
                           fdp->fd_files[new].fileflags |= UF_EXCLOSE;
                   spin_unlock(&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 ((flags & DUP_VARIABLE) || new >= fdp->fd_nfiles) {
                   spin_unlock(&fdp->fd_spin);
                   error = fdalloc(p, new, &newfd);
                   spin_lock(&fdp->fd_spin);
                   if (error) {
                           spin_unlock(&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(&fdp->fd_spin);
                           fdrop(fp);
                           goto retry;
                   }
                   /*
                    * Check for expansion race
                    */
                   if ((flags & DUP_VARIABLE) == 0 && new != newfd) {
                           fsetfd_locked(fdp, NULL, newfd);
                           spin_unlock(&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(&fdp->fd_spin);
                           fdrop(fp);
                           goto retry;
                   }
                   new = newfd;
                   delfp = NULL;
           } else {
                   if (fdp->fd_files[new].reserved) {
                           spin_unlock(&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 || (flags & 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);
           if ((flags & DUP_CLOEXEC) != 0)
                   fdp->fd_files[new].fileflags = oldflags | UF_EXCLOSE;
           else
                   fdp->fd_files[new].fileflags = oldflags & ~UF_EXCLOSE;
           spin_unlock(&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) {
                   if (SLIST_FIRST(&delfp->f_klist))
                           knote_fdclose(delfp, fdp, new);
                   closef(delfp, p);
                   if (holdleaders) {
                           spin_lock(&fdp->fd_spin);
                           fdp->fd_holdleaderscount--;
                           if (fdp->fd_holdleaderscount == 0 &&
                               fdp->fd_holdleaderswakeup != 0) {
                                   fdp->fd_holdleaderswakeup = 0;
                                   spin_unlock(&fdp->fd_spin);
                                   wakeup(&fdp->fd_holdleaderscount);
                           } else {
                                   spin_unlock(&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.
    *
    * MPSAFE
    */
   void
   funsetown(struct sigio **sigiop)
   {
           struct pgrp *pgrp;
           struct proc *p;
           struct sigio *sigio;
   
           if ((sigio = *sigiop) != NULL) {
                   lwkt_gettoken(&sigio_token);    /* protect sigio */
                   KKASSERT(sigiop == sigio->sio_myref);
                   sigio = *sigiop;
                   *sigiop = NULL;
                   lwkt_reltoken(&sigio_token);
           }
           if (sigio == NULL)
                   return;
   
           if (sigio->sio_pgid < 0) {
                   pgrp = sigio->sio_pgrp;
                   sigio->sio_pgrp = NULL;
                   lwkt_gettoken(&pgrp->pg_token);
                   SLIST_REMOVE(&pgrp->pg_sigiolst, sigio, sigio, sio_pgsigio);
                   lwkt_reltoken(&pgrp->pg_token);
                   pgrel(pgrp);
           } else /* if ((*sigiop)->sio_pgid > 0) */ {
                   p = sigio->sio_proc;
                   sigio->sio_proc = NULL;
                   PHOLD(p);
                   lwkt_gettoken(&p->p_token);
                   SLIST_REMOVE(&p->p_sigiolst, sigio, sigio, sio_pgsigio);
                   lwkt_reltoken(&p->p_token);
                   PRELE(p);
           }
           crfree(sigio->sio_ucred);
           sigio->sio_ucred = NULL;
           kfree(sigio, M_SIGIO);
   }
   
   /*
    * Free a list of sigio structures.  Caller is responsible for ensuring
    * that the list is MPSAFE.
    *
    * MPSAFE
    */
   void
   funsetownlst(struct sigiolst *sigiolst)
   {
           struct sigio *sigio;
   
           while ((sigio = SLIST_FIRST(sigiolst)) != NULL)
                   funsetown(sigio->sio_myref);
   }
   
   /*
    * 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.
    *
    * MPSAFE
    */
   int
   fsetown(pid_t pgid, struct sigio **sigiop)
   {
           struct proc *proc = NULL;
           struct pgrp *pgrp = NULL;
           struct sigio *sigio;
           int error;
   
           if (pgid == 0) {
                   funsetown(sigiop);
                   return (0);
           }
   
           if (pgid > 0) {
                   proc = pfind(pgid);
                   if (proc == NULL) {
                           error = ESRCH;
                           goto done;
                   }
   
                   /*
                    * 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) {
                           error = EPERM;
                           goto done;
                   }
           } else /* if (pgid < 0) */ {
                   pgrp = pgfind(-pgid);
                   if (pgrp == NULL) {
                           error = ESRCH;
                           goto done;
                   }
   
                   /*
                    * 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) {
                           error = EPERM;
                           goto done;
                   }
           }
           sigio = kmalloc(sizeof(struct sigio), M_SIGIO, M_WAITOK | M_ZERO);
           if (pgid > 0) {
                   KKASSERT(pgrp == NULL);
                   lwkt_gettoken(&proc->p_token);
                   SLIST_INSERT_HEAD(&proc->p_sigiolst, sigio, sio_pgsigio);
                   sigio->sio_proc = proc;
                   lwkt_reltoken(&proc->p_token);
           } else {
                   KKASSERT(proc == NULL);
                   lwkt_gettoken(&pgrp->pg_token);
                   SLIST_INSERT_HEAD(&pgrp->pg_sigiolst, sigio, sio_pgsigio);
                   sigio->sio_pgrp = pgrp;
                   lwkt_reltoken(&pgrp->pg_token);
                   pgrp = NULL;
           }
           sigio->sio_pgid = pgid;
           sigio->sio_ucred = crhold(curthread->td_ucred);
           /* It would be convenient if p_ruid was in ucred. */
           sigio->sio_ruid = sigio->sio_ucred->cr_ruid;
           sigio->sio_myref = sigiop;
   
           lwkt_gettoken(&sigio_token);
           while (*sigiop)
                   funsetown(sigiop);
           *sigiop = sigio;
           lwkt_reltoken(&sigio_token);
           error = 0;
   done:
           if (pgrp)
                   pgrel(pgrp);
           if (proc)
                   PRELE(proc);
           return (error);
   }
   
   /*
    * This is common code for FIOGETOWN ioctl called by fcntl(fd, F_GETOWN, arg).
    *
    * MPSAFE
    */
   pid_t
   fgetown(struct sigio **sigiop)
   {
           struct sigio *sigio;
           pid_t own;
   
           lwkt_gettoken_shared(&sigio_token);
           sigio = *sigiop;
           own = (sigio != NULL ? sigio->sio_pgid : 0);
           lwkt_reltoken(&sigio_token);
   
           return (own);
   }
   
   /*
    * 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(&fdp->fd_spin);
           while (fd <= fdp->fd_lastfile) {
                   if (fdp->fd_files[fd].fp != NULL) {
                           spin_unlock(&fdp->fd_spin);
                           /* ok if this races another close */
                           if (kern_close(fd) == EINTR)
                                   return (EINTR);
                           spin_lock(&fdp->fd_spin);
                   }
                   ++fd;
           }
           spin_unlock(&fdp->fd_spin);
           return (0);
   }
   
   /*
    * Close a file descriptor.
    *
    * MPSAFE
    */
   int
   sys_close(struct close_args *uap)
   {
           return(kern_close(uap->fd));
   }
   
   /*
    * MPSAFE
    */
   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(&fdp->fd_spin);
           if ((fp = funsetfd_locked(fdp, fd)) == NULL) {
                   spin_unlock(&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(&fdp->fd_spin);
           if (SLIST_FIRST(&fp->f_klist))
                   knote_fdclose(fp, fdp, fd);
           error = closef(fp, p);
           if (holdleaders) {
                   spin_lock(&fdp->fd_spin);
                   fdp->fd_holdleaderscount--;
                   if (fdp->fd_holdleaderscount == 0 &&
                       fdp->fd_holdleaderswakeup != 0) {
                           fdp->fd_holdleaderswakeup = 0;
                           spin_unlock(&fdp->fd_spin);
                           wakeup(&fdp->fd_holdleaderscount);
                   } else {
                           spin_unlock(&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);
   }
   
   /*
    * MPALMOSTSAFE
    */
   int
   sys_shutdown(struct shutdown_args *uap)
   {
           int error;
   
           error = kern_shutdown(uap->s, uap->how);
   
           return (error);
   }
   
   /*
    * MPSAFE
    */
   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, td->td_ucred);
          fdrop(fp);
  
          return (error);
  }
  
  /*
   * Return status information about a file descriptor.
   *
   * MPSAFE
   */
  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.
   *
   * MPALMOSTSAFE
   */
  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;
  
          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_reg);
                  break;
          default:
                  error = EOPNOTSUPP;
                  break;
          }
          fdrop(fp);
          return(error);
  }
  
  static int fdexpand;
  SYSCTL_INT(_debug, OID_AUTO, fdexpand, CTLFLAG_RD, &fdexpand, 0,
      "Number of times a file table has been expanded");
  
  /*
   * 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(&fdp->fd_spin);
          newfiles = kmalloc(nf * sizeof(struct fdnode), M_FILEDESC, M_WAITOK);
          spin_lock(&fdp->fd_spin);
  
          /*
           * We could have raced another extend while we were not holding
           * the spinlock.
           */
          if (fdp->fd_nfiles >= nf) {
                  spin_unlock(&fdp->fd_spin);
                  kfree(newfiles, M_FILEDESC);
                  spin_lock(&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(&fdp->fd_spin);
                  kfree(oldfiles, M_FILEDESC);
                  spin_lock(&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;
          struct uidinfo *uip;
          int fd, rsize, rsum, node, lim;
  
          /*
           * Check dtable size limit
           */
          spin_lock(&p->p_limit->p_spin);
          if (p->p_rlimit[RLIMIT_NOFILE].rlim_cur > INT_MAX)
                  lim = INT_MAX;
          else
                  lim = (int)p->p_rlimit[RLIMIT_NOFILE].rlim_cur;
          spin_unlock(&p->p_limit->p_spin);
  
          if (lim > maxfilesperproc)
                  lim = maxfilesperproc;
          if (lim < minfilesperproc)
                  lim = minfilesperproc;
          if (want >= lim)
                  return (EMFILE);
  
          /*
           * Check that the user has not run out of descriptors (non-root only).
           * As a safety measure the dtable is allowed to have at least
           * minfilesperproc open fds regardless of the maxfilesperuser limit.
           */
          if (p->p_ucred->cr_uid && fdp->fd_nfiles >= minfilesperproc) {
                  uip = p->p_ucred->cr_uidinfo;
                  if (uip->ui_openfiles > maxfilesperuser) {
                          krateprintf(&krate_uidinfo,
                                      "Warning: user %d pid %d (%s) ran out of "
                                      "file descriptors (%d/%d)\n",
                                      p->p_ucred->cr_uid, (int)p->p_pid,
                                      p->p_comm,
                                      uip->ui_openfiles, maxfilesperuser);
                          return(ENFILE);
                  }
          }
  
          /*
           * Grow the dtable if necessary
           */
          spin_lock(&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(&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(&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(&p->p_limit->p_spin);
          if (p->p_rlimit[RLIMIT_NOFILE].rlim_cur > INT_MAX)
                  lim = INT_MAX;
          else
                  lim = (int)p->p_rlimit[RLIMIT_NOFILE].rlim_cur;
          spin_unlock(&p->p_limit->p_spin);
  
          if (lim > maxfilesperproc)
                  lim = maxfilesperproc;
          if (lim < minfilesperproc)
                  lim = minfilesperproc;
  
          spin_lock(&fdp->fd_spin);
          if ((i = lim - fdp->fd_nfiles) > 0 && (n -= i) <= 0) {
                  spin_unlock(&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(&fdp->fd_spin);
                          return (1);
                  }
          }
          spin_unlock(&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.
   *
   * WARNING: allfiles_scan_exclusive() holds a spinlock through these calls!
   */
  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);
          }
  
          /*
           * Softref the fdp to prevent it from being destroyed
           */
          spin_lock(&p->p_spin);
          if ((fdp = p->p_fd) == NULL) {
                  spin_unlock(&p->p_spin);
                  return(0);
          }
          atomic_add_int(&fdp->fd_softrefs, 1);
          spin_unlock(&p->p_spin);
  
          /*
           * Locate and close any matching file descriptors.
           */
          spin_lock(&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(&fdp->fd_spin);
                          knote_fdclose(fp, fdp, n);      /* XXX */
                          closef(fp, p);
                          spin_lock(&fdp->fd_spin);
                          --info->count;
                  }
          }
          spin_unlock(&fdp->fd_spin);
          atomic_subtract_int(&fdp->fd_softrefs, 1);
          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 lp, or assumed if lp is NULL.  If
   *      resultfd is non-NULL then lp must also be non-NULL.  No file
   *      descriptor is reserved (and no process context is needed) 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 lwp *lp, struct file **resultfp, int *resultfd)
  {
          static struct timeval lastfail;
          static int curfail;
          struct file *fp;
          struct ucred *cred = lp ? lp->lwp_thread->td_ucred : proc0.p_ucred;
          int error;
  
          fp = NULL;
  
          /*
           * Handle filetable full issues and root overfill.
           */
          if (nfiles >= maxfiles - maxfilesrootres &&
              (cred->cr_ruid != 0 || nfiles >= maxfiles)) {
                  if (ppsratecheck(&lastfail, &curfail, 1)) {
                          kprintf("kern.maxfiles limit exceeded by uid %d, "
                                  "please see tuning(7).\n",
                                  cred->cr_ruid);
                  }
                  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);
          SLIST_INIT(&fp->f_klist);
          fp->f_count = 1;
          fp->f_ops = &badfileops;
          fp->f_seqcount = 1;
          fsetcred(fp, cred);
          spin_lock(&filehead_spin);
          nfiles++;
          LIST_INSERT_HEAD(&filehead, fp, f_list);
          spin_unlock(&filehead_spin);
          if (resultfd) {
                  if ((error = fdalloc(lp->lwp_proc, 0, resultfd)) != 0) {
                          fdrop(fp);
                          fp = NULL;
                  }
          } else {
                  error = 0;
          }
  done:
          *resultfp = fp;
          return (error);
  }
  
  /*
   * Check for races against a file descriptor by determining that the
   * file pointer is still associated with the specified file descriptor,
   * and a close is not currently in progress.
   *
   * MPSAFE
   */
  int
  checkfdclosed(struct filedesc *fdp, int fd, struct file *fp)
  {
          int error;
  
          spin_lock_shared(&fdp->fd_spin);
          if ((unsigned)fd >= fdp->fd_nfiles || fp != fdp->fd_files[fd].fp)
                  error = EBADF;
          else
                  error = 0;
          spin_unlock_shared(&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;
          } else {
                  fdp->fd_files[fd].reserved = 0;
                  fdreserve_locked(fdp, fd, -1);
                  fdfixup_locked(fdp, fd);
          }
  }
  
  /*
   * MPSAFE
   */
  void
  fsetfd(struct filedesc *fdp, struct file *fp, int fd)
  {
          spin_lock(&fdp->fd_spin);
          fsetfd_locked(fdp, fp, fd);
          spin_unlock(&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(&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(&fdp->fd_spin);
          return (error);
  }
  
  /*
   * MPSAFE
   */
  int
  fsetfdflags(struct filedesc *fdp, int fd, int add_flags)
  {
          int error;
  
          spin_lock(&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(&fdp->fd_spin);
          return (error);
  }
  
  /*
   * MPSAFE
   */
  int
  fclrfdflags(struct filedesc *fdp, int fd, int rem_flags)
  {
          int error;
  
          spin_lock(&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(&fdp->fd_spin);
          return (error);
  }
  
  /*
   * Set/Change/Clear the creds for a fp and synchronize the uidinfo.
   */
  void
  fsetcred(struct file *fp, struct ucred *ncr)
  {
          struct ucred *ocr;
          struct uidinfo *uip;
  
          ocr = fp->f_cred;
          if (ocr == NULL || ncr == NULL || ocr->cr_uidinfo != ncr->cr_uidinfo) {
                  if (ocr) {
                          uip = ocr->cr_uidinfo;
                          atomic_add_int(&uip->ui_openfiles, -1);
                  }
                  if (ncr) {
                          uip = ncr->cr_uidinfo;
                          atomic_add_int(&uip->ui_openfiles, 1);
                  }
          }
          if (ncr)
                  crhold(ncr);
          fp->f_cred = ncr;
          if (ocr)
                  crfree(ocr);
  }
  
  /*
   * Free a file descriptor.
   */
  static
  void
  ffree(struct file *fp)
  {
          KASSERT((fp->f_count == 0), ("ffree: fp_fcount not 0!"));
          spin_lock(&filehead_spin);
          LIST_REMOVE(fp, f_list);
          nfiles--;
          spin_unlock(&filehead_spin);
          fsetcred(fp, NULL);
          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(&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(&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_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(&fdp->fd_spin);
          fdp->fd_refcnt++;
          spin_unlock(&fdp->fd_spin);
          return (fdp);
  }
  
  /*
   * Copy a filedesc structure.
   *
   * MPSAFE
   */
  int
  fdcopy(struct proc *p, struct filedesc **fpp)
  {
          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 (0);
  
          /*
           * 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 | M_NULLOK);
          if (newfdp == NULL) {
                  *fpp = NULL;
                  return (-1);
          }
  again:
          spin_lock(&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(&fdp->fd_spin);
                  newfdp->fd_files = kmalloc(i * sizeof(struct fdnode),
                                            M_FILEDESC, M_WAITOK | M_ZERO);
  
                  /*
                   * Check for race, retry
                   */
                  spin_lock(&fdp->fd_spin);
                  if (i <= fdp->fd_lastfile) {
                          spin_unlock(&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;
          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(&fdp->fd_spin);
          *fpp = newfdp;
          return (0);
  }
  
  /*
   * 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 *repl)
  {
          struct filedesc *fdp;
          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.
           */
          fdp = p->p_fd;
          if (fdp == NULL) {
                  p->p_fd = repl;
                  return;
          }
  
          /*
           * Severe messing around to follow.
           */
          spin_lock(&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_flags & 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(&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(&fdp->fd_spin);
                          }
                  }
          retry:
                  if (fdtol->fdl_refcount == 1) {
                          if (fdp->fd_holdleaderscount > 0 &&
                              (p->p_leader->p_flags & P_ADVLOCK) != 0) {
                                  /*
                                   * close() or do_dup() has cleared a reference
                                   * in a shared file descriptor table.
                                   */
                                  fdp->fd_holdleaderswakeup = 1;
                                  ssleep(&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;
                                  ssleep(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(&fdp->fd_spin);
                          kfree(fdtol, M_FILEDESC_TO_LEADER);
                          spin_lock(&fdp->fd_spin);
                  }
          }
          if (--fdp->fd_refcnt > 0) {
                  spin_unlock(&fdp->fd_spin);
                  spin_lock(&p->p_spin);
                  p->p_fd = repl;
                  spin_unlock(&p->p_spin);
                  return;
          }
  
          /*
           * Even though we are the last reference to the structure allproc
           * scans may still reference the structure.  Maintain proper
           * locks until we can replace p->p_fd.
           *
           * Also note that kqueue's closef still needs to reference the
           * fdp via p->p_fd, so we have to close the descriptors before
           * we replace p->p_fd.
           */
          for (i = 0; i <= fdp->fd_lastfile; ++i) {
                  if (fdp->fd_files[i].fp) {
                          fp = funsetfd_locked(fdp, i);
                          if (fp) {
                                  spin_unlock(&fdp->fd_spin);
                                  if (SLIST_FIRST(&fp->f_klist))
                                          knote_fdclose(fp, fdp, i);
                                  closef(fp, p);
                                  spin_lock(&fdp->fd_spin);
                          }
                  }
          }
          spin_unlock(&fdp->fd_spin);
  
          /*
           * Interlock against an allproc scan operations (typically frevoke).
           */
          spin_lock(&p->p_spin);
          p->p_fd = repl;
          spin_unlock(&p->p_spin);
  
          /*
           * Wait for any softrefs to go away.  This race rarely occurs so
           * we can use a non-critical-path style poll/sleep loop.  The
           * race only occurs against allproc scans.
           *
           * No new softrefs can occur with the fdp disconnected from the
           * process.
           */
          if (fdp->fd_softrefs) {
                  kprintf("pid %d: Warning, fdp race avoided\n", p->p_pid);
                  while (fdp->fd_softrefs)
                          tsleep(&fdp->fd_softrefs, 0, "fdsoft", 1);
          }
  
          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);
          }
          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_shared(&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_shared(&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_shared(&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_shared(&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_shared(&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_shared(&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;
  
                          /*
                           * NULL-out descriptor prior to close to avoid
                           * a race while close blocks.
                           */
                          if ((fp = funsetfd_locked(fdp, i)) != NULL) {
                                  knote_fdclose(fp, fdp, i);
                                  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;
  
                          /*
                           * NULL-out descriptor prior to close to avoid
                           * a race while close blocks.
                           */
                          if ((fp = funsetfd_locked(fdp, i)) != NULL) {
                                  knote_fdclose(fp, fdp, i);
                                  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 lwp *lp)
  {
          struct nlookupdata nd;
          struct filedesc *fdp;
          struct file *fp;
          int retval;
          int i, error, flags, devnull;
  
          fdp = lp->lwp_proc->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(lp, &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(fdp, fp, devnull);
                          else
                                  fsetfd(fdp, 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)
          ) {
                  if ((p->p_leader->p_flags & 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) {
                          lwkt_gettoken(&p->p_token);
                          /*
                           * 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_flags &
                                       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);
                                  }
                          }
                          lwkt_reltoken(&p->p_token);
                  }
          }
          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);
  
          KKASSERT(SLIST_FIRST(&fp->f_klist) == NULL);
  
          /*
           * 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);
          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).
   *
   * MPALMOSTSAFE
   */
  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.
   */
  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.
   *
   * MPSAFE
   */
  int
  dupfdopen(struct filedesc *fdp, int dfd, int sfd, int mode, int error)
  {
          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;
                  }
                  spin_lock(&fdp->fd_spin);
                  fdp->fd_files[dfd].fileflags = fdp->fd_files[sfd].fileflags;
                  fsetfd_locked(fdp, wfp, dfd);
                  spin_unlock(&fdp->fd_spin);
                  error = 0;
                  break;
          case ENXIO:
                  /*
                   * Steal away the file pointer from dfd, and stuff it into indx.
                   */
                  spin_lock(&fdp->fd_spin);
                  fdp->fd_files[dfd].fileflags = fdp->fd_files[sfd].fileflags;
                  fsetfd(fdp, wfp, dfd);
                  if ((xfp = funsetfd_locked(fdp, sfd)) != NULL) {
                          spin_unlock(&fdp->fd_spin);
                          fdrop(xfp);
                  } else {
                          spin_unlock(&fdp->fd_spin);
                  }
                  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 | M_ZERO);
          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(&filehead_spin);
          LIST_FOREACH(fp, &filehead, f_list) {
                  res = callback(fp, data);
                  if (res < 0)
                          break;
          }
          spin_unlock(&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_ucred, p->p_ucred) != 0)
                  return(0);
  
          /*
           * Softref the fdp to prevent it from being destroyed
           */
          spin_lock(&p->p_spin);
          if ((fdp = p->p_fd) == NULL) {
                  spin_unlock(&p->p_spin);
                  return(0);
          }
          atomic_add_int(&fdp->fd_softrefs, 1);
          spin_unlock(&p->p_spin);
  
          /*
           * The fdp's own spinlock prevents the contents from being
           * modified.
           */
          spin_lock_shared(&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_shared(&fdp->fd_spin);
                          info->error = SYSCTL_OUT(info->req, &kf, sizeof(kf));
                          spin_lock_shared(&fdp->fd_spin);
                          if (info->error)
                                  break;
                  }
          }
          spin_unlock_shared(&fdp->fd_spin);
          atomic_subtract_int(&fdp->fd_softrefs, 1);
          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, OID_AUTO, minfilesperproc, CTLFLAG_RW,
      &minfilesperproc, 0, "Minimum files allowed open per process");
  SYSCTL_INT(_kern, KERN_MAXFILESPERPROC, maxfilesperproc, CTLFLAG_RW, 
      &maxfilesperproc, 0, "Maximum files allowed open per process");
  SYSCTL_INT(_kern, OID_AUTO, maxfilesperuser, CTLFLAG_RW,
      &maxfilesperuser, 0, "Maximum files allowed open per user");
  
  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;
  
          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_kqfilter = badfo_kqfilter,
          .fo_stat = badfo_stat,
          .fo_close = badfo_close,
          .fo_shutdown = badfo_shutdown
  };
  
  int
  badfo_readwrite(
          struct file *fp,
          struct uio *uio,
          struct ucred *cred,
          int flags
  ) {
          return (EBADF);
  }
  
  int
  badfo_ioctl(struct file *fp, u_long com, caddr_t data,
              struct ucred *cred, struct sysmsg *msgv)
  {
          return (EBADF);
  }
  
  /*
   * Must return an error to prevent registration, typically
   * due to a revoked descriptor (file_filtops assigned).
   */
  int
  badfo_kqfilter(struct file *fp, struct knote *kn)
  {
          return (EOPNOTSUPP);
  }
  
  /*
   * MPSAFE
   */
  int
  badfo_stat(struct file *fp, struct stat *sb, struct ucred *cred)
  {
          return (EBADF);
  }
  
  /*
   * MPSAFE
   */
  int
  badfo_close(struct file *fp)
  {
          return (EBADF);
  }
  
  /*
   * MPSAFE
   */
  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)

Cache object: 1b24b56a8c27dfe7325543408f149784