FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_descrip.c

     /*-
      * 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.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)kern_descrip.c      8.6 (Berkeley) 4/19/94
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/8.0/sys/kern/kern_descrip.c 195104 2009-06-27 13:58:44Z rwatson $");
    
    #include "opt_compat.h"
    #include "opt_ddb.h"
    #include "opt_ktrace.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    
    #include <sys/conf.h>
    #include <sys/domain.h>
    #include <sys/fcntl.h>
    #include <sys/file.h>
    #include <sys/filedesc.h>
    #include <sys/filio.h>
    #include <sys/jail.h>
    #include <sys/kernel.h>
    #include <sys/limits.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/mount.h>
    #include <sys/mqueue.h>
    #include <sys/mutex.h>
    #include <sys/namei.h>
    #include <sys/priv.h>
    #include <sys/proc.h>
    #include <sys/protosw.h>
    #include <sys/resourcevar.h>
    #include <sys/signalvar.h>
    #include <sys/socketvar.h>
    #include <sys/stat.h>
    #include <sys/sx.h>
    #include <sys/syscallsubr.h>
    #include <sys/sysctl.h>
    #include <sys/sysproto.h>
    #include <sys/tty.h>
    #include <sys/unistd.h>
    #include <sys/user.h>
    #include <sys/vnode.h>
    #ifdef KTRACE
    #include <sys/ktrace.h>
    #endif
    
    #include <security/audit/audit.h>
    
    #include <vm/uma.h>
    
    #include <ddb/ddb.h>
    
    static MALLOC_DEFINE(M_FILEDESC, "filedesc", "Open file descriptor table");
    static MALLOC_DEFINE(M_FILEDESC_TO_LEADER, "filedesc_to_leader",
                         "file desc to leader structures");
    static MALLOC_DEFINE(M_SIGIO, "sigio", "sigio structures");
    
    static uma_zone_t file_zone;
    
    
    /* Flags for do_dup() */
    #define DUP_FIXED       0x1     /* Force fixed allocation */
    #define DUP_FCNTL       0x2     /* fcntl()-style errors */
    
    static int do_dup(struct thread *td, int flags, int old, int new,
       register_t *retval);
   static int      fd_first_free(struct filedesc *, int, int);
   static int      fd_last_used(struct filedesc *, int, int);
   static void     fdgrowtable(struct filedesc *, int);
   static void     fdunused(struct filedesc *fdp, int fd);
   static void     fdused(struct filedesc *fdp, int fd);
   
   /*
    * A process is initially started out with NDFILE descriptors stored within
    * this structure, selected to be enough for typical applications based on
    * the historical limit of 20 open files (and the usage of descriptors by
    * shells).  If these descriptors are exhausted, a larger descriptor table
    * may be allocated, up to a process' resource limit; the internal arrays
    * are then unused.
    */
   #define NDFILE          20
   #define NDSLOTSIZE      sizeof(NDSLOTTYPE)
   #define NDENTRIES       (NDSLOTSIZE * __CHAR_BIT)
   #define NDSLOT(x)       ((x) / NDENTRIES)
   #define NDBIT(x)        ((NDSLOTTYPE)1 << ((x) % NDENTRIES))
   #define NDSLOTS(x)      (((x) + NDENTRIES - 1) / NDENTRIES)
   
   /*
    * Storage required per open file descriptor.
    */
   #define OFILESIZE (sizeof(struct file *) + sizeof(char))
   
   /*
    * Storage to hold unused ofiles that need to be reclaimed.
    */
   struct freetable {
           struct file     **ft_table;
           SLIST_ENTRY(freetable) ft_next;
   };
   
   /*
    * Basic allocation of descriptors:
    * one of the above, plus arrays for NDFILE descriptors.
    */
   struct filedesc0 {
           struct  filedesc fd_fd;
           /*
            * ofiles which need to be reclaimed on free.
            */
           SLIST_HEAD(,freetable) fd_free;
           /*
            * These arrays are used when the number of open files is
            * <= NDFILE, and are then pointed to by the pointers above.
            */
           struct  file *fd_dfiles[NDFILE];
           char    fd_dfileflags[NDFILE];
           NDSLOTTYPE fd_dmap[NDSLOTS(NDFILE)];
   };
   
   /*
    * Descriptor management.
    */
   volatile int openfiles;                 /* actual number of open files */
   struct mtx sigio_lock;          /* mtx to protect pointers to sigio */
   void    (*mq_fdclose)(struct thread *td, int fd, struct file *fp);
   
   /* A mutex to protect the association between a proc and filedesc. */
   static struct mtx       fdesc_mtx;
   
   /*
    * Find the first zero bit in the given bitmap, starting at low and not
    * exceeding size - 1.
    */
   static int
   fd_first_free(struct filedesc *fdp, int low, int size)
   {
           NDSLOTTYPE *map = fdp->fd_map;
           NDSLOTTYPE mask;
           int off, maxoff;
   
           if (low >= size)
                   return (low);
   
           off = NDSLOT(low);
           if (low % NDENTRIES) {
                   mask = ~(~(NDSLOTTYPE)0 >> (NDENTRIES - (low % NDENTRIES)));
                   if ((mask &= ~map[off]) != 0UL)
                           return (off * NDENTRIES + ffsl(mask) - 1);
                   ++off;
           }
           for (maxoff = NDSLOTS(size); off < maxoff; ++off)
                   if (map[off] != ~0UL)
                           return (off * NDENTRIES + ffsl(~map[off]) - 1);
           return (size);
   }
   
   /*
    * Find the highest non-zero bit in the given bitmap, starting at low and
    * not exceeding size - 1.
    */
   static int
   fd_last_used(struct filedesc *fdp, int low, int size)
   {
           NDSLOTTYPE *map = fdp->fd_map;
           NDSLOTTYPE mask;
           int off, minoff;
   
           if (low >= size)
                   return (-1);
   
           off = NDSLOT(size);
           if (size % NDENTRIES) {
                   mask = ~(~(NDSLOTTYPE)0 << (size % NDENTRIES));
                   if ((mask &= map[off]) != 0)
                           return (off * NDENTRIES + flsl(mask) - 1);
                   --off;
           }
           for (minoff = NDSLOT(low); off >= minoff; --off)
                   if (map[off] != 0)
                           return (off * NDENTRIES + flsl(map[off]) - 1);
           return (low - 1);
   }
   
   static int
   fdisused(struct filedesc *fdp, int fd)
   {
           KASSERT(fd >= 0 && fd < fdp->fd_nfiles,
               ("file descriptor %d out of range (0, %d)", fd, fdp->fd_nfiles));
           return ((fdp->fd_map[NDSLOT(fd)] & NDBIT(fd)) != 0);
   }
   
   /*
    * Mark a file descriptor as used.
    */
   static void
   fdused(struct filedesc *fdp, int fd)
   {
   
           FILEDESC_XLOCK_ASSERT(fdp);
           KASSERT(!fdisused(fdp, fd),
               ("fd already used"));
   
           fdp->fd_map[NDSLOT(fd)] |= NDBIT(fd);
           if (fd > fdp->fd_lastfile)
                   fdp->fd_lastfile = fd;
           if (fd == fdp->fd_freefile)
                   fdp->fd_freefile = fd_first_free(fdp, fd, fdp->fd_nfiles);
   }
   
   /*
    * Mark a file descriptor as unused.
    */
   static void
   fdunused(struct filedesc *fdp, int fd)
   {
   
           FILEDESC_XLOCK_ASSERT(fdp);
           KASSERT(fdisused(fdp, fd),
               ("fd is already unused"));
           KASSERT(fdp->fd_ofiles[fd] == NULL,
               ("fd is still in use"));
   
           fdp->fd_map[NDSLOT(fd)] &= ~NDBIT(fd);
           if (fd < fdp->fd_freefile)
                   fdp->fd_freefile = fd;
           if (fd == fdp->fd_lastfile)
                   fdp->fd_lastfile = fd_last_used(fdp, 0, fd);
   }
   
   /*
    * System calls on descriptors.
    */
   #ifndef _SYS_SYSPROTO_H_
   struct getdtablesize_args {
           int     dummy;
   };
   #endif
   /* ARGSUSED */
   int
   getdtablesize(struct thread *td, struct getdtablesize_args *uap)
   {
           struct proc *p = td->td_proc;
   
           PROC_LOCK(p);
           td->td_retval[0] =
               min((int)lim_cur(p, RLIMIT_NOFILE), maxfilesperproc);
           PROC_UNLOCK(p);
           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).
    */
   #ifndef _SYS_SYSPROTO_H_
   struct dup2_args {
           u_int   from;
           u_int   to;
   };
   #endif
   /* ARGSUSED */
   int
   dup2(struct thread *td, struct dup2_args *uap)
   {
   
           return (do_dup(td, DUP_FIXED, (int)uap->from, (int)uap->to,
                       td->td_retval));
   }
   
   /*
    * Duplicate a file descriptor.
    */
   #ifndef _SYS_SYSPROTO_H_
   struct dup_args {
           u_int   fd;
   };
   #endif
   /* ARGSUSED */
   int
   dup(struct thread *td, struct dup_args *uap)
   {
   
           return (do_dup(td, 0, (int)uap->fd, 0, td->td_retval));
   }
   
   /*
    * The file control system call.
    */
   #ifndef _SYS_SYSPROTO_H_
   struct fcntl_args {
           int     fd;
           int     cmd;
           long    arg;
   };
   #endif
   /* ARGSUSED */
   int
   fcntl(struct thread *td, struct fcntl_args *uap)
   {
           struct flock fl;
           struct oflock ofl;
           intptr_t arg;
           int error;
           int cmd;
   
           error = 0;
           cmd = uap->cmd;
           switch (uap->cmd) {
           case F_OGETLK:
           case F_OSETLK:
           case F_OSETLKW:
                   /*
                    * Convert old flock structure to new.
                    */
                   error = copyin((void *)(intptr_t)uap->arg, &ofl, sizeof(ofl));
                   fl.l_start = ofl.l_start;
                   fl.l_len = ofl.l_len;
                   fl.l_pid = ofl.l_pid;
                   fl.l_type = ofl.l_type;
                   fl.l_whence = ofl.l_whence;
                   fl.l_sysid = 0;
   
                   switch (uap->cmd) {
                   case F_OGETLK:
                       cmd = F_GETLK;
                       break;
                   case F_OSETLK:
                       cmd = F_SETLK;
                       break;
                   case F_OSETLKW:
                       cmd = F_SETLKW;
                       break;
                   }
                   arg = (intptr_t)&fl;
                   break;
           case F_GETLK:
           case F_SETLK:
           case F_SETLKW:
           case F_SETLK_REMOTE:
                   error = copyin((void *)(intptr_t)uap->arg, &fl, sizeof(fl));
                   arg = (intptr_t)&fl;
                   break;
           default:
                   arg = uap->arg;
                   break;
           }
           if (error)
                   return (error);
           error = kern_fcntl(td, uap->fd, cmd, arg);
           if (error)
                   return (error);
           if (uap->cmd == F_OGETLK) {
                   ofl.l_start = fl.l_start;
                   ofl.l_len = fl.l_len;
                   ofl.l_pid = fl.l_pid;
                   ofl.l_type = fl.l_type;
                   ofl.l_whence = fl.l_whence;
                   error = copyout(&ofl, (void *)(intptr_t)uap->arg, sizeof(ofl));
           } else if (uap->cmd == F_GETLK) {
                   error = copyout(&fl, (void *)(intptr_t)uap->arg, sizeof(fl));
           }
           return (error);
   }
   
   static inline struct file *
   fdtofp(int fd, struct filedesc *fdp)
   {
           struct file *fp;
   
           FILEDESC_LOCK_ASSERT(fdp);
           if ((unsigned)fd >= fdp->fd_nfiles ||
               (fp = fdp->fd_ofiles[fd]) == NULL)
                   return (NULL);
           return (fp);
   }
   
   int
   kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
   {
           struct filedesc *fdp;
           struct flock *flp;
           struct file *fp;
           struct proc *p;
           char *pop;
           struct vnode *vp;
           int error, flg, tmp;
           int vfslocked;
   
           vfslocked = 0;
           error = 0;
           flg = F_POSIX;
           p = td->td_proc;
           fdp = p->p_fd;
   
           switch (cmd) {
           case F_DUPFD:
                   tmp = arg;
                   error = do_dup(td, DUP_FCNTL, fd, tmp, td->td_retval);
                   break;
   
           case F_DUP2FD:
                   tmp = arg;
                   error = do_dup(td, DUP_FIXED, fd, tmp, td->td_retval);
                   break;
   
           case F_GETFD:
                   FILEDESC_SLOCK(fdp);
                   if ((fp = fdtofp(fd, fdp)) == NULL) {
                           FILEDESC_SUNLOCK(fdp);
                           error = EBADF;
                           break;
                   }
                   pop = &fdp->fd_ofileflags[fd];
                   td->td_retval[0] = (*pop & UF_EXCLOSE) ? FD_CLOEXEC : 0;
                   FILEDESC_SUNLOCK(fdp);
                   break;
   
           case F_SETFD:
                   FILEDESC_XLOCK(fdp);
                   if ((fp = fdtofp(fd, fdp)) == NULL) {
                           FILEDESC_XUNLOCK(fdp);
                           error = EBADF;
                           break;
                   }
                   pop = &fdp->fd_ofileflags[fd];
                   *pop = (*pop &~ UF_EXCLOSE) |
                       (arg & FD_CLOEXEC ? UF_EXCLOSE : 0);
                   FILEDESC_XUNLOCK(fdp);
                   break;
   
           case F_GETFL:
                   FILEDESC_SLOCK(fdp);
                   if ((fp = fdtofp(fd, fdp)) == NULL) {
                           FILEDESC_SUNLOCK(fdp);
                           error = EBADF;
                           break;
                   }
                   td->td_retval[0] = OFLAGS(fp->f_flag);
                   FILEDESC_SUNLOCK(fdp);
                   break;
   
           case F_SETFL:
                   FILEDESC_SLOCK(fdp);
                   if ((fp = fdtofp(fd, fdp)) == NULL) {
                           FILEDESC_SUNLOCK(fdp);
                           error = EBADF;
                           break;
                   }
                   fhold(fp);
                   FILEDESC_SUNLOCK(fdp);
                   do {
                           tmp = flg = fp->f_flag;
                           tmp &= ~FCNTLFLAGS;
                           tmp |= FFLAGS(arg & ~O_ACCMODE) & FCNTLFLAGS;
                   } while(atomic_cmpset_int(&fp->f_flag, flg, tmp) == 0);
                   tmp = fp->f_flag & FNONBLOCK;
                   error = fo_ioctl(fp, FIONBIO, &tmp, td->td_ucred, td);
                   if (error) {
                           fdrop(fp, td);
                           break;
                   }
                   tmp = fp->f_flag & FASYNC;
                   error = fo_ioctl(fp, FIOASYNC, &tmp, td->td_ucred, td);
                   if (error == 0) {
                           fdrop(fp, td);
                           break;
                   }
                   atomic_clear_int(&fp->f_flag, FNONBLOCK);
                   tmp = 0;
                   (void)fo_ioctl(fp, FIONBIO, &tmp, td->td_ucred, td);
                   fdrop(fp, td);
                   break;
   
           case F_GETOWN:
                   FILEDESC_SLOCK(fdp);
                   if ((fp = fdtofp(fd, fdp)) == NULL) {
                           FILEDESC_SUNLOCK(fdp);
                           error = EBADF;
                           break;
                   }
                   fhold(fp);
                   FILEDESC_SUNLOCK(fdp);
                   error = fo_ioctl(fp, FIOGETOWN, &tmp, td->td_ucred, td);
                   if (error == 0)
                           td->td_retval[0] = tmp;
                   fdrop(fp, td);
                   break;
   
           case F_SETOWN:
                   FILEDESC_SLOCK(fdp);
                   if ((fp = fdtofp(fd, fdp)) == NULL) {
                           FILEDESC_SUNLOCK(fdp);
                           error = EBADF;
                           break;
                   }
                   fhold(fp);
                   FILEDESC_SUNLOCK(fdp);
                   tmp = arg;
                   error = fo_ioctl(fp, FIOSETOWN, &tmp, td->td_ucred, td);
                   fdrop(fp, td);
                   break;
   
           case F_SETLK_REMOTE:
                   error = priv_check(td, PRIV_NFS_LOCKD);
                   if (error)
                           return (error);
                   flg = F_REMOTE;
                   goto do_setlk;
   
           case F_SETLKW:
                   flg |= F_WAIT;
                   /* FALLTHROUGH F_SETLK */
   
           case F_SETLK:
           do_setlk:
                   FILEDESC_SLOCK(fdp);
                   if ((fp = fdtofp(fd, fdp)) == NULL) {
                           FILEDESC_SUNLOCK(fdp);
                           error = EBADF;
                           break;
                   }
                   if (fp->f_type != DTYPE_VNODE) {
                           FILEDESC_SUNLOCK(fdp);
                           error = EBADF;
                           break;
                   }
                   flp = (struct flock *)arg;
                   if (flp->l_whence == SEEK_CUR) {
                           if (fp->f_offset < 0 ||
                               (flp->l_start > 0 &&
                                fp->f_offset > OFF_MAX - flp->l_start)) {
                                   FILEDESC_SUNLOCK(fdp);
                                   error = EOVERFLOW;
                                   break;
                           }
                           flp->l_start += fp->f_offset;
                   }
   
                   /*
                    * VOP_ADVLOCK() may block.
                    */
                   fhold(fp);
                   FILEDESC_SUNLOCK(fdp);
                   vp = fp->f_vnode;
                   vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                   switch (flp->l_type) {
                   case F_RDLCK:
                           if ((fp->f_flag & FREAD) == 0) {
                                   error = EBADF;
                                   break;
                           }
                           PROC_LOCK(p->p_leader);
                           p->p_leader->p_flag |= P_ADVLOCK;
                           PROC_UNLOCK(p->p_leader);
                           error = VOP_ADVLOCK(vp, (caddr_t)p->p_leader, F_SETLK,
                               flp, flg);
                           break;
                   case F_WRLCK:
                           if ((fp->f_flag & FWRITE) == 0) {
                                   error = EBADF;
                                   break;
                           }
                           PROC_LOCK(p->p_leader);
                           p->p_leader->p_flag |= P_ADVLOCK;
                           PROC_UNLOCK(p->p_leader);
                           error = VOP_ADVLOCK(vp, (caddr_t)p->p_leader, F_SETLK,
                               flp, flg);
                           break;
                   case F_UNLCK:
                           error = VOP_ADVLOCK(vp, (caddr_t)p->p_leader, F_UNLCK,
                               flp, flg);
                           break;
                   case F_UNLCKSYS:
                           /*
                            * Temporary api for testing remote lock
                            * infrastructure.
                            */
                           if (flg != F_REMOTE) {
                                   error = EINVAL;
                                   break;
                           }
                           error = VOP_ADVLOCK(vp, (caddr_t)p->p_leader,
                               F_UNLCKSYS, flp, flg);
                           break;
                   default:
                           error = EINVAL;
                           break;
                   }
                   VFS_UNLOCK_GIANT(vfslocked);
                   vfslocked = 0;
                   /* Check for race with close */
                   FILEDESC_SLOCK(fdp);
                   if ((unsigned) fd >= fdp->fd_nfiles ||
                       fp != fdp->fd_ofiles[fd]) {
                           FILEDESC_SUNLOCK(fdp);
                           flp->l_whence = SEEK_SET;
                           flp->l_start = 0;
                           flp->l_len = 0;
                           flp->l_type = F_UNLCK;
                           vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                           (void) VOP_ADVLOCK(vp, (caddr_t)p->p_leader,
                                              F_UNLCK, flp, F_POSIX);
                           VFS_UNLOCK_GIANT(vfslocked);
                           vfslocked = 0;
                   } else
                           FILEDESC_SUNLOCK(fdp);
                   fdrop(fp, td);
                   break;
   
           case F_GETLK:
                   FILEDESC_SLOCK(fdp);
                   if ((fp = fdtofp(fd, fdp)) == NULL) {
                           FILEDESC_SUNLOCK(fdp);
                           error = EBADF;
                           break;
                   }
                   if (fp->f_type != DTYPE_VNODE) {
                           FILEDESC_SUNLOCK(fdp);
                           error = EBADF;
                           break;
                   }
                   flp = (struct flock *)arg;
                   if (flp->l_type != F_RDLCK && flp->l_type != F_WRLCK &&
                       flp->l_type != F_UNLCK) {
                           FILEDESC_SUNLOCK(fdp);
                           error = EINVAL;
                           break;
                   }
                   if (flp->l_whence == SEEK_CUR) {
                           if ((flp->l_start > 0 &&
                               fp->f_offset > OFF_MAX - flp->l_start) ||
                               (flp->l_start < 0 &&
                                fp->f_offset < OFF_MIN - flp->l_start)) {
                                   FILEDESC_SUNLOCK(fdp);
                                   error = EOVERFLOW;
                                   break;
                           }
                           flp->l_start += fp->f_offset;
                   }
                   /*
                    * VOP_ADVLOCK() may block.
                    */
                   fhold(fp);
                   FILEDESC_SUNLOCK(fdp);
                   vp = fp->f_vnode;
                   vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                   error = VOP_ADVLOCK(vp, (caddr_t)p->p_leader, F_GETLK, flp,
                       F_POSIX);
                   VFS_UNLOCK_GIANT(vfslocked);
                   vfslocked = 0;
                   fdrop(fp, td);
                   break;
           default:
                   error = EINVAL;
                   break;
           }
           VFS_UNLOCK_GIANT(vfslocked);
           return (error);
   }
   
   /*
    * Common code for dup, dup2, fcntl(F_DUPFD) and fcntl(F_DUP2FD).
    */
   static int
   do_dup(struct thread *td, int flags, int old, int new,
       register_t *retval)
   {
           struct filedesc *fdp;
           struct proc *p;
           struct file *fp;
           struct file *delfp;
           int error, holdleaders, maxfd;
   
           p = td->td_proc;
           fdp = p->p_fd;
   
           /*
            * Verify we have a valid descriptor to dup from and possibly to
            * dup to. Unlike dup() and dup2(), fcntl()'s F_DUPFD should
            * return EINVAL when the new descriptor is out of bounds.
            */
           if (old < 0)
                   return (EBADF);
           if (new < 0)
                   return (flags & DUP_FCNTL ? EINVAL : EBADF);
           PROC_LOCK(p);
           maxfd = min((int)lim_cur(p, RLIMIT_NOFILE), maxfilesperproc);
           PROC_UNLOCK(p);
           if (new >= maxfd)
                   return (flags & DUP_FCNTL ? EINVAL : EMFILE);
   
           FILEDESC_XLOCK(fdp);
           if (old >= fdp->fd_nfiles || fdp->fd_ofiles[old] == NULL) {
                   FILEDESC_XUNLOCK(fdp);
                   return (EBADF);
           }
           if (flags & DUP_FIXED && old == new) {
                   *retval = new;
                   FILEDESC_XUNLOCK(fdp);
                   return (0);
           }
           fp = fdp->fd_ofiles[old];
           fhold(fp);
   
           /*
            * If the caller specified a file descriptor, make sure the file
            * table is large enough to hold it, and grab it.  Otherwise, just
            * allocate a new descriptor the usual way.  Since the filedesc
            * lock may be temporarily dropped in the process, we have to look
            * out for a race.
            */
           if (flags & DUP_FIXED) {
                   if (new >= fdp->fd_nfiles)
                           fdgrowtable(fdp, new + 1);
                   if (fdp->fd_ofiles[new] == NULL)
                           fdused(fdp, new);
           } else {
                   if ((error = fdalloc(td, new, &new)) != 0) {
                           FILEDESC_XUNLOCK(fdp);
                           fdrop(fp, td);
                           return (error);
                   }
           }
   
           /*
            * If the old file changed out from under us then treat it as a
            * bad file descriptor.  Userland should do its own locking to
            * avoid this case.
            */
           if (fdp->fd_ofiles[old] != fp) {
                   /* we've allocated a descriptor which we won't use */
                   if (fdp->fd_ofiles[new] == NULL)
                           fdunused(fdp, new);
                   FILEDESC_XUNLOCK(fdp);
                   fdrop(fp, td);
                   return (EBADF);
           }
           KASSERT(old != new,
               ("new fd is same as old"));
   
           /*
            * Save info on the descriptor being overwritten.  We cannot close
            * it without introducing an ownership race for the slot, since we
            * need to drop the filedesc lock to call closef().
            *
            * XXX this duplicates parts of close().
            */
           delfp = fdp->fd_ofiles[new];
           holdleaders = 0;
           if (delfp != NULL) {
                   if (td->td_proc->p_fdtol != NULL) {
                           /*
                            * Ask fdfree() to sleep to ensure that all relevant
                            * process leaders can be traversed in closef().
                            */
                           fdp->fd_holdleaderscount++;
                           holdleaders = 1;
                   }
           }
   
           /*
            * Duplicate the source descriptor
            */
           fdp->fd_ofiles[new] = fp;
           fdp->fd_ofileflags[new] = fdp->fd_ofileflags[old] &~ UF_EXCLOSE;
           if (new > fdp->fd_lastfile)
                   fdp->fd_lastfile = new;
           *retval = 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).
            *
            * XXX this duplicates parts of close().
            */
           if (delfp != NULL) {
                   knote_fdclose(td, new);
                   if (delfp->f_type == DTYPE_MQUEUE)
                           mq_fdclose(td, new, delfp);
                   FILEDESC_XUNLOCK(fdp);
                   (void) closef(delfp, td);
                   if (holdleaders) {
                           FILEDESC_XLOCK(fdp);
                           fdp->fd_holdleaderscount--;
                           if (fdp->fd_holdleaderscount == 0 &&
                               fdp->fd_holdleaderswakeup != 0) {
                                   fdp->fd_holdleaderswakeup = 0;
                                   wakeup(&fdp->fd_holdleaderscount);
                           }
                           FILEDESC_XUNLOCK(fdp);
                   }
           } else {
                   FILEDESC_XUNLOCK(fdp);
           }
           return (0);
   }
   
   /*
    * If sigio is on the list associated with a process or process group,
    * disable signalling from the device, remove sigio from the list and
    * free sigio.
    */
   void
   funsetown(struct sigio **sigiop)
   {
           struct sigio *sigio;
   
           SIGIO_LOCK();
           sigio = *sigiop;
           if (sigio == NULL) {
                   SIGIO_UNLOCK();
                   return;
           }
           *(sigio->sio_myref) = NULL;
           if ((sigio)->sio_pgid < 0) {
                   struct pgrp *pg = (sigio)->sio_pgrp;
                   PGRP_LOCK(pg);
                   SLIST_REMOVE(&sigio->sio_pgrp->pg_sigiolst, sigio,
                                sigio, sio_pgsigio);
                   PGRP_UNLOCK(pg);
           } else {
                   struct proc *p = (sigio)->sio_proc;
                   PROC_LOCK(p);
                   SLIST_REMOVE(&sigio->sio_proc->p_sigiolst, sigio,
                                sigio, sio_pgsigio);
                   PROC_UNLOCK(p);
           }
           SIGIO_UNLOCK();
           crfree(sigio->sio_ucred);
           free(sigio, M_SIGIO);
   }
   
   /*
    * Free a list of sigio structures.
    * We only need to lock the SIGIO_LOCK because we have made ourselves
    * inaccessible to callers of fsetown and therefore do not need to lock
    * the proc or pgrp struct for the list manipulation.
    */
   void
   funsetownlst(struct sigiolst *sigiolst)
   {
           struct proc *p;
           struct pgrp *pg;
           struct sigio *sigio;
   
           sigio = SLIST_FIRST(sigiolst);
           if (sigio == NULL)
                   return;
           p = NULL;
           pg = NULL;
   
           /*
            * Every entry of the list should belong
            * to a single proc or pgrp.
            */
           if (sigio->sio_pgid < 0) {
                   pg = sigio->sio_pgrp;
                   PGRP_LOCK_ASSERT(pg, MA_NOTOWNED);
           } else /* if (sigio->sio_pgid > 0) */ {
                   p = sigio->sio_proc;
                   PROC_LOCK_ASSERT(p, MA_NOTOWNED);
           }
   
           SIGIO_LOCK();
           while ((sigio = SLIST_FIRST(sigiolst)) != NULL) {
                   *(sigio->sio_myref) = NULL;
                   if (pg != NULL) {
                           KASSERT(sigio->sio_pgid < 0,
                               ("Proc sigio in pgrp sigio list"));
                           KASSERT(sigio->sio_pgrp == pg,
                               ("Bogus pgrp in sigio list"));
                           PGRP_LOCK(pg);
                           SLIST_REMOVE(&pg->pg_sigiolst, sigio, sigio,
                               sio_pgsigio);
                           PGRP_UNLOCK(pg);
                   } else /* if (p != NULL) */ {
                           KASSERT(sigio->sio_pgid > 0,
                               ("Pgrp sigio in proc sigio list"));
                           KASSERT(sigio->sio_proc == p,
                               ("Bogus proc in sigio list"));
                           PROC_LOCK(p);
                           SLIST_REMOVE(&p->p_sigiolst, sigio, sigio,
                               sio_pgsigio);
                           PROC_UNLOCK(p);
                   }
                   SIGIO_UNLOCK();
                   crfree(sigio->sio_ucred);
                   free(sigio, M_SIGIO);
                   SIGIO_LOCK();
           }
           SIGIO_UNLOCK();
   }
   
   /*
    * This is common code for FIOSETOWN ioctl called by fcntl(fd, F_SETOWN, arg).
    *
    * After permission checking, add a sigio structure to the sigio list for
    * the process or process group.
    */
   int
   fsetown(pid_t pgid, struct sigio **sigiop)
   {
           struct proc *proc;
           struct pgrp *pgrp;
           struct sigio *sigio;
           int ret;
   
           if (pgid == 0) {
                   funsetown(sigiop);
                   return (0);
           }
   
           ret = 0;
   
           /* Allocate and fill in the new sigio out of locks. */
           sigio = malloc(sizeof(struct sigio), M_SIGIO, M_WAITOK);
           sigio->sio_pgid = pgid;
           sigio->sio_ucred = crhold(curthread->td_ucred);
           sigio->sio_myref = sigiop;
   
           sx_slock(&proctree_lock);
           if (pgid > 0) {
                   proc = pfind(pgid);
                   if (proc == NULL) {
                           ret = ESRCH;
                           goto fail;
                   }
   
                   /*
                    * 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.
                    */
                   PROC_UNLOCK(proc);
                   if (proc->p_session != curthread->td_proc->p_session) {
                           ret = EPERM;
                           goto fail;
                   }
   
                   pgrp = NULL;
           } else /* if (pgid < 0) */ {
                   pgrp = pgfind(-pgid);
                   if (pgrp == NULL) {
                           ret = ESRCH;
                           goto fail;
                   }
                   PGRP_UNLOCK(pgrp);
   
                   /*
                    * 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 != curthread->td_proc->p_session) {
                           ret = EPERM;
                           goto fail;
                  }
  
                  proc = NULL;
          }
          funsetown(sigiop);
          if (pgid > 0) {
                  PROC_LOCK(proc);
                  /*
                   * Since funsetownlst() is called without the proctree
                   * locked, we need to check for P_WEXIT.
                   * XXX: is ESRCH correct?
                   */
                  if ((proc->p_flag & P_WEXIT) != 0) {
                          PROC_UNLOCK(proc);
                          ret = ESRCH;
                          goto fail;
                  }
                  SLIST_INSERT_HEAD(&proc->p_sigiolst, sigio, sio_pgsigio);
                  sigio->sio_proc = proc;
                  PROC_UNLOCK(proc);
          } else {
                  PGRP_LOCK(pgrp);
                  SLIST_INSERT_HEAD(&pgrp->pg_sigiolst, sigio, sio_pgsigio);
                  sigio->sio_pgrp = pgrp;
                  PGRP_UNLOCK(pgrp);
          }
          sx_sunlock(&proctree_lock);
          SIGIO_LOCK();
          *sigiop = sigio;
          SIGIO_UNLOCK();
          return (0);
  
  fail:
          sx_sunlock(&proctree_lock);
          crfree(sigio->sio_ucred);
          free(sigio, M_SIGIO);
          return (ret);
  }
  
  /*
   * This is common code for FIOGETOWN ioctl called by fcntl(fd, F_GETOWN, arg).
   */
  pid_t
  fgetown(sigiop)
          struct sigio **sigiop;
  {
          pid_t pgid;
  
          SIGIO_LOCK();
          pgid = (*sigiop != NULL) ? (*sigiop)->sio_pgid : 0;
          SIGIO_UNLOCK();
          return (pgid);
  }
  
  /*
   * Close a file descriptor.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct close_args {
          int     fd;
  };
  #endif
  /* ARGSUSED */
  int
  close(td, uap)
          struct thread *td;
          struct close_args *uap;
  {
  
          return (kern_close(td, uap->fd));
  }
  
  int
  kern_close(td, fd)
          struct thread *td;
          int fd;
  {
          struct filedesc *fdp;
          struct file *fp;
          int error;
          int holdleaders;
  
          error = 0;
          holdleaders = 0;
          fdp = td->td_proc->p_fd;
  
          AUDIT_SYSCLOSE(td, fd);
  
          FILEDESC_XLOCK(fdp);
          if ((unsigned)fd >= fdp->fd_nfiles ||
              (fp = fdp->fd_ofiles[fd]) == NULL) {
                  FILEDESC_XUNLOCK(fdp);
                  return (EBADF);
          }
          fdp->fd_ofiles[fd] = NULL;
          fdp->fd_ofileflags[fd] = 0;
          fdunused(fdp, fd);
          if (td->td_proc->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.  We have to unlock the FILEDESC *AFTER*
           * knote_fdclose to prevent a race of the fd getting opened, a knote
           * added, and deleteing a knote for the new fd.
           */
          knote_fdclose(td, fd);
          if (fp->f_type == DTYPE_MQUEUE)
                  mq_fdclose(td, fd, fp);
          FILEDESC_XUNLOCK(fdp);
  
          error = closef(fp, td);
          if (holdleaders) {
                  FILEDESC_XLOCK(fdp);
                  fdp->fd_holdleaderscount--;
                  if (fdp->fd_holdleaderscount == 0 &&
                      fdp->fd_holdleaderswakeup != 0) {
                          fdp->fd_holdleaderswakeup = 0;
                          wakeup(&fdp->fd_holdleaderscount);
                  }
                  FILEDESC_XUNLOCK(fdp);
          }
          return (error);
  }
  
  /*
   * Close open file descriptors.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct closefrom_args {
          int     lowfd;
  };
  #endif
  /* ARGSUSED */
  int
  closefrom(struct thread *td, struct closefrom_args *uap)
  {
          struct filedesc *fdp;
          int fd;
  
          fdp = td->td_proc->p_fd;
          AUDIT_ARG_FD(uap->lowfd);
  
          /*
           * Treat negative starting file descriptor values identical to
           * closefrom(0) which closes all files.
           */
          if (uap->lowfd < 0)
                  uap->lowfd = 0;
          FILEDESC_SLOCK(fdp);
          for (fd = uap->lowfd; fd < fdp->fd_nfiles; fd++) {
                  if (fdp->fd_ofiles[fd] != NULL) {
                          FILEDESC_SUNLOCK(fdp);
                          (void)kern_close(td, fd);
                          FILEDESC_SLOCK(fdp);
                  }
          }
          FILEDESC_SUNLOCK(fdp);
          return (0);
  }
  
  #if defined(COMPAT_43)
  /*
   * Return status information about a file descriptor.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct ofstat_args {
          int     fd;
          struct  ostat *sb;
  };
  #endif
  /* ARGSUSED */
  int
  ofstat(struct thread *td, struct ofstat_args *uap)
  {
          struct ostat oub;
          struct stat ub;
          int error;
  
          error = kern_fstat(td, uap->fd, &ub);
          if (error == 0) {
                  cvtstat(&ub, &oub);
                  error = copyout(&oub, uap->sb, sizeof(oub));
          }
          return (error);
  }
  #endif /* COMPAT_43 */
  
  /*
   * Return status information about a file descriptor.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct fstat_args {
          int     fd;
          struct  stat *sb;
  };
  #endif
  /* ARGSUSED */
  int
  fstat(struct thread *td, struct fstat_args *uap)
  {
          struct stat ub;
          int error;
  
          error = kern_fstat(td, uap->fd, &ub);
          if (error == 0)
                  error = copyout(&ub, uap->sb, sizeof(ub));
          return (error);
  }
  
  int
  kern_fstat(struct thread *td, int fd, struct stat *sbp)
  {
          struct file *fp;
          int error;
  
          AUDIT_ARG_FD(fd);
  
          if ((error = fget(td, fd, &fp)) != 0)
                  return (error);
  
          AUDIT_ARG_FILE(td->td_proc, fp);
  
          error = fo_stat(fp, sbp, td->td_ucred, td);
          fdrop(fp, td);
  #ifdef KTRACE
          if (error == 0 && KTRPOINT(td, KTR_STRUCT))
                  ktrstat(sbp);
  #endif
          return (error);
  }
  
  /*
   * Return status information about a file descriptor.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct nfstat_args {
          int     fd;
          struct  nstat *sb;
  };
  #endif
  /* ARGSUSED */
  int
  nfstat(struct thread *td, struct nfstat_args *uap)
  {
          struct nstat nub;
          struct stat ub;
          int error;
  
          error = kern_fstat(td, uap->fd, &ub);
          if (error == 0) {
                  cvtnstat(&ub, &nub);
                  error = copyout(&nub, uap->sb, sizeof(nub));
          }
          return (error);
  }
  
  /*
   * Return pathconf information about a file descriptor.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct fpathconf_args {
          int     fd;
          int     name;
  };
  #endif
  /* ARGSUSED */
  int
  fpathconf(struct thread *td, struct fpathconf_args *uap)
  {
          struct file *fp;
          struct vnode *vp;
          int error;
  
          if ((error = fget(td, uap->fd, &fp)) != 0)
                  return (error);
  
          /* If asynchronous I/O is available, it works for all descriptors. */
          if (uap->name == _PC_ASYNC_IO) {
                  td->td_retval[0] = async_io_version;
                  goto out;
          }
          vp = fp->f_vnode;
          if (vp != NULL) {
                  int vfslocked;
                  vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                  vn_lock(vp, LK_SHARED | LK_RETRY);
                  error = VOP_PATHCONF(vp, uap->name, td->td_retval);
                  VOP_UNLOCK(vp, 0);
                  VFS_UNLOCK_GIANT(vfslocked);
          } else if (fp->f_type == DTYPE_PIPE || fp->f_type == DTYPE_SOCKET) {
                  if (uap->name != _PC_PIPE_BUF) {
                          error = EINVAL;
                  } else {
                          td->td_retval[0] = PIPE_BUF;
                  error = 0;
                  }
          } else {
                  error = EOPNOTSUPP;
          }
  out:
          fdrop(fp, td);
          return (error);
  }
  
  /*
   * Grow the file table to accomodate (at least) nfd descriptors.  This may
   * block and drop the filedesc lock, but it will reacquire it before
   * returning.
   */
  static void
  fdgrowtable(struct filedesc *fdp, int nfd)
  {
          struct filedesc0 *fdp0;
          struct freetable *fo;
          struct file **ntable;
          struct file **otable;
          char *nfileflags;
          int nnfiles, onfiles;
          NDSLOTTYPE *nmap;
  
          FILEDESC_XLOCK_ASSERT(fdp);
  
          KASSERT(fdp->fd_nfiles > 0,
              ("zero-length file table"));
  
          /* compute the size of the new table */
          onfiles = fdp->fd_nfiles;
          nnfiles = NDSLOTS(nfd) * NDENTRIES; /* round up */
          if (nnfiles <= onfiles)
                  /* the table is already large enough */
                  return;
  
          /* allocate a new table and (if required) new bitmaps */
          FILEDESC_XUNLOCK(fdp);
          ntable = malloc((nnfiles * OFILESIZE) + sizeof(struct freetable),
              M_FILEDESC, M_ZERO | M_WAITOK);
          nfileflags = (char *)&ntable[nnfiles];
          if (NDSLOTS(nnfiles) > NDSLOTS(onfiles))
                  nmap = malloc(NDSLOTS(nnfiles) * NDSLOTSIZE,
                      M_FILEDESC, M_ZERO | M_WAITOK);
          else
                  nmap = NULL;
          FILEDESC_XLOCK(fdp);
  
          /*
           * We now have new tables ready to go.  Since we dropped the
           * filedesc lock to call malloc(), watch out for a race.
           */
          onfiles = fdp->fd_nfiles;
          if (onfiles >= nnfiles) {
                  /* we lost the race, but that's OK */
                  free(ntable, M_FILEDESC);
                  if (nmap != NULL)
                          free(nmap, M_FILEDESC);
                  return;
          }
          bcopy(fdp->fd_ofiles, ntable, onfiles * sizeof(*ntable));
          bcopy(fdp->fd_ofileflags, nfileflags, onfiles);
          otable = fdp->fd_ofiles;
          fdp->fd_ofileflags = nfileflags;
          fdp->fd_ofiles = ntable;
          /*
           * We must preserve ofiles until the process exits because we can't
           * be certain that no threads have references to the old table via
           * _fget().
           */
          if (onfiles > NDFILE) {
                  fo = (struct freetable *)&otable[onfiles];
                  fdp0 = (struct filedesc0 *)fdp;
                  fo->ft_table = otable;
                  SLIST_INSERT_HEAD(&fdp0->fd_free, fo, ft_next);
          }
          if (NDSLOTS(nnfiles) > NDSLOTS(onfiles)) {
                  bcopy(fdp->fd_map, nmap, NDSLOTS(onfiles) * sizeof(*nmap));
                  if (NDSLOTS(onfiles) > NDSLOTS(NDFILE))
                          free(fdp->fd_map, M_FILEDESC);
                  fdp->fd_map = nmap;
          }
          fdp->fd_nfiles = nnfiles;
  }
  
  /*
   * Allocate a file descriptor for the process.
   */
  int
  fdalloc(struct thread *td, int minfd, int *result)
  {
          struct proc *p = td->td_proc;
          struct filedesc *fdp = p->p_fd;
          int fd = -1, maxfd;
  
          FILEDESC_XLOCK_ASSERT(fdp);
  
          if (fdp->fd_freefile > minfd)
                  minfd = fdp->fd_freefile;          
  
          PROC_LOCK(p);
          maxfd = min((int)lim_cur(p, RLIMIT_NOFILE), maxfilesperproc);
          PROC_UNLOCK(p);
  
          /*
           * Search the bitmap for a free descriptor.  If none is found, try
           * to grow the file table.  Keep at it until we either get a file
           * descriptor or run into process or system limits; fdgrowtable()
           * may drop the filedesc lock, so we're in a race.
           */
          for (;;) {
                  fd = fd_first_free(fdp, minfd, fdp->fd_nfiles);
                  if (fd >= maxfd)
                          return (EMFILE);
                  if (fd < fdp->fd_nfiles)
                          break;
                  fdgrowtable(fdp, min(fdp->fd_nfiles * 2, maxfd));
          }
  
          /*
           * Perform some sanity checks, then mark the file descriptor as
           * used and return it to the caller.
           */
          KASSERT(!fdisused(fdp, fd),
              ("fd_first_free() returned non-free descriptor"));
          KASSERT(fdp->fd_ofiles[fd] == NULL,
              ("free descriptor isn't"));
          fdp->fd_ofileflags[fd] = 0; /* XXX needed? */
          fdused(fdp, fd);
          *result = fd;
          return (0);
  }
  
  /*
   * Check to see whether n user file descriptors are available to the process
   * p.
   */
  int
  fdavail(struct thread *td, int n)
  {
          struct proc *p = td->td_proc;
          struct filedesc *fdp = td->td_proc->p_fd;
          struct file **fpp;
          int i, lim, last;
  
          FILEDESC_LOCK_ASSERT(fdp);
  
          PROC_LOCK(p);
          lim = min((int)lim_cur(p, RLIMIT_NOFILE), maxfilesperproc);
          PROC_UNLOCK(p);
          if ((i = lim - fdp->fd_nfiles) > 0 && (n -= i) <= 0)
                  return (1);
          last = min(fdp->fd_nfiles, lim);
          fpp = &fdp->fd_ofiles[fdp->fd_freefile];
          for (i = last - fdp->fd_freefile; --i >= 0; fpp++) {
                  if (*fpp == NULL && --n <= 0)
                          return (1);
          }
          return (0);
  }
  
  /*
   * Create a new open file structure and allocate a file decriptor for the
   * process that refers to it.  We add one reference to the file for the
   * descriptor table and one reference for resultfp. This is to prevent us
   * being preempted and the entry in the descriptor table closed after we
   * release the FILEDESC lock.
   */
  int
  falloc(struct thread *td, struct file **resultfp, int *resultfd)
  {
          struct proc *p = td->td_proc;
          struct file *fp;
          int error, i;
          int maxuserfiles = maxfiles - (maxfiles / 20);
          static struct timeval lastfail;
          static int curfail;
  
          fp = uma_zalloc(file_zone, M_WAITOK | M_ZERO);
          if ((openfiles >= maxuserfiles &&
              priv_check(td, PRIV_MAXFILES) != 0) ||
              openfiles >= maxfiles) {
                  if (ppsratecheck(&lastfail, &curfail, 1)) {
                          printf("kern.maxfiles limit exceeded by uid %i, please see tuning(7).\n",
                                  td->td_ucred->cr_ruid);
                  }
                  uma_zfree(file_zone, fp);
                  return (ENFILE);
          }
          atomic_add_int(&openfiles, 1);
  
          /*
           * If the process has file descriptor zero open, add the new file
           * descriptor to the list of open files at that point, otherwise
           * put it at the front of the list of open files.
           */
          refcount_init(&fp->f_count, 1);
          if (resultfp)
                  fhold(fp);
          fp->f_cred = crhold(td->td_ucred);
          fp->f_ops = &badfileops;
          fp->f_data = NULL;
          fp->f_vnode = NULL;
          FILEDESC_XLOCK(p->p_fd);
          if ((error = fdalloc(td, 0, &i))) {
                  FILEDESC_XUNLOCK(p->p_fd);
                  fdrop(fp, td);
                  if (resultfp)
                          fdrop(fp, td);
                  return (error);
          }
          p->p_fd->fd_ofiles[i] = fp;
          FILEDESC_XUNLOCK(p->p_fd);
          if (resultfp)
                  *resultfp = fp;
          if (resultfd)
                  *resultfd = i;
          return (0);
  }
  
  /*
   * Build a new filedesc structure from another.
   * Copy the current, root, and jail root vnode references.
   */
  struct filedesc *
  fdinit(struct filedesc *fdp)
  {
          struct filedesc0 *newfdp;
  
          newfdp = malloc(sizeof *newfdp, M_FILEDESC, M_WAITOK | M_ZERO);
          FILEDESC_LOCK_INIT(&newfdp->fd_fd);
          if (fdp != NULL) {
                  FILEDESC_XLOCK(fdp);
                  newfdp->fd_fd.fd_cdir = fdp->fd_cdir;
                  if (newfdp->fd_fd.fd_cdir)
                          VREF(newfdp->fd_fd.fd_cdir);
                  newfdp->fd_fd.fd_rdir = fdp->fd_rdir;
                  if (newfdp->fd_fd.fd_rdir)
                          VREF(newfdp->fd_fd.fd_rdir);
                  newfdp->fd_fd.fd_jdir = fdp->fd_jdir;
                  if (newfdp->fd_fd.fd_jdir)
                          VREF(newfdp->fd_fd.fd_jdir);
                  FILEDESC_XUNLOCK(fdp);
          }
  
          /* Create the file descriptor table. */
          newfdp->fd_fd.fd_refcnt = 1;
          newfdp->fd_fd.fd_holdcnt = 1;
          newfdp->fd_fd.fd_cmask = CMASK;
          newfdp->fd_fd.fd_ofiles = newfdp->fd_dfiles;
          newfdp->fd_fd.fd_ofileflags = newfdp->fd_dfileflags;
          newfdp->fd_fd.fd_nfiles = NDFILE;
          newfdp->fd_fd.fd_map = newfdp->fd_dmap;
          newfdp->fd_fd.fd_lastfile = -1;
          return (&newfdp->fd_fd);
  }
  
  static struct filedesc *
  fdhold(struct proc *p)
  {
          struct filedesc *fdp;
  
          mtx_lock(&fdesc_mtx);
          fdp = p->p_fd;
          if (fdp != NULL)
                  fdp->fd_holdcnt++;
          mtx_unlock(&fdesc_mtx);
          return (fdp);
  }
  
  static void
  fddrop(struct filedesc *fdp)
  {
          struct filedesc0 *fdp0;
          struct freetable *ft;
          int i;
  
          mtx_lock(&fdesc_mtx);
          i = --fdp->fd_holdcnt;
          mtx_unlock(&fdesc_mtx);
          if (i > 0)
                  return;
  
          FILEDESC_LOCK_DESTROY(fdp);
          fdp0 = (struct filedesc0 *)fdp;
          while ((ft = SLIST_FIRST(&fdp0->fd_free)) != NULL) {
                  SLIST_REMOVE_HEAD(&fdp0->fd_free, ft_next);
                  free(ft->ft_table, M_FILEDESC);
          }
          free(fdp, M_FILEDESC);
  }
  
  /*
   * Share a filedesc structure.
   */
  struct filedesc *
  fdshare(struct filedesc *fdp)
  {
  
          FILEDESC_XLOCK(fdp);
          fdp->fd_refcnt++;
          FILEDESC_XUNLOCK(fdp);
          return (fdp);
  }
  
  /*
   * Unshare a filedesc structure, if necessary by making a copy
   */
  void
  fdunshare(struct proc *p, struct thread *td)
  {
  
          FILEDESC_XLOCK(p->p_fd);
          if (p->p_fd->fd_refcnt > 1) {
                  struct filedesc *tmp;
  
                  FILEDESC_XUNLOCK(p->p_fd);
                  tmp = fdcopy(p->p_fd);
                  fdfree(td);
                  p->p_fd = tmp;
          } else
                  FILEDESC_XUNLOCK(p->p_fd);
  }
  
  /*
   * Copy a filedesc structure.  A NULL pointer in returns a NULL reference,
   * this is to ease callers, not catch errors.
   */
  struct filedesc *
  fdcopy(struct filedesc *fdp)
  {
          struct filedesc *newfdp;
          int i;
  
          /* Certain daemons might not have file descriptors. */
          if (fdp == NULL)
                  return (NULL);
  
          newfdp = fdinit(fdp);
          FILEDESC_SLOCK(fdp);
          while (fdp->fd_lastfile >= newfdp->fd_nfiles) {
                  FILEDESC_SUNLOCK(fdp);
                  FILEDESC_XLOCK(newfdp);
                  fdgrowtable(newfdp, fdp->fd_lastfile + 1);
                  FILEDESC_XUNLOCK(newfdp);
                  FILEDESC_SLOCK(fdp);
          }
          /* copy everything except kqueue descriptors */
          newfdp->fd_freefile = -1;
          for (i = 0; i <= fdp->fd_lastfile; ++i) {
                  if (fdisused(fdp, i) &&
                      fdp->fd_ofiles[i]->f_type != DTYPE_KQUEUE &&
                      fdp->fd_ofiles[i]->f_ops != &badfileops) {
                          newfdp->fd_ofiles[i] = fdp->fd_ofiles[i];
                          newfdp->fd_ofileflags[i] = fdp->fd_ofileflags[i];
                          fhold(newfdp->fd_ofiles[i]);
                          newfdp->fd_lastfile = i;
                  } else {
                          if (newfdp->fd_freefile == -1)
                                  newfdp->fd_freefile = i;
                  }
          }
          newfdp->fd_cmask = fdp->fd_cmask;
          FILEDESC_SUNLOCK(fdp);
          FILEDESC_XLOCK(newfdp);
          for (i = 0; i <= newfdp->fd_lastfile; ++i)
                  if (newfdp->fd_ofiles[i] != NULL)
                          fdused(newfdp, i);
          if (newfdp->fd_freefile == -1)
                  newfdp->fd_freefile = i;
          FILEDESC_XUNLOCK(newfdp);
          return (newfdp);
  }
  
  /*
   * Release a filedesc structure.
   */
  void
  fdfree(struct thread *td)
  {
          struct filedesc *fdp;
          struct file **fpp;
          int i, locked;
          struct filedesc_to_leader *fdtol;
          struct file *fp;
          struct vnode *cdir, *jdir, *rdir, *vp;
          struct flock lf;
  
          /* Certain daemons might not have file descriptors. */
          fdp = td->td_proc->p_fd;
          if (fdp == NULL)
                  return;
  
          /* Check for special need to clear POSIX style locks */
          fdtol = td->td_proc->p_fdtol;
          if (fdtol != NULL) {
                  FILEDESC_XLOCK(fdp);
                  KASSERT(fdtol->fdl_refcount > 0,
                          ("filedesc_to_refcount botch: fdl_refcount=%d",
                           fdtol->fdl_refcount));
                  if (fdtol->fdl_refcount == 1 &&
                      (td->td_proc->p_leader->p_flag & P_ADVLOCK) != 0) {
                          for (i = 0, fpp = fdp->fd_ofiles;
                               i <= fdp->fd_lastfile;
                               i++, fpp++) {
                                  if (*fpp == NULL ||
                                      (*fpp)->f_type != DTYPE_VNODE)
                                          continue;
                                  fp = *fpp;
                                  fhold(fp);
                                  FILEDESC_XUNLOCK(fdp);
                                  lf.l_whence = SEEK_SET;
                                  lf.l_start = 0;
                                  lf.l_len = 0;
                                  lf.l_type = F_UNLCK;
                                  vp = fp->f_vnode;
                                  locked = VFS_LOCK_GIANT(vp->v_mount);
                                  (void) VOP_ADVLOCK(vp,
                                                     (caddr_t)td->td_proc->
                                                     p_leader,
                                                     F_UNLCK,
                                                     &lf,
                                                     F_POSIX);
                                  VFS_UNLOCK_GIANT(locked);
                                  FILEDESC_XLOCK(fdp);
                                  fdrop(fp, td);
                                  fpp = fdp->fd_ofiles + i;
                          }
                  }
          retry:
                  if (fdtol->fdl_refcount == 1) {
                          if (fdp->fd_holdleaderscount > 0 &&
                              (td->td_proc->p_leader->p_flag & P_ADVLOCK) != 0) {
                                  /*
                                   * close() or do_dup() has cleared a reference
                                   * in a shared file descriptor table.
                                   */
                                  fdp->fd_holdleaderswakeup = 1;
                                  sx_sleep(&fdp->fd_holdleaderscount,
                                      FILEDESC_LOCK(fdp), PLOCK, "fdlhold", 0);
                                  goto retry;
                          }
                          if (fdtol->fdl_holdcount > 0) {
                                  /*
                                   * Ensure that fdtol->fdl_leader remains
                                   * valid in closef().
                                   */
                                  fdtol->fdl_wakeup = 1;
                                  sx_sleep(fdtol, FILEDESC_LOCK(fdp), PLOCK,
                                      "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;
                  td->td_proc->p_fdtol = NULL;
                  FILEDESC_XUNLOCK(fdp);
                  if (fdtol != NULL)
                          free(fdtol, M_FILEDESC_TO_LEADER);
          }
          FILEDESC_XLOCK(fdp);
          i = --fdp->fd_refcnt;
          FILEDESC_XUNLOCK(fdp);
          if (i > 0)
                  return;
  
          fpp = fdp->fd_ofiles;
          for (i = fdp->fd_lastfile; i-- >= 0; fpp++) {
                  if (*fpp) {
                          FILEDESC_XLOCK(fdp);
                          fp = *fpp;
                          *fpp = NULL;
                          FILEDESC_XUNLOCK(fdp);
                          (void) closef(fp, td);
                  }
          }
          FILEDESC_XLOCK(fdp);
  
          /* XXX This should happen earlier. */
          mtx_lock(&fdesc_mtx);
          td->td_proc->p_fd = NULL;
          mtx_unlock(&fdesc_mtx);
  
          if (fdp->fd_nfiles > NDFILE)
                  free(fdp->fd_ofiles, M_FILEDESC);
          if (NDSLOTS(fdp->fd_nfiles) > NDSLOTS(NDFILE))
                  free(fdp->fd_map, M_FILEDESC);
  
          fdp->fd_nfiles = 0;
  
          cdir = fdp->fd_cdir;
          fdp->fd_cdir = NULL;
          rdir = fdp->fd_rdir;
          fdp->fd_rdir = NULL;
          jdir = fdp->fd_jdir;
          fdp->fd_jdir = NULL;
          FILEDESC_XUNLOCK(fdp);
  
          if (cdir) {
                  locked = VFS_LOCK_GIANT(cdir->v_mount);
                  vrele(cdir);
                  VFS_UNLOCK_GIANT(locked);
          }
          if (rdir) {
                  locked = VFS_LOCK_GIANT(rdir->v_mount);
                  vrele(rdir);
                  VFS_UNLOCK_GIANT(locked);
          }
          if (jdir) {
                  locked = VFS_LOCK_GIANT(jdir->v_mount);
                  vrele(jdir);
                  VFS_UNLOCK_GIANT(locked);
          }
  
          fddrop(fdp);
  }
  
  /*
   * 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.  We check for filesystems where
   * the vnode can change out from under us after execve (like [lin]procfs).
   *
   * Since setugidsafety calls this only for fd 0, 1 and 2, this check is
   * sufficient.  We also don't check for setugidness since we know we are.
   */
  static int
  is_unsafe(struct file *fp)
  {
          if (fp->f_type == DTYPE_VNODE) {
                  struct vnode *vp = fp->f_vnode;
  
                  if ((vp->v_vflag & VV_PROCDEP) != 0)
                          return (1);
          }
          return (0);
  }
  
  /*
   * Make this setguid thing safe, if at all possible.
   */
  void
  setugidsafety(struct thread *td)
  {
          struct filedesc *fdp;
          int i;
  
          /* Certain daemons might not have file descriptors. */
          fdp = td->td_proc->p_fd;
          if (fdp == NULL)
                  return;
  
          /*
           * Note: fdp->fd_ofiles may be reallocated out from under us while
           * we are blocked in a close.  Be careful!
           */
          FILEDESC_XLOCK(fdp);
          for (i = 0; i <= fdp->fd_lastfile; i++) {
                  if (i > 2)
                          break;
                  if (fdp->fd_ofiles[i] && is_unsafe(fdp->fd_ofiles[i])) {
                          struct file *fp;
  
                          knote_fdclose(td, i);
                          /*
                           * NULL-out descriptor prior to close to avoid
                           * a race while close blocks.
                           */
                          fp = fdp->fd_ofiles[i];
                          fdp->fd_ofiles[i] = NULL;
                          fdp->fd_ofileflags[i] = 0;
                          fdunused(fdp, i);
                          FILEDESC_XUNLOCK(fdp);
                          (void) closef(fp, td);
                          FILEDESC_XLOCK(fdp);
                  }
          }
          FILEDESC_XUNLOCK(fdp);
  }
  
  /*
   * If a specific file object occupies a specific file descriptor, close the
   * file descriptor entry and drop a reference on the file object.  This is a
   * convenience function to handle a subsequent error in a function that calls
   * falloc() that handles the race that another thread might have closed the
   * file descriptor out from under the thread creating the file object.
   */
  void
  fdclose(struct filedesc *fdp, struct file *fp, int idx, struct thread *td)
  {
  
          FILEDESC_XLOCK(fdp);
          if (fdp->fd_ofiles[idx] == fp) {
                  fdp->fd_ofiles[idx] = NULL;
                  fdunused(fdp, idx);
                  FILEDESC_XUNLOCK(fdp);
                  fdrop(fp, td);
          } else
                  FILEDESC_XUNLOCK(fdp);
  }
  
  /*
   * Close any files on exec?
   */
  void
  fdcloseexec(struct thread *td)
  {
          struct filedesc *fdp;
          int i;
  
          /* Certain daemons might not have file descriptors. */
          fdp = td->td_proc->p_fd;
          if (fdp == NULL)
                  return;
  
          FILEDESC_XLOCK(fdp);
  
          /*
           * We cannot cache fd_ofiles or fd_ofileflags since operations
           * may block and rip them out from under us.
           */
          for (i = 0; i <= fdp->fd_lastfile; i++) {
                  if (fdp->fd_ofiles[i] != NULL &&
                      (fdp->fd_ofiles[i]->f_type == DTYPE_MQUEUE ||
                      (fdp->fd_ofileflags[i] & UF_EXCLOSE))) {
                          struct file *fp;
  
                          knote_fdclose(td, i);
                          /*
                           * NULL-out descriptor prior to close to avoid
                           * a race while close blocks.
                           */
                          fp = fdp->fd_ofiles[i];
                          fdp->fd_ofiles[i] = NULL;
                          fdp->fd_ofileflags[i] = 0;
                          fdunused(fdp, i);
                          if (fp->f_type == DTYPE_MQUEUE)
                                  mq_fdclose(td, i, fp);
                          FILEDESC_XUNLOCK(fdp);
                          (void) closef(fp, td);
                          FILEDESC_XLOCK(fdp);
                  }
          }
          FILEDESC_XUNLOCK(fdp);
  }
  
  /*
   * 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.
   */
  int
  fdcheckstd(struct thread *td)
  {
          struct filedesc *fdp;
          register_t retval, save;
          int i, error, devnull;
  
          fdp = td->td_proc->p_fd;
          if (fdp == NULL)
                  return (0);
          KASSERT(fdp->fd_refcnt == 1, ("the fdtable should not be shared"));
          devnull = -1;
          error = 0;
          for (i = 0; i < 3; i++) {
                  if (fdp->fd_ofiles[i] != NULL)
                          continue;
                  if (devnull < 0) {
                          save = td->td_retval[0];
                          error = kern_open(td, "/dev/null", UIO_SYSSPACE,
                              O_RDWR, 0);
                          devnull = td->td_retval[0];
                          KASSERT(devnull == i, ("oof, we didn't get our fd"));
                          td->td_retval[0] = save;
                          if (error)
                                  break;
                  } else {
                          error = do_dup(td, DUP_FIXED, devnull, i, &retval);
                          if (error != 0)
                                  break;
                  }
          }
          return (error);
  }
  
  /*
   * Internal form of close.  Decrement reference count on file structure.
   * Note: td may be NULL when closing a file that was being passed in a
   * message.
   *
   * XXXRW: Giant is not required for the caller, but often will be held; this
   * makes it moderately likely the Giant will be recursed in the VFS case.
   */
  int
  closef(struct file *fp, struct thread *td)
  {
          struct vnode *vp;
          struct flock lf;
          struct filedesc_to_leader *fdtol;
          struct filedesc *fdp;
  
          /*
           * 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, and the thread pointer
           * will be NULL.  Callers should be careful only to pass a
           * NULL thread pointer when there really is no owning
           * context that might have locks, or the locks will be
           * leaked.
           */
          if (fp->f_type == DTYPE_VNODE && td != NULL) {
                  int vfslocked;
  
                  vp = fp->f_vnode;
                  vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                  if ((td->td_proc->p_leader->p_flag & P_ADVLOCK) != 0) {
                          lf.l_whence = SEEK_SET;
                          lf.l_start = 0;
                          lf.l_len = 0;
                          lf.l_type = F_UNLCK;
                          (void) VOP_ADVLOCK(vp, (caddr_t)td->td_proc->p_leader,
                                             F_UNLCK, &lf, F_POSIX);
                  }
                  fdtol = td->td_proc->p_fdtol;
                  if (fdtol != NULL) {
                          /*
                           * Handle special case where file descriptor table is
                           * shared between multiple process leaders.
                           */
                          fdp = td->td_proc->p_fd;
                          FILEDESC_XLOCK(fdp);
                          for (fdtol = fdtol->fdl_next;
                               fdtol != td->td_proc->p_fdtol;
                               fdtol = fdtol->fdl_next) {
                                  if ((fdtol->fdl_leader->p_flag &
                                       P_ADVLOCK) == 0)
                                          continue;
                                  fdtol->fdl_holdcount++;
                                  FILEDESC_XUNLOCK(fdp);
                                  lf.l_whence = SEEK_SET;
                                  lf.l_start = 0;
                                  lf.l_len = 0;
                                  lf.l_type = F_UNLCK;
                                  vp = fp->f_vnode;
                                  (void) VOP_ADVLOCK(vp,
                                                     (caddr_t)fdtol->fdl_leader,
                                                     F_UNLCK, &lf, F_POSIX);
                                  FILEDESC_XLOCK(fdp);
                                  fdtol->fdl_holdcount--;
                                  if (fdtol->fdl_holdcount == 0 &&
                                      fdtol->fdl_wakeup != 0) {
                                          fdtol->fdl_wakeup = 0;
                                          wakeup(fdtol);
                                  }
                          }
                          FILEDESC_XUNLOCK(fdp);
                  }
                  VFS_UNLOCK_GIANT(vfslocked);
          }
          return (fdrop(fp, td));
  }
  
  /*
   * Initialize the file pointer with the specified properties.
   * 
   * The ops are set with release semantics to be certain that the flags, type,
   * and data are visible when ops is.  This is to prevent ops methods from being
   * called with bad data.
   */
  void
  finit(struct file *fp, u_int flag, short type, void *data, struct fileops *ops)
  {
          fp->f_data = data;
          fp->f_flag = flag;
          fp->f_type = type;
          atomic_store_rel_ptr((volatile uintptr_t *)&fp->f_ops, (uintptr_t)ops);
  }
  
  struct file *
  fget_unlocked(struct filedesc *fdp, int fd)
  {
          struct file *fp;
          u_int count;
  
          if (fd < 0 || fd >= fdp->fd_nfiles)
                  return (NULL);
          /*
           * Fetch the descriptor locklessly.  We avoid fdrop() races by
           * never raising a refcount above 0.  To accomplish this we have
           * to use a cmpset loop rather than an atomic_add.  The descriptor
           * must be re-verified once we acquire a reference to be certain
           * that the identity is still correct and we did not lose a race
           * due to preemption.
           */
          for (;;) {
                  fp = fdp->fd_ofiles[fd];
                  if (fp == NULL)
                          break;
                  count = fp->f_count;
                  if (count == 0)
                          continue;
                  /*
                   * Use an acquire barrier to prevent caching of fd_ofiles
                   * so it is refreshed for verification.
                   */
                  if (atomic_cmpset_acq_int(&fp->f_count, count, count + 1) != 1)
                          continue;
                  if (fp == fdp->fd_ofiles[fd])
                          break;
                  fdrop(fp, curthread);
          }
  
          return (fp);
  }
  
  /*
   * Extract the file pointer associated with the specified descriptor for the
   * current user process.
   *
   * If the descriptor doesn't exist or doesn't match 'flags', EBADF is
   * returned.
   *
   * If an error occured the non-zero error is returned and *fpp is set to
   * NULL.  Otherwise *fpp is held and set and zero is returned.  Caller is
   * responsible for fdrop().
   */
  static __inline int
  _fget(struct thread *td, int fd, struct file **fpp, int flags)
  {
          struct filedesc *fdp;
          struct file *fp;
  
          *fpp = NULL;
          if (td == NULL || (fdp = td->td_proc->p_fd) == NULL)
                  return (EBADF);
          if ((fp = fget_unlocked(fdp, fd)) == NULL)
                  return (EBADF);
          if (fp->f_ops == &badfileops) {
                  fdrop(fp, td);
                  return (EBADF);
          }
          /*
           * FREAD and FWRITE failure return EBADF as per POSIX.
           *
           * Only one flag, or 0, may be specified.
           */
          if ((flags == FREAD && (fp->f_flag & FREAD) == 0) ||
              (flags == FWRITE && (fp->f_flag & FWRITE) == 0)) {
                  fdrop(fp, td);
                  return (EBADF);
          }
          *fpp = fp;
          return (0);
  }
  
  int
  fget(struct thread *td, int fd, struct file **fpp)
  {
  
          return(_fget(td, fd, fpp, 0));
  }
  
  int
  fget_read(struct thread *td, int fd, struct file **fpp)
  {
  
          return(_fget(td, fd, fpp, FREAD));
  }
  
  int
  fget_write(struct thread *td, int fd, struct file **fpp)
  {
  
          return(_fget(td, fd, fpp, FWRITE));
  }
  
  /*
   * Like fget() but loads the underlying vnode, or returns an error if the
   * descriptor does not represent a vnode.  Note that pipes use vnodes but
   * never have VM objects.  The returned vnode will be vref()'d.
   *
   * XXX: what about the unused flags ?
   */
  static __inline int
  _fgetvp(struct thread *td, int fd, struct vnode **vpp, int flags)
  {
          struct file *fp;
          int error;
  
          *vpp = NULL;
          if ((error = _fget(td, fd, &fp, flags)) != 0)
                  return (error);
          if (fp->f_vnode == NULL) {
                  error = EINVAL;
          } else {
                  *vpp = fp->f_vnode;
                  vref(*vpp);
          }
          fdrop(fp, td);
  
          return (error);
  }
  
  int
  fgetvp(struct thread *td, int fd, struct vnode **vpp)
  {
  
          return (_fgetvp(td, fd, vpp, 0));
  }
  
  int
  fgetvp_read(struct thread *td, int fd, struct vnode **vpp)
  {
  
          return (_fgetvp(td, fd, vpp, FREAD));
  }
  
  #ifdef notyet
  int
  fgetvp_write(struct thread *td, int fd, struct vnode **vpp)
  {
  
          return (_fgetvp(td, fd, vpp, FWRITE));
  }
  #endif
  
  /*
   * Like fget() but loads the underlying socket, or returns an error if the
   * descriptor does not represent a socket.
   *
   * We bump the ref count on the returned socket.  XXX Also obtain the SX lock
   * in the future.
   *
   * Note: fgetsock() and fputsock() are deprecated, as consumers should rely
   * on their file descriptor reference to prevent the socket from being free'd
   * during use.
   */
  int
  fgetsock(struct thread *td, int fd, struct socket **spp, u_int *fflagp)
  {
          struct file *fp;
          int error;
  
          *spp = NULL;
          if (fflagp != NULL)
                  *fflagp = 0;
          if ((error = _fget(td, fd, &fp, 0)) != 0)
                  return (error);
          if (fp->f_type != DTYPE_SOCKET) {
                  error = ENOTSOCK;
          } else {
                  *spp = fp->f_data;
                  if (fflagp)
                          *fflagp = fp->f_flag;
                  SOCK_LOCK(*spp);
                  soref(*spp);
                  SOCK_UNLOCK(*spp);
          }
          fdrop(fp, td);
  
          return (error);
  }
  
  /*
   * Drop the reference count on the socket and XXX release the SX lock in the
   * future.  The last reference closes the socket.
   *
   * Note: fputsock() is deprecated, see comment for fgetsock().
   */
  void
  fputsock(struct socket *so)
  {
  
          ACCEPT_LOCK();
          SOCK_LOCK(so);
          sorele(so);
  }
  
  /*
   * Handle the last reference to a file being closed.
   */
  int
  _fdrop(struct file *fp, struct thread *td)
  {
          int error;
  
          error = 0;
          if (fp->f_count != 0)
                  panic("fdrop: count %d", fp->f_count);
          if (fp->f_ops != &badfileops)
                  error = fo_close(fp, td);
          /*
           * The f_cdevpriv cannot be assigned non-NULL value while we
           * are destroying the file.
           */
          if (fp->f_cdevpriv != NULL)
                  devfs_fpdrop(fp);
          atomic_subtract_int(&openfiles, 1);
          crfree(fp->f_cred);
          uma_zfree(file_zone, 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).
   */
  #ifndef _SYS_SYSPROTO_H_
  struct flock_args {
          int     fd;
          int     how;
  };
  #endif
  /* ARGSUSED */
  int
  flock(struct thread *td, struct flock_args *uap)
  {
          struct file *fp;
          struct vnode *vp;
          struct flock lf;
          int vfslocked;
          int error;
  
          if ((error = fget(td, uap->fd, &fp)) != 0)
                  return (error);
          if (fp->f_type != DTYPE_VNODE) {
                  fdrop(fp, td);
                  return (EOPNOTSUPP);
          }
  
          vp = fp->f_vnode;
          vfslocked = VFS_LOCK_GIANT(vp->v_mount);
          lf.l_whence = SEEK_SET;
          lf.l_start = 0;
          lf.l_len = 0;
          if (uap->how & LOCK_UN) {
                  lf.l_type = F_UNLCK;
                  atomic_clear_int(&fp->f_flag, FHASLOCK);
                  error = VOP_ADVLOCK(vp, (caddr_t)fp, F_UNLCK, &lf, F_FLOCK);
                  goto done2;
          }
          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 done2;
          }
          atomic_set_int(&fp->f_flag, FHASLOCK);
          error = VOP_ADVLOCK(vp, (caddr_t)fp, F_SETLK, &lf,
              (uap->how & LOCK_NB) ? F_FLOCK : F_FLOCK | F_WAIT);
  done2:
          fdrop(fp, td);
          VFS_UNLOCK_GIANT(vfslocked);
          return (error);
  }
  /*
   * Duplicate the specified descriptor to a free descriptor.
   */
  int
  dupfdopen(struct thread *td, struct filedesc *fdp, int indx, int dfd, int mode, int error)
  {
          struct file *wfp;
          struct file *fp;
  
          /*
           * If the to-be-dup'd fd number is greater than the allowed number
           * of file descriptors, or the fd to be dup'd has already been
           * closed, then reject.
           */
          FILEDESC_XLOCK(fdp);
          if (dfd < 0 || dfd >= fdp->fd_nfiles ||
              (wfp = fdp->fd_ofiles[dfd]) == NULL) {
                  FILEDESC_XUNLOCK(fdp);
                  return (EBADF);
          }
  
          /*
           * There are two cases of interest here.
           *
           * For ENODEV simply dup (dfd) to file descriptor (indx) and return.
           *
           * For ENXIO steal away the file structure from (dfd) and store it in
           * (indx).  (dfd) is effectively closed by this operation.
           *
           * Any other error code is just returned.
           */
          switch (error) {
          case 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) {
                          FILEDESC_XUNLOCK(fdp);
                          return (EACCES);
                  }
                  fp = fdp->fd_ofiles[indx];
                  fdp->fd_ofiles[indx] = wfp;
                  fdp->fd_ofileflags[indx] = fdp->fd_ofileflags[dfd];
                  if (fp == NULL)
                          fdused(fdp, indx);
                  fhold(wfp);
                  FILEDESC_XUNLOCK(fdp);
                  if (fp != NULL)
                          /*
                           * We now own the reference to fp that the ofiles[]
                           * array used to own.  Release it.
                           */
                          fdrop(fp, td);
                  return (0);
  
          case ENXIO:
                  /*
                   * Steal away the file pointer from dfd and stuff it into indx.
                   */
                  fp = fdp->fd_ofiles[indx];
                  fdp->fd_ofiles[indx] = fdp->fd_ofiles[dfd];
                  fdp->fd_ofiles[dfd] = NULL;
                  fdp->fd_ofileflags[indx] = fdp->fd_ofileflags[dfd];
                  fdp->fd_ofileflags[dfd] = 0;
                  fdunused(fdp, dfd);
                  if (fp == NULL)
                          fdused(fdp, indx);
                  FILEDESC_XUNLOCK(fdp);
  
                  /*
                   * We now own the reference to fp that the ofiles[] array
                   * used to own.  Release it.
                   */
                  if (fp != NULL)
                          fdrop(fp, td);
                  return (0);
  
          default:
                  FILEDESC_XUNLOCK(fdp);
                  return (error);
          }
          /* NOTREACHED */
  }
  
  /*
   * Scan all active processes and prisons to see if any of them have a current
   * or root directory of `olddp'. If so, replace them with the new mount point.
   */
  void
  mountcheckdirs(struct vnode *olddp, struct vnode *newdp)
  {
          struct filedesc *fdp;
          struct prison *pr;
          struct proc *p;
          int nrele;
  
          if (vrefcnt(olddp) == 1)
                  return;
          nrele = 0;
          sx_slock(&allproc_lock);
          FOREACH_PROC_IN_SYSTEM(p) {
                  fdp = fdhold(p);
                  if (fdp == NULL)
                          continue;
                  FILEDESC_XLOCK(fdp);
                  if (fdp->fd_cdir == olddp) {
                          vref(newdp);
                          fdp->fd_cdir = newdp;
                          nrele++;
                  }
                  if (fdp->fd_rdir == olddp) {
                          vref(newdp);
                          fdp->fd_rdir = newdp;
                          nrele++;
                  }
                  if (fdp->fd_jdir == olddp) {
                          vref(newdp);
                          fdp->fd_jdir = newdp;
                          nrele++;
                  }
                  FILEDESC_XUNLOCK(fdp);
                  fddrop(fdp);
          }
          sx_sunlock(&allproc_lock);
          if (rootvnode == olddp) {
                  vref(newdp);
                  rootvnode = newdp;
                  nrele++;
          }
          mtx_lock(&prison0.pr_mtx);
          if (prison0.pr_root == olddp) {
                  vref(newdp);
                  prison0.pr_root = newdp;
                  nrele++;
          }
          mtx_unlock(&prison0.pr_mtx);
          sx_slock(&allprison_lock);
          TAILQ_FOREACH(pr, &allprison, pr_list) {
                  mtx_lock(&pr->pr_mtx);
                  if (pr->pr_root == olddp) {
                          vref(newdp);
                          pr->pr_root = newdp;
                          nrele++;
                  }
                  mtx_unlock(&pr->pr_mtx);
          }
          sx_sunlock(&allprison_lock);
          while (nrele--)
                  vrele(olddp);
  }
  
  struct filedesc_to_leader *
  filedesc_to_leader_alloc(struct filedesc_to_leader *old, struct filedesc *fdp, struct proc *leader)
  {
          struct filedesc_to_leader *fdtol;
  
          fdtol = malloc(sizeof(struct filedesc_to_leader),
                 M_FILEDESC_TO_LEADER,
                 M_WAITOK);
          fdtol->fdl_refcount = 1;
          fdtol->fdl_holdcount = 0;
          fdtol->fdl_wakeup = 0;
          fdtol->fdl_leader = leader;
          if (old != NULL) {
                  FILEDESC_XLOCK(fdp);
                  fdtol->fdl_next = old->fdl_next;
                  fdtol->fdl_prev = old;
                  old->fdl_next = fdtol;
                  fdtol->fdl_next->fdl_prev = fdtol;
                  FILEDESC_XUNLOCK(fdp);
          } else {
                  fdtol->fdl_next = fdtol;
                  fdtol->fdl_prev = fdtol;
          }
          return (fdtol);
  }
  
  /*
   * Get file structures globally.
   */
  static int
  sysctl_kern_file(SYSCTL_HANDLER_ARGS)
  {
          struct xfile xf;
          struct filedesc *fdp;
          struct file *fp;
          struct proc *p;
          int error, n;
  
          error = sysctl_wire_old_buffer(req, 0);
          if (error != 0)
                  return (error);
          if (req->oldptr == NULL) {
                  n = 0;
                  sx_slock(&allproc_lock);
                  FOREACH_PROC_IN_SYSTEM(p) {
                          if (p->p_state == PRS_NEW)
                                  continue;
                          fdp = fdhold(p);
                          if (fdp == NULL)
                                  continue;
                          /* overestimates sparse tables. */
                          if (fdp->fd_lastfile > 0)
                                  n += fdp->fd_lastfile;
                          fddrop(fdp);
                  }
                  sx_sunlock(&allproc_lock);
                  return (SYSCTL_OUT(req, 0, n * sizeof(xf)));
          }
          error = 0;
          bzero(&xf, sizeof(xf));
          xf.xf_size = sizeof(xf);
          sx_slock(&allproc_lock);
          FOREACH_PROC_IN_SYSTEM(p) {
                  if (p->p_state == PRS_NEW)
                          continue;
                  PROC_LOCK(p);
                  if (p_cansee(req->td, p) != 0) {
                          PROC_UNLOCK(p);
                          continue;
                  }
                  xf.xf_pid = p->p_pid;
                  xf.xf_uid = p->p_ucred->cr_uid;
                  PROC_UNLOCK(p);
                  fdp = fdhold(p);
                  if (fdp == NULL)
                          continue;
                  FILEDESC_SLOCK(fdp);
                  for (n = 0; fdp->fd_refcnt > 0 && n < fdp->fd_nfiles; ++n) {
                          if ((fp = fdp->fd_ofiles[n]) == NULL)
                                  continue;
                          xf.xf_fd = n;
                          xf.xf_file = fp;
                          xf.xf_data = fp->f_data;
                          xf.xf_vnode = fp->f_vnode;
                          xf.xf_type = fp->f_type;
                          xf.xf_count = fp->f_count;
                          xf.xf_msgcount = 0;
                          xf.xf_offset = fp->f_offset;
                          xf.xf_flag = fp->f_flag;
                          error = SYSCTL_OUT(req, &xf, sizeof(xf));
                          if (error)
                                  break;
                  }
                  FILEDESC_SUNLOCK(fdp);
                  fddrop(fdp);
                  if (error)
                          break;
          }
          sx_sunlock(&allproc_lock);
          return (error);
  }
  
  SYSCTL_PROC(_kern, KERN_FILE, file, CTLTYPE_OPAQUE|CTLFLAG_RD,
      0, 0, sysctl_kern_file, "S,xfile", "Entire file table");
  
  #ifdef KINFO_OFILE_SIZE
  CTASSERT(sizeof(struct kinfo_ofile) == KINFO_OFILE_SIZE);
  #endif
  
  #ifdef COMPAT_FREEBSD7
  static int
  export_vnode_for_osysctl(struct vnode *vp, int type,
      struct kinfo_ofile *kif, struct filedesc *fdp, struct sysctl_req *req)
  {
          int error;
          char *fullpath, *freepath;
          int vfslocked;
  
          bzero(kif, sizeof(*kif));
          kif->kf_structsize = sizeof(*kif);
  
          vref(vp);
          kif->kf_fd = type;
          kif->kf_type = KF_TYPE_VNODE;
          /* This function only handles directories. */
          if (vp->v_type != VDIR) {
                  vrele(vp);
                  return (ENOTDIR);
          }
          kif->kf_vnode_type = KF_VTYPE_VDIR;
  
          /*
           * This is not a true file descriptor, so we set a bogus refcount
           * and offset to indicate these fields should be ignored.
           */
          kif->kf_ref_count = -1;
          kif->kf_offset = -1;
  
          freepath = NULL;
          fullpath = "-";
          FILEDESC_SUNLOCK(fdp);
          vn_fullpath(curthread, vp, &fullpath, &freepath);
          vfslocked = VFS_LOCK_GIANT(vp->v_mount);
          vrele(vp);
          VFS_UNLOCK_GIANT(vfslocked);
          strlcpy(kif->kf_path, fullpath, sizeof(kif->kf_path));
          if (freepath != NULL)
                  free(freepath, M_TEMP);
          error = SYSCTL_OUT(req, kif, sizeof(*kif));
          FILEDESC_SLOCK(fdp);
          return (error);
  }
  
  /*
   * Get per-process file descriptors for use by procstat(1), et al.
   */
  static int
  sysctl_kern_proc_ofiledesc(SYSCTL_HANDLER_ARGS)
  {
          char *fullpath, *freepath;
          struct kinfo_ofile *kif;
          struct filedesc *fdp;
          int error, i, *name;
          struct socket *so;
          struct vnode *vp;
          struct file *fp;
          struct proc *p;
          struct tty *tp;
          int vfslocked;
  
          name = (int *)arg1;
          if ((p = pfind((pid_t)name[0])) == NULL)
                  return (ESRCH);
          if ((error = p_candebug(curthread, p))) {
                  PROC_UNLOCK(p);
                  return (error);
          }
          fdp = fdhold(p);
          PROC_UNLOCK(p);
          if (fdp == NULL)
                  return (ENOENT);
          kif = malloc(sizeof(*kif), M_TEMP, M_WAITOK);
          FILEDESC_SLOCK(fdp);
          if (fdp->fd_cdir != NULL)
                  export_vnode_for_osysctl(fdp->fd_cdir, KF_FD_TYPE_CWD, kif,
                                  fdp, req);
          if (fdp->fd_rdir != NULL)
                  export_vnode_for_osysctl(fdp->fd_rdir, KF_FD_TYPE_ROOT, kif,
                                  fdp, req);
          if (fdp->fd_jdir != NULL)
                  export_vnode_for_osysctl(fdp->fd_jdir, KF_FD_TYPE_JAIL, kif,
                                  fdp, req);
          for (i = 0; i < fdp->fd_nfiles; i++) {
                  if ((fp = fdp->fd_ofiles[i]) == NULL)
                          continue;
                  bzero(kif, sizeof(*kif));
                  kif->kf_structsize = sizeof(*kif);
                  vp = NULL;
                  so = NULL;
                  tp = NULL;
                  kif->kf_fd = i;
                  switch (fp->f_type) {
                  case DTYPE_VNODE:
                          kif->kf_type = KF_TYPE_VNODE;
                          vp = fp->f_vnode;
                          break;
  
                  case DTYPE_SOCKET:
                          kif->kf_type = KF_TYPE_SOCKET;
                          so = fp->f_data;
                          break;
  
                  case DTYPE_PIPE:
                          kif->kf_type = KF_TYPE_PIPE;
                          break;
  
                  case DTYPE_FIFO:
                          kif->kf_type = KF_TYPE_FIFO;
                          vp = fp->f_vnode;
                          break;
  
                  case DTYPE_KQUEUE:
                          kif->kf_type = KF_TYPE_KQUEUE;
                          break;
  
                  case DTYPE_CRYPTO:
                          kif->kf_type = KF_TYPE_CRYPTO;
                          break;
  
                  case DTYPE_MQUEUE:
                          kif->kf_type = KF_TYPE_MQUEUE;
                          break;
  
                  case DTYPE_SHM:
                          kif->kf_type = KF_TYPE_SHM;
                          break;
  
                  case DTYPE_SEM:
                          kif->kf_type = KF_TYPE_SEM;
                          break;
  
                  case DTYPE_PTS:
                          kif->kf_type = KF_TYPE_PTS;
                          tp = fp->f_data;
                          break;
  
                  default:
                          kif->kf_type = KF_TYPE_UNKNOWN;
                          break;
                  }
                  kif->kf_ref_count = fp->f_count;
                  if (fp->f_flag & FREAD)
                          kif->kf_flags |= KF_FLAG_READ;
                  if (fp->f_flag & FWRITE)
                          kif->kf_flags |= KF_FLAG_WRITE;
                  if (fp->f_flag & FAPPEND)
                          kif->kf_flags |= KF_FLAG_APPEND;
                  if (fp->f_flag & FASYNC)
                          kif->kf_flags |= KF_FLAG_ASYNC;
                  if (fp->f_flag & FFSYNC)
                          kif->kf_flags |= KF_FLAG_FSYNC;
                  if (fp->f_flag & FNONBLOCK)
                          kif->kf_flags |= KF_FLAG_NONBLOCK;
                  if (fp->f_flag & O_DIRECT)
                          kif->kf_flags |= KF_FLAG_DIRECT;
                  if (fp->f_flag & FHASLOCK)
                          kif->kf_flags |= KF_FLAG_HASLOCK;
                  kif->kf_offset = fp->f_offset;
                  if (vp != NULL) {
                          vref(vp);
                          switch (vp->v_type) {
                          case VNON:
                                  kif->kf_vnode_type = KF_VTYPE_VNON;
                                  break;
                          case VREG:
                                  kif->kf_vnode_type = KF_VTYPE_VREG;
                                  break;
                          case VDIR:
                                  kif->kf_vnode_type = KF_VTYPE_VDIR;
                                  break;
                          case VBLK:
                                  kif->kf_vnode_type = KF_VTYPE_VBLK;
                                  break;
                          case VCHR:
                                  kif->kf_vnode_type = KF_VTYPE_VCHR;
                                  break;
                          case VLNK:
                                  kif->kf_vnode_type = KF_VTYPE_VLNK;
                                  break;
                          case VSOCK:
                                  kif->kf_vnode_type = KF_VTYPE_VSOCK;
                                  break;
                          case VFIFO:
                                  kif->kf_vnode_type = KF_VTYPE_VFIFO;
                                  break;
                          case VBAD:
                                  kif->kf_vnode_type = KF_VTYPE_VBAD;
                                  break;
                          default:
                                  kif->kf_vnode_type = KF_VTYPE_UNKNOWN;
                                  break;
                          }
                          /*
                           * It is OK to drop the filedesc lock here as we will
                           * re-validate and re-evaluate its properties when
                           * the loop continues.
                           */
                          freepath = NULL;
                          fullpath = "-";
                          FILEDESC_SUNLOCK(fdp);
                          vn_fullpath(curthread, vp, &fullpath, &freepath);
                          vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                          vrele(vp);
                          VFS_UNLOCK_GIANT(vfslocked);
                          strlcpy(kif->kf_path, fullpath,
                              sizeof(kif->kf_path));
                          if (freepath != NULL)
                                  free(freepath, M_TEMP);
                          FILEDESC_SLOCK(fdp);
                  }
                  if (so != NULL) {
                          struct sockaddr *sa;
  
                          if (so->so_proto->pr_usrreqs->pru_sockaddr(so, &sa)
                              == 0 && sa->sa_len <= sizeof(kif->kf_sa_local)) {
                                  bcopy(sa, &kif->kf_sa_local, sa->sa_len);
                                  free(sa, M_SONAME);
                          }
                          if (so->so_proto->pr_usrreqs->pru_peeraddr(so, &sa)
                              == 00 && sa->sa_len <= sizeof(kif->kf_sa_peer)) {
                                  bcopy(sa, &kif->kf_sa_peer, sa->sa_len);
                                  free(sa, M_SONAME);
                          }
                          kif->kf_sock_domain =
                              so->so_proto->pr_domain->dom_family;
                          kif->kf_sock_type = so->so_type;
                          kif->kf_sock_protocol = so->so_proto->pr_protocol;
                  }
                  if (tp != NULL) {
                          strlcpy(kif->kf_path, tty_devname(tp),
                              sizeof(kif->kf_path));
                  }
                  error = SYSCTL_OUT(req, kif, sizeof(*kif));
                  if (error)
                          break;
          }
          FILEDESC_SUNLOCK(fdp);
          fddrop(fdp);
          free(kif, M_TEMP);
          return (0);
  }
  
  static SYSCTL_NODE(_kern_proc, KERN_PROC_OFILEDESC, ofiledesc, CTLFLAG_RD,
      sysctl_kern_proc_ofiledesc, "Process ofiledesc entries");
  #endif  /* COMPAT_FREEBSD7 */
  
  #ifdef KINFO_FILE_SIZE
  CTASSERT(sizeof(struct kinfo_file) == KINFO_FILE_SIZE);
  #endif
  
  static int
  export_vnode_for_sysctl(struct vnode *vp, int type,
      struct kinfo_file *kif, struct filedesc *fdp, struct sysctl_req *req)
  {
          int error;
          char *fullpath, *freepath;
          int vfslocked;
  
          bzero(kif, sizeof(*kif));
  
          vref(vp);
          kif->kf_fd = type;
          kif->kf_type = KF_TYPE_VNODE;
          /* This function only handles directories. */
          if (vp->v_type != VDIR) {
                  vrele(vp);
                  return (ENOTDIR);
          }
          kif->kf_vnode_type = KF_VTYPE_VDIR;
  
          /*
           * This is not a true file descriptor, so we set a bogus refcount
           * and offset to indicate these fields should be ignored.
           */
          kif->kf_ref_count = -1;
          kif->kf_offset = -1;
  
          freepath = NULL;
          fullpath = "-";
          FILEDESC_SUNLOCK(fdp);
          vn_fullpath(curthread, vp, &fullpath, &freepath);
          vfslocked = VFS_LOCK_GIANT(vp->v_mount);
          vrele(vp);
          VFS_UNLOCK_GIANT(vfslocked);
          strlcpy(kif->kf_path, fullpath, sizeof(kif->kf_path));
          if (freepath != NULL)
                  free(freepath, M_TEMP);
          /* Pack record size down */
          kif->kf_structsize = offsetof(struct kinfo_file, kf_path) +
              strlen(kif->kf_path) + 1;
          kif->kf_structsize = roundup(kif->kf_structsize, sizeof(uint64_t));
          error = SYSCTL_OUT(req, kif, kif->kf_structsize);
          FILEDESC_SLOCK(fdp);
          return (error);
  }
  
  /*
   * Get per-process file descriptors for use by procstat(1), et al.
   */
  static int
  sysctl_kern_proc_filedesc(SYSCTL_HANDLER_ARGS)
  {
          char *fullpath, *freepath;
          struct kinfo_file *kif;
          struct filedesc *fdp;
          int error, i, *name;
          struct socket *so;
          struct vnode *vp;
          struct file *fp;
          struct proc *p;
          struct tty *tp;
          int vfslocked;
          size_t oldidx;
  
          name = (int *)arg1;
          if ((p = pfind((pid_t)name[0])) == NULL)
                  return (ESRCH);
          if ((error = p_candebug(curthread, p))) {
                  PROC_UNLOCK(p);
                  return (error);
          }
          fdp = fdhold(p);
          PROC_UNLOCK(p);
          if (fdp == NULL)
                  return (ENOENT);
          kif = malloc(sizeof(*kif), M_TEMP, M_WAITOK);
          FILEDESC_SLOCK(fdp);
          if (fdp->fd_cdir != NULL)
                  export_vnode_for_sysctl(fdp->fd_cdir, KF_FD_TYPE_CWD, kif,
                                  fdp, req);
          if (fdp->fd_rdir != NULL)
                  export_vnode_for_sysctl(fdp->fd_rdir, KF_FD_TYPE_ROOT, kif,
                                  fdp, req);
          if (fdp->fd_jdir != NULL)
                  export_vnode_for_sysctl(fdp->fd_jdir, KF_FD_TYPE_JAIL, kif,
                                  fdp, req);
          for (i = 0; i < fdp->fd_nfiles; i++) {
                  if ((fp = fdp->fd_ofiles[i]) == NULL)
                          continue;
                  bzero(kif, sizeof(*kif));
                  vp = NULL;
                  so = NULL;
                  tp = NULL;
                  kif->kf_fd = i;
                  switch (fp->f_type) {
                  case DTYPE_VNODE:
                          kif->kf_type = KF_TYPE_VNODE;
                          vp = fp->f_vnode;
                          break;
  
                  case DTYPE_SOCKET:
                          kif->kf_type = KF_TYPE_SOCKET;
                          so = fp->f_data;
                          break;
  
                  case DTYPE_PIPE:
                          kif->kf_type = KF_TYPE_PIPE;
                          break;
  
                  case DTYPE_FIFO:
                          kif->kf_type = KF_TYPE_FIFO;
                          vp = fp->f_vnode;
                          break;
  
                  case DTYPE_KQUEUE:
                          kif->kf_type = KF_TYPE_KQUEUE;
                          break;
  
                  case DTYPE_CRYPTO:
                          kif->kf_type = KF_TYPE_CRYPTO;
                          break;
  
                  case DTYPE_MQUEUE:
                          kif->kf_type = KF_TYPE_MQUEUE;
                          break;
  
                  case DTYPE_SHM:
                          kif->kf_type = KF_TYPE_SHM;
                          break;
  
                  case DTYPE_SEM:
                          kif->kf_type = KF_TYPE_SEM;
                          break;
  
                  case DTYPE_PTS:
                          kif->kf_type = KF_TYPE_PTS;
                          tp = fp->f_data;
                          break;
  
                  default:
                          kif->kf_type = KF_TYPE_UNKNOWN;
                          break;
                  }
                  kif->kf_ref_count = fp->f_count;
                  if (fp->f_flag & FREAD)
                          kif->kf_flags |= KF_FLAG_READ;
                  if (fp->f_flag & FWRITE)
                          kif->kf_flags |= KF_FLAG_WRITE;
                  if (fp->f_flag & FAPPEND)
                          kif->kf_flags |= KF_FLAG_APPEND;
                  if (fp->f_flag & FASYNC)
                          kif->kf_flags |= KF_FLAG_ASYNC;
                  if (fp->f_flag & FFSYNC)
                          kif->kf_flags |= KF_FLAG_FSYNC;
                  if (fp->f_flag & FNONBLOCK)
                          kif->kf_flags |= KF_FLAG_NONBLOCK;
                  if (fp->f_flag & O_DIRECT)
                          kif->kf_flags |= KF_FLAG_DIRECT;
                  if (fp->f_flag & FHASLOCK)
                          kif->kf_flags |= KF_FLAG_HASLOCK;
                  kif->kf_offset = fp->f_offset;
                  if (vp != NULL) {
                          vref(vp);
                          switch (vp->v_type) {
                          case VNON:
                                  kif->kf_vnode_type = KF_VTYPE_VNON;
                                  break;
                          case VREG:
                                  kif->kf_vnode_type = KF_VTYPE_VREG;
                                  break;
                          case VDIR:
                                  kif->kf_vnode_type = KF_VTYPE_VDIR;
                                  break;
                          case VBLK:
                                  kif->kf_vnode_type = KF_VTYPE_VBLK;
                                  break;
                          case VCHR:
                                  kif->kf_vnode_type = KF_VTYPE_VCHR;
                                  break;
                          case VLNK:
                                  kif->kf_vnode_type = KF_VTYPE_VLNK;
                                  break;
                          case VSOCK:
                                  kif->kf_vnode_type = KF_VTYPE_VSOCK;
                                  break;
                          case VFIFO:
                                  kif->kf_vnode_type = KF_VTYPE_VFIFO;
                                  break;
                          case VBAD:
                                  kif->kf_vnode_type = KF_VTYPE_VBAD;
                                  break;
                          default:
                                  kif->kf_vnode_type = KF_VTYPE_UNKNOWN;
                                  break;
                          }
                          /*
                           * It is OK to drop the filedesc lock here as we will
                           * re-validate and re-evaluate its properties when
                           * the loop continues.
                           */
                          freepath = NULL;
                          fullpath = "-";
                          FILEDESC_SUNLOCK(fdp);
                          vn_fullpath(curthread, vp, &fullpath, &freepath);
                          vfslocked = VFS_LOCK_GIANT(vp->v_mount);
                          vrele(vp);
                          VFS_UNLOCK_GIANT(vfslocked);
                          strlcpy(kif->kf_path, fullpath,
                              sizeof(kif->kf_path));
                          if (freepath != NULL)
                                  free(freepath, M_TEMP);
                          FILEDESC_SLOCK(fdp);
                  }
                  if (so != NULL) {
                          struct sockaddr *sa;
  
                          if (so->so_proto->pr_usrreqs->pru_sockaddr(so, &sa)
                              == 0 && sa->sa_len <= sizeof(kif->kf_sa_local)) {
                                  bcopy(sa, &kif->kf_sa_local, sa->sa_len);
                                  free(sa, M_SONAME);
                          }
                          if (so->so_proto->pr_usrreqs->pru_peeraddr(so, &sa)
                              == 00 && sa->sa_len <= sizeof(kif->kf_sa_peer)) {
                                  bcopy(sa, &kif->kf_sa_peer, sa->sa_len);
                                  free(sa, M_SONAME);
                          }
                          kif->kf_sock_domain =
                              so->so_proto->pr_domain->dom_family;
                          kif->kf_sock_type = so->so_type;
                          kif->kf_sock_protocol = so->so_proto->pr_protocol;
                  }
                  if (tp != NULL) {
                          strlcpy(kif->kf_path, tty_devname(tp),
                              sizeof(kif->kf_path));
                  }
                  /* Pack record size down */
                  kif->kf_structsize = offsetof(struct kinfo_file, kf_path) +
                      strlen(kif->kf_path) + 1;
                  kif->kf_structsize = roundup(kif->kf_structsize,
                      sizeof(uint64_t));
                  oldidx = req->oldidx;
                  error = SYSCTL_OUT(req, kif, kif->kf_structsize);
                  if (error) {
                          if (error == ENOMEM) {
                                  /*
                                   * The hack to keep the ABI of sysctl
                                   * kern.proc.filedesc intact, but not
                                   * to account a partially copied
                                   * kinfo_file into the oldidx.
                                   */
                                  req->oldidx = oldidx;
                                  error = 0;
                          }
                          break;
                  }
          }
          FILEDESC_SUNLOCK(fdp);
          fddrop(fdp);
          free(kif, M_TEMP);
          return (error);
  }
  
  static SYSCTL_NODE(_kern_proc, KERN_PROC_FILEDESC, filedesc, CTLFLAG_RD,
      sysctl_kern_proc_filedesc, "Process filedesc entries");
  
  #ifdef DDB
  /*
   * For the purposes of debugging, generate a human-readable string for the
   * file type.
   */
  static const char *
  file_type_to_name(short type)
  {
  
          switch (type) {
          case 0:
                  return ("zero");
          case DTYPE_VNODE:
                  return ("vnod");
          case DTYPE_SOCKET:
                  return ("sock");
          case DTYPE_PIPE:
                  return ("pipe");
          case DTYPE_FIFO:
                  return ("fifo");
          case DTYPE_KQUEUE:
                  return ("kque");
          case DTYPE_CRYPTO:
                  return ("crpt");
          case DTYPE_MQUEUE:
                  return ("mque");
          case DTYPE_SHM:
                  return ("shm");
          case DTYPE_SEM:
                  return ("ksem");
          default:
                  return ("unkn");
          }
  }
  
  /*
   * For the purposes of debugging, identify a process (if any, perhaps one of
   * many) that references the passed file in its file descriptor array. Return
   * NULL if none.
   */
  static struct proc *
  file_to_first_proc(struct file *fp)
  {
          struct filedesc *fdp;
          struct proc *p;
          int n;
  
          FOREACH_PROC_IN_SYSTEM(p) {
                  if (p->p_state == PRS_NEW)
                          continue;
                  fdp = p->p_fd;
                  if (fdp == NULL)
                          continue;
                  for (n = 0; n < fdp->fd_nfiles; n++) {
                          if (fp == fdp->fd_ofiles[n])
                                  return (p);
                  }
          }
          return (NULL);
  }
  
  static void
  db_print_file(struct file *fp, int header)
  {
          struct proc *p;
  
          if (header)
                  db_printf("%8s %4s %8s %8s %4s %5s %6s %8s %5s %12s\n",
                      "File", "Type", "Data", "Flag", "GCFl", "Count",
                      "MCount", "Vnode", "FPID", "FCmd");
          p = file_to_first_proc(fp);
          db_printf("%8p %4s %8p %08x %04x %5d %6d %8p %5d %12s\n", fp,
              file_type_to_name(fp->f_type), fp->f_data, fp->f_flag,
              0, fp->f_count, 0, fp->f_vnode,
              p != NULL ? p->p_pid : -1, p != NULL ? p->p_comm : "-");
  }
  
  DB_SHOW_COMMAND(file, db_show_file)
  {
          struct file *fp;
  
          if (!have_addr) {
                  db_printf("usage: show file <addr>\n");
                  return;
          }
          fp = (struct file *)addr;
          db_print_file(fp, 1);
  }
  
  DB_SHOW_COMMAND(files, db_show_files)
  {
          struct filedesc *fdp;
          struct file *fp;
          struct proc *p;
          int header;
          int n;
  
          header = 1;
          FOREACH_PROC_IN_SYSTEM(p) {
                  if (p->p_state == PRS_NEW)
                          continue;
                  if ((fdp = p->p_fd) == NULL)
                          continue;
                  for (n = 0; n < fdp->fd_nfiles; ++n) {
                          if ((fp = fdp->fd_ofiles[n]) == NULL)
                                  continue;
                          db_print_file(fp, header);
                          header = 0;
                  }
          }
  }
  #endif
  
  SYSCTL_INT(_kern, KERN_MAXFILESPERPROC, maxfilesperproc, CTLFLAG_RW,
      &maxfilesperproc, 0, "Maximum files allowed open per process");
  
  SYSCTL_INT(_kern, KERN_MAXFILES, maxfiles, CTLFLAG_RW,
      &maxfiles, 0, "Maximum number of files");
  
  SYSCTL_INT(_kern, OID_AUTO, openfiles, CTLFLAG_RD,
      __DEVOLATILE(int *, &openfiles), 0, "System-wide number of open files");
  
  /* ARGSUSED*/
  static void
  filelistinit(void *dummy)
  {
  
          file_zone = uma_zcreate("Files", sizeof(struct file), NULL, NULL,
              NULL, NULL, UMA_ALIGN_PTR, UMA_ZONE_NOFREE);
          mtx_init(&sigio_lock, "sigio lock", NULL, MTX_DEF);
          mtx_init(&fdesc_mtx, "fdesc", NULL, MTX_DEF);
  }
  SYSINIT(select, SI_SUB_LOCK, SI_ORDER_FIRST, filelistinit, NULL);
  
  /*-------------------------------------------------------------------*/
  
  static int
  badfo_readwrite(struct file *fp, struct uio *uio, struct ucred *active_cred, int flags, struct thread *td)
  {
  
          return (EBADF);
  }
  
  static int
  badfo_truncate(struct file *fp, off_t length, struct ucred *active_cred, struct thread *td)
  {
  
          return (EINVAL);
  }
  
  static int
  badfo_ioctl(struct file *fp, u_long com, void *data, struct ucred *active_cred, struct thread *td)
  {
  
          return (EBADF);
  }
  
  static int
  badfo_poll(struct file *fp, int events, struct ucred *active_cred, struct thread *td)
  {
  
          return (0);
  }
  
  static int
  badfo_kqfilter(struct file *fp, struct knote *kn)
  {
  
          return (EBADF);
  }
  
  static int
  badfo_stat(struct file *fp, struct stat *sb, struct ucred *active_cred, struct thread *td)
  {
  
          return (EBADF);
  }
  
  static int
  badfo_close(struct file *fp, struct thread *td)
  {
  
          return (EBADF);
  }
  
  struct fileops badfileops = {
          .fo_read = badfo_readwrite,
          .fo_write = badfo_readwrite,
          .fo_truncate = badfo_truncate,
          .fo_ioctl = badfo_ioctl,
          .fo_poll = badfo_poll,
          .fo_kqfilter = badfo_kqfilter,
          .fo_stat = badfo_stat,
          .fo_close = badfo_close,
  };
  
  
  /*-------------------------------------------------------------------*/
  
  /*
   * 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.
   *
   * XXX: we could give this one a cloning event handler if necessary.
   */
  
  /* ARGSUSED */
  static int
  fdopen(struct cdev *dev, int mode, int type, struct thread *td)
  {
  
          /*
           * XXX Kludge: set curthread->td_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_dupfd = dev2unit(dev);
          return (ENODEV);
  }
  
  static struct cdevsw fildesc_cdevsw = {
          .d_version =    D_VERSION,
          .d_open =       fdopen,
          .d_name =       "FD",
  };
  
  static void
  fildesc_drvinit(void *unused)
  {
          struct cdev *dev;
  
          dev = make_dev(&fildesc_cdevsw, 0, UID_ROOT, GID_WHEEL, 0666, "fd/0");
          make_dev_alias(dev, "stdin");
          dev = make_dev(&fildesc_cdevsw, 1, UID_ROOT, GID_WHEEL, 0666, "fd/1");
          make_dev_alias(dev, "stdout");
          dev = make_dev(&fildesc_cdevsw, 2, UID_ROOT, GID_WHEEL, 0666, "fd/2");
          make_dev_alias(dev, "stderr");
  }
  
  SYSINIT(fildescdev, SI_SUB_DRIVERS, SI_ORDER_MIDDLE, fildesc_drvinit, NULL);