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

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * Copyright (c) 1982, 1986, 1989, 1991, 1993
      *      The Regents of the University of California.  All rights reserved.
      * (c) UNIX System Laboratories, Inc.
      * All or some portions of this file are derived from material licensed
      * to the University of California by American Telephone and Telegraph
      * Co. or Unix System Laboratories, Inc. and are reproduced herein with
     * the permission of UNIX System Laboratories, Inc.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      @(#)kern_descrip.c      8.6 (Berkeley) 4/19/94
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/12.0/sys/kern/kern_descrip.c 339341 2018-10-12 23:48:10Z mjg $");
    
    #include "opt_capsicum.h"
    #include "opt_ddb.h"
    #include "opt_ktrace.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    
    #include <sys/capsicum.h>
    #include <sys/conf.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/mutex.h>
    #include <sys/namei.h>
    #include <sys/selinfo.h>
    #include <sys/priv.h>
    #include <sys/proc.h>
    #include <sys/protosw.h>
    #include <sys/racct.h>
    #include <sys/resourcevar.h>
    #include <sys/sbuf.h>
    #include <sys/signalvar.h>
    #include <sys/kdb.h>
    #include <sys/stat.h>
    #include <sys/sx.h>
    #include <sys/syscallsubr.h>
    #include <sys/sysctl.h>
    #include <sys/sysproto.h>
    #include <sys/unistd.h>
    #include <sys/user.h>
    #include <sys/vnode.h>
    #ifdef KTRACE
    #include <sys/ktrace.h>
    #endif
    
    #include <net/vnet.h>
    
    #include <security/audit/audit.h>
    
    #include <vm/uma.h>
    #include <vm/vm.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");
    MALLOC_DEFINE(M_FILECAPS, "filecaps", "descriptor capabilities");
    
    MALLOC_DECLARE(M_FADVISE);
   
   static __read_mostly uma_zone_t file_zone;
   static __read_mostly uma_zone_t filedesc0_zone;
   
   static int      closefp(struct filedesc *fdp, int fd, struct file *fp,
                       struct thread *td, int holdleaders);
   static int      fd_first_free(struct filedesc *fdp, int low, int size);
   static int      fd_last_used(struct filedesc *fdp, int size);
   static void     fdgrowtable(struct filedesc *fdp, int nfd);
   static void     fdgrowtable_exp(struct filedesc *fdp, int nfd);
   static void     fdunused(struct filedesc *fdp, int fd);
   static void     fdused(struct filedesc *fdp, int fd);
   static int      getmaxfd(struct thread *td);
   static u_long   *filecaps_copy_prep(const struct filecaps *src);
   static void     filecaps_copy_finish(const struct filecaps *src,
                       struct filecaps *dst, u_long *ioctls);
   static u_long   *filecaps_free_prep(struct filecaps *fcaps);
   static void     filecaps_free_finish(u_long *ioctls);
   
   /*
    * Each process has:
    *
    * - An array of open file descriptors (fd_ofiles)
    * - An array of file flags (fd_ofileflags)
    * - A bitmap recording which descriptors are in use (fd_map)
    *
    * A process starts out with NDFILE descriptors.  The value of NDFILE has
    * been selected based the historical limit of 20 open files, and an
    * assumption that the majority of processes, especially short-lived
    * processes like shells, will never need more.
    *
    * If this initial allocation is exhausted, a larger descriptor table and
    * map are allocated dynamically, and the pointers in the process's struct
    * filedesc are updated to point to those.  This is repeated every time
    * the process runs out of file descriptors (provided it hasn't hit its
    * resource limit).
    *
    * Since threads may hold references to individual descriptor table
    * entries, the tables are never freed.  Instead, they are placed on a
    * linked list and freed only when the struct filedesc is released.
    */
   #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)
   
   /*
    * SLIST entry used to keep track of ofiles which must be reclaimed when
    * the process exits.
    */
   struct freetable {
           struct fdescenttbl *ft_table;
           SLIST_ENTRY(freetable) ft_next;
   };
   
   /*
    * Initial allocation: a filedesc structure + the head of SLIST used to
    * keep track of old ofiles + enough space for NDFILE descriptors.
    */
   
   struct fdescenttbl0 {
           int     fdt_nfiles;
           struct  filedescent fdt_ofiles[NDFILE];
   };
   
   struct filedesc0 {
           struct filedesc fd_fd;
           SLIST_HEAD(, freetable) fd_free;
           struct  fdescenttbl0 fd_dfiles;
           NDSLOTTYPE fd_dmap[NDSLOTS(NDFILE)];
   };
   
   /*
    * Descriptor management.
    */
   volatile int __exclusive_cache_line openfiles; /* actual number of open files */
   struct mtx sigio_lock;          /* mtx to protect pointers to sigio */
   void __read_mostly (*mq_fdclose)(struct thread *td, int fd, struct file *fp);
   
   /*
    * If low >= size, just return low. Otherwise find the first zero bit in the
    * given bitmap, starting at low and not exceeding size - 1. Return size if
    * not found.
    */
   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 0 and
    * not exceeding size - 1. Return -1 if not found.
    */
   static int
   fd_last_used(struct filedesc *fdp, int size)
   {
           NDSLOTTYPE *map = fdp->fd_map;
           NDSLOTTYPE mask;
           int off, minoff;
   
           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(0); off >= minoff; --off)
                   if (map[off] != 0)
                           return (off * NDENTRIES + flsl(map[off]) - 1);
           return (-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_init(struct filedesc *fdp, int fd)
   {
   
           KASSERT(!fdisused(fdp, fd), ("fd=%d is already used", fd));
   
           fdp->fd_map[NDSLOT(fd)] |= NDBIT(fd);
   }
   
   static void
   fdused(struct filedesc *fdp, int fd)
   {
   
           FILEDESC_XLOCK_ASSERT(fdp);
   
           fdused_init(fdp, 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=%d is already unused", fd));
           KASSERT(fdp->fd_ofiles[fd].fde_file == NULL,
               ("fd=%d is still in use", fd));
   
           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, fd);
   }
   
   /*
    * Free a file descriptor.
    *
    * Avoid some work if fdp is about to be destroyed.
    */
   static inline void
   fdefree_last(struct filedescent *fde)
   {
   
           filecaps_free(&fde->fde_caps);
   }
   
   static inline void
   fdfree(struct filedesc *fdp, int fd)
   {
           struct filedescent *fde;
   
           fde = &fdp->fd_ofiles[fd];
   #ifdef CAPABILITIES
           seq_write_begin(&fde->fde_seq);
   #endif
           fde->fde_file = NULL;
   #ifdef CAPABILITIES
           seq_write_end(&fde->fde_seq);
   #endif
           fdefree_last(fde);
           fdunused(fdp, fd);
   }
   
   void
   pwd_ensure_dirs(void)
   {
           struct filedesc *fdp;
   
           fdp = curproc->p_fd;
           FILEDESC_XLOCK(fdp);
           if (fdp->fd_cdir == NULL) {
                   fdp->fd_cdir = rootvnode;
                   vrefact(rootvnode);
           }
           if (fdp->fd_rdir == NULL) {
                   fdp->fd_rdir = rootvnode;
                   vrefact(rootvnode);
           }
           FILEDESC_XUNLOCK(fdp);
   }
   
   /*
    * System calls on descriptors.
    */
   #ifndef _SYS_SYSPROTO_H_
   struct getdtablesize_args {
           int     dummy;
   };
   #endif
   /* ARGSUSED */
   int
   sys_getdtablesize(struct thread *td, struct getdtablesize_args *uap)
   {
   #ifdef  RACCT
           uint64_t lim;
   #endif
   
           td->td_retval[0] =
               min((int)lim_cur(td, RLIMIT_NOFILE), maxfilesperproc);
   #ifdef  RACCT
           PROC_LOCK(td->td_proc);
           lim = racct_get_limit(td->td_proc, RACCT_NOFILE);
           PROC_UNLOCK(td->td_proc);
           if (lim < td->td_retval[0])
                   td->td_retval[0] = lim;
   #endif
           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
   sys_dup2(struct thread *td, struct dup2_args *uap)
   {
   
           return (kern_dup(td, FDDUP_FIXED, 0, (int)uap->from, (int)uap->to));
   }
   
   /*
    * Duplicate a file descriptor.
    */
   #ifndef _SYS_SYSPROTO_H_
   struct dup_args {
           u_int   fd;
   };
   #endif
   /* ARGSUSED */
   int
   sys_dup(struct thread *td, struct dup_args *uap)
   {
   
           return (kern_dup(td, FDDUP_NORMAL, 0, (int)uap->fd, 0));
   }
   
   /*
    * The file control system call.
    */
   #ifndef _SYS_SYSPROTO_H_
   struct fcntl_args {
           int     fd;
           int     cmd;
           long    arg;
   };
   #endif
   /* ARGSUSED */
   int
   sys_fcntl(struct thread *td, struct fcntl_args *uap)
   {
   
           return (kern_fcntl_freebsd(td, uap->fd, uap->cmd, uap->arg));
   }
   
   int
   kern_fcntl_freebsd(struct thread *td, int fd, int cmd, long arg)
   {
           struct flock fl;
           struct __oflock ofl;
           intptr_t arg1;
           int error, newcmd;
   
           error = 0;
           newcmd = cmd;
           switch (cmd) {
           case F_OGETLK:
           case F_OSETLK:
           case F_OSETLKW:
                   /*
                    * Convert old flock structure to new.
                    */
                   error = copyin((void *)(intptr_t)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 (cmd) {
                   case F_OGETLK:
                           newcmd = F_GETLK;
                           break;
                   case F_OSETLK:
                           newcmd = F_SETLK;
                           break;
                   case F_OSETLKW:
                           newcmd = F_SETLKW;
                           break;
                   }
                   arg1 = (intptr_t)&fl;
                   break;
           case F_GETLK:
           case F_SETLK:
           case F_SETLKW:
           case F_SETLK_REMOTE:
                   error = copyin((void *)(intptr_t)arg, &fl, sizeof(fl));
                   arg1 = (intptr_t)&fl;
                   break;
           default:
                   arg1 = arg;
                   break;
           }
           if (error)
                   return (error);
           error = kern_fcntl(td, fd, newcmd, arg1);
           if (error)
                   return (error);
           if (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)arg, sizeof(ofl));
           } else if (cmd == F_GETLK) {
                   error = copyout(&fl, (void *)(intptr_t)arg, sizeof(fl));
           }
           return (error);
   }
   
   int
   kern_fcntl(struct thread *td, int fd, int cmd, intptr_t arg)
   {
           struct filedesc *fdp;
           struct flock *flp;
           struct file *fp, *fp2;
           struct filedescent *fde;
           struct proc *p;
           struct vnode *vp;
           int error, flg, tmp;
           uint64_t bsize;
           off_t foffset;
   
           error = 0;
           flg = F_POSIX;
           p = td->td_proc;
           fdp = p->p_fd;
   
           AUDIT_ARG_FD(cmd);
           AUDIT_ARG_CMD(cmd);
           switch (cmd) {
           case F_DUPFD:
                   tmp = arg;
                   error = kern_dup(td, FDDUP_FCNTL, 0, fd, tmp);
                   break;
   
           case F_DUPFD_CLOEXEC:
                   tmp = arg;
                   error = kern_dup(td, FDDUP_FCNTL, FDDUP_FLAG_CLOEXEC, fd, tmp);
                   break;
   
           case F_DUP2FD:
                   tmp = arg;
                   error = kern_dup(td, FDDUP_FIXED, 0, fd, tmp);
                   break;
   
           case F_DUP2FD_CLOEXEC:
                   tmp = arg;
                   error = kern_dup(td, FDDUP_FIXED, FDDUP_FLAG_CLOEXEC, fd, tmp);
                   break;
   
           case F_GETFD:
                   error = EBADF;
                   FILEDESC_SLOCK(fdp);
                   fde = fdeget_locked(fdp, fd);
                   if (fde != NULL) {
                           td->td_retval[0] =
                               (fde->fde_flags & UF_EXCLOSE) ? FD_CLOEXEC : 0;
                           error = 0;
                   }
                   FILEDESC_SUNLOCK(fdp);
                   break;
   
           case F_SETFD:
                   error = EBADF;
                   FILEDESC_XLOCK(fdp);
                   fde = fdeget_locked(fdp, fd);
                   if (fde != NULL) {
                           fde->fde_flags = (fde->fde_flags & ~UF_EXCLOSE) |
                               (arg & FD_CLOEXEC ? UF_EXCLOSE : 0);
                           error = 0;
                   }
                   FILEDESC_XUNLOCK(fdp);
                   break;
   
           case F_GETFL:
                   error = fget_fcntl(td, fd, &cap_fcntl_rights, F_GETFL, &fp);
                   if (error != 0)
                           break;
                   td->td_retval[0] = OFLAGS(fp->f_flag);
                   fdrop(fp, td);
                   break;
   
           case F_SETFL:
                   error = fget_fcntl(td, fd, &cap_fcntl_rights, F_SETFL, &fp);
                   if (error != 0)
                           break;
                   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 != 0) {
                           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:
                   error = fget_fcntl(td, fd, &cap_fcntl_rights, F_GETOWN, &fp);
                   if (error != 0)
                           break;
                   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:
                   error = fget_fcntl(td, fd, &cap_fcntl_rights, F_SETOWN, &fp);
                   if (error != 0)
                           break;
                   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:
                   error = fget_unlocked(fdp, fd, &cap_flock_rights, &fp, NULL);
                   if (error != 0)
                           break;
                   if (fp->f_type != DTYPE_VNODE) {
                           error = EBADF;
                           fdrop(fp, td);
                           break;
                   }
   
                   flp = (struct flock *)arg;
                   if (flp->l_whence == SEEK_CUR) {
                           foffset = foffset_get(fp);
                           if (foffset < 0 ||
                               (flp->l_start > 0 &&
                                foffset > OFF_MAX - flp->l_start)) {
                                   error = EOVERFLOW;
                                   fdrop(fp, td);
                                   break;
                           }
                           flp->l_start += foffset;
                   }
   
                   vp = fp->f_vnode;
                   switch (flp->l_type) {
                   case F_RDLCK:
                           if ((fp->f_flag & FREAD) == 0) {
                                   error = EBADF;
                                   break;
                           }
                           if ((p->p_leader->p_flag & P_ADVLOCK) == 0) {
                                   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;
                           }
                           if ((p->p_leader->p_flag & P_ADVLOCK) == 0) {
                                   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;
                   }
                   if (error != 0 || flp->l_type == F_UNLCK ||
                       flp->l_type == F_UNLCKSYS) {
                           fdrop(fp, td);
                           break;
                   }
   
                   /*
                    * Check for a race with close.
                    *
                    * The vnode is now advisory locked (or unlocked, but this case
                    * is not really important) as the caller requested.
                    * We had to drop the filedesc lock, so we need to recheck if
                    * the descriptor is still valid, because if it was closed
                    * in the meantime we need to remove advisory lock from the
                    * vnode - close on any descriptor leading to an advisory
                    * locked vnode, removes that lock.
                    * We will return 0 on purpose in that case, as the result of
                    * successful advisory lock might have been externally visible
                    * already. This is fine - effectively we pretend to the caller
                    * that the closing thread was a bit slower and that the
                    * advisory lock succeeded before the close.
                    */
                   error = fget_unlocked(fdp, fd, &cap_no_rights, &fp2, NULL);
                   if (error != 0) {
                           fdrop(fp, td);
                           break;
                   }
                   if (fp != fp2) {
                           flp->l_whence = SEEK_SET;
                           flp->l_start = 0;
                           flp->l_len = 0;
                           flp->l_type = F_UNLCK;
                           (void) VOP_ADVLOCK(vp, (caddr_t)p->p_leader,
                               F_UNLCK, flp, F_POSIX);
                   }
                   fdrop(fp, td);
                   fdrop(fp2, td);
                   break;
   
           case F_GETLK:
                   error = fget_unlocked(fdp, fd, &cap_flock_rights, &fp, NULL);
                   if (error != 0)
                           break;
                   if (fp->f_type != DTYPE_VNODE) {
                           error = EBADF;
                           fdrop(fp, td);
                           break;
                   }
                   flp = (struct flock *)arg;
                   if (flp->l_type != F_RDLCK && flp->l_type != F_WRLCK &&
                       flp->l_type != F_UNLCK) {
                           error = EINVAL;
                           fdrop(fp, td);
                           break;
                   }
                   if (flp->l_whence == SEEK_CUR) {
                           foffset = foffset_get(fp);
                           if ((flp->l_start > 0 &&
                               foffset > OFF_MAX - flp->l_start) ||
                               (flp->l_start < 0 &&
                               foffset < OFF_MIN - flp->l_start)) {
                                   error = EOVERFLOW;
                                   fdrop(fp, td);
                                   break;
                           }
                           flp->l_start += foffset;
                   }
                   vp = fp->f_vnode;
                   error = VOP_ADVLOCK(vp, (caddr_t)p->p_leader, F_GETLK, flp,
                       F_POSIX);
                   fdrop(fp, td);
                   break;
   
           case F_RDAHEAD:
                   arg = arg ? 128 * 1024: 0;
                   /* FALLTHROUGH */
           case F_READAHEAD:
                   error = fget_unlocked(fdp, fd, &cap_no_rights, &fp, NULL);
                   if (error != 0)
                           break;
                   if (fp->f_type != DTYPE_VNODE) {
                           fdrop(fp, td);
                           error = EBADF;
                           break;
                   }
                   vp = fp->f_vnode;
                   /*
                    * Exclusive lock synchronizes against f_seqcount reads and
                    * writes in sequential_heuristic().
                    */
                   error = vn_lock(vp, LK_EXCLUSIVE);
                   if (error != 0) {
                           fdrop(fp, td);
                           break;
                   }
                   if (arg >= 0) {
                           bsize = fp->f_vnode->v_mount->mnt_stat.f_iosize;
                           fp->f_seqcount = (arg + bsize - 1) / bsize;
                           atomic_set_int(&fp->f_flag, FRDAHEAD);
                   } else {
                           atomic_clear_int(&fp->f_flag, FRDAHEAD);
                   }
                   VOP_UNLOCK(vp, 0);
                   fdrop(fp, td);
                   break;
   
           default:
                   error = EINVAL;
                   break;
           }
           return (error);
   }
   
   static int
   getmaxfd(struct thread *td)
   {
   
           return (min((int)lim_cur(td, RLIMIT_NOFILE), maxfilesperproc));
   }
   
   /*
    * Common code for dup, dup2, fcntl(F_DUPFD) and fcntl(F_DUP2FD).
    */
   int
   kern_dup(struct thread *td, u_int mode, int flags, int old, int new)
   {
           struct filedesc *fdp;
           struct filedescent *oldfde, *newfde;
           struct proc *p;
           struct file *delfp;
           u_long *oioctls, *nioctls;
           int error, maxfd;
   
           p = td->td_proc;
           fdp = p->p_fd;
   
           MPASS((flags & ~(FDDUP_FLAG_CLOEXEC)) == 0);
           MPASS(mode < FDDUP_LASTMODE);
   
           AUDIT_ARG_FD(old);
           /* XXXRW: if (flags & FDDUP_FIXED) AUDIT_ARG_FD2(new); */
   
           /*
            * 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 (mode == FDDUP_FCNTL ? EINVAL : EBADF);
           maxfd = getmaxfd(td);
           if (new >= maxfd)
                   return (mode == FDDUP_FCNTL ? EINVAL : EBADF);
   
           error = EBADF;
           FILEDESC_XLOCK(fdp);
           if (fget_locked(fdp, old) == NULL)
                   goto unlock;
           if ((mode == FDDUP_FIXED || mode == FDDUP_MUSTREPLACE) && old == new) {
                   td->td_retval[0] = new;
                   if (flags & FDDUP_FLAG_CLOEXEC)
                           fdp->fd_ofiles[new].fde_flags |= UF_EXCLOSE;
                   error = 0;
                   goto unlock;
           }
   
           /*
            * 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.
            */
           switch (mode) {
           case FDDUP_NORMAL:
           case FDDUP_FCNTL:
                   if ((error = fdalloc(td, new, &new)) != 0)
                           goto unlock;
                   break;
           case FDDUP_MUSTREPLACE:
                   /* Target file descriptor must exist. */
                   if (fget_locked(fdp, new) == NULL)
                           goto unlock;
                   break;
           case FDDUP_FIXED:
                   if (new >= fdp->fd_nfiles) {
                           /*
                            * The resource limits are here instead of e.g.
                            * fdalloc(), because the file descriptor table may be
                            * shared between processes, so we can't really use
                            * racct_add()/racct_sub().  Instead of counting the
                            * number of actually allocated descriptors, just put
                            * the limit on the size of the file descriptor table.
                            */
   #ifdef RACCT
                           if (racct_enable) {
                                   PROC_LOCK(p);
                                   error = racct_set(p, RACCT_NOFILE, new + 1);
                                   PROC_UNLOCK(p);
                                   if (error != 0) {
                                           error = EMFILE;
                                           goto unlock;
                                   }
                           }
   #endif
                           fdgrowtable_exp(fdp, new + 1);
                   }
                   if (!fdisused(fdp, new))
                           fdused(fdp, new);
                   break;
           default:
                   KASSERT(0, ("%s unsupported mode %d", __func__, mode));
           }
   
           KASSERT(old != new, ("new fd is same as old"));
   
           oldfde = &fdp->fd_ofiles[old];
           fhold(oldfde->fde_file);
           newfde = &fdp->fd_ofiles[new];
           delfp = newfde->fde_file;
   
           oioctls = filecaps_free_prep(&newfde->fde_caps);
           nioctls = filecaps_copy_prep(&oldfde->fde_caps);
   
           /*
            * Duplicate the source descriptor.
            */
   #ifdef CAPABILITIES
           seq_write_begin(&newfde->fde_seq);
   #endif
           memcpy(newfde, oldfde, fde_change_size);
           filecaps_copy_finish(&oldfde->fde_caps, &newfde->fde_caps,
               nioctls);
           if ((flags & FDDUP_FLAG_CLOEXEC) != 0)
                   newfde->fde_flags = oldfde->fde_flags | UF_EXCLOSE;
           else
                   newfde->fde_flags = oldfde->fde_flags & ~UF_EXCLOSE;
   #ifdef CAPABILITIES
           seq_write_end(&newfde->fde_seq);
   #endif
           filecaps_free_finish(oioctls);
           td->td_retval[0] = new;
   
           error = 0;
   
           if (delfp != NULL) {
                   (void) closefp(fdp, new, delfp, td, 1);
                   FILEDESC_UNLOCK_ASSERT(fdp);
           } else {
   unlock:
                   FILEDESC_XUNLOCK(fdp);
           }
   
           return (error);
   }
   
   /*
    * 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;
   
           if (*sigiop == NULL)
                   return;
           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(struct sigio **sigiop)
  {
          pid_t pgid;
  
          SIGIO_LOCK();
          pgid = (*sigiop != NULL) ? (*sigiop)->sio_pgid : 0;
          SIGIO_UNLOCK();
          return (pgid);
  }
  
  /*
   * Function drops the filedesc lock on return.
   */
  static int
  closefp(struct filedesc *fdp, int fd, struct file *fp, struct thread *td,
      int holdleaders)
  {
          int error;
  
          FILEDESC_XLOCK_ASSERT(fdp);
  
          if (holdleaders) {
                  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++;
                  } else {
                          holdleaders = 0;
                  }
          }
  
          /*
           * 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);
  
          /*
           * We need to notify mqueue if the object is of type mqueue.
           */
          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 a file descriptor.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct close_args {
          int     fd;
  };
  #endif
  /* ARGSUSED */
  int
  sys_close(struct thread *td, struct close_args *uap)
  {
  
          return (kern_close(td, uap->fd));
  }
  
  int
  kern_close(struct thread *td, int fd)
  {
          struct filedesc *fdp;
          struct file *fp;
  
          fdp = td->td_proc->p_fd;
  
          AUDIT_SYSCLOSE(td, fd);
  
          FILEDESC_XLOCK(fdp);
          if ((fp = fget_locked(fdp, fd)) == NULL) {
                  FILEDESC_XUNLOCK(fdp);
                  return (EBADF);
          }
          fdfree(fdp, fd);
  
          /* closefp() drops the FILEDESC lock for us. */
          return (closefp(fdp, fd, fp, td, 1));
  }
  
  /*
   * Close open file descriptors.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct closefrom_args {
          int     lowfd;
  };
  #endif
  /* ARGSUSED */
  int
  sys_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_lastfile; fd++) {
                  if (fdp->fd_ofiles[fd].fde_file != 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 */
  
  #if defined(COMPAT_FREEBSD11)
  int
  freebsd11_fstat(struct thread *td, struct freebsd11_fstat_args *uap)
  {
          struct stat sb;
          struct freebsd11_stat osb;
          int error;
  
          error = kern_fstat(td, uap->fd, &sb);
          if (error != 0)
                  return (error);
          error = freebsd11_cvtstat(&sb, &osb);
          if (error == 0)
                  error = copyout(&osb, uap->sb, sizeof(osb));
          return (error);
  }
  #endif  /* COMPAT_FREEBSD11 */
  
  /*
   * Return status information about a file descriptor.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct fstat_args {
          int     fd;
          struct  stat *sb;
  };
  #endif
  /* ARGSUSED */
  int
  sys_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);
  
          error = fget(td, fd, &cap_fstat_rights, &fp);
          if (error != 0)
                  return (error);
  
          AUDIT_ARG_FILE(td->td_proc, fp);
  
          error = fo_stat(fp, sbp, td->td_ucred, td);
          fdrop(fp, td);
  #ifdef __STAT_TIME_T_EXT
          if (error == 0) {
                  sbp->st_atim_ext = 0;
                  sbp->st_mtim_ext = 0;
                  sbp->st_ctim_ext = 0;
                  sbp->st_btim_ext = 0;
          }
  #endif
  #ifdef KTRACE
          if (error == 0 && KTRPOINT(td, KTR_STRUCT))
                  ktrstat(sbp);
  #endif
          return (error);
  }
  
  #if defined(COMPAT_FREEBSD11)
  /*
   * Return status information about a file descriptor.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct freebsd11_nfstat_args {
          int     fd;
          struct  nstat *sb;
  };
  #endif
  /* ARGSUSED */
  int
  freebsd11_nfstat(struct thread *td, struct freebsd11_nfstat_args *uap)
  {
          struct nstat nub;
          struct stat ub;
          int error;
  
          error = kern_fstat(td, uap->fd, &ub);
          if (error == 0) {
                  freebsd11_cvtnstat(&ub, &nub);
                  error = copyout(&nub, uap->sb, sizeof(nub));
          }
          return (error);
  }
  #endif /* COMPAT_FREEBSD11 */
  
  /*
   * Return pathconf information about a file descriptor.
   */
  #ifndef _SYS_SYSPROTO_H_
  struct fpathconf_args {
          int     fd;
          int     name;
  };
  #endif
  /* ARGSUSED */
  int
  sys_fpathconf(struct thread *td, struct fpathconf_args *uap)
  {
          long value;
          int error;
  
          error = kern_fpathconf(td, uap->fd, uap->name, &value);
          if (error == 0)
                  td->td_retval[0] = value;
          return (error);
  }
  
  int
  kern_fpathconf(struct thread *td, int fd, int name, long *valuep)
  {
          struct file *fp;
          struct vnode *vp;
          int error;
  
          error = fget(td, fd, &cap_fpathconf_rights, &fp);
          if (error != 0)
                  return (error);
  
          if (name == _PC_ASYNC_IO) {
                  *valuep = _POSIX_ASYNCHRONOUS_IO;
                  goto out;
          }
          vp = fp->f_vnode;
          if (vp != NULL) {
                  vn_lock(vp, LK_SHARED | LK_RETRY);
                  error = VOP_PATHCONF(vp, name, valuep);
                  VOP_UNLOCK(vp, 0);
          } else if (fp->f_type == DTYPE_PIPE || fp->f_type == DTYPE_SOCKET) {
                  if (name != _PC_PIPE_BUF) {
                          error = EINVAL;
                  } else {
                          *valuep = PIPE_BUF;
                          error = 0;
                  }
          } else {
                  error = EOPNOTSUPP;
          }
  out:
          fdrop(fp, td);
          return (error);
  }
  
  /*
   * Initialize filecaps structure.
   */
  void
  filecaps_init(struct filecaps *fcaps)
  {
  
          bzero(fcaps, sizeof(*fcaps));
          fcaps->fc_nioctls = -1;
  }
  
  /*
   * Copy filecaps structure allocating memory for ioctls array if needed.
   *
   * The last parameter indicates whether the fdtable is locked. If it is not and
   * ioctls are encountered, copying fails and the caller must lock the table.
   *
   * Note that if the table was not locked, the caller has to check the relevant
   * sequence counter to determine whether the operation was successful.
   */
  bool
  filecaps_copy(const struct filecaps *src, struct filecaps *dst, bool locked)
  {
          size_t size;
  
          if (src->fc_ioctls != NULL && !locked)
                  return (false);
          memcpy(dst, src, sizeof(*src));
          if (src->fc_ioctls == NULL)
                  return (true);
  
          KASSERT(src->fc_nioctls > 0,
              ("fc_ioctls != NULL, but fc_nioctls=%hd", src->fc_nioctls));
  
          size = sizeof(src->fc_ioctls[0]) * src->fc_nioctls;
          dst->fc_ioctls = malloc(size, M_FILECAPS, M_WAITOK);
          memcpy(dst->fc_ioctls, src->fc_ioctls, size);
          return (true);
  }
  
  static u_long *
  filecaps_copy_prep(const struct filecaps *src)
  {
          u_long *ioctls;
          size_t size;
  
          if (src->fc_ioctls == NULL)
                  return (NULL);
  
          KASSERT(src->fc_nioctls > 0,
              ("fc_ioctls != NULL, but fc_nioctls=%hd", src->fc_nioctls));
  
          size = sizeof(src->fc_ioctls[0]) * src->fc_nioctls;
          ioctls = malloc(size, M_FILECAPS, M_WAITOK);
          return (ioctls);
  }
  
  static void
  filecaps_copy_finish(const struct filecaps *src, struct filecaps *dst,
      u_long *ioctls)
  {
          size_t size;
  
          *dst = *src;
          if (src->fc_ioctls == NULL) {
                  MPASS(ioctls == NULL);
                  return;
          }
  
          size = sizeof(src->fc_ioctls[0]) * src->fc_nioctls;
          dst->fc_ioctls = ioctls;
          bcopy(src->fc_ioctls, dst->fc_ioctls, size);
  }
  
  /*
   * Move filecaps structure to the new place and clear the old place.
   */
  void
  filecaps_move(struct filecaps *src, struct filecaps *dst)
  {
  
          *dst = *src;
          bzero(src, sizeof(*src));
  }
  
  /*
   * Fill the given filecaps structure with full rights.
   */
  static void
  filecaps_fill(struct filecaps *fcaps)
  {
  
          CAP_ALL(&fcaps->fc_rights);
          fcaps->fc_ioctls = NULL;
          fcaps->fc_nioctls = -1;
          fcaps->fc_fcntls = CAP_FCNTL_ALL;
  }
  
  /*
   * Free memory allocated within filecaps structure.
   */
  void
  filecaps_free(struct filecaps *fcaps)
  {
  
          free(fcaps->fc_ioctls, M_FILECAPS);
          bzero(fcaps, sizeof(*fcaps));
  }
  
  static u_long *
  filecaps_free_prep(struct filecaps *fcaps)
  {
          u_long *ioctls;
  
          ioctls = fcaps->fc_ioctls;
          bzero(fcaps, sizeof(*fcaps));
          return (ioctls);
  }
  
  static void
  filecaps_free_finish(u_long *ioctls)
  {
  
          free(ioctls, M_FILECAPS);
  }
  
  /*
   * Validate the given filecaps structure.
   */
  static void
  filecaps_validate(const struct filecaps *fcaps, const char *func)
  {
  
          KASSERT(cap_rights_is_valid(&fcaps->fc_rights),
              ("%s: invalid rights", func));
          KASSERT((fcaps->fc_fcntls & ~CAP_FCNTL_ALL) == 0,
              ("%s: invalid fcntls", func));
          KASSERT(fcaps->fc_fcntls == 0 ||
              cap_rights_is_set(&fcaps->fc_rights, CAP_FCNTL),
              ("%s: fcntls without CAP_FCNTL", func));
          KASSERT(fcaps->fc_ioctls != NULL ? fcaps->fc_nioctls > 0 :
              (fcaps->fc_nioctls == -1 || fcaps->fc_nioctls == 0),
              ("%s: invalid ioctls", func));
          KASSERT(fcaps->fc_nioctls == 0 ||
              cap_rights_is_set(&fcaps->fc_rights, CAP_IOCTL),
              ("%s: ioctls without CAP_IOCTL", func));
  }
  
  static void
  fdgrowtable_exp(struct filedesc *fdp, int nfd)
  {
          int nfd1;
  
          FILEDESC_XLOCK_ASSERT(fdp);
  
          nfd1 = fdp->fd_nfiles * 2;
          if (nfd1 < nfd)
                  nfd1 = nfd;
          fdgrowtable(fdp, nfd1);
  }
  
  /*
   * Grow the file table to accommodate (at least) nfd descriptors.
   */
  static void
  fdgrowtable(struct filedesc *fdp, int nfd)
  {
          struct filedesc0 *fdp0;
          struct freetable *ft;
          struct fdescenttbl *ntable;
          struct fdescenttbl *otable;
          int nnfiles, onfiles;
          NDSLOTTYPE *nmap, *omap;
  
          /*
           * If lastfile is -1 this struct filedesc was just allocated and we are
           * growing it to accommodate for the one we are going to copy from. There
           * is no need to have a lock on this one as it's not visible to anyone.
           */
          if (fdp->fd_lastfile != -1)
                  FILEDESC_XLOCK_ASSERT(fdp);
  
          KASSERT(fdp->fd_nfiles > 0, ("zero-length file table"));
  
          /* save old values */
          onfiles = fdp->fd_nfiles;
          otable = fdp->fd_files;
          omap = fdp->fd_map;
  
          /* compute the size of the new table */
          nnfiles = NDSLOTS(nfd) * NDENTRIES; /* round up */
          if (nnfiles <= onfiles)
                  /* the table is already large enough */
                  return;
  
          /*
           * Allocate a new table.  We need enough space for the number of
           * entries, file entries themselves and the struct freetable we will use
           * when we decommission the table and place it on the freelist.
           * We place the struct freetable in the middle so we don't have
           * to worry about padding.
           */
          ntable = malloc(offsetof(struct fdescenttbl, fdt_ofiles) +
              nnfiles * sizeof(ntable->fdt_ofiles[0]) +
              sizeof(struct freetable),
              M_FILEDESC, M_ZERO | M_WAITOK);
          /* copy the old data */
          ntable->fdt_nfiles = nnfiles;
          memcpy(ntable->fdt_ofiles, otable->fdt_ofiles,
              onfiles * sizeof(ntable->fdt_ofiles[0]));
  
          /*
           * Allocate a new map only if the old is not large enough.  It will
           * grow at a slower rate than the table as it can map more
           * entries than the table can hold.
           */
          if (NDSLOTS(nnfiles) > NDSLOTS(onfiles)) {
                  nmap = malloc(NDSLOTS(nnfiles) * NDSLOTSIZE, M_FILEDESC,
                      M_ZERO | M_WAITOK);
                  /* copy over the old data and update the pointer */
                  memcpy(nmap, omap, NDSLOTS(onfiles) * sizeof(*omap));
                  fdp->fd_map = nmap;
          }
  
          /*
           * Make sure that ntable is correctly initialized before we replace
           * fd_files poiner. Otherwise fget_unlocked() may see inconsistent
           * data.
           */
          atomic_store_rel_ptr((volatile void *)&fdp->fd_files, (uintptr_t)ntable);
  
          /*
           * Do not free the old file table, as some threads may still
           * reference entries within it.  Instead, place it on a freelist
           * which will be processed when the struct filedesc is released.
           *
           * Note that if onfiles == NDFILE, we're dealing with the original
           * static allocation contained within (struct filedesc0 *)fdp,
           * which must not be freed.
           */
          if (onfiles > NDFILE) {
                  ft = (struct freetable *)&otable->fdt_ofiles[onfiles];
                  fdp0 = (struct filedesc0 *)fdp;
                  ft->ft_table = otable;
                  SLIST_INSERT_HEAD(&fdp0->fd_free, ft, ft_next);
          }
          /*
           * The map does not have the same possibility of threads still
           * holding references to it.  So always free it as long as it
           * does not reference the original static allocation.
           */
          if (NDSLOTS(onfiles) > NDSLOTS(NDFILE))
                  free(omap, M_FILEDESC);
  }
  
  /*
   * 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, maxfd, allocfd;
  #ifdef RACCT
          int error;
  #endif
  
          FILEDESC_XLOCK_ASSERT(fdp);
  
          if (fdp->fd_freefile > minfd)
                  minfd = fdp->fd_freefile;
  
          maxfd = getmaxfd(td);
  
          /*
           * Search the bitmap for a free descriptor starting at minfd.
           * If none is found, grow the file table.
           */
          fd = fd_first_free(fdp, minfd, fdp->fd_nfiles);
          if (fd >= maxfd)
                  return (EMFILE);
          if (fd >= fdp->fd_nfiles) {
                  allocfd = min(fd * 2, maxfd);
  #ifdef RACCT
                  if (racct_enable) {
                          PROC_LOCK(p);
                          error = racct_set(p, RACCT_NOFILE, allocfd);
                          PROC_UNLOCK(p);
                          if (error != 0)
                                  return (EMFILE);
                  }
  #endif
                  /*
                   * fd is already equal to first free descriptor >= minfd, so
                   * we only need to grow the table and we are done.
                   */
                  fdgrowtable_exp(fdp, allocfd);
          }
  
          /*
           * Perform some sanity checks, then mark the file descriptor as
           * used and return it to the caller.
           */
          KASSERT(fd >= 0 && fd < min(maxfd, fdp->fd_nfiles),
              ("invalid descriptor %d", fd));
          KASSERT(!fdisused(fdp, fd),
              ("fd_first_free() returned non-free descriptor"));
          KASSERT(fdp->fd_ofiles[fd].fde_file == NULL,
              ("file descriptor isn't free"));
          fdused(fdp, fd);
          *result = fd;
          return (0);
  }
  
  /*
   * Allocate n file descriptors for the process.
   */
  int
  fdallocn(struct thread *td, int minfd, int *fds, int n)
  {
          struct proc *p = td->td_proc;
          struct filedesc *fdp = p->p_fd;
          int i;
  
          FILEDESC_XLOCK_ASSERT(fdp);
  
          for (i = 0; i < n; i++)
                  if (fdalloc(td, 0, &fds[i]) != 0)
                          break;
  
          if (i < n) {
                  for (i--; i >= 0; i--)
                          fdunused(fdp, fds[i]);
                  return (EMFILE);
          }
  
          return (0);
  }
  
  /*
   * Create a new open file structure and allocate a file descriptor 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_caps(struct thread *td, struct file **resultfp, int *resultfd, int flags,
      struct filecaps *fcaps)
  {
          struct file *fp;
          int error, fd;
  
          error = falloc_noinstall(td, &fp);
          if (error)
                  return (error);         /* no reference held on error */
  
          error = finstall(td, fp, &fd, flags, fcaps);
          if (error) {
                  fdrop(fp, td);          /* one reference (fp only) */
                  return (error);
          }
  
          if (resultfp != NULL)
                  *resultfp = fp;         /* copy out result */
          else
                  fdrop(fp, td);          /* release local reference */
  
          if (resultfd != NULL)
                  *resultfd = fd;
  
          return (0);
  }
  
  /*
   * Create a new open file structure without allocating a file descriptor.
   */
  int
  falloc_noinstall(struct thread *td, struct file **resultfp)
  {
          struct file *fp;
          int maxuserfiles = maxfiles - (maxfiles / 20);
          int openfiles_new;
          static struct timeval lastfail;
          static int curfail;
  
          KASSERT(resultfp != NULL, ("%s: resultfp == NULL", __func__));
  
          openfiles_new = atomic_fetchadd_int(&openfiles, 1) + 1;
          if ((openfiles_new >= maxuserfiles &&
              priv_check(td, PRIV_MAXFILES) != 0) ||
              openfiles_new >= maxfiles) {
                  atomic_subtract_int(&openfiles, 1);
                  if (ppsratecheck(&lastfail, &curfail, 1)) {
                          printf("kern.maxfiles limit exceeded by uid %i, (%s) "
                              "please see tuning(7).\n", td->td_ucred->cr_ruid, td->td_proc->p_comm);
                  }
                  return (ENFILE);
          }
          fp = uma_zalloc(file_zone, M_WAITOK);
          bzero(fp, sizeof(*fp));
          refcount_init(&fp->f_count, 1);
          fp->f_cred = crhold(td->td_ucred);
          fp->f_ops = &badfileops;
          *resultfp = fp;
          return (0);
  }
  
  /*
   * Install a file in a file descriptor table.
   */
  void
  _finstall(struct filedesc *fdp, struct file *fp, int fd, int flags,
      struct filecaps *fcaps)
  {
          struct filedescent *fde;
  
          MPASS(fp != NULL);
          if (fcaps != NULL)
                  filecaps_validate(fcaps, __func__);
          FILEDESC_XLOCK_ASSERT(fdp);
  
          fde = &fdp->fd_ofiles[fd];
  #ifdef CAPABILITIES
          seq_write_begin(&fde->fde_seq);
  #endif
          fde->fde_file = fp;
          fde->fde_flags = (flags & O_CLOEXEC) != 0 ? UF_EXCLOSE : 0;
          if (fcaps != NULL)
                  filecaps_move(fcaps, &fde->fde_caps);
          else
                  filecaps_fill(&fde->fde_caps);
  #ifdef CAPABILITIES
          seq_write_end(&fde->fde_seq);
  #endif
  }
  
  int
  finstall(struct thread *td, struct file *fp, int *fd, int flags,
      struct filecaps *fcaps)
  {
          struct filedesc *fdp = td->td_proc->p_fd;
          int error;
  
          MPASS(fd != NULL);
  
          FILEDESC_XLOCK(fdp);
          if ((error = fdalloc(td, 0, fd))) {
                  FILEDESC_XUNLOCK(fdp);
                  return (error);
          }
          fhold(fp);
          _finstall(fdp, fp, *fd, flags, fcaps);
          FILEDESC_XUNLOCK(fdp);
          return (0);
  }
  
  /*
   * Build a new filedesc structure from another.
   * Copy the current, root, and jail root vnode references.
   *
   * If fdp is not NULL, return with it shared locked.
   */
  struct filedesc *
  fdinit(struct filedesc *fdp, bool prepfiles)
  {
          struct filedesc0 *newfdp0;
          struct filedesc *newfdp;
  
          newfdp0 = uma_zalloc(filedesc0_zone, M_WAITOK | M_ZERO);
          newfdp = &newfdp0->fd_fd;
  
          /* Create the file descriptor table. */
          FILEDESC_LOCK_INIT(newfdp);
          refcount_init(&newfdp->fd_refcnt, 1);
          refcount_init(&newfdp->fd_holdcnt, 1);
          newfdp->fd_cmask = CMASK;
          newfdp->fd_map = newfdp0->fd_dmap;
          newfdp->fd_lastfile = -1;
          newfdp->fd_files = (struct fdescenttbl *)&newfdp0->fd_dfiles;
          newfdp->fd_files->fdt_nfiles = NDFILE;
  
          if (fdp == NULL)
                  return (newfdp);
  
          if (prepfiles && fdp->fd_lastfile >= newfdp->fd_nfiles)
                  fdgrowtable(newfdp, fdp->fd_lastfile + 1);
  
          FILEDESC_SLOCK(fdp);
          newfdp->fd_cdir = fdp->fd_cdir;
          if (newfdp->fd_cdir)
                  vrefact(newfdp->fd_cdir);
          newfdp->fd_rdir = fdp->fd_rdir;
          if (newfdp->fd_rdir)
                  vrefact(newfdp->fd_rdir);
          newfdp->fd_jdir = fdp->fd_jdir;
          if (newfdp->fd_jdir)
                  vrefact(newfdp->fd_jdir);
  
          if (!prepfiles) {
                  FILEDESC_SUNLOCK(fdp);
          } else {
                  while (fdp->fd_lastfile >= newfdp->fd_nfiles) {
                          FILEDESC_SUNLOCK(fdp);
                          fdgrowtable(newfdp, fdp->fd_lastfile + 1);
                          FILEDESC_SLOCK(fdp);
                  }
          }
  
          return (newfdp);
  }
  
  static struct filedesc *
  fdhold(struct proc *p)
  {
          struct filedesc *fdp;
  
          PROC_LOCK_ASSERT(p, MA_OWNED);
          fdp = p->p_fd;
          if (fdp != NULL)
                  refcount_acquire(&fdp->fd_holdcnt);
          return (fdp);
  }
  
  static void
  fddrop(struct filedesc *fdp)
  {
  
          if (fdp->fd_holdcnt > 1) {
                  if (refcount_release(&fdp->fd_holdcnt) == 0)
                          return;
          }
  
          FILEDESC_LOCK_DESTROY(fdp);
          uma_zfree(filedesc0_zone, fdp);
  }
  
  /*
   * Share a filedesc structure.
   */
  struct filedesc *
  fdshare(struct filedesc *fdp)
  {
  
          refcount_acquire(&fdp->fd_refcnt);
          return (fdp);
  }
  
  /*
   * Unshare a filedesc structure, if necessary by making a copy
   */
  void
  fdunshare(struct thread *td)
  {
          struct filedesc *tmp;
          struct proc *p = td->td_proc;
  
          if (p->p_fd->fd_refcnt == 1)
                  return;
  
          tmp = fdcopy(p->p_fd);
          fdescfree(td);
          p->p_fd = tmp;
  }
  
  void
  fdinstall_remapped(struct thread *td, struct filedesc *fdp)
  {
  
          fdescfree(td);
          td->td_proc->p_fd = fdp;
  }
  
  /*
   * 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;
          struct filedescent *nfde, *ofde;
          int i;
  
          MPASS(fdp != NULL);
  
          newfdp = fdinit(fdp, true);
          /* copy all passable descriptors (i.e. not kqueue) */
          newfdp->fd_freefile = -1;
          for (i = 0; i <= fdp->fd_lastfile; ++i) {
                  ofde = &fdp->fd_ofiles[i];
                  if (ofde->fde_file == NULL ||
                      (ofde->fde_file->f_ops->fo_flags & DFLAG_PASSABLE) == 0) {
                          if (newfdp->fd_freefile == -1)
                                  newfdp->fd_freefile = i;
                          continue;
                  }
                  nfde = &newfdp->fd_ofiles[i];
                  *nfde = *ofde;
                  filecaps_copy(&ofde->fde_caps, &nfde->fde_caps, true);
                  fhold(nfde->fde_file);
                  fdused_init(newfdp, i);
                  newfdp->fd_lastfile = i;
          }
          if (newfdp->fd_freefile == -1)
                  newfdp->fd_freefile = i;
          newfdp->fd_cmask = fdp->fd_cmask;
          FILEDESC_SUNLOCK(fdp);
          return (newfdp);
  }
  
  /*
   * Copies a filedesc structure, while remapping all file descriptors
   * stored inside using a translation table.
   *
   * File descriptors are copied over to the new file descriptor table,
   * regardless of whether the close-on-exec flag is set.
   */
  int
  fdcopy_remapped(struct filedesc *fdp, const int *fds, size_t nfds,
      struct filedesc **ret)
  {
          struct filedesc *newfdp;
          struct filedescent *nfde, *ofde;
          int error, i;
  
          MPASS(fdp != NULL);
  
          newfdp = fdinit(fdp, true);
          if (nfds > fdp->fd_lastfile + 1) {
                  /* New table cannot be larger than the old one. */
                  error = E2BIG;
                  goto bad;
          }
          /* Copy all passable descriptors (i.e. not kqueue). */
          newfdp->fd_freefile = nfds;
          for (i = 0; i < nfds; ++i) {
                  if (fds[i] < 0 || fds[i] > fdp->fd_lastfile) {
                          /* File descriptor out of bounds. */
                          error = EBADF;
                          goto bad;
                  }
                  ofde = &fdp->fd_ofiles[fds[i]];
                  if (ofde->fde_file == NULL) {
                          /* Unused file descriptor. */
                          error = EBADF;
                          goto bad;
                  }
                  if ((ofde->fde_file->f_ops->fo_flags & DFLAG_PASSABLE) == 0) {
                          /* File descriptor cannot be passed. */
                          error = EINVAL;
                          goto bad;
                  }
                  nfde = &newfdp->fd_ofiles[i];
                  *nfde = *ofde;
                  filecaps_copy(&ofde->fde_caps, &nfde->fde_caps, true);
                  fhold(nfde->fde_file);
                  fdused_init(newfdp, i);
                  newfdp->fd_lastfile = i;
          }
          newfdp->fd_cmask = fdp->fd_cmask;
          FILEDESC_SUNLOCK(fdp);
          *ret = newfdp;
          return (0);
  bad:
          FILEDESC_SUNLOCK(fdp);
          fdescfree_remapped(newfdp);
          return (error);
  }
  
  /*
   * Clear POSIX style locks. This is only used when fdp looses a reference (i.e.
   * one of processes using it exits) and the table used to be shared.
   */
  static void
  fdclearlocks(struct thread *td)
  {
          struct filedesc *fdp;
          struct filedesc_to_leader *fdtol;
          struct flock lf;
          struct file *fp;
          struct proc *p;
          struct vnode *vp;
          int i;
  
          p = td->td_proc;
          fdp = p->p_fd;
          fdtol = p->p_fdtol;
          MPASS(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 &&
              (p->p_leader->p_flag & P_ADVLOCK) != 0) {
                  for (i = 0; i <= fdp->fd_lastfile; i++) {
                          fp = fdp->fd_ofiles[i].fde_file;
                          if (fp == NULL || fp->f_type != DTYPE_VNODE)
                                  continue;
                          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;
                          (void) VOP_ADVLOCK(vp,
                              (caddr_t)p->p_leader, F_UNLCK,
                              &lf, F_POSIX);
                          FILEDESC_XLOCK(fdp);
                          fdrop(fp, td);
                  }
          }
  retry:
          if (fdtol->fdl_refcount == 1) {
                  if (fdp->fd_holdleaderscount > 0 &&
                      (p->p_leader->p_flag & P_ADVLOCK) != 0) {
                          /*
                           * close() or kern_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;
          p->p_fdtol = NULL;
          FILEDESC_XUNLOCK(fdp);
          if (fdtol != NULL)
                  free(fdtol, M_FILEDESC_TO_LEADER);
  }
  
  /*
   * Release a filedesc structure.
   */
  static void
  fdescfree_fds(struct thread *td, struct filedesc *fdp, bool needclose)
  {
          struct filedesc0 *fdp0;
          struct freetable *ft, *tft;
          struct filedescent *fde;
          struct file *fp;
          int i;
  
          for (i = 0; i <= fdp->fd_lastfile; i++) {
                  fde = &fdp->fd_ofiles[i];
                  fp = fde->fde_file;
                  if (fp != NULL) {
                          fdefree_last(fde);
                          if (needclose)
                                  (void) closef(fp, td);
                          else
                                  fdrop(fp, td);
                  }
          }
  
          if (NDSLOTS(fdp->fd_nfiles) > NDSLOTS(NDFILE))
                  free(fdp->fd_map, M_FILEDESC);
          if (fdp->fd_nfiles > NDFILE)
                  free(fdp->fd_files, M_FILEDESC);
  
          fdp0 = (struct filedesc0 *)fdp;
          SLIST_FOREACH_SAFE(ft, &fdp0->fd_free, ft_next, tft)
                  free(ft->ft_table, M_FILEDESC);
  
          fddrop(fdp);
  }
  
  void
  fdescfree(struct thread *td)
  {
          struct proc *p;
          struct filedesc *fdp;
          struct vnode *cdir, *jdir, *rdir;
  
          p = td->td_proc;
          fdp = p->p_fd;
          MPASS(fdp != NULL);
  
  #ifdef RACCT
          if (racct_enable) {
                  PROC_LOCK(p);
                  racct_set(p, RACCT_NOFILE, 0);
                  PROC_UNLOCK(p);
          }
  #endif
  
          if (p->p_fdtol != NULL)
                  fdclearlocks(td);
  
          PROC_LOCK(p);
          p->p_fd = NULL;
          PROC_UNLOCK(p);
  
          if (refcount_release(&fdp->fd_refcnt) == 0)
                  return;
  
          FILEDESC_XLOCK(fdp);
          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 != NULL)
                  vrele(cdir);
          if (rdir != NULL)
                  vrele(rdir);
          if (jdir != NULL)
                  vrele(jdir);
  
          fdescfree_fds(td, fdp, 1);
  }
  
  void
  fdescfree_remapped(struct filedesc *fdp)
  {
  
          if (fdp->fd_cdir != NULL)
                  vrele(fdp->fd_cdir);
          if (fdp->fd_rdir != NULL)
                  vrele(fdp->fd_rdir);
          if (fdp->fd_jdir != NULL)
                  vrele(fdp->fd_jdir);
  
          fdescfree_fds(curthread, fdp, 0);
  }
  
  /*
   * 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 fdsetugidsafety 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 bool
  is_unsafe(struct file *fp)
  {
          struct vnode *vp;
  
          if (fp->f_type != DTYPE_VNODE)
                  return (false);
  
          vp = fp->f_vnode;
          return ((vp->v_vflag & VV_PROCDEP) != 0);
  }
  
  /*
   * Make this setguid thing safe, if at all possible.
   */
  void
  fdsetugidsafety(struct thread *td)
  {
          struct filedesc *fdp;
          struct file *fp;
          int i;
  
          fdp = td->td_proc->p_fd;
          KASSERT(fdp->fd_refcnt == 1, ("the fdtable should not be shared"));
          MPASS(fdp->fd_nfiles >= 3);
          for (i = 0; i <= 2; i++) {
                  fp = fdp->fd_ofiles[i].fde_file;
                  if (fp != NULL && is_unsafe(fp)) {
                          FILEDESC_XLOCK(fdp);
                          knote_fdclose(td, i);
                          /*
                           * NULL-out descriptor prior to close to avoid
                           * a race while close blocks.
                           */
                          fdfree(fdp, i);
                          FILEDESC_XUNLOCK(fdp);
                          (void) closef(fp, td);
                  }
          }
  }
  
  /*
   * 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 thread *td, struct file *fp, int idx)
  {
          struct filedesc *fdp = td->td_proc->p_fd;
  
          FILEDESC_XLOCK(fdp);
          if (fdp->fd_ofiles[idx].fde_file == fp) {
                  fdfree(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;
          struct filedescent *fde;
          struct file *fp;
          int i;
  
          fdp = td->td_proc->p_fd;
          KASSERT(fdp->fd_refcnt == 1, ("the fdtable should not be shared"));
          for (i = 0; i <= fdp->fd_lastfile; i++) {
                  fde = &fdp->fd_ofiles[i];
                  fp = fde->fde_file;
                  if (fp != NULL && (fp->f_type == DTYPE_MQUEUE ||
                      (fde->fde_flags & UF_EXCLOSE))) {
                          FILEDESC_XLOCK(fdp);
                          fdfree(fdp, i);
                          (void) closefp(fdp, i, fp, td, 0);
                          FILEDESC_UNLOCK_ASSERT(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 save;
          int i, error, devnull;
  
          fdp = td->td_proc->p_fd;
          KASSERT(fdp->fd_refcnt == 1, ("the fdtable should not be shared"));
          MPASS(fdp->fd_nfiles >= 3);
          devnull = -1;
          for (i = 0; i <= 2; i++) {
                  if (fdp->fd_ofiles[i].fde_file != NULL)
                          continue;
  
                  save = td->td_retval[0];
                  if (devnull != -1) {
                          error = kern_dup(td, FDDUP_FIXED, 0, devnull, i);
                  } else {
                          error = kern_openat(td, AT_FDCWD, "/dev/null",
                              UIO_SYSSPACE, O_RDWR, 0);
                          if (error == 0) {
                                  devnull = td->td_retval[0];
                                  KASSERT(devnull == i, ("we didn't get our fd"));
                          }
                  }
                  td->td_retval[0] = save;
                  if (error != 0)
                          return (error);
          }
          return (0);
  }
  
  /*
   * 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) {
                  vp = fp->f_vnode;
                  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);
                  }
          }
          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);
  }
  
  int
  fget_cap_locked(struct filedesc *fdp, int fd, cap_rights_t *needrightsp,
      struct file **fpp, struct filecaps *havecapsp)
  {
          struct filedescent *fde;
          int error;
  
          FILEDESC_LOCK_ASSERT(fdp);
  
          fde = fdeget_locked(fdp, fd);
          if (fde == NULL) {
                  error = EBADF;
                  goto out;
          }
  
  #ifdef CAPABILITIES
          error = cap_check(cap_rights_fde_inline(fde), needrightsp);
          if (error != 0)
                  goto out;
  #endif
  
          if (havecapsp != NULL)
                  filecaps_copy(&fde->fde_caps, havecapsp, true);
  
          *fpp = fde->fde_file;
  
          error = 0;
  out:
          return (error);
  }
  
  int
  fget_cap(struct thread *td, int fd, cap_rights_t *needrightsp,
      struct file **fpp, struct filecaps *havecapsp)
  {
          struct filedesc *fdp = td->td_proc->p_fd;
          int error;
  #ifndef CAPABILITIES
          error = fget_unlocked(fdp, fd, needrightsp, fpp, NULL);
          if (error == 0 && havecapsp != NULL)
                  filecaps_fill(havecapsp);
  #else
          struct file *fp;
          seq_t seq;
  
          for (;;) {
                  error = fget_unlocked(fdp, fd, needrightsp, &fp, &seq);
                  if (error != 0)
                          return (error);
  
                  if (havecapsp != NULL) {
                          if (!filecaps_copy(&fdp->fd_ofiles[fd].fde_caps,
                              havecapsp, false)) {
                                  fdrop(fp, td);
                                  goto get_locked;
                          }
                  }
  
                  if (!fd_modified(fdp, fd, seq))
                          break;
                  fdrop(fp, td);
          }
  
          *fpp = fp;
          return (0);
  
  get_locked:
          FILEDESC_SLOCK(fdp);
          error = fget_cap_locked(fdp, fd, needrightsp, fpp, havecapsp);
          if (error == 0)
                  fhold(*fpp);
          FILEDESC_SUNLOCK(fdp);
  #endif
          return (error);
  }
  
  int
  fget_unlocked(struct filedesc *fdp, int fd, cap_rights_t *needrightsp,
      struct file **fpp, seq_t *seqp)
  {
  #ifdef CAPABILITIES
          const struct filedescent *fde;
  #endif
          const struct fdescenttbl *fdt;
          struct file *fp;
          u_int count;
  #ifdef CAPABILITIES
          seq_t seq;
          cap_rights_t haverights;
          int error;
  #endif
  
          fdt = fdp->fd_files;
          if ((u_int)fd >= fdt->fdt_nfiles)
                  return (EBADF);
          /*
           * 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 (;;) {
  #ifdef CAPABILITIES
                  seq = seq_read(fd_seq(fdt, fd));
                  fde = &fdt->fdt_ofiles[fd];
                  haverights = *cap_rights_fde_inline(fde);
                  fp = fde->fde_file;
                  if (!seq_consistent(fd_seq(fdt, fd), seq))
                          continue;
  #else
                  fp = fdt->fdt_ofiles[fd].fde_file;
  #endif
                  if (fp == NULL)
                          return (EBADF);
  #ifdef CAPABILITIES
                  error = cap_check(&haverights, needrightsp);
                  if (error != 0)
                          return (error);
  #endif
                  count = fp->f_count;
          retry:
                  if (count == 0) {
                          /*
                           * Force a reload. Other thread could reallocate the
                           * table before this fd was closed, so it possible that
                           * there is a stale fp pointer in cached version.
                           */
                          fdt = *(const struct fdescenttbl * const volatile *)&(fdp->fd_files);
                          continue;
                  }
                  /*
                   * Use an acquire barrier to force re-reading of fdt so it is
                   * refreshed for verification.
                   */
                  if (atomic_fcmpset_acq_int(&fp->f_count, &count, count + 1) == 0)
                          goto retry;
                  fdt = fdp->fd_files;
  #ifdef  CAPABILITIES
                  if (seq_consistent_nomb(fd_seq(fdt, fd), seq))
  #else
                  if (fp == fdt->fdt_ofiles[fd].fde_file)
  #endif
                          break;
                  fdrop(fp, curthread);
          }
          *fpp = fp;
          if (seqp != NULL) {
  #ifdef CAPABILITIES
                  *seqp = seq;
  #endif
          }
          return (0);
  }
  
  /*
   * 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.
   *
   * File's rights will be checked against the capability rights mask.
   *
   * If an error occurred 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,
      cap_rights_t *needrightsp, seq_t *seqp)
  {
          struct filedesc *fdp;
          struct file *fp;
          int error;
  
          *fpp = NULL;
          fdp = td->td_proc->p_fd;
          error = fget_unlocked(fdp, fd, needrightsp, &fp, seqp);
          if (error != 0)
                  return (error);
          if (fp->f_ops == &badfileops) {
                  fdrop(fp, td);
                  return (EBADF);
          }
  
          /*
           * FREAD and FWRITE failure return EBADF as per POSIX.
           */
          error = 0;
          switch (flags) {
          case FREAD:
          case FWRITE:
                  if ((fp->f_flag & flags) == 0)
                          error = EBADF;
                  break;
          case FEXEC:
                  if ((fp->f_flag & (FREAD | FEXEC)) == 0 ||
                      ((fp->f_flag & FWRITE) != 0))
                          error = EBADF;
                  break;
          case 0:
                  break;
          default:
                  KASSERT(0, ("wrong flags"));
          }
  
          if (error != 0) {
                  fdrop(fp, td);
                  return (error);
          }
  
          *fpp = fp;
          return (0);
  }
  
  int
  fget(struct thread *td, int fd, cap_rights_t *rightsp, struct file **fpp)
  {
  
          return (_fget(td, fd, fpp, 0, rightsp, NULL));
  }
  
  int
  fget_mmap(struct thread *td, int fd, cap_rights_t *rightsp, u_char *maxprotp,
      struct file **fpp)
  {
          int error;
  #ifndef CAPABILITIES
          error = _fget(td, fd, fpp, 0, rightsp, NULL);
          if (maxprotp != NULL)
                  *maxprotp = VM_PROT_ALL;
  #else
          struct filedesc *fdp = td->td_proc->p_fd;
          seq_t seq;
  
          MPASS(cap_rights_is_set(rightsp, CAP_MMAP));
          for (;;) {
                  error = _fget(td, fd, fpp, 0, rightsp, &seq);
                  if (error != 0)
                          return (error);
                  /*
                   * If requested, convert capability rights to access flags.
                   */
                  if (maxprotp != NULL)
                          *maxprotp = cap_rights_to_vmprot(cap_rights(fdp, fd));
                  if (!fd_modified(fdp, fd, seq))
                          break;
                  fdrop(*fpp, td);
          }
  #endif
          return (error);
  }
  
  int
  fget_read(struct thread *td, int fd, cap_rights_t *rightsp, struct file **fpp)
  {
  
          return (_fget(td, fd, fpp, FREAD, rightsp, NULL));
  }
  
  int
  fget_write(struct thread *td, int fd, cap_rights_t *rightsp, struct file **fpp)
  {
  
          return (_fget(td, fd, fpp, FWRITE, rightsp, NULL));
  }
  
  int
  fget_fcntl(struct thread *td, int fd, cap_rights_t *rightsp, int needfcntl,
      struct file **fpp)
  {
          struct filedesc *fdp = td->td_proc->p_fd;
  #ifndef CAPABILITIES
          return (fget_unlocked(fdp, fd, rightsp, fpp, NULL));
  #else
          int error;
          seq_t seq;
  
          MPASS(cap_rights_is_set(rightsp, CAP_FCNTL));
          for (;;) {
                  error = fget_unlocked(fdp, fd, rightsp, fpp, &seq);
                  if (error != 0)
                          return (error);
                  error = cap_fcntl_check(fdp, fd, needfcntl);
                  if (!fd_modified(fdp, fd, seq))
                          break;
                  fdrop(*fpp, td);
          }
          if (error != 0) {
                  fdrop(*fpp, td);
                  *fpp = NULL;
          }
          return (error);
  #endif
  }
  
  /*
   * 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, int flags, cap_rights_t *needrightsp,
      struct vnode **vpp)
  {
          struct file *fp;
          int error;
  
          *vpp = NULL;
          error = _fget(td, fd, &fp, flags, needrightsp, NULL);
          if (error != 0)
                  return (error);
          if (fp->f_vnode == NULL) {
                  error = EINVAL;
          } else {
                  *vpp = fp->f_vnode;
                  vrefact(*vpp);
          }
          fdrop(fp, td);
  
          return (error);
  }
  
  int
  fgetvp(struct thread *td, int fd, cap_rights_t *rightsp, struct vnode **vpp)
  {
  
          return (_fgetvp(td, fd, 0, rightsp, vpp));
  }
  
  int
  fgetvp_rights(struct thread *td, int fd, cap_rights_t *needrightsp,
      struct filecaps *havecaps, struct vnode **vpp)
  {
          struct filedesc *fdp;
          struct filecaps caps;
          struct file *fp;
          int error;
  
          fdp = td->td_proc->p_fd;
          error = fget_cap_locked(fdp, fd, needrightsp, &fp, &caps);
          if (error != 0)
                  return (error);
          if (fp->f_ops == &badfileops) {
                  error = EBADF;
                  goto out;
          }
          if (fp->f_vnode == NULL) {
                  error = EINVAL;
                  goto out;
          }
  
          *havecaps = caps;
          *vpp = fp->f_vnode;
          vrefact(*vpp);
  
          return (0);
  out:
          filecaps_free(&caps);
          return (error);
  }
  
  int
  fgetvp_read(struct thread *td, int fd, cap_rights_t *rightsp, struct vnode **vpp)
  {
  
          return (_fgetvp(td, fd, FREAD, rightsp, vpp));
  }
  
  int
  fgetvp_exec(struct thread *td, int fd, cap_rights_t *rightsp, struct vnode **vpp)
  {
  
          return (_fgetvp(td, fd, FEXEC, rightsp, vpp));
  }
  
  #ifdef notyet
  int
  fgetvp_write(struct thread *td, int fd, cap_rights_t *rightsp,
      struct vnode **vpp)
  {
  
          return (_fgetvp(td, fd, FWRITE, rightsp, vpp));
  }
  #endif
  
  /*
   * Handle the last reference to a file being closed.
   *
   * Without the noinline attribute clang keeps inlining the func thorough this
   * file when fdrop is used.
   */
  int __noinline
  _fdrop(struct file *fp, struct thread *td)
  {
          int error;
  
          if (fp->f_count != 0)
                  panic("fdrop: count %d", fp->f_count);
          error = fo_close(fp, td);
          atomic_subtract_int(&openfiles, 1);
          crfree(fp->f_cred);
          free(fp->f_advice, M_FADVISE);
          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
  sys_flock(struct thread *td, struct flock_args *uap)
  {
          struct file *fp;
          struct vnode *vp;
          struct flock lf;
          int error;
  
          error = fget(td, uap->fd, &cap_flock_rights, &fp);
          if (error != 0)
                  return (error);
          if (fp->f_type != DTYPE_VNODE) {
                  fdrop(fp, td);
                  return (EOPNOTSUPP);
          }
  
          vp = fp->f_vnode;
          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);
          return (error);
  }
  /*
   * Duplicate the specified descriptor to a free descriptor.
   */
  int
  dupfdopen(struct thread *td, struct filedesc *fdp, int dfd, int mode,
      int openerror, int *indxp)
  {
          struct filedescent *newfde, *oldfde;
          struct file *fp;
          u_long *ioctls;
          int error, indx;
  
          KASSERT(openerror == ENODEV || openerror == ENXIO,
              ("unexpected error %d in %s", openerror, __func__));
  
          /*
           * 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 ((fp = fget_locked(fdp, dfd)) == NULL) {
                  FILEDESC_XUNLOCK(fdp);
                  return (EBADF);
          }
  
          error = fdalloc(td, 0, &indx);
          if (error != 0) {
                  FILEDESC_XUNLOCK(fdp);
                  return (error);
          }
  
          /*
           * 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.
           */
          switch (openerror) {
          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)) | fp->f_flag) != fp->f_flag) {
                          fdunused(fdp, indx);
                          FILEDESC_XUNLOCK(fdp);
                          return (EACCES);
                  }
                  fhold(fp);
                  newfde = &fdp->fd_ofiles[indx];
                  oldfde = &fdp->fd_ofiles[dfd];
                  ioctls = filecaps_copy_prep(&oldfde->fde_caps);
  #ifdef CAPABILITIES
                  seq_write_begin(&newfde->fde_seq);
  #endif
                  memcpy(newfde, oldfde, fde_change_size);
                  filecaps_copy_finish(&oldfde->fde_caps, &newfde->fde_caps,
                      ioctls);
  #ifdef CAPABILITIES
                  seq_write_end(&newfde->fde_seq);
  #endif
                  break;
          case ENXIO:
                  /*
                   * Steal away the file pointer from dfd and stuff it into indx.
                   */
                  newfde = &fdp->fd_ofiles[indx];
                  oldfde = &fdp->fd_ofiles[dfd];
  #ifdef CAPABILITIES
                  seq_write_begin(&newfde->fde_seq);
  #endif
                  memcpy(newfde, oldfde, fde_change_size);
                  oldfde->fde_file = NULL;
                  fdunused(fdp, dfd);
  #ifdef CAPABILITIES
                  seq_write_end(&newfde->fde_seq);
  #endif
                  break;
          }
          FILEDESC_XUNLOCK(fdp);
          *indxp = indx;
          return (0);
  }
  
  /*
   * This sysctl determines if we will allow a process to chroot(2) if it
   * has a directory open:
   *      0: disallowed for all processes.
   *      1: allowed for processes that were not already chroot(2)'ed.
   *      2: allowed for all processes.
   */
  
  static int chroot_allow_open_directories = 1;
  
  SYSCTL_INT(_kern, OID_AUTO, chroot_allow_open_directories, CTLFLAG_RW,
      &chroot_allow_open_directories, 0,
      "Allow a process to chroot(2) if it has a directory open");
  
  /*
   * Helper function for raised chroot(2) security function:  Refuse if
   * any filedescriptors are open directories.
   */
  static int
  chroot_refuse_vdir_fds(struct filedesc *fdp)
  {
          struct vnode *vp;
          struct file *fp;
          int fd;
  
          FILEDESC_LOCK_ASSERT(fdp);
  
          for (fd = 0; fd <= fdp->fd_lastfile; fd++) {
                  fp = fget_locked(fdp, fd);
                  if (fp == NULL)
                          continue;
                  if (fp->f_type == DTYPE_VNODE) {
                          vp = fp->f_vnode;
                          if (vp->v_type == VDIR)
                                  return (EPERM);
                  }
          }
          return (0);
  }
  
  /*
   * Common routine for kern_chroot() and jail_attach().  The caller is
   * responsible for invoking priv_check() and mac_vnode_check_chroot() to
   * authorize this operation.
   */
  int
  pwd_chroot(struct thread *td, struct vnode *vp)
  {
          struct filedesc *fdp;
          struct vnode *oldvp;
          int error;
  
          fdp = td->td_proc->p_fd;
          FILEDESC_XLOCK(fdp);
          if (chroot_allow_open_directories == 0 ||
              (chroot_allow_open_directories == 1 && fdp->fd_rdir != rootvnode)) {
                  error = chroot_refuse_vdir_fds(fdp);
                  if (error != 0) {
                          FILEDESC_XUNLOCK(fdp);
                          return (error);
                  }
          }
          oldvp = fdp->fd_rdir;
          vrefact(vp);
          fdp->fd_rdir = vp;
          if (fdp->fd_jdir == NULL) {
                  vrefact(vp);
                  fdp->fd_jdir = vp;
          }
          FILEDESC_XUNLOCK(fdp);
          vrele(oldvp);
          return (0);
  }
  
  void
  pwd_chdir(struct thread *td, struct vnode *vp)
  {
          struct filedesc *fdp;
          struct vnode *oldvp;
  
          fdp = td->td_proc->p_fd;
          FILEDESC_XLOCK(fdp);
          VNASSERT(vp->v_usecount > 0, vp,
              ("chdir to a vnode with zero usecount"));
          oldvp = fdp->fd_cdir;
          fdp->fd_cdir = vp;
          FILEDESC_XUNLOCK(fdp);
          vrele(oldvp);
  }
  
  /*
   * 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) {
                  PROC_LOCK(p);
                  fdp = fdhold(p);
                  PROC_UNLOCK(p);
                  if (fdp == NULL)
                          continue;
                  FILEDESC_XLOCK(fdp);
                  if (fdp->fd_cdir == olddp) {
                          vrefact(newdp);
                          fdp->fd_cdir = newdp;
                          nrele++;
                  }
                  if (fdp->fd_rdir == olddp) {
                          vrefact(newdp);
                          fdp->fd_rdir = newdp;
                          nrele++;
                  }
                  if (fdp->fd_jdir == olddp) {
                          vrefact(newdp);
                          fdp->fd_jdir = newdp;
                          nrele++;
                  }
                  FILEDESC_XUNLOCK(fdp);
                  fddrop(fdp);
          }
          sx_sunlock(&allproc_lock);
          if (rootvnode == olddp) {
                  vrefact(newdp);
                  rootvnode = newdp;
                  nrele++;
          }
          mtx_lock(&prison0.pr_mtx);
          if (prison0.pr_root == olddp) {
                  vrefact(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) {
                          vrefact(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);
  }
  
  static int
  sysctl_kern_proc_nfds(SYSCTL_HANDLER_ARGS)
  {
          struct filedesc *fdp;
          int i, count, slots;
  
          if (*(int *)arg1 != 0)
                  return (EINVAL);
  
          fdp = curproc->p_fd;
          count = 0;
          FILEDESC_SLOCK(fdp);
          slots = NDSLOTS(fdp->fd_lastfile + 1);
          for (i = 0; i < slots; i++)
                  count += bitcountl(fdp->fd_map[i]);
          FILEDESC_SUNLOCK(fdp);
  
          return (SYSCTL_OUT(req, &count, sizeof(count)));
  }
  
  static SYSCTL_NODE(_kern_proc, KERN_PROC_NFDS, nfds,
      CTLFLAG_RD|CTLFLAG_CAPRD|CTLFLAG_MPSAFE, sysctl_kern_proc_nfds,
      "Number of open file descriptors");
  
  /*
   * 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) {
                          PROC_LOCK(p);
                          if (p->p_state == PRS_NEW) {
                                  PROC_UNLOCK(p);
                                  continue;
                          }
                          fdp = fdhold(p);
                          PROC_UNLOCK(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) {
                  PROC_LOCK(p);
                  if (p->p_state == PRS_NEW) {
                          PROC_UNLOCK(p);
                          continue;
                  }
                  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;
                  fdp = fdhold(p);
                  PROC_UNLOCK(p);
                  if (fdp == NULL)
                          continue;
                  FILEDESC_SLOCK(fdp);
                  for (n = 0; fdp->fd_refcnt > 0 && n <= fdp->fd_lastfile; ++n) {
                          if ((fp = fdp->fd_ofiles[n].fde_file) == NULL)
                                  continue;
                          xf.xf_fd = n;
                          xf.xf_file = (uintptr_t)fp;
                          xf.xf_data = (uintptr_t)fp->f_data;
                          xf.xf_vnode = (uintptr_t)fp->f_vnode;
                          xf.xf_type = (uintptr_t)fp->f_type;
                          xf.xf_count = fp->f_count;
                          xf.xf_msgcount = 0;
                          xf.xf_offset = foffset_get(fp);
                          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|CTLFLAG_MPSAFE,
      0, 0, sysctl_kern_file, "S,xfile", "Entire file table");
  
  #ifdef KINFO_FILE_SIZE
  CTASSERT(sizeof(struct kinfo_file) == KINFO_FILE_SIZE);
  #endif
  
  static int
  xlate_fflags(int fflags)
  {
          static const struct {
                  int     fflag;
                  int     kf_fflag;
          } fflags_table[] = {
                  { FAPPEND, KF_FLAG_APPEND },
                  { FASYNC, KF_FLAG_ASYNC },
                  { FFSYNC, KF_FLAG_FSYNC },
                  { FHASLOCK, KF_FLAG_HASLOCK },
                  { FNONBLOCK, KF_FLAG_NONBLOCK },
                  { FREAD, KF_FLAG_READ },
                  { FWRITE, KF_FLAG_WRITE },
                  { O_CREAT, KF_FLAG_CREAT },
                  { O_DIRECT, KF_FLAG_DIRECT },
                  { O_EXCL, KF_FLAG_EXCL },
                  { O_EXEC, KF_FLAG_EXEC },
                  { O_EXLOCK, KF_FLAG_EXLOCK },
                  { O_NOFOLLOW, KF_FLAG_NOFOLLOW },
                  { O_SHLOCK, KF_FLAG_SHLOCK },
                  { O_TRUNC, KF_FLAG_TRUNC }
          };
          unsigned int i;
          int kflags;
  
          kflags = 0;
          for (i = 0; i < nitems(fflags_table); i++)
                  if (fflags & fflags_table[i].fflag)
                          kflags |=  fflags_table[i].kf_fflag;
          return (kflags);
  }
  
  /* Trim unused data from kf_path by truncating the structure size. */
  static void
  pack_kinfo(struct kinfo_file *kif)
  {
  
          kif->kf_structsize = offsetof(struct kinfo_file, kf_path) +
              strlen(kif->kf_path) + 1;
          kif->kf_structsize = roundup(kif->kf_structsize, sizeof(uint64_t));
  }
  
  static void
  export_file_to_kinfo(struct file *fp, int fd, cap_rights_t *rightsp,
      struct kinfo_file *kif, struct filedesc *fdp, int flags)
  {
          int error;
  
          bzero(kif, sizeof(*kif));
  
          /* Set a default type to allow for empty fill_kinfo() methods. */
          kif->kf_type = KF_TYPE_UNKNOWN;
          kif->kf_flags = xlate_fflags(fp->f_flag);
          if (rightsp != NULL)
                  kif->kf_cap_rights = *rightsp;
          else
                  cap_rights_init(&kif->kf_cap_rights);
          kif->kf_fd = fd;
          kif->kf_ref_count = fp->f_count;
          kif->kf_offset = foffset_get(fp);
  
          /*
           * This may drop the filedesc lock, so the 'fp' cannot be
           * accessed after this call.
           */
          error = fo_fill_kinfo(fp, kif, fdp);
          if (error == 0)
                  kif->kf_status |= KF_ATTR_VALID;
          if ((flags & KERN_FILEDESC_PACK_KINFO) != 0)
                  pack_kinfo(kif);
          else
                  kif->kf_structsize = roundup2(sizeof(*kif), sizeof(uint64_t));
  }
  
  static void
  export_vnode_to_kinfo(struct vnode *vp, int fd, int fflags,
      struct kinfo_file *kif, int flags)
  {
          int error;
  
          bzero(kif, sizeof(*kif));
  
          kif->kf_type = KF_TYPE_VNODE;
          error = vn_fill_kinfo_vnode(vp, kif);
          if (error == 0)
                  kif->kf_status |= KF_ATTR_VALID;
          kif->kf_flags = xlate_fflags(fflags);
          cap_rights_init(&kif->kf_cap_rights);
          kif->kf_fd = fd;
          kif->kf_ref_count = -1;
          kif->kf_offset = -1;
          if ((flags & KERN_FILEDESC_PACK_KINFO) != 0)
                  pack_kinfo(kif);
          else
                  kif->kf_structsize = roundup2(sizeof(*kif), sizeof(uint64_t));
          vrele(vp);
  }
  
  struct export_fd_buf {
          struct filedesc         *fdp;
          struct sbuf             *sb;
          ssize_t                 remainder;
          struct kinfo_file       kif;
          int                     flags;
  };
  
  static int
  export_kinfo_to_sb(struct export_fd_buf *efbuf)
  {
          struct kinfo_file *kif;
  
          kif = &efbuf->kif;
          if (efbuf->remainder != -1) {
                  if (efbuf->remainder < kif->kf_structsize) {
                          /* Terminate export. */
                          efbuf->remainder = 0;
                          return (0);
                  }
                  efbuf->remainder -= kif->kf_structsize;
          }
          return (sbuf_bcat(efbuf->sb, kif, kif->kf_structsize) == 0 ? 0 : ENOMEM);
  }
  
  static int
  export_file_to_sb(struct file *fp, int fd, cap_rights_t *rightsp,
      struct export_fd_buf *efbuf)
  {
          int error;
  
          if (efbuf->remainder == 0)
                  return (0);
          export_file_to_kinfo(fp, fd, rightsp, &efbuf->kif, efbuf->fdp,
              efbuf->flags);
          FILEDESC_SUNLOCK(efbuf->fdp);
          error = export_kinfo_to_sb(efbuf);
          FILEDESC_SLOCK(efbuf->fdp);
          return (error);
  }
  
  static int
  export_vnode_to_sb(struct vnode *vp, int fd, int fflags,
      struct export_fd_buf *efbuf)
  {
          int error;
  
          if (efbuf->remainder == 0)
                  return (0);
          if (efbuf->fdp != NULL)
                  FILEDESC_SUNLOCK(efbuf->fdp);
          export_vnode_to_kinfo(vp, fd, fflags, &efbuf->kif, efbuf->flags);
          error = export_kinfo_to_sb(efbuf);
          if (efbuf->fdp != NULL)
                  FILEDESC_SLOCK(efbuf->fdp);
          return (error);
  }
  
  /*
   * Store a process file descriptor information to sbuf.
   *
   * Takes a locked proc as argument, and returns with the proc unlocked.
   */
  int
  kern_proc_filedesc_out(struct proc *p,  struct sbuf *sb, ssize_t maxlen,
      int flags)
  {
          struct file *fp;
          struct filedesc *fdp;
          struct export_fd_buf *efbuf;
          struct vnode *cttyvp, *textvp, *tracevp;
          int error, i;
          cap_rights_t rights;
  
          PROC_LOCK_ASSERT(p, MA_OWNED);
  
          /* ktrace vnode */
          tracevp = p->p_tracevp;
          if (tracevp != NULL)
                  vrefact(tracevp);
          /* text vnode */
          textvp = p->p_textvp;
          if (textvp != NULL)
                  vrefact(textvp);
          /* Controlling tty. */
          cttyvp = NULL;
          if (p->p_pgrp != NULL && p->p_pgrp->pg_session != NULL) {
                  cttyvp = p->p_pgrp->pg_session->s_ttyvp;
                  if (cttyvp != NULL)
                          vrefact(cttyvp);
          }
          fdp = fdhold(p);
          PROC_UNLOCK(p);
          efbuf = malloc(sizeof(*efbuf), M_TEMP, M_WAITOK);
          efbuf->fdp = NULL;
          efbuf->sb = sb;
          efbuf->remainder = maxlen;
          efbuf->flags = flags;
          if (tracevp != NULL)
                  export_vnode_to_sb(tracevp, KF_FD_TYPE_TRACE, FREAD | FWRITE,
                      efbuf);
          if (textvp != NULL)
                  export_vnode_to_sb(textvp, KF_FD_TYPE_TEXT, FREAD, efbuf);
          if (cttyvp != NULL)
                  export_vnode_to_sb(cttyvp, KF_FD_TYPE_CTTY, FREAD | FWRITE,
                      efbuf);
          error = 0;
          if (fdp == NULL)
                  goto fail;
          efbuf->fdp = fdp;
          FILEDESC_SLOCK(fdp);
          /* working directory */
          if (fdp->fd_cdir != NULL) {
                  vrefact(fdp->fd_cdir);
                  export_vnode_to_sb(fdp->fd_cdir, KF_FD_TYPE_CWD, FREAD, efbuf);
          }
          /* root directory */
          if (fdp->fd_rdir != NULL) {
                  vrefact(fdp->fd_rdir);
                  export_vnode_to_sb(fdp->fd_rdir, KF_FD_TYPE_ROOT, FREAD, efbuf);
          }
          /* jail directory */
          if (fdp->fd_jdir != NULL) {
                  vrefact(fdp->fd_jdir);
                  export_vnode_to_sb(fdp->fd_jdir, KF_FD_TYPE_JAIL, FREAD, efbuf);
          }
          for (i = 0; fdp->fd_refcnt > 0 && i <= fdp->fd_lastfile; i++) {
                  if ((fp = fdp->fd_ofiles[i].fde_file) == NULL)
                          continue;
  #ifdef CAPABILITIES
                  rights = *cap_rights(fdp, i);
  #else /* !CAPABILITIES */
                  rights = cap_no_rights;
  #endif
                  /*
                   * Create sysctl entry.  It is OK to drop the filedesc
                   * lock inside of export_file_to_sb() as we will
                   * re-validate and re-evaluate its properties when the
                   * loop continues.
                   */
                  error = export_file_to_sb(fp, i, &rights, efbuf);
                  if (error != 0 || efbuf->remainder == 0)
                          break;
          }
          FILEDESC_SUNLOCK(fdp);
          fddrop(fdp);
  fail:
          free(efbuf, M_TEMP);
          return (error);
  }
  
  #define FILEDESC_SBUF_SIZE      (sizeof(struct kinfo_file) * 5)
  
  /*
   * Get per-process file descriptors for use by procstat(1), et al.
   */
  static int
  sysctl_kern_proc_filedesc(SYSCTL_HANDLER_ARGS)
  {
          struct sbuf sb;
          struct proc *p;
          ssize_t maxlen;
          int error, error2, *name;
  
          name = (int *)arg1;
  
          sbuf_new_for_sysctl(&sb, NULL, FILEDESC_SBUF_SIZE, req);
          sbuf_clear_flags(&sb, SBUF_INCLUDENUL);
          error = pget((pid_t)name[0], PGET_CANDEBUG | PGET_NOTWEXIT, &p);
          if (error != 0) {
                  sbuf_delete(&sb);
                  return (error);
          }
          maxlen = req->oldptr != NULL ? req->oldlen : -1;
          error = kern_proc_filedesc_out(p, &sb, maxlen,
              KERN_FILEDESC_PACK_KINFO);
          error2 = sbuf_finish(&sb);
          sbuf_delete(&sb);
          return (error != 0 ? error : error2);
  }
  
  #ifdef COMPAT_FREEBSD7
  #ifdef KINFO_OFILE_SIZE
  CTASSERT(sizeof(struct kinfo_ofile) == KINFO_OFILE_SIZE);
  #endif
  
  static void
  kinfo_to_okinfo(struct kinfo_file *kif, struct kinfo_ofile *okif)
  {
  
          okif->kf_structsize = sizeof(*okif);
          okif->kf_type = kif->kf_type;
          okif->kf_fd = kif->kf_fd;
          okif->kf_ref_count = kif->kf_ref_count;
          okif->kf_flags = kif->kf_flags & (KF_FLAG_READ | KF_FLAG_WRITE |
              KF_FLAG_APPEND | KF_FLAG_ASYNC | KF_FLAG_FSYNC | KF_FLAG_NONBLOCK |
              KF_FLAG_DIRECT | KF_FLAG_HASLOCK);
          okif->kf_offset = kif->kf_offset;
          if (kif->kf_type == KF_TYPE_VNODE)
                  okif->kf_vnode_type = kif->kf_un.kf_file.kf_file_type;
          else
                  okif->kf_vnode_type = KF_VTYPE_VNON;
          strlcpy(okif->kf_path, kif->kf_path, sizeof(okif->kf_path));
          if (kif->kf_type == KF_TYPE_SOCKET) {
                  okif->kf_sock_domain = kif->kf_un.kf_sock.kf_sock_domain0;
                  okif->kf_sock_type = kif->kf_un.kf_sock.kf_sock_type0;
                  okif->kf_sock_protocol = kif->kf_un.kf_sock.kf_sock_protocol0;
                  okif->kf_sa_local = kif->kf_un.kf_sock.kf_sa_local;
                  okif->kf_sa_peer = kif->kf_un.kf_sock.kf_sa_peer;
          } else {
                  okif->kf_sa_local.ss_family = AF_UNSPEC;
                  okif->kf_sa_peer.ss_family = AF_UNSPEC;
          }
  }
  
  static int
  export_vnode_for_osysctl(struct vnode *vp, int type, struct kinfo_file *kif,
      struct kinfo_ofile *okif, struct filedesc *fdp, struct sysctl_req *req)
  {
          int error;
  
          vrefact(vp);
          FILEDESC_SUNLOCK(fdp);
          export_vnode_to_kinfo(vp, type, 0, kif, KERN_FILEDESC_PACK_KINFO);
          kinfo_to_okinfo(kif, okif);
          error = SYSCTL_OUT(req, okif, sizeof(*okif));
          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)
  {
          struct kinfo_ofile *okif;
          struct kinfo_file *kif;
          struct filedesc *fdp;
          int error, i, *name;
          struct file *fp;
          struct proc *p;
  
          name = (int *)arg1;
          error = pget((pid_t)name[0], PGET_CANDEBUG | PGET_NOTWEXIT, &p);
          if (error != 0)
                  return (error);
          fdp = fdhold(p);
          PROC_UNLOCK(p);
          if (fdp == NULL)
                  return (ENOENT);
          kif = malloc(sizeof(*kif), M_TEMP, M_WAITOK);
          okif = malloc(sizeof(*okif), M_TEMP, M_WAITOK);
          FILEDESC_SLOCK(fdp);
          if (fdp->fd_cdir != NULL)
                  export_vnode_for_osysctl(fdp->fd_cdir, KF_FD_TYPE_CWD, kif,
                      okif, fdp, req);
          if (fdp->fd_rdir != NULL)
                  export_vnode_for_osysctl(fdp->fd_rdir, KF_FD_TYPE_ROOT, kif,
                      okif, fdp, req);
          if (fdp->fd_jdir != NULL)
                  export_vnode_for_osysctl(fdp->fd_jdir, KF_FD_TYPE_JAIL, kif,
                      okif, fdp, req);
          for (i = 0; fdp->fd_refcnt > 0 && i <= fdp->fd_lastfile; i++) {
                  if ((fp = fdp->fd_ofiles[i].fde_file) == NULL)
                          continue;
                  export_file_to_kinfo(fp, i, NULL, kif, fdp,
                      KERN_FILEDESC_PACK_KINFO);
                  FILEDESC_SUNLOCK(fdp);
                  kinfo_to_okinfo(kif, okif);
                  error = SYSCTL_OUT(req, okif, sizeof(*okif));
                  FILEDESC_SLOCK(fdp);
                  if (error)
                          break;
          }
          FILEDESC_SUNLOCK(fdp);
          fddrop(fdp);
          free(kif, M_TEMP);
          free(okif, M_TEMP);
          return (0);
  }
  
  static SYSCTL_NODE(_kern_proc, KERN_PROC_OFILEDESC, ofiledesc,
      CTLFLAG_RD|CTLFLAG_MPSAFE, sysctl_kern_proc_ofiledesc,
      "Process ofiledesc entries");
  #endif  /* COMPAT_FREEBSD7 */
  
  int
  vntype_to_kinfo(int vtype)
  {
          struct {
                  int     vtype;
                  int     kf_vtype;
          } vtypes_table[] = {
                  { VBAD, KF_VTYPE_VBAD },
                  { VBLK, KF_VTYPE_VBLK },
                  { VCHR, KF_VTYPE_VCHR },
                  { VDIR, KF_VTYPE_VDIR },
                  { VFIFO, KF_VTYPE_VFIFO },
                  { VLNK, KF_VTYPE_VLNK },
                  { VNON, KF_VTYPE_VNON },
                  { VREG, KF_VTYPE_VREG },
                  { VSOCK, KF_VTYPE_VSOCK }
          };
          unsigned int i;
  
          /*
           * Perform vtype translation.
           */
          for (i = 0; i < nitems(vtypes_table); i++)
                  if (vtypes_table[i].vtype == vtype)
                          return (vtypes_table[i].kf_vtype);
  
          return (KF_VTYPE_UNKNOWN);
  }
  
  static SYSCTL_NODE(_kern_proc, KERN_PROC_FILEDESC, filedesc,
      CTLFLAG_RD|CTLFLAG_MPSAFE, sysctl_kern_proc_filedesc,
      "Process filedesc entries");
  
  /*
   * Store a process current working directory information to sbuf.
   *
   * Takes a locked proc as argument, and returns with the proc unlocked.
   */
  int
  kern_proc_cwd_out(struct proc *p,  struct sbuf *sb, ssize_t maxlen)
  {
          struct filedesc *fdp;
          struct export_fd_buf *efbuf;
          int error;
  
          PROC_LOCK_ASSERT(p, MA_OWNED);
  
          fdp = fdhold(p);
          PROC_UNLOCK(p);
          if (fdp == NULL)
                  return (EINVAL);
  
          efbuf = malloc(sizeof(*efbuf), M_TEMP, M_WAITOK);
          efbuf->fdp = fdp;
          efbuf->sb = sb;
          efbuf->remainder = maxlen;
  
          FILEDESC_SLOCK(fdp);
          if (fdp->fd_cdir == NULL)
                  error = EINVAL;
          else {
                  vrefact(fdp->fd_cdir);
                  error = export_vnode_to_sb(fdp->fd_cdir, KF_FD_TYPE_CWD,
                      FREAD, efbuf);
          }
          FILEDESC_SUNLOCK(fdp);
          fddrop(fdp);
          free(efbuf, M_TEMP);
          return (error);
  }
  
  /*
   * Get per-process current working directory.
   */
  static int
  sysctl_kern_proc_cwd(SYSCTL_HANDLER_ARGS)
  {
          struct sbuf sb;
          struct proc *p;
          ssize_t maxlen;
          int error, error2, *name;
  
          name = (int *)arg1;
  
          sbuf_new_for_sysctl(&sb, NULL, sizeof(struct kinfo_file), req);
          sbuf_clear_flags(&sb, SBUF_INCLUDENUL);
          error = pget((pid_t)name[0], PGET_CANDEBUG | PGET_NOTWEXIT, &p);
          if (error != 0) {
                  sbuf_delete(&sb);
                  return (error);
          }
          maxlen = req->oldptr != NULL ? req->oldlen : -1;
          error = kern_proc_cwd_out(p, &sb, maxlen);
          error2 = sbuf_finish(&sb);
          sbuf_delete(&sb);
          return (error != 0 ? error : error2);
  }
  
  static SYSCTL_NODE(_kern_proc, KERN_PROC_CWD, cwd, CTLFLAG_RD|CTLFLAG_MPSAFE,
      sysctl_kern_proc_cwd, "Process current working directory");
  
  #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 ("vnode");
          case DTYPE_SOCKET:
                  return ("socket");
          case DTYPE_PIPE:
                  return ("pipe");
          case DTYPE_FIFO:
                  return ("fifo");
          case DTYPE_KQUEUE:
                  return ("kqueue");
          case DTYPE_CRYPTO:
                  return ("crypto");
          case DTYPE_MQUEUE:
                  return ("mqueue");
          case DTYPE_SHM:
                  return ("shm");
          case DTYPE_SEM:
                  return ("ksem");
          case DTYPE_PTS:
                  return ("pts");
          case DTYPE_DEV:
                  return ("dev");
          case DTYPE_PROCDESC:
                  return ("proc");
          case DTYPE_LINUXEFD:
                  return ("levent");
          case DTYPE_LINUXTFD:
                  return ("ltimer");
          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_lastfile; n++) {
                          if (fp == fdp->fd_ofiles[n].fde_file)
                                  return (p);
                  }
          }
          return (NULL);
  }
  
  static void
  db_print_file(struct file *fp, int header)
  {
  #define XPTRWIDTH ((int)howmany(sizeof(void *) * NBBY, 4))
          struct proc *p;
  
          if (header)
                  db_printf("%*s %6s %*s %8s %4s %5s %6s %*s %5s %s\n",
                      XPTRWIDTH, "File", "Type", XPTRWIDTH, "Data", "Flag",
                      "GCFl", "Count", "MCount", XPTRWIDTH, "Vnode", "FPID",
                      "FCmd");
          p = file_to_first_proc(fp);
          db_printf("%*p %6s %*p %08x %04x %5d %6d %*p %5d %s\n", XPTRWIDTH,
              fp, file_type_to_name(fp->f_type), XPTRWIDTH, fp->f_data,
              fp->f_flag, 0, fp->f_count, 0, XPTRWIDTH, fp->f_vnode,
              p != NULL ? p->p_pid : -1, p != NULL ? p->p_comm : "-");
  
  #undef XPTRWIDTH
  }
  
  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_lastfile; ++n) {
                          if ((fp = fdp->fd_ofiles[n].fde_file) == 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);
          filedesc0_zone = uma_zcreate("filedesc0", sizeof(struct filedesc0),
              NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
          mtx_init(&sigio_lock, "sigio lock", 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 (0);
  }
  
  static int
  badfo_chmod(struct file *fp, mode_t mode, struct ucred *active_cred,
      struct thread *td)
  {
  
          return (EBADF);
  }
  
  static int
  badfo_chown(struct file *fp, uid_t uid, gid_t gid, struct ucred *active_cred,
      struct thread *td)
  {
  
          return (EBADF);
  }
  
  static int
  badfo_sendfile(struct file *fp, int sockfd, struct uio *hdr_uio,
      struct uio *trl_uio, off_t offset, size_t nbytes, off_t *sent, int flags,
      struct thread *td)
  {
  
          return (EBADF);
  }
  
  static int
  badfo_fill_kinfo(struct file *fp, struct kinfo_file *kif, struct filedesc *fdp)
  {
  
          return (0);
  }
  
  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,
          .fo_chmod = badfo_chmod,
          .fo_chown = badfo_chown,
          .fo_sendfile = badfo_sendfile,
          .fo_fill_kinfo = badfo_fill_kinfo,
  };
  
  int
  invfo_rdwr(struct file *fp, struct uio *uio, struct ucred *active_cred,
      int flags, struct thread *td)
  {
  
          return (EOPNOTSUPP);
  }
  
  int
  invfo_truncate(struct file *fp, off_t length, struct ucred *active_cred,
      struct thread *td)
  {
  
          return (EINVAL);
  }
  
  int
  invfo_ioctl(struct file *fp, u_long com, void *data,
      struct ucred *active_cred, struct thread *td)
  {
  
          return (ENOTTY);
  }
  
  int
  invfo_poll(struct file *fp, int events, struct ucred *active_cred,
      struct thread *td)
  {
  
          return (poll_no_poll(events));
  }
  
  int
  invfo_kqfilter(struct file *fp, struct knote *kn)
  {
  
          return (EINVAL);
  }
  
  int
  invfo_chmod(struct file *fp, mode_t mode, struct ucred *active_cred,
      struct thread *td)
  {
  
          return (EINVAL);
  }
  
  int
  invfo_chown(struct file *fp, uid_t uid, gid_t gid, struct ucred *active_cred,
      struct thread *td)
  {
  
          return (EINVAL);
  }
  
  int
  invfo_sendfile(struct file *fp, int sockfd, struct uio *hdr_uio,
      struct uio *trl_uio, off_t offset, size_t nbytes, off_t *sent, int flags,
      struct thread *td)
  {
  
          return (EINVAL);
  }
  
  /*-------------------------------------------------------------------*/
  
  /*
   * 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_credf(MAKEDEV_ETERNAL, &fildesc_cdevsw, 0, NULL,
              UID_ROOT, GID_WHEEL, 0666, "fd/0");
          make_dev_alias(dev, "stdin");
          dev = make_dev_credf(MAKEDEV_ETERNAL, &fildesc_cdevsw, 1, NULL,
              UID_ROOT, GID_WHEEL, 0666, "fd/1");
          make_dev_alias(dev, "stdout");
          dev = make_dev_credf(MAKEDEV_ETERNAL, &fildesc_cdevsw, 2, NULL,
              UID_ROOT, GID_WHEEL, 0666, "fd/2");
          make_dev_alias(dev, "stderr");
  }
  
  SYSINIT(fildescdev, SI_SUB_DRIVERS, SI_ORDER_MIDDLE, fildesc_drvinit, NULL);