usr/src/boot/lib/libstand/lseek.c

   1 /*      $NetBSD: lseek.c,v 1.4 1997/01/22 00:38:10 cgd Exp $    */
   2
   3 /*-
   4  * Copyright (c) 1993
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * This code is derived from software contributed to Berkeley by
   8  * The Mach Operating System project at Carnegie-Mellon University.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  * 4. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  *
  34  *      @(#)lseek.c     8.1 (Berkeley) 6/11/93
  35  *
  36  *
  37  * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
  38  * All Rights Reserved.
  39  *
  40  * Author: Alessandro Forin
  41  *
  42  * Permission to use, copy, modify and distribute this software and its
  43  * documentation is hereby granted, provided that both the copyright
  44  * notice and this permission notice appear in all copies of the
  45  * software, derivative works or modified versions, and any portions
  46  * thereof, and that both notices appear in supporting documentation.
  47  *
  48  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
  49  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
  50  * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
  51  *
  52  * Carnegie Mellon requests users of this software to return to
  53  *
  54  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
  55  *  School of Computer Science
  56  *  Carnegie Mellon University
  57  *  Pittsburgh PA 15213-3890
  58  *
  59  * any improvements or extensions that they make and grant Carnegie the
  60  * rights to redistribute these changes.
  61  */
  62
  63 #include <sys/cdefs.h>
  64 #include "stand.h"
  65
  66 off_t
  67 lseek(int fd, off_t offset, int where)
  68 {
  69     off_t bufpos, filepos, target;
  70     struct open_file *f = &files[fd];
  71
  72     if ((unsigned)fd >= SOPEN_MAX || f->f_flags == 0) {
  73         errno = EBADF;
  74         return (-1);
  75     }
  76
  77     if (f->f_flags & F_RAW) {
  78         /*
  79          * On RAW devices, update internal offset.
  80          */
  81         switch (where) {
  82         case SEEK_SET:
  83             f->f_offset = offset;
  84             break;
  85         case SEEK_CUR:
  86             f->f_offset += offset;
  87             break;
  88         default:
  89             errno = EOFFSET;
  90             return (-1);
  91         }
  92         return (f->f_offset);
  93     }
  94
  95     /*
  96      * If there is some unconsumed data in the readahead buffer and it
  97      * contains the desired offset, simply adjust the buffer offset and
  98      * length.  We don't bother with SEEK_END here, since the code to
  99      * handle it would fail in the same cases where the non-readahead
 100      * code fails (namely, for streams which cannot seek backward and whose
 101      * size isn't known in advance).
 102      */
 103     if (f->f_ralen != 0 && where != SEEK_END) {
 104         if ((filepos = (f->f_ops->fo_seek)(f, (off_t)0, SEEK_CUR)) == -1)
 105             return (-1);
 106         bufpos = filepos - f->f_ralen;
 107         switch (where) {
 108         case SEEK_SET:
 109             target = offset;
 110             break;
 111         case SEEK_CUR:
 112             target = bufpos + offset;
 113             break;
 114         default:
 115             errno = EINVAL;
 116             return (-1);
 117         }
 118         if (bufpos <= target && target < filepos) {
 119             f->f_raoffset += target - bufpos;
 120             f->f_ralen -= target - bufpos;
 121             return (target);
 122         }
 123     }
 124
 125     /*
 126      * If this is a relative seek, we need to correct the offset for
 127      * bytes that we have already read but the caller doesn't know
 128      * about.
 129      */
 130     if (where == SEEK_CUR)
 131         offset -= f->f_ralen;
 132
 133     /*
 134      * Invalidate the readahead buffer.
 135      */
 136     f->f_ralen = 0;
 137
 138     return (f->f_ops->fo_seek)(f, offset, where);
 139 }