lib/libstand/lseek.c

   1 /* $FreeBSD: src/lib/libstand/lseek.c,v 1.1.1.1.6.2 2001/08/30 03:14:16 jdp Exp $ */
   2 /* $DragonFly: src/lib/libstand/lseek.c,v 1.2 2003/06/17 04:26:51 dillon Exp $ */
   3 /*      $NetBSD: lseek.c,v 1.4 1997/01/22 00:38:10 cgd Exp $    */
   4
   5 /*-
   6  * Copyright (c) 1993
   7  *      The Regents of the University of California.  All rights reserved.
   8  *
   9  * This code is derived from software contributed to Berkeley by
  10  * The Mach Operating System project at Carnegie-Mellon University.
  11  *
  12  * Redistribution and use in source and binary forms, with or without
  13  * modification, are permitted provided that the following conditions
  14  * are met:
  15  * 1. Redistributions of source code must retain the above copyright
  16  *    notice, this list of conditions and the following disclaimer.
  17  * 2. Redistributions in binary form must reproduce the above copyright
  18  *    notice, this list of conditions and the following disclaimer in the
  19  *    documentation and/or other materials provided with the distribution.
  20  * 3. Neither the name of the University nor the names of its contributors
  21  *    may be used to endorse or promote products derived from this software
  22  *    without specific prior written permission.
  23  *
  24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  34  * SUCH DAMAGE.
  35  *
  36  *      @(#)lseek.c     8.1 (Berkeley) 6/11/93
  37  *
  38  *
  39  * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
  40  * All Rights Reserved.
  41  *
  42  * Author: Alessandro Forin
  43  *
  44  * Permission to use, copy, modify and distribute this software and its
  45  * documentation is hereby granted, provided that both the copyright
  46  * notice and this permission notice appear in all copies of the
  47  * software, derivative works or modified versions, and any portions
  48  * thereof, and that both notices appear in supporting documentation.
  49  *
  50  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
  51  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
  52  * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
  53  *
  54  * Carnegie Mellon requests users of this software to return to
  55  *
  56  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
  57  *  School of Computer Science
  58  *  Carnegie Mellon University
  59  *  Pittsburgh PA 15213-3890
  60  *
  61  * any improvements or extensions that they make and grant Carnegie the
  62  * rights to redistribute these changes.
  63  */
  64
  65 #include "stand.h"
  66
  67 off_t
  68 lseek(int fd, off_t offset, int where)
  69 {
  70     off_t bufpos, filepos, target;
  71     struct open_file *f = &files[fd];
  72
  73     if ((unsigned)fd >= SOPEN_MAX || f->f_flags == 0) {
  74         errno = EBADF;
  75         return (-1);
  76     }
  77
  78     if (f->f_flags & F_RAW) {
  79         /*
  80          * On RAW devices, update internal offset.
  81          */
  82         switch (where) {
  83         case SEEK_SET:
  84             f->f_offset = offset;
  85             break;
  86         case SEEK_CUR:
  87             f->f_offset += offset;
  88             break;
  89         case SEEK_END:
  90         default:
  91             errno = EOFFSET;
  92             return (-1);
  93         }
  94         return (f->f_offset);
  95     }
  96
  97     /*
  98      * If there is some unconsumed data in the readahead buffer and it
  99      * contains the desired offset, simply adjust the buffer offset and
 100      * length.  We don't bother with SEEK_END here, since the code to
 101      * handle it would fail in the same cases where the non-readahead
 102      * code fails (namely, for streams which cannot seek backward and whose
 103      * size isn't known in advance).
 104      */
 105     if (f->f_ralen != 0 && where != SEEK_END) {
 106         if ((filepos = (f->f_ops->fo_seek)(f, (off_t)0, SEEK_CUR)) == -1)
 107             return (-1);
 108         bufpos = filepos - f->f_ralen;
 109         switch (where) {
 110         case SEEK_SET:
 111             target = offset;
 112             break;
 113         case SEEK_CUR:
 114             target = bufpos + offset;
 115             break;
 116         default:
 117             errno = EINVAL;
 118             return (-1);
 119         }
 120         if (bufpos <= target && target < filepos) {
 121             f->f_raoffset += target - bufpos;
 122             f->f_ralen -= target - bufpos;
 123             return (target);
 124         }
 125     }
 126
 127     /*
 128      * If this is a relative seek, we need to correct the offset for
 129      * bytes that we have already read but the caller doesn't know
 130      * about.
 131      */
 132     if (where == SEEK_CUR)
 133         offset -= f->f_ralen;
 134
 135     /*
 136      * Invalidate the readahead buffer.
 137      */
 138     f->f_ralen = 0;
 139
 140     return (f->f_ops->fo_seek)(f, offset, where);
 141 }