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. All advertising materials mentioning features or use of this software
  21  *    must display the following acknowledgement:
  22  *      This product includes software developed by the University of
  23  *      California, Berkeley and its contributors.
  24  * 4. Neither the name of the University nor the names of its contributors
  25  *    may be used to endorse or promote products derived from this software
  26  *    without specific prior written permission.
  27  *
  28  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  29  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  30  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  31  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  32  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  33  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  34  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  35  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  36  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  37  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  38  * SUCH DAMAGE.
  39  *
  40  *      @(#)lseek.c     8.1 (Berkeley) 6/11/93
  41  *
  42  *
  43  * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
  44  * All Rights Reserved.
  45  *
  46  * Author: Alessandro Forin
  47  *
  48  * Permission to use, copy, modify and distribute this software and its
  49  * documentation is hereby granted, provided that both the copyright
  50  * notice and this permission notice appear in all copies of the
  51  * software, derivative works or modified versions, and any portions
  52  * thereof, and that both notices appear in supporting documentation.
  53  *
  54  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
  55  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
  56  * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
  57  *
  58  * Carnegie Mellon requests users of this software to return to
  59  *
  60  *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
  61  *  School of Computer Science
  62  *  Carnegie Mellon University
  63  *  Pittsburgh PA 15213-3890
  64  *
  65  * any improvements or extensions that they make and grant Carnegie the
  66  * rights to redistribute these changes.
  67  */
  68
  69 #include "stand.h"
  70
  71 off_t
  72 lseek(int fd, off_t offset, int where)
  73 {
  74     off_t bufpos, filepos, target;
  75     struct open_file *f = &files[fd];
  76
  77     if ((unsigned)fd >= SOPEN_MAX || f->f_flags == 0) {
  78         errno = EBADF;
  79         return (-1);
  80     }
  81
  82     if (f->f_flags & F_RAW) {
  83         /*
  84          * On RAW devices, update internal offset.
  85          */
  86         switch (where) {
  87         case SEEK_SET:
  88             f->f_offset = offset;
  89             break;
  90         case SEEK_CUR:
  91             f->f_offset += offset;
  92             break;
  93         case SEEK_END:
  94         default:
  95             errno = EOFFSET;
  96             return (-1);
  97         }
  98         return (f->f_offset);
  99     }
 100
 101     /*
 102      * If there is some unconsumed data in the readahead buffer and it
 103      * contains the desired offset, simply adjust the buffer offset and
 104      * length.  We don't bother with SEEK_END here, since the code to
 105      * handle it would fail in the same cases where the non-readahead
 106      * code fails (namely, for streams which cannot seek backward and whose
 107      * size isn't known in advance).
 108      */
 109     if (f->f_ralen != 0 && where != SEEK_END) {
 110         if ((filepos = (f->f_ops->fo_seek)(f, (off_t)0, SEEK_CUR)) == -1)
 111             return (-1);
 112         bufpos = filepos - f->f_ralen;
 113         switch (where) {
 114         case SEEK_SET:
 115             target = offset;
 116             break;
 117         case SEEK_CUR:
 118             target = bufpos + offset;
 119             break;
 120         default:
 121             errno = EINVAL;
 122             return (-1);
 123         }
 124         if (bufpos <= target && target < filepos) {
 125             f->f_raoffset += target - bufpos;
 126             f->f_ralen -= target - bufpos;
 127             return (target);
 128         }
 129     }
 130
 131     /*
 132      * If this is a relative seek, we need to correct the offset for
 133      * bytes that we have already read but the caller doesn't know
 134      * about.
 135      */
 136     if (where == SEEK_CUR)
 137         offset -= f->f_ralen;
 138
 139     /*
 140      * Invalidate the readahead buffer.
 141      */
 142     f->f_ralen = 0;
 143
 144     return (f->f_ops->fo_seek)(f, offset, where);
 145 }