lib/libstand/read.c

   1 /* $FreeBSD: src/lib/libstand/read.c,v 1.1.1.1.6.1 2000/09/10 01:32:06 ps Exp $ */
   2 /* $DragonFly: src/lib/libstand/read.c,v 1.2 2003/06/17 04:26:51 dillon Exp $ */
   3 /*      $NetBSD: read.c,v 1.8 1997/01/22 00:38:12 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  *      @(#)read.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 <sys/param.h>
  66 #include "stand.h"
  67
  68 int no_io_error;
  69
  70 ssize_t
  71 read(int fd, void *dest, size_t bcount)
  72 {
  73     struct open_file    *f = &files[fd];
  74     size_t              resid;
  75
  76     if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) {
  77         errno = EBADF;
  78         return (-1);
  79     }
  80     if (f->f_flags & F_RAW) {
  81         twiddle();
  82         errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ,
  83                                         btodb(f->f_offset), bcount, dest, &resid);
  84         if (errno)
  85             return (-1);
  86         f->f_offset += resid;
  87         return (resid);
  88     }
  89
  90     /*
  91      * Optimise reads from regular files using a readahead buffer.
  92      * If the request can't be satisfied from the current buffer contents,
  93      * check to see if it should be bypassed, or refill the buffer and complete
  94      * the request.
  95      */
  96     resid = bcount;
  97     for (;;) {
  98         size_t  ccount, cresid;
  99         /* how much can we supply? */
 100         ccount = imin(f->f_ralen, resid);
 101         if (ccount > 0) {
 102             bcopy(f->f_rabuf + f->f_raoffset, dest, ccount);
 103             f->f_raoffset += ccount;
 104             f->f_ralen -= ccount;
 105             resid -= ccount;
 106             if (resid == 0)
 107                 return(bcount);
 108             dest += ccount;
 109         }
 110
 111         /* will filling the readahead buffer again not help? */
 112         if (resid >= SOPEN_RASIZE) {
 113             /* bypass the rest of the request and leave the buffer empty */
 114             if ((errno = (f->f_ops->fo_read)(f, dest, resid, &cresid)))
 115                 return(bcount - resid);
 116             return(bcount - cresid);
 117         }
 118
 119         /* fetch more data */
 120         if ((errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, &cresid)))
 121             return(bcount - resid);     /* behave like fread() */
 122         f->f_raoffset = 0;
 123         f->f_ralen = SOPEN_RASIZE - cresid;
 124         /* no more data, return what we had */
 125         if (f->f_ralen == 0)
 126             return(bcount - resid);
 127     }
 128 }