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

   1 /*      $NetBSD: read.c,v 1.8 1997/01/22 00:38:12 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  * 3. 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  *      @(#)read.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
  65 #include <sys/param.h>
  66 #include "stand.h"
  67
  68 ssize_t
  69 read(int fd, void *dest, size_t bcount)
  70 {
  71         struct open_file *f = &files[fd];
  72         size_t resid;
  73
  74         if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) {
  75                 errno = EBADF;
  76                 return (-1);
  77         }
  78         if (f->f_flags & F_RAW) {
  79                 twiddle(8);
  80                 errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ,
  81                     btodb(f->f_offset), bcount, dest, &resid);
  82                 if (errno)
  83                         return (-1);
  84                 f->f_offset += resid;
  85                 return (resid);
  86         }
  87
  88         /*
  89          * Optimise reads from regular files using a readahead buffer.
  90          * If the request can't be satisfied from the current buffer contents,
  91          * check to see if it should be bypassed, or refill the buffer and
  92          * complete the request.
  93          */
  94         resid = bcount;
  95         for (;;) {
  96                 size_t  ccount, cresid;
  97                 /* how much can we supply? */
  98                 ccount = imin(f->f_ralen, resid);
  99                 if (ccount > 0) {
 100                         bcopy(f->f_rabuf + f->f_raoffset, dest, ccount);
 101                         f->f_raoffset += ccount;
 102                         f->f_ralen -= ccount;
 103                         resid -= ccount;
 104                         if (resid == 0)
 105                                 return (bcount);
 106                         dest = (char *)dest + ccount;
 107                 }
 108
 109                 /* will filling the readahead buffer again not help? */
 110                 if (f->f_rabuf == NULL || resid >= SOPEN_RASIZE) {
 111                         /*
 112                          * bypass the rest of the request and leave the
 113                          * buffer empty
 114                          */
 115                         errno = (f->f_ops->fo_read)(f, dest, resid, &cresid);
 116                         if (errno != 0)
 117                                 return (-1);
 118                         return (bcount - cresid);
 119                 }
 120
 121                 /* fetch more data */
 122                 errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE,
 123                     &cresid);
 124                 if (errno != 0)
 125                         return (-1);
 126                 f->f_raoffset = 0;
 127                 f->f_ralen = SOPEN_RASIZE - cresid;
 128                 /* no more data, return what we had */
 129                 if (f->f_ralen == 0)
 130                         return (bcount - resid);
 131         }
 132 }