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  * 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  *      @(#)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 __FBSDID("$FreeBSD$");
  65
  66 #include <sys/param.h>
  67 #include "stand.h"
  68
  69 ssize_t
  70 read(int fd, void *dest, size_t bcount)
  71 {
  72     struct open_file    *f = &files[fd];
  73     size_t              resid;
  74
  75     if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) {
  76         errno = EBADF;
  77         return (-1);
  78     }
  79     if (f->f_flags & F_RAW) {
  80         twiddle(4);
  81         errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ,
  82                                         btodb(f->f_offset), bcount, dest, &resid);
  83         if (errno)
  84             return (-1);
  85         f->f_offset += resid;
  86         return (resid);
  87     }
  88
  89     /*
  90      * Optimise reads from regular files using a readahead buffer.
  91      * If the request can't be satisfied from the current buffer contents,
  92      * check to see if it should be bypassed, or refill the buffer and complete
  93      * the request.
  94      */
  95     resid = bcount;
  96     for (;;) {
  97         size_t  ccount, cresid;
  98         /* how much can we supply? */
  99         ccount = imin(f->f_ralen, resid);
 100         if (ccount > 0) {
 101             bcopy(f->f_rabuf + f->f_raoffset, dest, ccount);
 102             f->f_raoffset += ccount;
 103             f->f_ralen -= ccount;
 104             resid -= ccount;
 105             if (resid == 0)
 106                 return(bcount);
 107             dest = (char *)dest + ccount;
 108         }
 109
 110         /* will filling the readahead buffer again not help? */
 111         if (resid >= SOPEN_RASIZE) {
 112             /* bypass the rest of the request and leave the buffer empty */
 113             if ((errno = (f->f_ops->fo_read)(f, dest, resid, &cresid)))
 114                     return (-1);
 115             return(bcount - cresid);
 116         }
 117
 118         /* fetch more data */
 119         if ((errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, &cresid)))
 120             return (-1);
 121         f->f_raoffset = 0;
 122         f->f_ralen = SOPEN_RASIZE - cresid;
 123         /* no more data, return what we had */
 124         if (f->f_ralen == 0)
 125             return(bcount - resid);
 126     }
 127 }