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