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
69ssize_t
70read(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();
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}
128