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
68ssize_t
69read(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}
133