read.c revision 136093 
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. All advertising materials mentioning features or use of this software
19 *    must display the following acknowledgement:
20 *	This product includes software developed by the University of
21 *	California, Berkeley and its contributors.
22 * 4. Neither the name of the University nor the names of its contributors
23 *    may be used to endorse or promote products derived from this software
24 *    without specific prior written permission.
25 *
26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
29 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
36 * SUCH DAMAGE.
37 *
38 *	@(#)read.c	8.1 (Berkeley) 6/11/93
39 *
40 *
41 * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
42 * All Rights Reserved.
43 *
44 * Author: Alessandro Forin
45 *
46 * Permission to use, copy, modify and distribute this software and its
47 * documentation is hereby granted, provided that both the copyright
48 * notice and this permission notice appear in all copies of the
49 * software, derivative works or modified versions, and any portions
50 * thereof, and that both notices appear in supporting documentation.
51 *
52 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
53 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
54 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
55 *
56 * Carnegie Mellon requests users of this software to return to
57 *
58 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
59 *  School of Computer Science
60 *  Carnegie Mellon University
61 *  Pittsburgh PA 15213-3890
62 *
63 * any improvements or extensions that they make and grant Carnegie the
64 * rights to redistribute these changes.
65 */
66
67#include <sys/cdefs.h>
68__FBSDID("$FreeBSD: head/lib/libstand/read.c 136093 2004-10-03 15:58:20Z stefanf $");
69
70#include <sys/param.h>
71#include "stand.h"
72
73ssize_t
74read(int fd, void *dest, size_t bcount)
75{
76    struct open_file	*f = &files[fd];
77    size_t		resid;
78
79    if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) {
80	errno = EBADF;
81	return (-1);
82    }
83    if (f->f_flags & F_RAW) {
84	twiddle();
85	errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ,
86					btodb(f->f_offset), bcount, dest, &resid);
87	if (errno)
88	    return (-1);
89	f->f_offset += resid;
90	return (resid);
91    }
92
93    /*
94     * Optimise reads from regular files using a readahead buffer.
95     * If the request can't be satisfied from the current buffer contents,
96     * check to see if it should be bypassed, or refill the buffer and complete
97     * the request.
98     */
99    resid = bcount;
100    for (;;) {
101	size_t	ccount, cresid;
102	/* how much can we supply? */
103	ccount = imin(f->f_ralen, resid);
104	if (ccount > 0) {
105	    bcopy(f->f_rabuf + f->f_raoffset, dest, ccount);
106	    f->f_raoffset += ccount;
107	    f->f_ralen -= ccount;
108	    resid -= ccount;
109	    if (resid == 0)
110		return(bcount);
111	    dest = (char *)dest + ccount;
112	}
113
114	/* will filling the readahead buffer again not help? */
115	if (resid >= SOPEN_RASIZE) {
116	    /* bypass the rest of the request and leave the buffer empty */
117	    if ((errno = (f->f_ops->fo_read)(f, dest, resid, &cresid)))
118		    return (-1);
119	    return(bcount - cresid);
120	}
121
122	/* fetch more data */
123	if ((errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, &cresid)))
124	    return (-1);
125	f->f_raoffset = 0;
126	f->f_ralen = SOPEN_RASIZE - cresid;
127	/* no more data, return what we had */
128	if (f->f_ralen == 0)
129	    return(bcount - resid);
130    }
131}
132