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
68 ssize_t
read(int fd,void * dest,size_t bcount)69 read(int fd, void *dest, size_t bcount)
70 {
71 struct open_file *f;
72 size_t resid;
73
74 f = fd2open_file(fd);
75 if (f == NULL || !(f->f_flags & F_READ)) {
76 errno = EBADF;
77 return (-1);
78 }
79 if (f->f_flags & F_RAW) {
80 twiddle(8);
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
93 * complete 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 (f->f_rabuf == NULL || resid >= SOPEN_RASIZE) {
112 /*
113 * bypass the rest of the request and leave the
114 * buffer empty
115 */
116 errno = (f->f_ops->fo_read)(f, dest, resid, &cresid);
117 if (errno != 0)
118 return (-1);
119 return (bcount - cresid);
120 }
121
122 /* fetch more data */
123 errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE,
124 &cresid);
125 if (errno != 0)
126 return (-1);
127 f->f_raoffset = 0;
128 f->f_ralen = SOPEN_RASIZE - cresid;
129 /* no more data, return what we had */
130 if (f->f_ralen == 0)
131 return (bcount - resid);
132 }
133 }
134