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 *
35 * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
36 * All Rights Reserved.
37 *
38 * Author: Alessandro Forin
39 *
40 * Permission to use, copy, modify and distribute this software and its
41 * documentation is hereby granted, provided that both the copyright
42 * notice and this permission notice appear in all copies of the
43 * software, derivative works or modified versions, and any portions
44 * thereof, and that both notices appear in supporting documentation.
45 *
46 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
47 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
48 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
49 *
50 * Carnegie Mellon requests users of this software to return to
51 *
52 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
53 * School of Computer Science
54 * Carnegie Mellon University
55 * Pittsburgh PA 15213-3890
56 *
57 * any improvements or extensions that they make and grant Carnegie the
58 * rights to redistribute these changes.
59 */
60
61 #include <sys/param.h>
62 #include "stand.h"
63
64 ssize_t
read(int fd,void * dest,size_t bcount)65 read(int fd, void *dest, size_t bcount)
66 {
67 struct open_file *f;
68 size_t resid;
69
70 TSENTER();
71
72 f = fd2open_file(fd);
73 if (f == NULL || !(f->f_flags & F_READ)) {
74 errno = EBADF;
75 return (-1);
76 }
77 if (f->f_flags & F_RAW) {
78 twiddle(4);
79 errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ,
80 btodb(f->f_offset), bcount, dest, &resid);
81 if (errno)
82 return (-1);
83 f->f_offset += resid;
84 TSEXIT();
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 TSEXIT();
106 return (bcount);
107 }
108 dest = (char *)dest + ccount;
109 }
110
111 /* will filling the readahead buffer again not help? */
112 if (f->f_rabuf == NULL || resid >= SOPEN_RASIZE) {
113 /*
114 * bypass the rest of the request and leave the
115 * buffer empty
116 */
117 errno = (f->f_ops->fo_read)(f, dest, resid, &cresid);
118 if (errno != 0)
119 return (-1);
120 TSEXIT();
121 return (bcount - cresid);
122 }
123
124 /* fetch more data */
125 errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE,
126 &cresid);
127 if (errno != 0)
128 return (-1);
129 f->f_raoffset = 0;
130 f->f_ralen = SOPEN_RASIZE - cresid;
131 /* no more data, return what we had */
132 if (f->f_ralen == 0) {
133 TSEXIT();
134 return (bcount - resid);
135 }
136 }
137 }
138