xref: /illumos-gate/usr/src/boot/libsa/read.c (revision 22028508fd28d36ff74dc02c5774a8ba1f0db045)
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