1 /* $FreeBSD: src/lib/libstand/read.c,v 1.1.1.1.6.1 2000/09/10 01:32:06 ps Exp $ */
2 /* $NetBSD: read.c,v 1.8 1997/01/22 00:38:12 cgd Exp $ */
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8 * This code is derived from software contributed to Berkeley by
9 * The Mach Operating System project at Carnegie-Mellon University.
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21 * This product includes software developed by the University of
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39 * @(#)read.c 8.1 (Berkeley) 6/11/93
42 * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
43 * All Rights Reserved.
45 * Author: Alessandro Forin
47 * Permission to use, copy, modify and distribute this software and its
48 * documentation is hereby granted, provided that both the copyright
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53 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
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55 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
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59 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
60 * School of Computer Science
61 * Carnegie Mellon University
62 * Pittsburgh PA 15213-3890
64 * any improvements or extensions that they make and grant Carnegie the
65 * rights to redistribute these changes.
68 #include <sys/param.h>
72 read(int fd, void *dest, size_t bcount)
74 struct open_file *f = &files[fd];
77 if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) {
81 if (f->f_flags & F_RAW) {
83 errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ,
84 btodb(f->f_offset), bcount, dest, &resid);
92 * Optimise reads from regular files using a readahead buffer.
93 * If the request can't be satisfied from the current buffer contents,
94 * check to see if it should be bypassed, or refill the buffer and complete
99 size_t ccount, cresid;
100 /* how much can we supply? */
101 ccount = imin(f->f_ralen, resid);
103 bcopy(f->f_rabuf + f->f_raoffset, dest, ccount);
104 f->f_raoffset += ccount;
105 f->f_ralen -= ccount;
112 /* will filling the readahead buffer again not help? */
113 if (resid >= SOPEN_RASIZE) {
114 /* bypass the rest of the request and leave the buffer empty */
115 if ((errno = (f->f_ops->fo_read)(f, dest, resid, &cresid)))
116 return(bcount - resid);
117 return(bcount - cresid);
120 /* fetch more data */
121 if ((errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, &cresid)))
122 return(bcount - resid); /* behave like fread() */
124 f->f_ralen = SOPEN_RASIZE - cresid;
125 /* no more data, return what we had */
127 return(bcount - resid);