1 /* $NetBSD: read.c,v 1.8 1997/01/22 00:38:12 cgd Exp $ */
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38 * @(#)read.c 8.1 (Berkeley) 6/11/93
41 * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
42 * All Rights Reserved.
44 * Author: Alessandro Forin
46 * Permission to use, copy, modify and distribute this software and its
47 * documentation is hereby granted, provided that both the copyright
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52 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
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54 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
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58 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
59 * School of Computer Science
60 * Carnegie Mellon University
61 * Pittsburgh PA 15213-3890
63 * any improvements or extensions that they make and grant Carnegie the
64 * rights to redistribute these changes.
67 #include <sys/cdefs.h>
68 __FBSDID("$FreeBSD$");
70 #include <sys/param.h>
74 read(int fd, void *dest, size_t bcount)
76 struct open_file *f = &files[fd];
79 if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) {
83 if (f->f_flags & F_RAW) {
85 errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ,
86 btodb(f->f_offset), bcount, dest, &resid);
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
101 size_t ccount, cresid;
102 /* how much can we supply? */
103 ccount = imin(f->f_ralen, resid);
105 bcopy(f->f_rabuf + f->f_raoffset, dest, ccount);
106 f->f_raoffset += ccount;
107 f->f_ralen -= ccount;
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(bcount - resid);
119 return(bcount - cresid);
122 /* fetch more data */
123 if ((errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, &cresid)))
124 return(bcount - resid); /* behave like fread() */
126 f->f_ralen = SOPEN_RASIZE - cresid;
127 /* no more data, return what we had */
129 return(bcount - resid);