1 /* $FreeBSD: src/lib/libstand/read.c,v 1.1.1.1.6.1 2000/09/10 01:32:06 ps Exp $ */
2 /* $DragonFly: src/lib/libstand/read.c,v 1.2 2003/06/17 04:26:51 dillon Exp $ */
3 /* $NetBSD: read.c,v 1.8 1997/01/22 00:38:12 cgd Exp $ */
7 * The Regents of the University of California. All rights reserved.
9 * This code is derived from software contributed to Berkeley by
10 * The Mach Operating System project at Carnegie-Mellon University.
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13 * modification, are permitted provided that the following conditions
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32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
36 * @(#)read.c 8.1 (Berkeley) 6/11/93
39 * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
40 * All Rights Reserved.
42 * Author: Alessandro Forin
44 * Permission to use, copy, modify and distribute this software and its
45 * documentation is hereby granted, provided that both the copyright
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50 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
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52 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
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56 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
57 * School of Computer Science
58 * Carnegie Mellon University
59 * Pittsburgh PA 15213-3890
61 * any improvements or extensions that they make and grant Carnegie the
62 * rights to redistribute these changes.
65 #include <sys/param.h>
69 read(int fd, void *dest, size_t bcount)
71 struct open_file *f = &files[fd];
74 if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) {
78 if (f->f_flags & F_RAW) {
80 errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ,
81 btodb(f->f_offset), bcount, dest, &resid);
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 complete
96 size_t ccount, cresid;
97 /* how much can we supply? */
98 ccount = imin(f->f_ralen, resid);
100 bcopy(f->f_rabuf + f->f_raoffset, dest, ccount);
101 f->f_raoffset += ccount;
102 f->f_ralen -= ccount;
109 /* will filling the readahead buffer again not help? */
110 if (resid >= SOPEN_RASIZE) {
111 /* bypass the rest of the request and leave the buffer empty */
112 if ((errno = (f->f_ops->fo_read)(f, dest, resid, &cresid)))
113 return(bcount - resid);
114 return(bcount - cresid);
117 /* fetch more data */
118 if ((errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, &cresid)))
119 return(bcount - resid); /* behave like fread() */
121 f->f_ralen = SOPEN_RASIZE - cresid;
122 /* no more data, return what we had */
124 return(bcount - resid);