read.c revision 124811
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. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 * 38 * @(#)read.c 8.1 (Berkeley) 6/11/93 39 * 40 * 41 * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University 42 * All Rights Reserved. 43 * 44 * Author: Alessandro Forin 45 * 46 * Permission to use, copy, modify and distribute this software and its 47 * documentation is hereby granted, provided that both the copyright 48 * notice and this permission notice appear in all copies of the 49 * software, derivative works or modified versions, and any portions 50 * thereof, and that both notices appear in supporting documentation. 51 * 52 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" 53 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR 54 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. 55 * 56 * Carnegie Mellon requests users of this software to return to 57 * 58 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU 59 * School of Computer Science 60 * Carnegie Mellon University 61 * Pittsburgh PA 15213-3890 62 * 63 * any improvements or extensions that they make and grant Carnegie the 64 * rights to redistribute these changes. 65 */ 66 67#include <sys/cdefs.h> 68__FBSDID("$FreeBSD: head/lib/libstand/read.c 124811 2004-01-21 20:12:23Z jhb $"); 69 70#include <sys/param.h> 71#include "stand.h" 72 73ssize_t 74read(int fd, void *dest, size_t bcount) 75{ 76 struct open_file *f = &files[fd]; 77 size_t resid; 78 79 if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) { 80 errno = EBADF; 81 return (-1); 82 } 83 if (f->f_flags & F_RAW) { 84 twiddle(); 85 errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ, 86 btodb(f->f_offset), bcount, dest, &resid); 87 if (errno) 88 return (-1); 89 f->f_offset += resid; 90 return (resid); 91 } 92 93 /* 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 97 * the request. 98 */ 99 resid = bcount; 100 for (;;) { 101 size_t ccount, cresid; 102 /* how much can we supply? */ 103 ccount = imin(f->f_ralen, resid); 104 if (ccount > 0) { 105 bcopy(f->f_rabuf + f->f_raoffset, dest, ccount); 106 f->f_raoffset += ccount; 107 f->f_ralen -= ccount; 108 resid -= ccount; 109 if (resid == 0) 110 return(bcount); 111 dest += ccount; 112 } 113 114 /* 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 (-1); 119 return(bcount - cresid); 120 } 121 122 /* fetch more data */ 123 if ((errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, &cresid))) 124 return (-1); 125 f->f_raoffset = 0; 126 f->f_ralen = SOPEN_RASIZE - cresid; 127 /* no more data, return what we had */ 128 if (f->f_ralen == 0) 129 return(bcount - resid); 130 } 131} 132