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 __FBSDID("$FreeBSD$"); 65 66 #include <sys/param.h> 67 #include "stand.h" 68 69 ssize_t 70 read(int fd, void *dest, size_t bcount) 71 { 72 struct open_file *f = &files[fd]; 73 size_t resid; 74 75 TSENTER(); 76 77 if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) { 78 errno = EBADF; 79 return (-1); 80 } 81 if (f->f_flags & F_RAW) { 82 twiddle(4); 83 errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ, 84 btodb(f->f_offset), bcount, dest, &resid); 85 if (errno) 86 return (-1); 87 f->f_offset += resid; 88 TSEXIT(); 89 return (resid); 90 } 91 92 /* 93 * Optimise reads from regular files using a readahead buffer. 94 * If the request can't be satisfied from the current buffer contents, 95 * check to see if it should be bypassed, or refill the buffer and 96 * complete the request. 97 */ 98 resid = bcount; 99 for (;;) { 100 size_t ccount, cresid; 101 /* how much can we supply? */ 102 ccount = imin(f->f_ralen, resid); 103 if (ccount > 0) { 104 bcopy(f->f_rabuf + f->f_raoffset, dest, ccount); 105 f->f_raoffset += ccount; 106 f->f_ralen -= ccount; 107 resid -= ccount; 108 if (resid == 0) { 109 TSEXIT(); 110 return (bcount); 111 } 112 dest = (char *)dest + ccount; 113 } 114 115 /* will filling the readahead buffer again not help? */ 116 if (f->f_rabuf == NULL || resid >= SOPEN_RASIZE) { 117 /* 118 * bypass the rest of the request and leave the 119 * buffer empty 120 */ 121 errno = (f->f_ops->fo_read)(f, dest, resid, &cresid); 122 if (errno != 0) 123 return (-1); 124 TSEXIT(); 125 return (bcount - cresid); 126 } 127 128 /* fetch more data */ 129 errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, 130 &cresid); 131 if (errno != 0) 132 return (-1); 133 f->f_raoffset = 0; 134 f->f_ralen = SOPEN_RASIZE - cresid; 135 /* no more data, return what we had */ 136 if (f->f_ralen == 0) { 137 TSEXIT(); 138 return (bcount - resid); 139 } 140 } 141 } 142