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 * 35 * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University 36 * All Rights Reserved. 37 * 38 * Author: Alessandro Forin 39 * 40 * Permission to use, copy, modify and distribute this software and its 41 * documentation is hereby granted, provided that both the copyright 42 * notice and this permission notice appear in all copies of the 43 * software, derivative works or modified versions, and any portions 44 * thereof, and that both notices appear in supporting documentation. 45 * 46 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" 47 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR 48 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. 49 * 50 * Carnegie Mellon requests users of this software to return to 51 * 52 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU 53 * School of Computer Science 54 * Carnegie Mellon University 55 * Pittsburgh PA 15213-3890 56 * 57 * any improvements or extensions that they make and grant Carnegie the 58 * rights to redistribute these changes. 59 */ 60 61 #include <sys/cdefs.h> 62 #include <sys/param.h> 63 #include "stand.h" 64 65 ssize_t 66 read(int fd, void *dest, size_t bcount) 67 { 68 struct open_file *f; 69 size_t resid; 70 71 TSENTER(); 72 73 f = fd2open_file(fd); 74 if (f == NULL || !(f->f_flags & F_READ)) { 75 errno = EBADF; 76 return (-1); 77 } 78 if (f->f_flags & F_RAW) { 79 twiddle(4); 80 errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ, 81 btodb(f->f_offset), bcount, dest, &resid); 82 if (errno) 83 return (-1); 84 f->f_offset += resid; 85 TSEXIT(); 86 return (resid); 87 } 88 89 /* 90 * Optimise reads from regular files using a readahead buffer. 91 * If the request can't be satisfied from the current buffer contents, 92 * check to see if it should be bypassed, or refill the buffer and 93 * complete the request. 94 */ 95 resid = bcount; 96 for (;;) { 97 size_t ccount, cresid; 98 /* how much can we supply? */ 99 ccount = imin(f->f_ralen, resid); 100 if (ccount > 0) { 101 bcopy(f->f_rabuf + f->f_raoffset, dest, ccount); 102 f->f_raoffset += ccount; 103 f->f_ralen -= ccount; 104 resid -= ccount; 105 if (resid == 0) { 106 TSEXIT(); 107 return (bcount); 108 } 109 dest = (char *)dest + ccount; 110 } 111 112 /* will filling the readahead buffer again not help? */ 113 if (f->f_rabuf == NULL || resid >= SOPEN_RASIZE) { 114 /* 115 * bypass the rest of the request and leave the 116 * buffer empty 117 */ 118 errno = (f->f_ops->fo_read)(f, dest, resid, &cresid); 119 if (errno != 0) 120 return (-1); 121 TSEXIT(); 122 return (bcount - cresid); 123 } 124 125 /* fetch more data */ 126 errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, 127 &cresid); 128 if (errno != 0) 129 return (-1); 130 f->f_raoffset = 0; 131 f->f_ralen = SOPEN_RASIZE - cresid; 132 /* no more data, return what we had */ 133 if (f->f_ralen == 0) { 134 TSEXIT(); 135 return (bcount - resid); 136 } 137 } 138 } 139