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 65 #include <sys/param.h> 66 #include "stand.h" 67 68 ssize_t 69 read(int fd, void *dest, size_t bcount) 70 { 71 struct open_file *f; 72 size_t resid; 73 74 f = fd2open_file(fd); 75 if (f == NULL || !(f->f_flags & F_READ)) { 76 errno = EBADF; 77 return (-1); 78 } 79 if (f->f_flags & F_RAW) { 80 twiddle(8); 81 errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ, 82 btodb(f->f_offset), bcount, dest, &resid); 83 if (errno) 84 return (-1); 85 f->f_offset += resid; 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 return (bcount); 107 dest = (char *)dest + ccount; 108 } 109 110 /* will filling the readahead buffer again not help? */ 111 if (f->f_rabuf == NULL || resid >= SOPEN_RASIZE) { 112 /* 113 * bypass the rest of the request and leave the 114 * buffer empty 115 */ 116 errno = (f->f_ops->fo_read)(f, dest, resid, &cresid); 117 if (errno != 0) 118 return (-1); 119 return (bcount - cresid); 120 } 121 122 /* fetch more data */ 123 errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, 124 &cresid); 125 if (errno != 0) 126 return (-1); 127 f->f_raoffset = 0; 128 f->f_ralen = SOPEN_RASIZE - cresid; 129 /* no more data, return what we had */ 130 if (f->f_ralen == 0) 131 return (bcount - resid); 132 } 133 } 134