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 $ */ 4 5 /*- 6 * Copyright (c) 1993 7 * The Regents of the University of California. All rights reserved. 8 * 9 * This code is derived from software contributed to Berkeley by 10 * The Mach Operating System project at Carnegie-Mellon University. 11 * 12 * Redistribution and use in source and binary forms, with or without 13 * modification, are permitted provided that the following conditions 14 * are met: 15 * 1. Redistributions of source code must retain the above copyright 16 * notice, this list of conditions and the following disclaimer. 17 * 2. Redistributions in binary form must reproduce the above copyright 18 * notice, this list of conditions and the following disclaimer in the 19 * documentation and/or other materials provided with the distribution. 20 * 3. Neither the name of the University nor the names of its contributors 21 * may be used to endorse or promote products derived from this software 22 * without specific prior written permission. 23 * 24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 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 34 * SUCH DAMAGE. 35 * 36 * @(#)read.c 8.1 (Berkeley) 6/11/93 37 * 38 * 39 * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University 40 * All Rights Reserved. 41 * 42 * Author: Alessandro Forin 43 * 44 * Permission to use, copy, modify and distribute this software and its 45 * documentation is hereby granted, provided that both the copyright 46 * notice and this permission notice appear in all copies of the 47 * software, derivative works or modified versions, and any portions 48 * thereof, and that both notices appear in supporting documentation. 49 * 50 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" 51 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR 52 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. 53 * 54 * Carnegie Mellon requests users of this software to return to 55 * 56 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU 57 * School of Computer Science 58 * Carnegie Mellon University 59 * Pittsburgh PA 15213-3890 60 * 61 * any improvements or extensions that they make and grant Carnegie the 62 * rights to redistribute these changes. 63 */ 64 65 #include <sys/param.h> 66 #include "stand.h" 67 68 int no_io_error; 69 70 ssize_t 71 read(int fd, void *dest, size_t bcount) 72 { 73 struct open_file *f = &files[fd]; 74 size_t resid; 75 76 if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) { 77 errno = EBADF; 78 return (-1); 79 } 80 if (f->f_flags & F_RAW) { 81 twiddle(); 82 errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ, 83 btodb(f->f_offset), bcount, dest, &resid); 84 if (errno) 85 return (-1); 86 f->f_offset += resid; 87 return (resid); 88 } 89 90 /* 91 * Optimise reads from regular files using a readahead buffer. 92 * If the request can't be satisfied from the current buffer contents, 93 * check to see if it should be bypassed, or refill the buffer and complete 94 * the request. 95 */ 96 resid = bcount; 97 for (;;) { 98 size_t ccount, cresid; 99 /* how much can we supply? */ 100 ccount = imin(f->f_ralen, resid); 101 if (ccount > 0) { 102 bcopy(f->f_rabuf + f->f_raoffset, dest, ccount); 103 f->f_raoffset += ccount; 104 f->f_ralen -= ccount; 105 resid -= ccount; 106 if (resid == 0) 107 return(bcount); 108 dest += ccount; 109 } 110 111 /* will filling the readahead buffer again not help? */ 112 if (resid >= SOPEN_RASIZE) { 113 /* bypass the rest of the request and leave the buffer empty */ 114 if ((errno = (f->f_ops->fo_read)(f, dest, resid, &cresid))) 115 return(bcount - resid); 116 return(bcount - cresid); 117 } 118 119 /* fetch more data */ 120 if ((errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, &cresid))) 121 return(bcount - resid); /* behave like fread() */ 122 f->f_raoffset = 0; 123 f->f_ralen = SOPEN_RASIZE - cresid; 124 /* no more data, return what we had */ 125 if (f->f_ralen == 0) 126 return(bcount - resid); 127 } 128 } 129