read.c revision 65470
1/* $FreeBSD: head/lib/libstand/read.c 65470 2000-09-05 09:52:50Z msmith $ */ 2/* $NetBSD: read.c,v 1.8 1997/01/22 00:38:12 cgd Exp $ */ 3 4/*- 5 * Copyright (c) 1993 6 * The Regents of the University of California. All rights reserved. 7 * 8 * This code is derived from software contributed to Berkeley by 9 * The Mach Operating System project at Carnegie-Mellon University. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 3. All advertising materials mentioning features or use of this software 20 * must display the following acknowledgement: 21 * This product includes software developed by the University of 22 * California, Berkeley and its contributors. 23 * 4. Neither the name of the University nor the names of its contributors 24 * may be used to endorse or promote products derived from this software 25 * without specific prior written permission. 26 * 27 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 28 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 29 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 30 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 31 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 32 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 33 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 34 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 35 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 36 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 37 * SUCH DAMAGE. 38 * 39 * @(#)read.c 8.1 (Berkeley) 6/11/93 40 * 41 * 42 * Copyright (c) 1989, 1990, 1991 Carnegie Mellon University 43 * All Rights Reserved. 44 * 45 * Author: Alessandro Forin 46 * 47 * Permission to use, copy, modify and distribute this software and its 48 * documentation is hereby granted, provided that both the copyright 49 * notice and this permission notice appear in all copies of the 50 * software, derivative works or modified versions, and any portions 51 * thereof, and that both notices appear in supporting documentation. 52 * 53 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" 54 * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR 55 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. 56 * 57 * Carnegie Mellon requests users of this software to return to 58 * 59 * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU 60 * School of Computer Science 61 * Carnegie Mellon University 62 * Pittsburgh PA 15213-3890 63 * 64 * any improvements or extensions that they make and grant Carnegie the 65 * rights to redistribute these changes. 66 */ 67 68#include <sys/param.h> 69#include "stand.h" 70 71ssize_t 72read(int fd, void *dest, size_t bcount) 73{ 74 struct open_file *f = &files[fd]; 75 size_t resid; 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(); 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 return (resid); 89 } 90 91 /* 92 * Optimise reads from regular files using a readahead buffer. 93 * If the request can't be satisfied from the current buffer contents, 94 * check to see if it should be bypassed, or refill the buffer and complete 95 * the request. 96 */ 97 resid = bcount; 98 for (;;) { 99 size_t ccount, cresid; 100 /* how much can we supply? */ 101 ccount = imin(f->f_ralen, resid); 102 if (ccount > 0) { 103 bcopy(f->f_rabuf + f->f_raoffset, dest, ccount); 104 f->f_raoffset += ccount; 105 f->f_ralen -= ccount; 106 resid -= ccount; 107 if (resid == 0) 108 return(bcount); 109 dest += ccount; 110 } 111 112 /* will filling the readahead buffer again not help? */ 113 if (resid >= SOPEN_RASIZE) { 114 /* bypass the rest of the request and leave the buffer empty */ 115 if ((errno = (f->f_ops->fo_read)(f, dest, resid, &cresid))) 116 return(bcount - resid); 117 return(bcount - cresid); 118 } 119 120 /* fetch more data */ 121 if ((errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, &cresid))) 122 return(bcount - resid); /* behave like fread() */ 123 f->f_raoffset = 0; 124 f->f_ralen = SOPEN_RASIZE - cresid; 125 /* no more data, return what we had */ 126 if (f->f_ralen == 0) 127 return(bcount - resid); 128 } 129} 130