128 lines
4.4 KiB
C
128 lines
4.4 KiB
C
/* $NetBSD: read.c,v 1.8 1997/01/22 00:38:12 cgd Exp $ */
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/*-
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* Copyright (c) 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* The Mach Operating System project at Carnegie-Mellon University.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)read.c 8.1 (Berkeley) 6/11/93
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*
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*
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* Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
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* All Rights Reserved.
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*
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* Author: Alessandro Forin
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*
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* Permission to use, copy, modify and distribute this software and its
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* documentation is hereby granted, provided that both the copyright
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* notice and this permission notice appear in all copies of the
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* software, derivative works or modified versions, and any portions
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* thereof, and that both notices appear in supporting documentation.
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*
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* CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
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* CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
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* ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
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*
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* Carnegie Mellon requests users of this software to return to
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*
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* Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
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* School of Computer Science
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* Carnegie Mellon University
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* Pittsburgh PA 15213-3890
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*
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* any improvements or extensions that they make and grant Carnegie the
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* rights to redistribute these changes.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include "stand.h"
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ssize_t
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read(int fd, void *dest, size_t bcount)
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{
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struct open_file *f = &files[fd];
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size_t resid;
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if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) {
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errno = EBADF;
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return (-1);
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}
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if (f->f_flags & F_RAW) {
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twiddle(4);
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errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ,
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btodb(f->f_offset), bcount, dest, &resid);
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if (errno)
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return (-1);
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f->f_offset += resid;
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return (resid);
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}
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/*
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* Optimise reads from regular files using a readahead buffer.
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* If the request can't be satisfied from the current buffer contents,
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* check to see if it should be bypassed, or refill the buffer and complete
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* the request.
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*/
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resid = bcount;
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for (;;) {
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size_t ccount, cresid;
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/* how much can we supply? */
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ccount = imin(f->f_ralen, resid);
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if (ccount > 0) {
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bcopy(f->f_rabuf + f->f_raoffset, dest, ccount);
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f->f_raoffset += ccount;
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f->f_ralen -= ccount;
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resid -= ccount;
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if (resid == 0)
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return(bcount);
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dest = (char *)dest + ccount;
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}
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/* will filling the readahead buffer again not help? */
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if (resid >= SOPEN_RASIZE) {
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/* bypass the rest of the request and leave the buffer empty */
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if ((errno = (f->f_ops->fo_read)(f, dest, resid, &cresid)))
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return (-1);
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return(bcount - cresid);
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}
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/* fetch more data */
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if ((errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, &cresid)))
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return (-1);
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f->f_raoffset = 0;
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f->f_ralen = SOPEN_RASIZE - cresid;
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/* no more data, return what we had */
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if (f->f_ralen == 0)
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return(bcount - resid);
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}
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}
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