7668336c8e
only happen on every Nth call. Update the existing twiddle() calls done in various IO loops to roughly reflect the relative IO sizes. That is, tftp and nfs call twiddle() on every 1K block, ufs on every filesystem block, so the network calls now use a much larger divisor than disk IO calls. Also add a new twiddle_divisor() function that allows an application to set a global divisor that is applied on top of the per-call divisors. Nothing calls this yet, but loader(8) will be using it to further throttle the cursor for slow serial consoles.
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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* 4. 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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