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/* $NetBSD: read.c,v 1.8 1997/01/22 00:38:12 cgd Exp $ */
/*
* Copyright (c) 1993
* The Regents of the University of California. All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* The Mach Operating System project at Carnegie-Mellon University.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @(#)read.c 8.1 (Berkeley) 6/11/93
*
*
* Copyright (c) 1989, 1990, 1991 Carnegie Mellon University
* All Rights Reserved.
*
* Author: Alessandro Forin
*
* Permission to use, copy, modify and distribute this software and its
* documentation is hereby granted, provided that both the copyright
* notice and this permission notice appear in all copies of the
* software, derivative works or modified versions, and any portions
* thereof, and that both notices appear in supporting documentation.
*
* CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
* CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
* ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
*
* Carnegie Mellon requests users of this software to return to
*
* Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
* School of Computer Science
* Carnegie Mellon University
* Pittsburgh PA 15213-3890
*
* any improvements or extensions that they make and grant Carnegie the
* rights to redistribute these changes.
*/
#include <sys/cdefs.h>
#include <sys/param.h>
#include "stand.h"
ssize_t
read(int fd, void *dest, size_t bcount)
{
struct open_file *f;
size_t resid;
f = fd2open_file(fd);
if (f == NULL || !(f->f_flags & F_READ)) {
errno = EBADF;
return (-1);
}
if (f->f_flags & F_RAW) {
twiddle(8);
errno = (f->f_dev->dv_strategy)(f->f_devdata, F_READ,
btodb(f->f_offset), bcount, dest, &resid);
if (errno)
return (-1);
f->f_offset += resid;
return (resid);
}
/*
* Optimise reads from regular files using a readahead buffer.
* If the request can't be satisfied from the current buffer contents,
* check to see if it should be bypassed, or refill the buffer and
* complete the request.
*/
resid = bcount;
for (;;) {
size_t ccount, cresid;
/* how much can we supply? */
ccount = imin(f->f_ralen, resid);
if (ccount > 0) {
bcopy(f->f_rabuf + f->f_raoffset, dest, ccount);
f->f_raoffset += ccount;
f->f_ralen -= ccount;
resid -= ccount;
if (resid == 0)
return (bcount);
dest = (char *)dest + ccount;
}
/* will filling the readahead buffer again not help? */
if (f->f_rabuf == NULL || resid >= SOPEN_RASIZE) {
/*
* bypass the rest of the request and leave the
* buffer empty
*/
errno = (f->f_ops->fo_read)(f, dest, resid, &cresid);
if (errno != 0)
return (-1);
return (bcount - cresid);
}
/* fetch more data */
errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE,
&cresid);
if (errno != 0)
return (-1);
f->f_raoffset = 0;
f->f_ralen = SOPEN_RASIZE - cresid;
/* no more data, return what we had */
if (f->f_ralen == 0)
return (bcount - resid);
}
}
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