diff options
Diffstat (limited to 'stand/libsa/read.c')
| -rw-r--r-- | stand/libsa/read.c | 127 |
1 files changed, 127 insertions, 0 deletions
diff --git a/stand/libsa/read.c b/stand/libsa/read.c new file mode 100644 index 000000000000..e48a4d864212 --- /dev/null +++ b/stand/libsa/read.c @@ -0,0 +1,127 @@ +/* $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> +__FBSDID("$FreeBSD$"); + +#include <sys/param.h> +#include "stand.h" + +ssize_t +read(int fd, void *dest, size_t bcount) +{ + struct open_file *f = &files[fd]; + size_t resid; + + if ((unsigned)fd >= SOPEN_MAX || !(f->f_flags & F_READ)) { + errno = EBADF; + return (-1); + } + if (f->f_flags & F_RAW) { + twiddle(4); + 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 (resid >= SOPEN_RASIZE) { + /* bypass the rest of the request and leave the buffer empty */ + if ((errno = (f->f_ops->fo_read)(f, dest, resid, &cresid))) + return (-1); + return(bcount - cresid); + } + + /* fetch more data */ + if ((errno = (f->f_ops->fo_read)(f, f->f_rabuf, SOPEN_RASIZE, &cresid))) + 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); + } +} |