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Fix broken conversion of private err() function and make ierr() and oerr()
back into functions, not macros.  Also make functions that call mmap()
return an int so we can fall back to non-mmap (slow) version on mmap failure.
Noticable effects:
 o when you tail multiple files, if one of the files doesn't exist or
   is otherwise broken, keep on going to the next file.
 o it is now possible to tail files > 2gig, though it will be *very* slow
   since tail will be unable to use mmap()

/*	$OpenBSD: forward.c,v 1.7 1999/02/03 02:09:30 millert Exp $	*/
/*	$NetBSD: forward.c,v 1.7 1996/02/13 16:49:10 ghudson Exp $	*/

/*-
 * Copyright (c) 1991, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Edward Sze-Tyan Wang.
 *
 * 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. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *	This product includes software developed by the University of
 *	California, Berkeley and its contributors.
 * 4. 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.
 */

#ifndef lint
#if 0
static char sccsid[] = "@(#)forward.c	8.1 (Berkeley) 6/6/93";
#endif
static char rcsid[] = "$OpenBSD: forward.c,v 1.7 1999/02/03 02:09:30 millert Exp $";
#endif /* not lint */

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>

#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "extern.h"

static int rlines __P((FILE *, long, struct stat *));

/*
 * forward -- display the file, from an offset, forward.
 *
 * There are eight separate cases for this -- regular and non-regular
 * files, by bytes or lines and from the beginning or end of the file.
 *
 * FBYTES	byte offset from the beginning of the file
 *	REG	seek
 *	NOREG	read, counting bytes
 *
 * FLINES	line offset from the beginning of the file
 *	REG	read, counting lines
 *	NOREG	read, counting lines
 *
 * RBYTES	byte offset from the end of the file
 *	REG	seek
 *	NOREG	cyclically read characters into a wrap-around buffer
 *
 * RLINES
 *	REG	mmap the file and step back until reach the correct offset.
 *	NOREG	cyclically read lines into a wrap-around array of buffers
 */
void
forward(fp, style, off, sbp)
	FILE *fp;
	enum STYLE style;
	long off;
	struct stat *sbp;
{
	register int ch;
	struct stat nsb;

	switch(style) {
	case FBYTES:
		if (off == 0)
			break;
		if (S_ISREG(sbp->st_mode)) {
			if (sbp->st_size < off)
				off = sbp->st_size;
			if (fseek(fp, off, SEEK_SET) == -1) {
				ierr();
				return;
			}
		} else while (off--)
			if ((ch = getc(fp)) == EOF) {
				if (ferror(fp)) {
					ierr();
					return;
				}
				break;
			}
		break;
	case FLINES:
		if (off == 0)
			break;
		for (;;) {
			if ((ch = getc(fp)) == EOF) {
				if (ferror(fp)) {
					ierr();
					return;
				}
				break;
			}
			if (ch == '\n' && !--off)
				break;
		}
		break;
	case RBYTES:
		if (S_ISREG(sbp->st_mode)) {
			if (sbp->st_size >= off &&
			    fseek(fp, -off, SEEK_END) == -1) {
				ierr();
				return;
			}
		} else if (off == 0) {
			while (getc(fp) != EOF)
				;
			if (ferror(fp)) {
				ierr();
				return;
			}
		} else
			bytes(fp, off);
		break;
	case RLINES:
		if (S_ISREG(sbp->st_mode)) {
			if (!off) {
				if (fseek(fp, 0L, SEEK_END) == -1) {
					ierr();
					return;
				}
			} else if (rlines(fp, off, sbp) != 0)
				lines(fp, off);
		} else if (off == 0) {
			while (getc(fp) != EOF)
				;
			if (ferror(fp)) {
				ierr();
				return;
			}
		} else
			lines(fp, off);
		break;
	}

	for (;;) {
		while (!feof(fp) && (ch = getc(fp)) != EOF)
			if (putchar(ch) == EOF)
				oerr();
		if (ferror(fp)) {
			ierr();
			return;
		}
		(void)fflush(stdout);
		if (!fflag)
			break;
		sleep(1);
		clearerr(fp);

		if (stat(fname, &nsb) != 0)
			continue;
		/* Reopen file if the inode changes or file was truncated */
		if (nsb.st_ino != sbp->st_ino) {
			warnx("%s has been replaced, reopening.", fname);
			if ((fp = freopen(fname, "r", fp)) == NULL) {
				ierr();
				return;
			}
			(void)memcpy(sbp, &nsb, sizeof(nsb));
		} else if (nsb.st_size < sbp->st_size) {
			warnx("%s has been truncated, resetting.", fname);
			rewind(fp);
			(void)memcpy(sbp, &nsb, sizeof(nsb));
		}
	}
}

/*
 * rlines -- display the last offset lines of the file.
 */
static int
rlines(fp, off, sbp)
	FILE *fp;
	long off;
	struct stat *sbp;
{
	register off_t size;
	register char *p;
	char *start;

	if (!(size = sbp->st_size))
		return (0);

	if (size > SIZE_T_MAX)
		return (1);

	if ((start = mmap(NULL, (size_t)size, PROT_READ, 0, fileno(fp),
	    (off_t)0)) == (caddr_t)-1)
		return (1);

	/* Last char is special, ignore whether newline or not. */
	for (p = start + size - 1; --size;)
		if (*--p == '\n' && !--off) {
			++p;
			break;
		}

	/* Set the file pointer to reflect the length displayed. */
	size = sbp->st_size - size;
	WR(p, size);
	if (fseek(fp, (long)sbp->st_size, SEEK_SET) == -1) {
		ierr();
		return (1);
	}
	if (munmap(start, (size_t)sbp->st_size)) {
		ierr();
		return (1);
	}

	return (0);
}