59a47ce7be
This succumbs to a race condition where data are written to the file while the sleep is occurring. If a stat is done immediately after, lastsize is updated but the file pointer wasn't pointing at the end of the file, so the number of bytes between the current pointer and the end of the file is added to the lastsize when lastsize already points to the end of the file.
281 lines
6.9 KiB
C
281 lines
6.9 KiB
C
/* $NetBSD: forward.c,v 1.13 1998/09/18 01:42:54 cjs Exp $ */
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/*-
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* Copyright (c) 1991, 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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* Edward Sze-Tyan Wang.
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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. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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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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#include <sys/cdefs.h>
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#ifndef lint
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#if 0
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static char sccsid[] = "@(#)forward.c 8.1 (Berkeley) 6/6/93";
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#endif
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__RCSID("$NetBSD: forward.c,v 1.13 1998/09/18 01:42:54 cjs Exp $");
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#endif /* not lint */
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <sys/time.h>
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#include <sys/mman.h>
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#include <limits.h>
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#include <fcntl.h>
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#include <errno.h>
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#include <unistd.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include "extern.h"
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static void rlines __P((FILE *, long, struct stat *));
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/*
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* forward -- display the file, from an offset, forward.
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*
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* There are eight separate cases for this -- regular and non-regular
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* files, by bytes or lines and from the beginning or end of the file.
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*
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* FBYTES byte offset from the beginning of the file
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* REG seek
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* NOREG read, counting bytes
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*
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* FLINES line offset from the beginning of the file
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* REG read, counting lines
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* NOREG read, counting lines
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*
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* RBYTES byte offset from the end of the file
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* REG seek
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* NOREG cyclically read characters into a wrap-around buffer
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*
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* RLINES
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* REG mmap the file and step back until reach the correct offset.
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* NOREG cyclically read lines into a wrap-around array of buffers
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*/
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void
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forward(fp, style, off, sbp)
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FILE *fp;
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enum STYLE style;
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long off;
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struct stat *sbp;
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{
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int ch;
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struct timeval second;
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int dostat = 0;
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struct stat statbuf;
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off_t lastsize = 0;
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dev_t lastdev;
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ino_t lastino;
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/* Keep track of file's previous incarnation. */
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lastdev = sbp->st_dev;
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lastino = sbp->st_ino;
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switch(style) {
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case FBYTES:
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if (off == 0)
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break;
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if (S_ISREG(sbp->st_mode)) {
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if (sbp->st_size < off)
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off = sbp->st_size;
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if (fseek(fp, off, SEEK_SET) == -1) {
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ierr();
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return;
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}
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} else while (off--)
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if ((ch = getc(fp)) == EOF) {
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if (ferror(fp)) {
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ierr();
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return;
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}
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break;
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}
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break;
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case FLINES:
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if (off == 0)
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break;
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for (;;) {
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if ((ch = getc(fp)) == EOF) {
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if (ferror(fp)) {
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ierr();
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return;
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}
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break;
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}
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if (ch == '\n' && !--off)
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break;
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}
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break;
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case RBYTES:
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if (S_ISREG(sbp->st_mode)) {
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if (sbp->st_size >= off &&
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fseek(fp, -off, SEEK_END) == -1) {
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ierr();
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return;
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}
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} else if (off == 0) {
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while (getc(fp) != EOF);
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if (ferror(fp)) {
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ierr();
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return;
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}
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} else
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bytes(fp, off);
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break;
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case RLINES:
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if (S_ISREG(sbp->st_mode))
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if (!off) {
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if (fseek(fp, 0L, SEEK_END) == -1) {
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ierr();
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return;
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}
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} else
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rlines(fp, off, sbp);
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else if (off == 0) {
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while (getc(fp) != EOF);
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if (ferror(fp)) {
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ierr();
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return;
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}
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} else
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lines(fp, off);
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break;
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default:
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break;
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}
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for (;;) {
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while ((ch = getc(fp)) != EOF) {
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if (putchar(ch) == EOF)
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oerr();
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}
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if (ferror(fp)) {
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ierr();
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return;
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}
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(void)fflush(stdout);
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if (!fflag)
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break;
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/*
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* We pause for one second after displaying any data that has
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* accumulated since we read the file. Since sleep(3) takes
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* eight system calls, use select() instead.
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*/
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second.tv_sec = 1;
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second.tv_usec = 0;
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if (select(0, NULL, NULL, NULL, &second) == -1)
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err(1, "select: %s", strerror(errno));
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clearerr(fp);
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if (fflag == 1)
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continue;
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/*
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* We restat the original filename every five seconds. If
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* the size is ever smaller than the last time we read it,
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* the file has probably been truncated; if the inode or
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* or device number are different, it has been rotated.
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* This causes us to close it, reopen it, and continue
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* the tail -f. If stat returns an error (say, because
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* the file has been removed), just continue with what
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* we've got open now.
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*/
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if (dostat > 0) {
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dostat -= 1;
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} else {
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dostat = 5;
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if (stat(fname, &statbuf) == 0) {
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if (statbuf.st_dev != lastdev ||
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statbuf.st_ino != lastino ||
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statbuf.st_size < lastsize) {
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lastdev = statbuf.st_dev;
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lastino = statbuf.st_ino;
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lastsize = 0;
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fclose(fp);
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if ((fp = fopen(fname, "r")) == NULL)
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err(1, "can't reopen %s: %s",
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fname, strerror(errno));
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} else {
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lastsize = statbuf.st_size;
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}
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}
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}
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}
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}
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/*
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* rlines -- display the last offset lines of the file.
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*/
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static void
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rlines(fp, off, sbp)
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FILE *fp;
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long off;
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struct stat *sbp;
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{
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off_t size;
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char *p;
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char *start;
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if (!(size = sbp->st_size))
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return;
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if (size > SIZE_T_MAX) {
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err(0, "%s: %s", fname, strerror(EFBIG));
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return;
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}
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if ((start = mmap(NULL, (size_t)size, PROT_READ,
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MAP_FILE|MAP_SHARED, fileno(fp), (off_t)0)) == (caddr_t)-1) {
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err(0, "%s: %s", fname, strerror(EFBIG));
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return;
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}
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/* Last char is special, ignore whether newline or not. */
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for (p = start + size - 1; --size;)
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if (*--p == '\n' && !--off) {
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++p;
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break;
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}
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/* Set the file pointer to reflect the length displayed. */
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size = sbp->st_size - size;
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WR(p, size);
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if (fseek(fp, (long)sbp->st_size, SEEK_SET) == -1) {
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ierr();
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return;
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}
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if (munmap(start, (size_t)sbp->st_size)) {
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err(0, "%s: %s", fname, strerror(errno));
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return;
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}
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}
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