forward.c revision 86888 
1/*-
2 * Copyright (c) 1991, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * This code is derived from software contributed to Berkeley by
6 * Edward Sze-Tyan Wang.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 *    notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 * 3. All advertising materials mentioning features or use of this software
17 *    must display the following acknowledgement:
18 *	This product includes software developed by the University of
19 *	California, Berkeley and its contributors.
20 * 4. Neither the name of the University nor the names of its contributors
21 *    may be used to endorse or promote products derived from this software
22 *    without specific prior written permission.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
34 * SUCH DAMAGE.
35 */
36
37#ifndef lint
38#if 0
39static char sccsid[] = "@(#)forward.c	8.1 (Berkeley) 6/6/93";
40#endif
41static const char rcsid[] =
42  "$FreeBSD: head/usr.bin/tail/forward.c 86888 2001-11-25 18:03:28Z iedowse $";
43#endif /* not lint */
44
45#include <sys/types.h>
46#include <sys/stat.h>
47#include <sys/time.h>
48#include <sys/mman.h>
49#include <sys/event.h>
50
51#include <limits.h>
52#include <fcntl.h>
53#include <errno.h>
54#include <unistd.h>
55#include <stdio.h>
56#include <stdlib.h>
57#include <string.h>
58#include <err.h>
59#include "extern.h"
60
61static void rlines __P((FILE *, off_t, struct stat *));
62
63/* defines for inner loop actions */
64#define USE_SLEEP	0
65#define USE_KQUEUE	1
66#define ADD_EVENTS	2
67
68/*
69 * forward -- display the file, from an offset, forward.
70 *
71 * There are eight separate cases for this -- regular and non-regular
72 * files, by bytes or lines and from the beginning or end of the file.
73 *
74 * FBYTES	byte offset from the beginning of the file
75 *	REG	seek
76 *	NOREG	read, counting bytes
77 *
78 * FLINES	line offset from the beginning of the file
79 *	REG	read, counting lines
80 *	NOREG	read, counting lines
81 *
82 * RBYTES	byte offset from the end of the file
83 *	REG	seek
84 *	NOREG	cyclically read characters into a wrap-around buffer
85 *
86 * RLINES
87 *	REG	mmap the file and step back until reach the correct offset.
88 *	NOREG	cyclically read lines into a wrap-around array of buffers
89 */
90void
91forward(fp, style, off, sbp)
92	FILE *fp;
93	enum STYLE style;
94	off_t off;
95	struct stat *sbp;
96{
97	int ch, n, kq = -1;
98	int action = USE_SLEEP;
99	struct kevent ev[2];
100	struct stat sb2;
101	struct timespec ts;
102
103	switch(style) {
104	case FBYTES:
105		if (off == 0)
106			break;
107		if (S_ISREG(sbp->st_mode)) {
108			if (sbp->st_size < off)
109				off = sbp->st_size;
110			if (fseeko(fp, off, SEEK_SET) == -1) {
111				ierr();
112				return;
113			}
114		} else while (off--)
115			if ((ch = getc(fp)) == EOF) {
116				if (ferror(fp)) {
117					ierr();
118					return;
119				}
120				break;
121			}
122		break;
123	case FLINES:
124		if (off == 0)
125			break;
126		for (;;) {
127			if ((ch = getc(fp)) == EOF) {
128				if (ferror(fp)) {
129					ierr();
130					return;
131				}
132				break;
133			}
134			if (ch == '\n' && !--off)
135				break;
136		}
137		break;
138	case RBYTES:
139		if (S_ISREG(sbp->st_mode)) {
140			if (sbp->st_size >= off &&
141			    fseeko(fp, -off, SEEK_END) == -1) {
142				ierr();
143				return;
144			}
145		} else if (off == 0) {
146			while (getc(fp) != EOF);
147			if (ferror(fp)) {
148				ierr();
149				return;
150			}
151		} else
152			if (bytes(fp, off))
153				return;
154		break;
155	case RLINES:
156		if (S_ISREG(sbp->st_mode))
157			if (!off) {
158				if (fseeko(fp, (off_t)0, SEEK_END) == -1) {
159					ierr();
160					return;
161				}
162			} else
163				rlines(fp, off, sbp);
164		else if (off == 0) {
165			while (getc(fp) != EOF);
166			if (ferror(fp)) {
167				ierr();
168				return;
169			}
170		} else
171			if (lines(fp, off))
172				return;
173		break;
174	}
175
176	if (fflag) {
177		kq = kqueue();
178		if (kq < 0)
179			err(1, "kqueue");
180		action = ADD_EVENTS;
181	}
182
183	for (;;) {
184		while ((ch = getc(fp)) != EOF)
185			if (putchar(ch) == EOF)
186				oerr();
187		if (ferror(fp)) {
188			ierr();
189			return;
190		}
191		(void)fflush(stdout);
192		if (! fflag)
193			break;
194		clearerr(fp);
195
196		switch (action) {
197		case ADD_EVENTS:
198			n = 0;
199			ts.tv_sec = 0;
200			ts.tv_nsec = 0;
201
202			if (Fflag && fileno(fp) != STDIN_FILENO) {
203				EV_SET(&ev[n], fileno(fp), EVFILT_VNODE,
204				    EV_ADD | EV_ENABLE | EV_CLEAR,
205				    NOTE_DELETE | NOTE_RENAME, 0, 0);
206				n++;
207			}
208			EV_SET(&ev[n], fileno(fp), EVFILT_READ,
209			    EV_ADD | EV_ENABLE | EV_CLEAR, 0, 0, 0);
210			n++;
211
212			if (kevent(kq, ev, n, NULL, 0, &ts) < 0) {
213				action = USE_SLEEP;
214			} else {
215				action = USE_KQUEUE;
216			}
217			break;
218
219		case USE_KQUEUE:
220			ts.tv_sec = 1;
221			ts.tv_nsec = 0;
222			/*
223			 * In the -F case we set a timeout to ensure that
224			 * we re-stat the file at least once every second.
225			 */
226			n = kevent(kq, NULL, 0, ev, 1, Fflag ? &ts : NULL);
227			if (n < 0)
228				err(1, "kevent");
229			if (n == 0) {
230				/* timeout */
231				break;
232			} else if (ev->filter == EVFILT_READ && ev->data < 0) {
233				 /* file shrank, reposition to end */
234				if (fseeko(fp, (off_t)0, SEEK_END) == -1) {
235					ierr();
236					return;
237				}
238			}
239			break;
240
241		case USE_SLEEP:
242                	(void) usleep(250000);
243	                clearerr(fp);
244			break;
245		}
246
247		if (Fflag && fileno(fp) != STDIN_FILENO) {
248			while (stat(fname, &sb2) != 0)
249				/* file was rotated, wait until it reappears */
250				(void)sleep(1);
251			if (sb2.st_ino != sbp->st_ino ||
252			    sb2.st_dev != sbp->st_dev ||
253			    sb2.st_rdev != sbp->st_rdev ||
254			    sb2.st_nlink == 0) {
255				fp = freopen(fname, "r", fp);
256				if (fp == NULL) {
257					ierr();
258				} else {
259					*sbp = sb2;
260					action = ADD_EVENTS;
261				}
262			}
263		}
264	}
265}
266
267/*
268 * rlines -- display the last offset lines of the file.
269 */
270static void
271rlines(fp, off, sbp)
272	FILE *fp;
273	off_t off;
274	struct stat *sbp;
275{
276	struct mapinfo map;
277	off_t curoff, size;
278	int i;
279
280	if (!(size = sbp->st_size))
281		return;
282	map.start = NULL;
283	map.fd = fileno(fp);
284	map.mapoff = map.maxoff = size;
285
286	/*
287	 * Last char is special, ignore whether newline or not. Note that
288	 * size == 0 is dealt with above, and size == 1 sets curoff to -1.
289	 */
290	curoff = size - 2;
291	while (curoff >= 0) {
292		if (curoff < map.mapoff && maparound(&map, curoff) != 0) {
293			ierr();
294			return;
295		}
296		for (i = curoff - map.mapoff; i >= 0; i--)
297			if (map.start[i] == '\n' && --off == 0)
298				break;
299		/* `i' is either the map offset of a '\n', or -1. */
300		curoff = map.mapoff + i;
301		if (i >= 0)
302			break;
303	}
304	curoff++;
305	if (mapprint(&map, curoff, size - curoff) != 0) {
306		ierr();
307		exit(1);
308	}
309
310	/* Set the file pointer to reflect the length displayed. */
311	if (fseeko(fp, sbp->st_size, SEEK_SET) == -1) {
312		ierr();
313		return;
314	}
315	if (map.start != NULL && munmap(map.start, map.maplen)) {
316		ierr();
317		return;
318	}
319}
320