xref: /netbsd-src/usr.bin/tail/forward.c (revision e39dc43f611302609dc6713ad9e10e682324af9a)
1 /*	$NetBSD: forward.c,v 1.34 2024/01/14 17:37:32 christos Exp $	*/
2 
3 /*-
4  * Copyright (c) 1991, 1993
5  *	The Regents of the University of California.  All rights reserved.
6  *
7  * This code is derived from software contributed to Berkeley by
8  * Edward Sze-Tyan Wang.
9  *
10  * Redistribution and use in source and binary forms, with or without
11  * modification, are permitted provided that the following conditions
12  * are met:
13  * 1. Redistributions of source code must retain the above copyright
14  *    notice, this list of conditions and the following disclaimer.
15  * 2. Redistributions in binary form must reproduce the above copyright
16  *    notice, this list of conditions and the following disclaimer in the
17  *    documentation and/or other materials provided with the distribution.
18  * 3. Neither the name of the University nor the names of its contributors
19  *    may be used to endorse or promote products derived from this software
20  *    without specific prior written permission.
21  *
22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32  * SUCH DAMAGE.
33  */
34 
35 #include <sys/cdefs.h>
36 #ifndef lint
37 #if 0
38 static char sccsid[] = "@(#)forward.c	8.1 (Berkeley) 6/6/93";
39 #endif
40 __RCSID("$NetBSD: forward.c,v 1.34 2024/01/14 17:37:32 christos Exp $");
41 #endif /* not lint */
42 
43 #include <sys/types.h>
44 #include <sys/stat.h>
45 #include <sys/time.h>
46 #include <sys/mman.h>
47 #include <sys/event.h>
48 
49 #include <limits.h>
50 #include <fcntl.h>
51 #include <errno.h>
52 #include <unistd.h>
53 #include <stdio.h>
54 #include <stdlib.h>
55 #include <string.h>
56 #include "extern.h"
57 
58 static int rlines(FILE *, off_t, struct stat *);
59 
60 /* defines for inner loop actions */
61 #define	USE_SLEEP	0
62 #define	USE_KQUEUE	1
63 #define	ADD_EVENTS	2
64 
65 /*
66  * forward -- display the file, from an offset, forward.
67  *
68  * There are eight separate cases for this -- regular and non-regular
69  * files, by bytes or lines and from the beginning or end of the file.
70  *
71  * FBYTES	byte offset from the beginning of the file
72  *	REG	seek
73  *	NOREG	read, counting bytes
74  *
75  * FLINES	line offset from the beginning of the file
76  *	REG	read, counting lines
77  *	NOREG	read, counting lines
78  *
79  * RBYTES	byte offset from the end of the file
80  *	REG	seek
81  *	NOREG	cyclically read characters into a wrap-around buffer
82  *
83  * RLINES
84  *	REG	mmap the file and step back until reach the correct offset.
85  *	NOREG	cyclically read lines into a wrap-around array of buffers
86  */
87 void
forward(FILE * fp,enum STYLE style,off_t off,struct stat * sbp)88 forward(FILE *fp, enum STYLE style, off_t off, struct stat *sbp)
89 {
90 	int ch, n;
91 	int kq=-1, action=USE_SLEEP;
92 	struct stat statbuf;
93 	struct kevent ev[2];
94 
95 	switch(style) {
96 	case FBYTES:
97 		if (off == 0)
98 			break;
99 		if (S_ISREG(sbp->st_mode) && sbp->st_size > 0) {
100 			if (sbp->st_size < off)
101 				off = sbp->st_size;
102 			if (fseeko(fp, off, SEEK_SET) == -1) {
103 				ierr();
104 				return;
105 			}
106 		} else while (off--)
107 			if ((ch = getc(fp)) == EOF) {
108 				if (ferror(fp)) {
109 					ierr();
110 					return;
111 				}
112 				break;
113 			}
114 		break;
115 	case FLINES:
116 		if (off == 0)
117 			break;
118 		for (;;) {
119 			if ((ch = getc(fp)) == EOF) {
120 				if (ferror(fp)) {
121 					ierr();
122 					return;
123 				}
124 				break;
125 			}
126 			if (ch == '\n' && !--off)
127 				break;
128 		}
129 		break;
130 	case RBYTES:
131 		if (S_ISREG(sbp->st_mode) && sbp->st_size > 0) {
132 			if (sbp->st_size >= off &&
133 			    fseeko(fp, -off, SEEK_END) == -1) {
134 				ierr();
135 				return;
136 			}
137 		} else if (off == 0) {
138 			while (getc(fp) != EOF);
139 			if (ferror(fp)) {
140 				ierr();
141 				return;
142 			}
143 		} else {
144 			if (displaybytes(fp, off))
145 				return;
146 		}
147 		break;
148 	case RLINES:
149 		if (S_ISREG(sbp->st_mode) && sbp->st_size > 0) {
150 			if (!off) {
151 				if (fseek(fp, 0L, SEEK_END) == -1) {
152 					ierr();
153 					return;
154 				}
155 			} else {
156 				if (rlines(fp, off, sbp))
157 					return;
158 			}
159 		} else if (off == 0) {
160 			while (getc(fp) != EOF);
161 			if (ferror(fp)) {
162 				ierr();
163 				return;
164 			}
165 		} else {
166 			if (displaylines(fp, off))
167 				return;
168 		}
169 		break;
170 	default:
171 		break;
172 	}
173 
174 	if (fflag) {
175 		kq = kqueue();
176 		if (kq < 0)
177 			xerr(1, "kqueue");
178 		action = ADD_EVENTS;
179 	}
180 
181 	for (;;) {
182 		while ((ch = getc(fp)) != EOF)  {
183 			if (putchar(ch) == EOF)
184 				oerr();
185 		}
186 		if (ferror(fp)) {
187 			ierr();
188 			return;
189 		}
190 		(void)fflush(stdout);
191 		if (!fflag)
192 			break;
193 
194 		clearerr(fp);
195 
196 		switch (action) {
197 		case ADD_EVENTS:
198 			n = 0;
199 
200 			memset(ev, 0, sizeof(ev));
201 			if (fflag == 2 && fp != stdin) {
202 				EV_SET(&ev[n], fileno(fp), EVFILT_VNODE,
203 				    EV_ADD | EV_ENABLE | EV_CLEAR,
204 				    NOTE_DELETE | NOTE_RENAME, 0, 0);
205 				n++;
206 			}
207 			EV_SET(&ev[n], fileno(fp), EVFILT_READ,
208 			    EV_ADD | EV_ENABLE, 0, 0, 0);
209 			n++;
210 
211 			if (kevent(kq, ev, n, NULL, 0, NULL) == -1) {
212 				close(kq);
213 				kq = -1;
214 				action = USE_SLEEP;
215 			} else {
216 				action = USE_KQUEUE;
217 			}
218 			break;
219 
220 		case USE_KQUEUE:
221 			if (kevent(kq, NULL, 0, ev, 1, NULL) == -1)
222 				xerr(1, "kevent");
223 
224 			if (ev[0].filter == EVFILT_VNODE) {
225 				/* file was rotated, wait until it reappears */
226 				action = USE_SLEEP;
227 			} else if (ev[0].data < 0) {
228 				/* file shrank, reposition to end */
229 				if (fseek(fp, 0L, SEEK_END) == -1) {
230 					ierr();
231 					return;
232 				}
233 			}
234 			break;
235 
236 		case USE_SLEEP:
237 			/*
238 			 * We pause for one second after displaying any data
239 			 * that has accumulated since we read the file.
240 			 */
241                 	(void) sleep(1);
242 
243 			if (fflag == 2 && fp != stdin &&
244 			    stat(fname, &statbuf) != -1) {
245 				if (statbuf.st_ino != sbp->st_ino ||
246 				    statbuf.st_dev != sbp->st_dev ||
247 				    statbuf.st_rdev != sbp->st_rdev ||
248 				    statbuf.st_nlink == 0) {
249 					fp = freopen(fname, "r", fp);
250 					if (fp == NULL) {
251 						ierr();
252 						goto out;
253 					}
254 					*sbp = statbuf;
255 					if (kq != -1)
256 						action = ADD_EVENTS;
257 				} else if (kq != -1)
258 					action = USE_KQUEUE;
259 			}
260 			break;
261 		}
262 	}
263 out:
264 	if (fflag && kq != -1)
265 		close(kq);
266 }
267 
268 /*
269  * rlines -- display the last offset lines of the file.
270  *
271  * Non-zero return means than a (non-fatal) error occurred.
272  */
273 static int
rlines(FILE * fp,off_t off,struct stat * sbp)274 rlines(FILE *fp, off_t off, struct stat *sbp)
275 {
276 	off_t file_size;
277 	off_t file_remaining;
278 	char *p = NULL;
279 	char *start = NULL;
280 	off_t mmap_size;
281 	off_t mmap_offset;
282 	off_t mmap_remaining = 0;
283 
284 #define MMAP_MAXSIZE  (10 * 1024 * 1024)
285 
286 	if (!(file_size = sbp->st_size))
287 		return 0;
288 	file_remaining = file_size;
289 
290 	if (file_remaining > MMAP_MAXSIZE) {
291 		mmap_size = MMAP_MAXSIZE;
292 		mmap_offset = file_remaining - MMAP_MAXSIZE;
293 	} else {
294 		mmap_size = file_remaining;
295 		mmap_offset = 0;
296 	}
297 
298 	while (off) {
299 		start = mmap(NULL, (size_t)mmap_size, PROT_READ,
300 			     MAP_FILE|MAP_SHARED, fileno(fp), mmap_offset);
301 		if (start == MAP_FAILED) {
302 			xerr(0, "%s", fname);
303 			return 1;
304 		}
305 
306 		mmap_remaining = mmap_size;
307 		/* Last char is special, ignore whether newline or not. */
308 		for (p = start + mmap_remaining - 1 ; --mmap_remaining ; )
309 			if (*--p == '\n' && !--off) {
310 				++p;
311 				break;
312 			}
313 
314 		file_remaining -= mmap_size - mmap_remaining;
315 
316 		if (off == 0)
317 			break;
318 
319 		if (file_remaining == 0)
320 			break;
321 
322 		if (munmap(start, mmap_size)) {
323 			xerr(0, "%s", fname);
324 			return 1;
325 		}
326 
327 		if (mmap_offset >= MMAP_MAXSIZE) {
328 			mmap_offset -= MMAP_MAXSIZE;
329 		} else {
330 			mmap_offset = 0;
331 			mmap_size = file_remaining;
332 		}
333 	}
334 
335 	/*
336 	 * Output the (perhaps partial) data in this mmap'd block.
337 	 */
338 	WR(p, mmap_size - mmap_remaining);
339 	file_remaining += mmap_size - mmap_remaining;
340 	if (munmap(start, mmap_size)) {
341 		xerr(0, "%s", fname);
342 		return 1;
343 	}
344 
345 	/*
346 	 * Set the file pointer to reflect the length displayed.
347 	 * This will cause the caller to redisplay the data if/when
348 	 * needed.
349 	 */
350 	if (fseeko(fp, file_remaining, SEEK_SET) == -1) {
351 		ierr();
352 		return 1;
353 	}
354 	return 0;
355 }
356