Linux debugging

Check our new training course

Linux debugging, tracing, profiling & perf. analysis

Check our new training course
with Creative Commons CC-BY-SA
lecture and lab materials

Bootlin logo

Elixir Cross Referencer

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
/* vi: set sw=4 ts=4: */
/*
 * Mini tail implementation for busybox
 *
 * Copyright (C) 2001 by Matt Kraai <kraai@alumni.carnegiemellon.edu>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */
/* Mar 16, 2003      Manuel Novoa III   (mjn3@codepoet.org)
 *
 * Pretty much rewritten to fix numerous bugs and reduce realloc() calls.
 * Bugs fixed (although I may have forgotten one or two... it was pretty bad)
 * 1) mixing printf/write without fflush()ing stdout
 * 2) no check that any open files are present
 * 3) optstring had -q taking an arg
 * 4) no error checking on write in some cases, and a warning even then
 * 5) q and s interaction bug
 * 6) no check for lseek error
 * 7) lseek attempted when count==0 even if arg was +0 (from top)
 */
//config:config TAIL
//config:	bool "tail (6.8 kb)"
//config:	default y
//config:	help
//config:	tail is used to print the last specified number of lines
//config:	from files.
//config:
//config:config FEATURE_FANCY_TAIL
//config:	bool "Enable -q, -s, -v, and -F options"
//config:	default y
//config:	depends on TAIL
//config:	help
//config:	These options are provided by GNU tail, but
//config:	are not specified in the SUSv3 standard:
//config:		-q      Never output headers giving file names
//config:		-s SEC  Wait SEC seconds between reads with -f
//config:		-v      Always output headers giving file names
//config:		-F      Same as -f, but keep retrying

//applet:IF_TAIL(APPLET(tail, BB_DIR_USR_BIN, BB_SUID_DROP))

//kbuild:lib-$(CONFIG_TAIL) += tail.o

/* BB_AUDIT SUSv3 compliant (need fancy for -c) */
/* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
/* http://www.opengroup.org/onlinepubs/007904975/utilities/tail.html */

//usage:#define tail_trivial_usage
//usage:       "[OPTIONS] [FILE]..."
//usage:#define tail_full_usage "\n\n"
//usage:       "Print last 10 lines of each FILE (or stdin) to stdout.\n"
//usage:       "With more than one FILE, precede each with a filename header.\n"
//usage:     "\n	-f		Print data as file grows"
//usage:     "\n	-c [+]N[kbm]	Print last N bytes"
//usage:     "\n	-n N[kbm]	Print last N lines"
//usage:     "\n	-n +N[kbm]	Start on Nth line and print the rest"
//usage:	IF_FEATURE_FANCY_TAIL(
//usage:     "\n	-q		Never print headers"
//usage:     "\n	-s SECONDS	Wait SECONDS between reads with -f"
//usage:     "\n	-v		Always print headers"
//usage:     "\n	-F		Same as -f, but keep retrying"
//usage:     "\n"
//usage:     "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
//usage:	)
//usage:
//usage:#define tail_example_usage
//usage:       "$ tail -n 1 /etc/resolv.conf\n"
//usage:       "nameserver 10.0.0.1\n"

#include "libbb.h"
#include "common_bufsiz.h"

struct globals {
	bool from_top;
	bool exitcode;
} FIX_ALIASING;
#define G (*(struct globals*)bb_common_bufsiz1)
#define INIT_G() do { setup_common_bufsiz(); } while (0)

static void tail_xprint_header(const char *fmt, const char *filename)
{
	if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
		bb_perror_nomsg_and_die();
}

static ssize_t tail_read(int fd, char *buf, size_t count)
{
	ssize_t r;

	r = full_read(fd, buf, count);
	if (r < 0) {
		bb_perror_msg(bb_msg_read_error);
		G.exitcode = EXIT_FAILURE;
	}

	return r;
}

#define header_fmt_str "\n==> %s <==\n"

static unsigned eat_num(const char *p)
{
	if (*p == '-')
		p++;
	else if (*p == '+') {
		p++;
		G.from_top = 1;
	}
	return xatou_sfx(p, bkm_suffixes);
}

int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int tail_main(int argc, char **argv)
{
	unsigned count = 10;
	unsigned sleep_period = 1;
	const char *str_c, *str_n;

	char *tailbuf;
	size_t tailbufsize;
	unsigned header_threshhold = 1;
	unsigned nfiles;
	int i, opt;

	int *fds;
	const char *fmt;
	int prev_fd;

	INIT_G();

#if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
	/* Allow legacy syntax of an initial numeric option without -n. */
	if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
	 && isdigit(argv[1][1])
	) {
		count = eat_num(argv[1]);
		argv++;
		argc--;
	}
#endif

	/* -s NUM, -F imlies -f */
	opt = getopt32(argv, IF_FEATURE_FANCY_TAIL("^")
			"fc:n:"IF_FEATURE_FANCY_TAIL("qs:+vF")
			IF_FEATURE_FANCY_TAIL("\0" "Ff"),
			&str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period)
	);
#define FOLLOW (opt & 0x1)
#define COUNT_BYTES (opt & 0x2)
	//if (opt & 0x1) // -f
	if (opt & 0x2) count = eat_num(str_c); // -c
	if (opt & 0x4) count = eat_num(str_n); // -n
#if ENABLE_FEATURE_FANCY_TAIL
	/* q: make it impossible for nfiles to be > header_threshhold */
	if (opt & 0x8) header_threshhold = UINT_MAX; // -q
	//if (opt & 0x10) // -s
	if (opt & 0x20) header_threshhold = 0; // -v
# define FOLLOW_RETRY (opt & 0x40)
#else
# define FOLLOW_RETRY 0
#endif
	argc -= optind;
	argv += optind;

	/* open all the files */
	fds = xmalloc(sizeof(fds[0]) * (argc + 1));
	if (!argv[0]) {
		struct stat statbuf;

		if (fstat(STDIN_FILENO, &statbuf) == 0
		 && S_ISFIFO(statbuf.st_mode)
		) {
			opt &= ~1; /* clear FOLLOW */
		}
		argv[0] = (char *) bb_msg_standard_input;
	}
	nfiles = i = 0;
	do {
		int fd = open_or_warn_stdin(argv[i]);
		if (fd < 0 && !FOLLOW_RETRY) {
			G.exitcode = EXIT_FAILURE;
			continue;
		}
		fds[nfiles] = fd;
		argv[nfiles++] = argv[i];
	} while (++i < argc);

	if (!nfiles)
		bb_error_msg_and_die("no files");

	/* prepare the buffer */
	tailbufsize = BUFSIZ;
	if (!G.from_top && COUNT_BYTES) {
		if (tailbufsize < count + BUFSIZ) {
			tailbufsize = count + BUFSIZ;
		}
	}
	/* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
	 * (In fact, it doesn't need ANY memory). So delay allocation.
	 */
	tailbuf = NULL;

	/* tail the files */

	fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
	i = 0;
	do {
		char *buf;
		int taillen;
		int newlines_seen;
		unsigned seen;
		int nread;
		int fd = fds[i];

		if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
			continue; /* may happen with -F */

		if (nfiles > header_threshhold) {
			tail_xprint_header(fmt, argv[i]);
			fmt = header_fmt_str;
		}

		if (!G.from_top) {
			off_t current = lseek(fd, 0, SEEK_END);
			if (current > 0) {
				unsigned off;
				if (COUNT_BYTES) {
				/* Optimizing count-bytes case if the file is seekable.
				 * Beware of backing up too far.
				 * Also we exclude files with size 0 (because of /proc/xxx) */
					if (count == 0)
						continue; /* showing zero bytes is easy :) */
					current -= count;
					if (current < 0)
						current = 0;
					xlseek(fd, current, SEEK_SET);
					bb_copyfd_size(fd, STDOUT_FILENO, count);
					continue;
				}
#if 1 /* This is technically incorrect for *LONG* strings, but very useful */
				/* Optimizing count-lines case if the file is seekable.
				 * We assume the lines are <64k.
				 * (Users complain that tail takes too long
				 * on multi-gigabyte files) */
				off = (count | 0xf); /* for small counts, be more paranoid */
				if (off > (INT_MAX / (64*1024)))
					off = (INT_MAX / (64*1024));
				current -= off * (64*1024);
				if (current < 0)
					current = 0;
				xlseek(fd, current, SEEK_SET);
#endif
			}
		}

		if (!tailbuf)
			tailbuf = xmalloc(tailbufsize);

		buf = tailbuf;
		taillen = 0;
		/* "We saw 1st line/byte".
		 * Used only by +N code ("start from Nth", 1-based): */
		seen = 1;
		newlines_seen = 0;
		while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
			if (G.from_top) {
				int nwrite = nread;
				if (seen < count) {
					/* We need to skip a few more bytes/lines */
					if (COUNT_BYTES) {
						nwrite -= (count - seen);
						seen += nread;
					} else {
						char *s = buf;
						do {
							--nwrite;
							if (*s++ == '\n' && ++seen == count) {
								break;
							}
						} while (nwrite);
					}
				}
				if (nwrite > 0)
					xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
			} else if (count) {
				if (COUNT_BYTES) {
					taillen += nread;
					if (taillen > (int)count) {
						memmove(tailbuf, tailbuf + taillen - count, count);
						taillen = count;
					}
				} else {
					int k = nread;
					int newlines_in_buf = 0;

					do { /* count '\n' in last read */
						k--;
						if (buf[k] == '\n') {
							newlines_in_buf++;
						}
					} while (k);

					if (newlines_seen + newlines_in_buf < (int)count) {
						newlines_seen += newlines_in_buf;
						taillen += nread;
					} else {
						int extra = (buf[nread-1] != '\n');
						char *s;

						k = newlines_seen + newlines_in_buf + extra - count;
						s = tailbuf;
						while (k) {
							if (*s == '\n') {
								k--;
							}
							s++;
						}
						taillen += nread - (s - tailbuf);
						memmove(tailbuf, s, taillen);
						newlines_seen = count - extra;
					}
					if (tailbufsize < (size_t)taillen + BUFSIZ) {
						tailbufsize = taillen + BUFSIZ;
						tailbuf = xrealloc(tailbuf, tailbufsize);
					}
				}
				buf = tailbuf + taillen;
			}
		} /* while (tail_read() > 0) */
		if (!G.from_top) {
			xwrite(STDOUT_FILENO, tailbuf, taillen);
		}
	} while (++i < nfiles);
	prev_fd = fds[i-1];

	tailbuf = xrealloc(tailbuf, BUFSIZ);

	fmt = NULL;

	if (FOLLOW) while (1) {
		sleep(sleep_period);

		i = 0;
		do {
			int nread;
			const char *filename = argv[i];
			int fd = fds[i];

			if (FOLLOW_RETRY) {
				struct stat sbuf, fsbuf;

				if (fd < 0
				 || fstat(fd, &fsbuf) < 0
				 || stat(filename, &sbuf) < 0
				 || fsbuf.st_dev != sbuf.st_dev
				 || fsbuf.st_ino != sbuf.st_ino
				) {
					int new_fd;

					if (fd >= 0)
						close(fd);
					new_fd = open(filename, O_RDONLY);
					if (new_fd >= 0) {
						bb_error_msg("%s has %s; following end of new file",
							filename, (fd < 0) ? "appeared" : "been replaced"
						);
					} else if (fd >= 0) {
						bb_perror_msg("%s has become inaccessible", filename);
					}
					fds[i] = fd = new_fd;
				}
			}
			if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
				continue;
			if (nfiles > header_threshhold) {
				fmt = header_fmt_str;
			}
			for (;;) {
				/* tail -f keeps following files even if they are truncated */
				struct stat sbuf;
				/* /proc files report zero st_size, don't lseek them */
				if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
					off_t current = lseek(fd, 0, SEEK_CUR);
					if (sbuf.st_size < current)
						xlseek(fd, 0, SEEK_SET);
				}

				nread = tail_read(fd, tailbuf, BUFSIZ);
				if (nread <= 0)
					break;
				if (fmt && (fd != prev_fd)) {
					tail_xprint_header(fmt, filename);
					fmt = NULL;
					prev_fd = fd;
				}
				xwrite(STDOUT_FILENO, tailbuf, nread);
			}
		} while (++i < nfiles);
	} /* while (1) */

	if (ENABLE_FEATURE_CLEAN_UP) {
		free(fds);
		free(tailbuf);
	}
	return G.exitcode;
}