1 /* tail.c - copy last lines from input to stdout.
2 *
3 * Copyright 2012 Timothy Elliott <tle@holymonkey.com>
4 *
5 * See http://opengroup.org/onlinepubs/9699919799/utilities/tail.html
6 *
7 * Deviations from posix: -f waits for pipe/fifo on stdin (nonblock?).
8
9 USE_TAIL(NEWTOY(tail, "?fc-n-[-cn]", TOYFLAG_USR|TOYFLAG_BIN))
10
11 config TAIL
12 bool "tail"
13 default y
14 help
15 usage: tail [-n|c NUMBER] [-f] [FILE...]
16
17 Copy last lines from files to stdout. If no files listed, copy from
18 stdin. Filename "-" is a synonym for stdin.
19
20 -n output the last NUMBER lines (default 10), +X counts from start
21 -c output the last NUMBER bytes, +NUMBER counts from start
22 -f follow FILE(s), waiting for more data to be appended
23
24 config TAIL_SEEK
25 bool "tail seek support"
26 default y
27 depends on TAIL
28 help
29 This version uses lseek, which is faster on large files.
30 */
31
32 #define FOR_tail
33 #include "toys.h"
34 #include <sys/inotify.h>
35
36 GLOBALS(
37 long lines;
38 long bytes;
39
40 int file_no, ffd, *files;
41 )
42
43 struct line_list {
44 struct line_list *next, *prev;
45 char *data;
46 int len;
47 };
48
get_chunk(int fd,int len)49 static struct line_list *get_chunk(int fd, int len)
50 {
51 struct line_list *line = xmalloc(sizeof(struct line_list)+len);
52
53 memset(line, 0, sizeof(struct line_list));
54 line->data = ((char *)line) + sizeof(struct line_list);
55 line->len = readall(fd, line->data, len);
56
57 if (line->len < 1) {
58 free(line);
59 return 0;
60 }
61
62 return line;
63 }
64
dump_chunk(void * ptr)65 static void dump_chunk(void *ptr)
66 {
67 struct line_list *list = ptr;
68
69 xwrite(1, list->data, list->len);
70 free(list);
71 }
72
73 // Reading through very large files is slow. Using lseek can speed things
74 // up a lot, but isn't applicable to all input (cat | tail).
75 // Note: bytes and lines are negative here.
try_lseek(int fd,long bytes,long lines)76 static int try_lseek(int fd, long bytes, long lines)
77 {
78 struct line_list *list = 0, *temp;
79 int flag = 0, chunk = sizeof(toybuf);
80 off_t pos = lseek(fd, 0, SEEK_END);
81
82 // If lseek() doesn't work on this stream, return now.
83 if (pos<0) return 0;
84
85 // Seek to the right spot, output data from there.
86 if (bytes) {
87 if (lseek(fd, bytes, SEEK_END)<0) lseek(fd, 0, SEEK_SET);
88 xsendfile(fd, 1);
89 return 1;
90 }
91
92 // Read from end to find enough lines, then output them.
93
94 bytes = pos;
95 while (lines && pos) {
96 int offset;
97
98 // Read in next chunk from end of file
99 if (chunk>pos) chunk = pos;
100 pos -= chunk;
101 if (pos != lseek(fd, pos, SEEK_SET)) {
102 perror_msg("seek failed");
103 break;
104 }
105 if (!(temp = get_chunk(fd, chunk))) break;
106 temp->next = list;
107 list = temp;
108
109 // Count newlines in this chunk.
110 offset = list->len;
111 while (offset--) {
112 // If the last line ends with a newline, that one doesn't count.
113 if (!flag) flag++;
114
115 // Start outputting data right after newline
116 else if (list->data[offset] == '\n' && !++lines) {
117 offset++;
118 list->data += offset;
119 list->len -= offset;
120
121 break;
122 }
123 }
124 }
125
126 // Output stored data
127 llist_traverse(list, dump_chunk);
128
129 // In case of -f
130 lseek(fd, bytes, SEEK_SET);
131 return 1;
132 }
133
134 // Called for each file listed on command line, and/or stdin
do_tail(int fd,char * name)135 static void do_tail(int fd, char *name)
136 {
137 long bytes = TT.bytes, lines = TT.lines;
138 int linepop = 1;
139
140 if (toys.optflags & FLAG_f) {
141 int f = TT.file_no*2;
142 char *s = name;
143
144 if (!fd) sprintf(s = toybuf, "/proc/self/fd/%d", fd);
145 TT.files[f++] = fd;
146 if (0 > (TT.files[f] = inotify_add_watch(TT.ffd, s, IN_MODIFY)))
147 perror_msg("bad -f on '%s'", name);
148 }
149
150 if (TT.file_no++) xputc('\n');
151 if (toys.optc > 1) xprintf("==> %s <==\n", name);
152
153 // Are we measuring from the end of the file?
154
155 if (bytes<0 || lines<0) {
156 struct line_list *list = 0, *new;
157
158 // The slow codepath is always needed, and can handle all input,
159 // so make lseek support optional.
160 if (CFG_TAIL_SEEK && try_lseek(fd, bytes, lines)) return;
161
162 // Read data until we run out, keep a trailing buffer
163 for (;;) {
164 // Read next page of data, appending to linked list in order
165 if (!(new = get_chunk(fd, sizeof(toybuf)))) break;
166 dlist_add_nomalloc((void *)&list, (void *)new);
167
168 // If tracing bytes, add until we have enough, discarding overflow.
169 if (TT.bytes) {
170 bytes += new->len;
171 if (bytes > 0) {
172 while (list->len <= bytes) {
173 bytes -= list->len;
174 free(dlist_pop(&list));
175 }
176 list->data += bytes;
177 list->len -= bytes;
178 bytes = 0;
179 }
180 } else {
181 int len = new->len, count;
182 char *try = new->data;
183
184 // First character _after_ a newline starts a new line, which
185 // works even if file doesn't end with a newline
186 for (count=0; count<len; count++) {
187 if (linepop) lines++;
188 linepop = try[count] == '\n';
189
190 if (lines > 0) {
191 char c;
192
193 do {
194 c = *list->data;
195 if (!--(list->len)) free(dlist_pop(&list));
196 else list->data++;
197 } while (c != '\n');
198 lines--;
199 }
200 }
201 }
202 }
203
204 // Output/free the buffer.
205 llist_traverse(list, dump_chunk);
206
207 // Measuring from the beginning of the file.
208 } else for (;;) {
209 int len, offset = 0;
210
211 // Error while reading does not exit. Error writing does.
212 len = read(fd, toybuf, sizeof(toybuf));
213 if (len<1) break;
214 while (bytes > 1 || lines > 1) {
215 bytes--;
216 if (toybuf[offset++] == '\n') lines--;
217 if (offset >= len) break;
218 }
219 if (offset<len) xwrite(1, toybuf+offset, len-offset);
220 }
221 }
222
tail_main(void)223 void tail_main(void)
224 {
225 char **args = toys.optargs;
226
227 if (!(toys.optflags&(FLAG_n|FLAG_c))) {
228 char *arg = *args;
229
230 // handle old "-42" style arguments
231 if (arg && *arg == '-' && arg[1]) {
232 TT.lines = atolx(*(args++));
233 toys.optc--;
234 } else {
235 // if nothing specified, default -n to -10
236 TT.lines = -10;
237 }
238 }
239
240 // Allocate 2 ints per optarg for -f
241 if (toys.optflags&FLAG_f) {
242 if ((TT.ffd = inotify_init()) < 0) perror_exit("inotify_init");
243 TT.files = xmalloc(toys.optc*8);
244 }
245 loopfiles_rw(args, O_RDONLY|WARN_ONLY|(O_CLOEXEC*!(toys.optflags&FLAG_f)),
246 0, do_tail);
247
248 if ((toys.optflags & FLAG_f) && TT.file_no) {
249 int len, last_fd = TT.files[(TT.file_no-1)*2], i, fd;
250 struct inotify_event ev;
251
252 for (;;) {
253 if (sizeof(ev)!=read(TT.ffd, &ev, sizeof(ev))) perror_exit("inotify");
254
255 for (i = 0; i<TT.file_no && ev.wd!=TT.files[(i*2)+1]; i++);
256 if (i==TT.file_no) continue;
257 fd = TT.files[i*2];
258
259 // Read new data.
260 while ((len = read(fd, toybuf, sizeof(toybuf)))>0) {
261 if (last_fd != fd) {
262 last_fd = fd;
263 xprintf("\n==> %s <==\n", args[i]);
264 }
265
266 xwrite(1, toybuf, len);
267 }
268 }
269 }
270 }
271