blob: 5b999730aeffbb829ed839f64cc23143b226f88a
1 | /* vi: set sw=4 ts=4: */ |
2 | /* |
3 | * circular buffer syslog implementation for busybox |
4 | * |
5 | * Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com> |
6 | * |
7 | * Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001 |
8 | * |
9 | * Licensed under GPLv2 or later, see file LICENSE in this source tree. |
10 | */ |
11 | //config:config LOGREAD |
12 | //config: bool "logread" |
13 | //config: default y |
14 | //config: depends on FEATURE_IPC_SYSLOG |
15 | //config: help |
16 | //config: If you enabled Circular Buffer support, you almost |
17 | //config: certainly want to enable this feature as well. This |
18 | //config: utility will allow you to read the messages that are |
19 | //config: stored in the syslogd circular buffer. |
20 | //config: |
21 | //config:config FEATURE_LOGREAD_REDUCED_LOCKING |
22 | //config: bool "Double buffering" |
23 | //config: default y |
24 | //config: depends on LOGREAD |
25 | //config: help |
26 | //config: 'logread' ouput to slow serial terminals can have |
27 | //config: side effects on syslog because of the semaphore. |
28 | //config: This option make logread to double buffer copy |
29 | //config: from circular buffer, minimizing semaphore |
30 | //config: contention at some minor memory expense. |
31 | //config: |
32 | |
33 | //applet:IF_LOGREAD(APPLET(logread, BB_DIR_SBIN, BB_SUID_DROP)) |
34 | |
35 | //kbuild:lib-$(CONFIG_LOGREAD) += logread.o |
36 | |
37 | //usage:#define logread_trivial_usage |
38 | //usage: "[-fF]" |
39 | //usage:#define logread_full_usage "\n\n" |
40 | //usage: "Show messages in syslogd's circular buffer\n" |
41 | //usage: "\n -f Output data as log grows" |
42 | //usage: "\n -F Same as -f, but dump buffer first" |
43 | |
44 | #include "libbb.h" |
45 | #include "common_bufsiz.h" |
46 | #include <sys/ipc.h> |
47 | #include <sys/sem.h> |
48 | #include <sys/shm.h> |
49 | |
50 | #define DEBUG 0 |
51 | |
52 | /* our shared key (syslogd.c and logread.c must be in sync) */ |
53 | enum { KEY_ID = 0x414e4547 }; /* "GENA" */ |
54 | |
55 | struct shbuf_ds { |
56 | int32_t size; // size of data - 1 |
57 | int32_t tail; // end of message list |
58 | char data[1]; // messages |
59 | }; |
60 | |
61 | static const struct sembuf init_sem[3] = { |
62 | {0, -1, IPC_NOWAIT | SEM_UNDO}, |
63 | {1, 0}, {0, +1, SEM_UNDO} |
64 | }; |
65 | |
66 | struct globals { |
67 | struct sembuf SMrup[1]; // {0, -1, IPC_NOWAIT | SEM_UNDO}, |
68 | struct sembuf SMrdn[2]; // {1, 0}, {0, +1, SEM_UNDO} |
69 | struct shbuf_ds *shbuf; |
70 | } FIX_ALIASING; |
71 | #define G (*(struct globals*)bb_common_bufsiz1) |
72 | #define SMrup (G.SMrup) |
73 | #define SMrdn (G.SMrdn) |
74 | #define shbuf (G.shbuf) |
75 | #define INIT_G() do { \ |
76 | setup_common_bufsiz(); \ |
77 | memcpy(SMrup, init_sem, sizeof(init_sem)); \ |
78 | } while (0) |
79 | |
80 | #if 0 |
81 | static void error_exit(const char *str) NORETURN; |
82 | static void error_exit(const char *str) |
83 | { |
84 | /* Release all acquired resources */ |
85 | shmdt(shbuf); |
86 | bb_perror_msg_and_die(str); |
87 | } |
88 | #else |
89 | /* On Linux, shmdt is not mandatory on exit */ |
90 | # define error_exit(str) bb_perror_msg_and_die(str) |
91 | #endif |
92 | |
93 | /* |
94 | * sem_up - up()'s a semaphore. |
95 | */ |
96 | static void sem_up(int semid) |
97 | { |
98 | if (semop(semid, SMrup, 1) == -1) |
99 | error_exit("semop[SMrup]"); |
100 | } |
101 | |
102 | static void interrupted(int sig) |
103 | { |
104 | /* shmdt(shbuf); - on Linux, shmdt is not mandatory on exit */ |
105 | kill_myself_with_sig(sig); |
106 | } |
107 | |
108 | int logread_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; |
109 | int logread_main(int argc UNUSED_PARAM, char **argv) |
110 | { |
111 | unsigned cur; |
112 | int log_semid; /* ipc semaphore id */ |
113 | int log_shmid; /* ipc shared memory id */ |
114 | int follow = getopt32(argv, "fF"); |
115 | |
116 | INIT_G(); |
117 | |
118 | log_shmid = shmget(KEY_ID, 0, 0); |
119 | if (log_shmid == -1) |
120 | bb_perror_msg_and_die("can't %s syslogd buffer", "find"); |
121 | |
122 | /* Attach shared memory to our char* */ |
123 | shbuf = shmat(log_shmid, NULL, SHM_RDONLY); |
124 | if (shbuf == NULL) |
125 | bb_perror_msg_and_die("can't %s syslogd buffer", "access"); |
126 | |
127 | log_semid = semget(KEY_ID, 0, 0); |
128 | if (log_semid == -1) |
129 | error_exit("can't get access to semaphores for syslogd buffer"); |
130 | |
131 | bb_signals(BB_FATAL_SIGS, interrupted); |
132 | |
133 | /* Suppose atomic memory read */ |
134 | /* Max possible value for tail is shbuf->size - 1 */ |
135 | cur = shbuf->tail; |
136 | |
137 | /* Loop for -f or -F, one pass otherwise */ |
138 | do { |
139 | unsigned shbuf_size; |
140 | unsigned shbuf_tail; |
141 | const char *shbuf_data; |
142 | #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING |
143 | int i; |
144 | int len_first_part; |
145 | int len_total = len_total; /* for gcc */ |
146 | char *copy = copy; /* for gcc */ |
147 | #endif |
148 | if (semop(log_semid, SMrdn, 2) == -1) |
149 | error_exit("semop[SMrdn]"); |
150 | |
151 | /* Copy the info, helps gcc to realize that it doesn't change */ |
152 | shbuf_size = shbuf->size; |
153 | shbuf_tail = shbuf->tail; |
154 | shbuf_data = shbuf->data; /* pointer! */ |
155 | |
156 | if (DEBUG) |
157 | printf("cur:%u tail:%u size:%u\n", |
158 | cur, shbuf_tail, shbuf_size); |
159 | |
160 | if (!(follow & 1)) { /* not -f */ |
161 | /* if -F, "convert" it to -f, so that we dont |
162 | * dump the entire buffer on each iteration |
163 | */ |
164 | follow >>= 1; |
165 | |
166 | /* advance to oldest complete message */ |
167 | /* find NUL */ |
168 | cur += strlen(shbuf_data + cur); |
169 | if (cur >= shbuf_size) { /* last byte in buffer? */ |
170 | cur = strnlen(shbuf_data, shbuf_tail); |
171 | if (cur == shbuf_tail) |
172 | goto unlock; /* no complete messages */ |
173 | } |
174 | /* advance to first byte of the message */ |
175 | cur++; |
176 | if (cur >= shbuf_size) /* last byte in buffer? */ |
177 | cur = 0; |
178 | } else { /* -f */ |
179 | if (cur == shbuf_tail) { |
180 | sem_up(log_semid); |
181 | fflush_all(); |
182 | sleep(1); /* TODO: replace me with a sleep_on */ |
183 | continue; |
184 | } |
185 | } |
186 | |
187 | /* Read from cur to tail */ |
188 | #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING |
189 | len_first_part = len_total = shbuf_tail - cur; |
190 | if (len_total < 0) { |
191 | /* message wraps: */ |
192 | /* [SECOND PART.........FIRST PART] */ |
193 | /* ^data ^tail ^cur ^size */ |
194 | len_total += shbuf_size; |
195 | } |
196 | copy = xmalloc(len_total + 1); |
197 | if (len_first_part < 0) { |
198 | /* message wraps (see above) */ |
199 | len_first_part = shbuf_size - cur; |
200 | memcpy(copy + len_first_part, shbuf_data, shbuf_tail); |
201 | } |
202 | memcpy(copy, shbuf_data + cur, len_first_part); |
203 | copy[len_total] = '\0'; |
204 | cur = shbuf_tail; |
205 | #else |
206 | while (cur != shbuf_tail) { |
207 | fputs(shbuf_data + cur, stdout); |
208 | cur += strlen(shbuf_data + cur) + 1; |
209 | if (cur >= shbuf_size) |
210 | cur = 0; |
211 | } |
212 | #endif |
213 | unlock: |
214 | /* release the lock on the log chain */ |
215 | sem_up(log_semid); |
216 | |
217 | #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING |
218 | for (i = 0; i < len_total; i += strlen(copy + i) + 1) { |
219 | fputs(copy + i, stdout); |
220 | } |
221 | free(copy); |
222 | #endif |
223 | fflush_all(); |
224 | } while (follow); |
225 | |
226 | /* shmdt(shbuf); - on Linux, shmdt is not mandatory on exit */ |
227 | |
228 | fflush_stdout_and_exit(EXIT_SUCCESS); |
229 | } |
230 |