1 /* vi: set sw=4 ts=4: */
3 * circular buffer syslog implementation for busybox
5 * Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com>
7 * Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001
9 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
12 //usage:#define logread_trivial_usage
14 //usage:#define logread_full_usage "\n\n"
15 //usage: "Show messages in syslogd's circular buffer\n"
17 //usage: "\n -f Output data as log grows"
26 /* our shared key (syslogd.c and logread.c must be in sync) */
27 enum { KEY_ID = 0x414e4547 }; /* "GENA" */
30 int32_t size; // size of data - 1
31 int32_t tail; // end of message list
32 char data[1]; // messages
35 static const struct sembuf init_sem[3] = {
36 {0, -1, IPC_NOWAIT | SEM_UNDO},
37 {1, 0}, {0, +1, SEM_UNDO}
41 struct sembuf SMrup[1]; // {0, -1, IPC_NOWAIT | SEM_UNDO},
42 struct sembuf SMrdn[2]; // {1, 0}, {0, +1, SEM_UNDO}
43 struct shbuf_ds *shbuf;
45 #define G (*(struct globals*)&bb_common_bufsiz1)
46 #define SMrup (G.SMrup)
47 #define SMrdn (G.SMrdn)
48 #define shbuf (G.shbuf)
49 #define INIT_G() do { \
50 memcpy(SMrup, init_sem, sizeof(init_sem)); \
53 static void error_exit(const char *str) NORETURN;
54 static void error_exit(const char *str)
56 //release all acquired resources
58 bb_perror_msg_and_die(str);
62 * sem_up - up()'s a semaphore.
64 static void sem_up(int semid)
66 if (semop(semid, SMrup, 1) == -1)
67 error_exit("semop[SMrup]");
70 static void interrupted(int sig UNUSED_PARAM)
72 signal(SIGINT, SIG_IGN);
77 int logread_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
78 int logread_main(int argc UNUSED_PARAM, char **argv)
81 int log_semid; /* ipc semaphore id */
82 int log_shmid; /* ipc shared memory id */
83 smallint follow = getopt32(argv, "f");
87 log_shmid = shmget(KEY_ID, 0, 0);
89 bb_perror_msg_and_die("can't find syslogd buffer");
91 /* Attach shared memory to our char* */
92 shbuf = shmat(log_shmid, NULL, SHM_RDONLY);
94 bb_perror_msg_and_die("can't access syslogd buffer");
96 log_semid = semget(KEY_ID, 0, 0);
98 error_exit("can't get access to semaphores for syslogd buffer");
100 signal(SIGINT, interrupted);
102 /* Suppose atomic memory read */
103 /* Max possible value for tail is shbuf->size - 1 */
106 /* Loop for logread -f, one pass if there was no -f */
110 const char *shbuf_data;
111 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
114 int len_total = len_total; /* for gcc */
115 char *copy = copy; /* for gcc */
117 if (semop(log_semid, SMrdn, 2) == -1)
118 error_exit("semop[SMrdn]");
120 /* Copy the info, helps gcc to realize that it doesn't change */
121 shbuf_size = shbuf->size;
122 shbuf_tail = shbuf->tail;
123 shbuf_data = shbuf->data; /* pointer! */
126 printf("cur:%d tail:%i size:%i\n",
127 cur, shbuf_tail, shbuf_size);
130 /* advance to oldest complete message */
132 cur += strlen(shbuf_data + cur);
133 if (cur >= shbuf_size) { /* last byte in buffer? */
134 cur = strnlen(shbuf_data, shbuf_tail);
135 if (cur == shbuf_tail)
136 goto unlock; /* no complete messages */
138 /* advance to first byte of the message */
140 if (cur >= shbuf_size) /* last byte in buffer? */
142 } else { /* logread -f */
143 if (cur == shbuf_tail) {
146 sleep(1); /* TODO: replace me with a sleep_on */
151 /* Read from cur to tail */
152 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
153 len_first_part = len_total = shbuf_tail - cur;
156 /* [SECOND PART.........FIRST PART] */
157 /* ^data ^tail ^cur ^size */
158 len_total += shbuf_size;
160 copy = xmalloc(len_total + 1);
161 if (len_first_part < 0) {
162 /* message wraps (see above) */
163 len_first_part = shbuf_size - cur;
164 memcpy(copy + len_first_part, shbuf_data, shbuf_tail);
166 memcpy(copy, shbuf_data + cur, len_first_part);
167 copy[len_total] = '\0';
170 while (cur != shbuf_tail) {
171 fputs(shbuf_data + cur, stdout);
172 cur += strlen(shbuf_data + cur) + 1;
173 if (cur >= shbuf_size)
178 /* release the lock on the log chain */
181 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
182 for (i = 0; i < len_total; i += strlen(copy + i) + 1) {
183 fputs(copy + i, stdout);
191 fflush_stdout_and_exit(EXIT_SUCCESS);