lh | 9ed821d | 2023-04-07 01:36:19 -0700 | [diff] [blame] | 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 | |
| 12 | //usage:#define logread_trivial_usage |
| 13 | //usage: "[-f]" |
| 14 | //usage:#define logread_full_usage "\n\n" |
| 15 | //usage: "Show messages in syslogd's circular buffer\n" |
| 16 | //usage: "\n -f Output data as log grows" |
| 17 | |
| 18 | #include "libbb.h" |
| 19 | #include <sys/ipc.h> |
| 20 | #include <sys/sem.h> |
| 21 | #include <sys/shm.h> |
| 22 | |
| 23 | #define DEBUG 0 |
| 24 | |
| 25 | /* our shared key (syslogd.c and logread.c must be in sync) */ |
| 26 | enum { KEY_ID = 0x414e4547 }; /* "GENA" */ |
| 27 | |
| 28 | struct shbuf_ds { |
| 29 | int32_t size; // size of data - 1 |
| 30 | int32_t tail; // end of message list |
| 31 | char data[1]; // messages |
| 32 | }; |
| 33 | |
| 34 | static const struct sembuf init_sem[3] = { |
| 35 | {0, -1, IPC_NOWAIT | SEM_UNDO}, |
| 36 | {1, 0}, {0, +1, SEM_UNDO} |
| 37 | }; |
| 38 | |
| 39 | struct globals { |
| 40 | struct sembuf SMrup[1]; // {0, -1, IPC_NOWAIT | SEM_UNDO}, |
| 41 | struct sembuf SMrdn[2]; // {1, 0}, {0, +1, SEM_UNDO} |
| 42 | struct shbuf_ds *shbuf; |
| 43 | } FIX_ALIASING; |
| 44 | #define G (*(struct globals*)&bb_common_bufsiz1) |
| 45 | #define SMrup (G.SMrup) |
| 46 | #define SMrdn (G.SMrdn) |
| 47 | #define shbuf (G.shbuf) |
| 48 | #define INIT_G() do { \ |
| 49 | memcpy(SMrup, init_sem, sizeof(init_sem)); \ |
| 50 | } while (0) |
| 51 | |
| 52 | static void error_exit(const char *str) NORETURN; |
| 53 | static void error_exit(const char *str) |
| 54 | { |
| 55 | //release all acquired resources |
| 56 | shmdt(shbuf); |
| 57 | bb_perror_msg_and_die(str); |
| 58 | } |
| 59 | |
| 60 | /* |
| 61 | * sem_up - up()'s a semaphore. |
| 62 | */ |
| 63 | static void sem_up(int semid) |
| 64 | { |
| 65 | if (semop(semid, SMrup, 1) == -1) |
| 66 | error_exit("semop[SMrup]"); |
| 67 | } |
| 68 | |
| 69 | static void interrupted(int sig UNUSED_PARAM) |
| 70 | { |
| 71 | signal(SIGINT, SIG_IGN); |
| 72 | shmdt(shbuf); |
| 73 | exit(EXIT_SUCCESS); |
| 74 | } |
| 75 | |
| 76 | int logread_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; |
| 77 | int logread_main(int argc UNUSED_PARAM, char **argv) |
| 78 | { |
| 79 | unsigned cur; |
| 80 | int log_semid; /* ipc semaphore id */ |
| 81 | int log_shmid; /* ipc shared memory id */ |
| 82 | smallint follow = getopt32(argv, "f"); |
| 83 | |
| 84 | INIT_G(); |
| 85 | |
| 86 | log_shmid = shmget(KEY_ID, 0, 0); |
| 87 | if (log_shmid == -1) |
| 88 | bb_perror_msg_and_die("can't find syslogd buffer"); |
| 89 | |
| 90 | /* Attach shared memory to our char* */ |
| 91 | shbuf = shmat(log_shmid, NULL, SHM_RDONLY); |
| 92 | if (shbuf == NULL) |
| 93 | bb_perror_msg_and_die("can't access syslogd buffer"); |
| 94 | |
| 95 | log_semid = semget(KEY_ID, 0, 0); |
| 96 | if (log_semid == -1) |
| 97 | error_exit("can't get access to semaphores for syslogd buffer"); |
| 98 | |
| 99 | signal(SIGINT, interrupted); |
| 100 | |
| 101 | /* Suppose atomic memory read */ |
| 102 | /* Max possible value for tail is shbuf->size - 1 */ |
| 103 | cur = shbuf->tail; |
| 104 | |
| 105 | /* Loop for logread -f, one pass if there was no -f */ |
| 106 | do { |
| 107 | unsigned shbuf_size; |
| 108 | unsigned shbuf_tail; |
| 109 | const char *shbuf_data; |
| 110 | #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING |
| 111 | int i; |
| 112 | int len_first_part; |
| 113 | int len_total = len_total; /* for gcc */ |
| 114 | char *copy = copy; /* for gcc */ |
| 115 | #endif |
| 116 | if (semop(log_semid, SMrdn, 2) == -1) |
| 117 | error_exit("semop[SMrdn]"); |
| 118 | |
| 119 | /* Copy the info, helps gcc to realize that it doesn't change */ |
| 120 | shbuf_size = shbuf->size; |
| 121 | shbuf_tail = shbuf->tail; |
| 122 | shbuf_data = shbuf->data; /* pointer! */ |
| 123 | |
| 124 | if (DEBUG) |
| 125 | printf("cur:%d tail:%i size:%i\n", |
| 126 | cur, shbuf_tail, shbuf_size); |
| 127 | |
| 128 | if (!follow) { |
| 129 | /* advance to oldest complete message */ |
| 130 | /* find NUL */ |
| 131 | cur += strlen(shbuf_data + cur); |
| 132 | if (cur >= shbuf_size) { /* last byte in buffer? */ |
| 133 | cur = strnlen(shbuf_data, shbuf_tail); |
| 134 | if (cur == shbuf_tail) |
| 135 | goto unlock; /* no complete messages */ |
| 136 | } |
| 137 | /* advance to first byte of the message */ |
| 138 | cur++; |
| 139 | if (cur >= shbuf_size) /* last byte in buffer? */ |
| 140 | cur = 0; |
| 141 | } else { /* logread -f */ |
| 142 | if (cur == shbuf_tail) { |
| 143 | sem_up(log_semid); |
| 144 | fflush_all(); |
| 145 | sleep(1); /* TODO: replace me with a sleep_on */ |
| 146 | continue; |
| 147 | } |
| 148 | } |
| 149 | |
| 150 | /* Read from cur to tail */ |
| 151 | #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING |
| 152 | len_first_part = len_total = shbuf_tail - cur; |
| 153 | if (len_total < 0) { |
| 154 | /* message wraps: */ |
| 155 | /* [SECOND PART.........FIRST PART] */ |
| 156 | /* ^data ^tail ^cur ^size */ |
| 157 | len_total += shbuf_size; |
| 158 | } |
| 159 | copy = xmalloc(len_total + 1); |
| 160 | if (len_first_part < 0) { |
| 161 | /* message wraps (see above) */ |
| 162 | len_first_part = shbuf_size - cur; |
| 163 | memcpy(copy + len_first_part, shbuf_data, shbuf_tail); |
| 164 | } |
| 165 | memcpy(copy, shbuf_data + cur, len_first_part); |
| 166 | copy[len_total] = '\0'; |
| 167 | cur = shbuf_tail; |
| 168 | #else |
| 169 | while (cur != shbuf_tail) { |
| 170 | fputs(shbuf_data + cur, stdout); |
| 171 | cur += strlen(shbuf_data + cur) + 1; |
| 172 | if (cur >= shbuf_size) |
| 173 | cur = 0; |
| 174 | } |
| 175 | #endif |
| 176 | unlock: |
| 177 | /* release the lock on the log chain */ |
| 178 | sem_up(log_semid); |
| 179 | |
| 180 | #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING |
| 181 | for (i = 0; i < len_total; i += strlen(copy + i) + 1) { |
| 182 | fputs(copy + i, stdout); |
| 183 | } |
| 184 | free(copy); |
| 185 | #endif |
| 186 | } while (follow); |
| 187 | |
| 188 | shmdt(shbuf); |
| 189 | |
| 190 | fflush_stdout_and_exit(EXIT_SUCCESS); |
| 191 | } |