[821] | 1 | /* vi: set sw=4 ts=4: */
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| 2 | /*
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| 3 | * circular buffer syslog implementation for busybox
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| 4 | *
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| 5 | * Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com>
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| 6 | *
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| 7 | * Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001
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| 8 | *
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[2725] | 9 | * Licensed under GPLv2 or later, see file LICENSE in this source tree.
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[821] | 10 | */
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| 11 |
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[3232] | 12 | //usage:#define logread_trivial_usage
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| 13 | //usage: "[-f]"
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| 14 | //usage:#define logread_full_usage "\n\n"
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| 15 | //usage: "Show messages in syslogd's circular buffer\n"
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| 16 | //usage: "\n -f Output data as log grows"
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| 17 |
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[1765] | 18 | #include "libbb.h"
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[821] | 19 | #include <sys/ipc.h>
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| 20 | #include <sys/sem.h>
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| 21 | #include <sys/shm.h>
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| 22 |
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[1765] | 23 | #define DEBUG 0
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[821] | 24 |
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[2725] | 25 | /* our shared key (syslogd.c and logread.c must be in sync) */
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[1765] | 26 | enum { KEY_ID = 0x414e4547 }; /* "GENA" */
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| 27 |
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[2725] | 28 | struct shbuf_ds {
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[1765] | 29 | int32_t size; // size of data - 1
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| 30 | int32_t tail; // end of message list
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| 31 | char data[1]; // messages
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[2725] | 32 | };
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[821] | 33 |
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[2725] | 34 | static const struct sembuf init_sem[3] = {
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| 35 | {0, -1, IPC_NOWAIT | SEM_UNDO},
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| 36 | {1, 0}, {0, +1, SEM_UNDO}
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| 37 | };
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[821] | 38 |
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[2725] | 39 | struct globals {
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| 40 | struct sembuf SMrup[1]; // {0, -1, IPC_NOWAIT | SEM_UNDO},
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| 41 | struct sembuf SMrdn[2]; // {1, 0}, {0, +1, SEM_UNDO}
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| 42 | struct shbuf_ds *shbuf;
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| 43 | } FIX_ALIASING;
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| 44 | #define G (*(struct globals*)&bb_common_bufsiz1)
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| 45 | #define SMrup (G.SMrup)
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| 46 | #define SMrdn (G.SMrdn)
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| 47 | #define shbuf (G.shbuf)
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| 48 | #define INIT_G() do { \
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| 49 | memcpy(SMrup, init_sem, sizeof(init_sem)); \
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| 50 | } while (0)
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[821] | 51 |
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[2725] | 52 | static void error_exit(const char *str) NORETURN;
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[1765] | 53 | static void error_exit(const char *str)
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| 54 | {
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| 55 | //release all acquired resources
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| 56 | shmdt(shbuf);
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| 57 | bb_perror_msg_and_die(str);
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| 58 | }
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[821] | 59 |
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| 60 | /*
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| 61 | * sem_up - up()'s a semaphore.
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| 62 | */
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[1765] | 63 | static void sem_up(int semid)
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[821] | 64 | {
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[1765] | 65 | if (semop(semid, SMrup, 1) == -1)
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[821] | 66 | error_exit("semop[SMrup]");
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| 67 | }
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| 68 |
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[2725] | 69 | static void interrupted(int sig UNUSED_PARAM)
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[821] | 70 | {
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[1765] | 71 | signal(SIGINT, SIG_IGN);
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| 72 | shmdt(shbuf);
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[2725] | 73 | exit(EXIT_SUCCESS);
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[821] | 74 | }
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| 75 |
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[2725] | 76 | int logread_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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| 77 | int logread_main(int argc UNUSED_PARAM, char **argv)
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[821] | 78 | {
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[2725] | 79 | unsigned cur;
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[1765] | 80 | int log_semid; /* ipc semaphore id */
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| 81 | int log_shmid; /* ipc shared memory id */
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| 82 | smallint follow = getopt32(argv, "f");
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[821] | 83 |
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[2725] | 84 | INIT_G();
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| 85 |
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[1765] | 86 | log_shmid = shmget(KEY_ID, 0, 0);
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| 87 | if (log_shmid == -1)
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| 88 | bb_perror_msg_and_die("can't find syslogd buffer");
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[821] | 89 |
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[1765] | 90 | /* Attach shared memory to our char* */
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| 91 | shbuf = shmat(log_shmid, NULL, SHM_RDONLY);
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| 92 | if (shbuf == NULL)
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| 93 | bb_perror_msg_and_die("can't access syslogd buffer");
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[821] | 94 |
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[1765] | 95 | log_semid = semget(KEY_ID, 0, 0);
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| 96 | if (log_semid == -1)
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| 97 | error_exit("can't get access to semaphores for syslogd buffer");
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| 98 |
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[821] | 99 | signal(SIGINT, interrupted);
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| 100 |
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[1765] | 101 | /* Suppose atomic memory read */
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| 102 | /* Max possible value for tail is shbuf->size - 1 */
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| 103 | cur = shbuf->tail;
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[821] | 104 |
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[1765] | 105 | /* Loop for logread -f, one pass if there was no -f */
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[821] | 106 | do {
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[1765] | 107 | unsigned shbuf_size;
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| 108 | unsigned shbuf_tail;
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| 109 | const char *shbuf_data;
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| 110 | #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
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| 111 | int i;
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| 112 | int len_first_part;
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| 113 | int len_total = len_total; /* for gcc */
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| 114 | char *copy = copy; /* for gcc */
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[821] | 115 | #endif
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[1765] | 116 | if (semop(log_semid, SMrdn, 2) == -1)
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| 117 | error_exit("semop[SMrdn]");
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[821] | 118 |
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[1765] | 119 | /* Copy the info, helps gcc to realize that it doesn't change */
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| 120 | shbuf_size = shbuf->size;
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| 121 | shbuf_tail = shbuf->tail;
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| 122 | shbuf_data = shbuf->data; /* pointer! */
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[821] | 123 |
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[1765] | 124 | if (DEBUG)
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| 125 | printf("cur:%d tail:%i size:%i\n",
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| 126 | cur, shbuf_tail, shbuf_size);
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| 127 |
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| 128 | if (!follow) {
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| 129 | /* advance to oldest complete message */
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| 130 | /* find NUL */
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| 131 | cur += strlen(shbuf_data + cur);
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| 132 | if (cur >= shbuf_size) { /* last byte in buffer? */
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| 133 | cur = strnlen(shbuf_data, shbuf_tail);
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| 134 | if (cur == shbuf_tail)
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| 135 | goto unlock; /* no complete messages */
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| 136 | }
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| 137 | /* advance to first byte of the message */
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| 138 | cur++;
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| 139 | if (cur >= shbuf_size) /* last byte in buffer? */
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| 140 | cur = 0;
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| 141 | } else { /* logread -f */
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| 142 | if (cur == shbuf_tail) {
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[821] | 143 | sem_up(log_semid);
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[2725] | 144 | fflush_all();
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[1765] | 145 | sleep(1); /* TODO: replace me with a sleep_on */
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[821] | 146 | continue;
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| 147 | }
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| 148 | }
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| 149 |
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[1765] | 150 | /* Read from cur to tail */
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| 151 | #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
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| 152 | len_first_part = len_total = shbuf_tail - cur;
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| 153 | if (len_total < 0) {
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| 154 | /* message wraps: */
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| 155 | /* [SECOND PART.........FIRST PART] */
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| 156 | /* ^data ^tail ^cur ^size */
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| 157 | len_total += shbuf_size;
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[821] | 158 | }
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[1765] | 159 | copy = xmalloc(len_total + 1);
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| 160 | if (len_first_part < 0) {
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| 161 | /* message wraps (see above) */
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| 162 | len_first_part = shbuf_size - cur;
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| 163 | memcpy(copy + len_first_part, shbuf_data, shbuf_tail);
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| 164 | }
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| 165 | memcpy(copy, shbuf_data + cur, len_first_part);
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| 166 | copy[len_total] = '\0';
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| 167 | cur = shbuf_tail;
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[821] | 168 | #else
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[1765] | 169 | while (cur != shbuf_tail) {
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| 170 | fputs(shbuf_data + cur, stdout);
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| 171 | cur += strlen(shbuf_data + cur) + 1;
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| 172 | if (cur >= shbuf_size)
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| 173 | cur = 0;
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[821] | 174 | }
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| 175 | #endif
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[1765] | 176 | unlock:
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| 177 | /* release the lock on the log chain */
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[821] | 178 | sem_up(log_semid);
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| 179 |
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[1765] | 180 | #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
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| 181 | for (i = 0; i < len_total; i += strlen(copy + i) + 1) {
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| 182 | fputs(copy + i, stdout);
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[821] | 183 | }
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[1765] | 184 | free(copy);
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[821] | 185 | #endif
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| 186 | } while (follow);
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| 187 |
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[1765] | 188 | shmdt(shbuf);
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[821] | 189 |
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[1765] | 190 | fflush_stdout_and_exit(EXIT_SUCCESS);
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[821] | 191 | }
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