/* vi: set sw=4 ts=4: */ /* * circular buffer syslog implementation for busybox * * Copyright (C) 2000 by Gennady Feldman * * Maintainer: Gennady Feldman as of Mar 12, 2001 * * Licensed under GPLv2 or later, see file LICENSE in this tarball for details. */ #include "busybox.h" #include #include #include #define DEBUG 0 enum { KEY_ID = 0x414e4547 }; /* "GENA" */ static struct shbuf_ds { int32_t size; // size of data written int32_t head; // start of message list int32_t tail; // end of message list char data[1]; // data/messages } *buf; // shared memory pointer // Semaphore operation structures static struct sembuf SMrup[1] = {{0, -1, IPC_NOWAIT | SEM_UNDO}}; // set SMrup static struct sembuf SMrdn[2] = {{1, 0}, {0, +1, SEM_UNDO}}; // set SMrdn static void error_exit(const char *str) ATTRIBUTE_NORETURN; static void error_exit(const char *str) { //release all acquired resources shmdt(buf); bb_perror_msg_and_die(str); } /* * sem_up - up()'s a semaphore. */ static void sem_up(int semid) { if (semop(semid, SMrup, 1) == -1) error_exit("semop[SMrup]"); } static void interrupted(int sig ATTRIBUTE_UNUSED) { signal(SIGINT, SIG_IGN); shmdt(buf); exit(0); } int logread_main(int argc, char **argv); int logread_main(int argc, char **argv) { int cur; int log_semid; /* ipc semaphore id */ int log_shmid; /* ipc shared memory id */ smallint follow = getopt32(argc, argv, "f"); log_shmid = shmget(KEY_ID, 0, 0); if (log_shmid == -1) bb_perror_msg_and_die("can't find syslogd buffer"); // Attach shared memory to our char* buf = shmat(log_shmid, NULL, SHM_RDONLY); if (buf == NULL) bb_perror_msg_and_die("can't access syslogd buffer"); log_semid = semget(KEY_ID, 0, 0); if (log_semid == -1) error_exit("can't get access to semaphores for syslogd buffer"); // attempt to redefine ^C signal signal(SIGINT, interrupted); // Suppose atomic memory move cur = follow ? buf->tail : buf->head; do { #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING char *buf_data; int log_len, j; #endif if (semop(log_semid, SMrdn, 2) == -1) error_exit("semop[SMrdn]"); if (DEBUG) printf("head:%i cur:%d tail:%i size:%i\n", buf->head, cur, buf->tail, buf->size); if (buf->head == buf->tail || cur == buf->tail) { if (follow) { sem_up(log_semid); fflush(stdout); sleep(1); /* TODO: replace me with a sleep_on */ continue; } puts(""); } // Read Memory #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING log_len = buf->tail - cur; if (log_len < 0) log_len += buf->size; buf_data = xmalloc(log_len); if (buf->tail >= cur) j = log_len; else j = buf->size - cur; memcpy(buf_data, buf->data + cur, j); if (buf->tail < cur) memcpy(buf_data + buf->size - cur, buf->data, buf->tail); cur = buf->tail; #else while (cur != buf->tail) { fputs(buf->data + cur, stdout); cur += strlen(buf->data + cur) + 1; if (cur >= buf->size) cur = 0; } #endif // release the lock on the log chain sem_up(log_semid); #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING for (j = 0; j < log_len; j += strlen(buf_data+j) + 1) { fputs(buf_data + j, stdout); } free(buf_data); #endif } while (follow); shmdt(buf); fflush_stdout_and_exit(EXIT_SUCCESS); }