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/* vi: set sw=4 ts=4: */
/*
* circular buffer syslog implementation for busybox
*
* Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com>
*
* Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001
*
* Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
*/
#include "busybox.h"
#include <sys/ipc.h>
//#include <sys/types.h>
#include <sys/sem.h>
#include <sys/shm.h>
//#include <signal.h>
//#include <setjmp.h>
#define DEBUG 0
static const long 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 int log_shmid = -1; // ipc shared memory id
static int log_semid = -1; // ipc semaphore id
static void error_exit(const char *str) ATTRIBUTE_NORETURN;
static void error_exit(const char *str)
{
//release all acquired resources
if (log_shmid != -1)
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]");
}
/*
* sem_down - down()'s a semaphore
*/
static void sem_down(int semid)
{
if (semop(semid, SMrdn, 2) == -1)
error_exit("semop[SMrdn]");
}
static void interrupted(int sig)
{
signal(SIGINT, SIG_IGN);
shmdt(buf);
exit(0);
}
int logread_main(int argc, char **argv)
{
int cur;
int follow = 1;
if (argc != 2 || argv[1][0]!='-' || argv[1][1]!='f' ) {
follow = 0;
/* no options, no getopt */
if (argc > 1)
bb_show_usage();
}
log_shmid = shmget(KEY_ID, 0, 0);
if (log_shmid == -1)
error_exit("can't find circular buffer");
// Attach shared memory to our char*
buf = shmat(log_shmid, NULL, SHM_RDONLY);
if (buf == NULL)
error_exit("can't get access to 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 {
#ifdef CONFIG_FEATURE_LOGREAD_REDUCED_LOCKING
char *buf_data;
int log_len, j;
#endif
sem_down(log_semid);
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);
sleep(1); /* TODO: replace me with a sleep_on */
continue;
} else {
printf("<empty syslog>\n");
}
}
// Read Memory
#ifdef CONFIG_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) {
memcpy(buf_data, buf->data + cur, log_len);
} else {
memcpy(buf_data, buf->data + cur, buf->size - 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);
#ifdef CONFIG_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
fflush(stdout);
} while (follow);
shmdt(buf);
return EXIT_SUCCESS;
}
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