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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 "libbb.h"
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>
#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("<empty syslog>");
}
// 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);
}
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