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branch: master
Denys Vlasenko
192 lines (166 sloc) 4.842 kb
/* 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 source tree.
*/
//usage:#define logread_trivial_usage
//usage: "[-f]"
//usage:#define logread_full_usage "\n\n"
//usage: "Show messages in syslogd's circular buffer\n"
//usage: "\n -f Output data as log grows"
#include "libbb.h"
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>
#define DEBUG 0
/* our shared key (syslogd.c and logread.c must be in sync) */
enum { KEY_ID = 0x414e4547 }; /* "GENA" */
struct shbuf_ds {
int32_t size; // size of data - 1
int32_t tail; // end of message list
char data[1]; // messages
};
static const struct sembuf init_sem[3] = {
{0, -1, IPC_NOWAIT | SEM_UNDO},
{1, 0}, {0, +1, SEM_UNDO}
};
struct globals {
struct sembuf SMrup[1]; // {0, -1, IPC_NOWAIT | SEM_UNDO},
struct sembuf SMrdn[2]; // {1, 0}, {0, +1, SEM_UNDO}
struct shbuf_ds *shbuf;
} FIX_ALIASING;
#define G (*(struct globals*)&bb_common_bufsiz1)
#define SMrup (G.SMrup)
#define SMrdn (G.SMrdn)
#define shbuf (G.shbuf)
#define INIT_G() do { \
memcpy(SMrup, init_sem, sizeof(init_sem)); \
} while (0)
static void error_exit(const char *str) NORETURN;
static void error_exit(const char *str)
{
//release all acquired resources
shmdt(shbuf);
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 UNUSED_PARAM)
{
signal(SIGINT, SIG_IGN);
shmdt(shbuf);
exit(EXIT_SUCCESS);
}
int logread_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int logread_main(int argc UNUSED_PARAM, char **argv)
{
unsigned cur;
int log_semid; /* ipc semaphore id */
int log_shmid; /* ipc shared memory id */
smallint follow = getopt32(argv, "f");
INIT_G();
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* */
shbuf = shmat(log_shmid, NULL, SHM_RDONLY);
if (shbuf == 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");
signal(SIGINT, interrupted);
/* Suppose atomic memory read */
/* Max possible value for tail is shbuf->size - 1 */
cur = shbuf->tail;
/* Loop for logread -f, one pass if there was no -f */
do {
unsigned shbuf_size;
unsigned shbuf_tail;
const char *shbuf_data;
#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
int i;
int len_first_part;
int len_total = len_total; /* for gcc */
char *copy = copy; /* for gcc */
#endif
if (semop(log_semid, SMrdn, 2) == -1)
error_exit("semop[SMrdn]");
/* Copy the info, helps gcc to realize that it doesn't change */
shbuf_size = shbuf->size;
shbuf_tail = shbuf->tail;
shbuf_data = shbuf->data; /* pointer! */
if (DEBUG)
printf("cur:%d tail:%i size:%i\n",
cur, shbuf_tail, shbuf_size);
if (!follow) {
/* advance to oldest complete message */
/* find NUL */
cur += strlen(shbuf_data + cur);
if (cur >= shbuf_size) { /* last byte in buffer? */
cur = strnlen(shbuf_data, shbuf_tail);
if (cur == shbuf_tail)
goto unlock; /* no complete messages */
}
/* advance to first byte of the message */
cur++;
if (cur >= shbuf_size) /* last byte in buffer? */
cur = 0;
} else { /* logread -f */
if (cur == shbuf_tail) {
sem_up(log_semid);
fflush_all();
sleep(1); /* TODO: replace me with a sleep_on */
continue;
}
}
/* Read from cur to tail */
#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
len_first_part = len_total = shbuf_tail - cur;
if (len_total < 0) {
/* message wraps: */
/* [SECOND PART.........FIRST PART] */
/* ^data ^tail ^cur ^size */
len_total += shbuf_size;
}
copy = xmalloc(len_total + 1);
if (len_first_part < 0) {
/* message wraps (see above) */
len_first_part = shbuf_size - cur;
memcpy(copy + len_first_part, shbuf_data, shbuf_tail);
}
memcpy(copy, shbuf_data + cur, len_first_part);
copy[len_total] = '\0';
cur = shbuf_tail;
#else
while (cur != shbuf_tail) {
fputs(shbuf_data + cur, stdout);
cur += strlen(shbuf_data + cur) + 1;
if (cur >= shbuf_size)
cur = 0;
}
#endif
unlock:
/* release the lock on the log chain */
sem_up(log_semid);
#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
for (i = 0; i < len_total; i += strlen(copy + i) + 1) {
fputs(copy + i, stdout);
}
free(copy);
#endif
} while (follow);
shmdt(shbuf);
fflush_stdout_and_exit(EXIT_SUCCESS);
}
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