toolbox/dmesg: do not hardcode KLOG_BUF_LEN

#include <sys/klog.h>

#include <string.h>

#define KLOG_BUF_SHIFT	17	/* CONFIG_LOG_BUF_SHIFT from our kernel */

#define KLOG_BUF_LEN	(1 << KLOG_BUF_SHIFT)

#define FALLBACK_KLOG_BUF_SHIFT	17	/* CONFIG_LOG_BUF_SHIFT from our kernel */

#define FALLBACK_KLOG_BUF_LEN	(1 << FALLBACK_KLOG_BUF_SHIFT)

int dmesg_main(int argc, char **argv)

{

    char buffer[KLOG_BUF_LEN + 1];

    char *p = buffer;

    char *buffer;

    char *p;

    ssize_t ret;

    int n, op;

    int n, op, klog_buf_len;

    klog_buf_len = klogctl(KLOG_SIZE_BUFFER, 0, 0);

    if (klog_buf_len <= 0) {

        klog_buf_len = FALLBACK_KLOG_BUF_LEN;

    }

    buffer = (char *)malloc(klog_buf_len + 1);

    if (!buffer) {

        perror("malloc");

        return EXIT_FAILURE;

    }

    p = buffer;

    if((argc == 2) && (!strcmp(argv[1],"-c"))) {

        op = KLOG_READ_CLEAR;

        op = KLOG_READ_ALL;

    }

    n = klogctl(op, buffer, KLOG_BUF_LEN);

    n = klogctl(op, buffer, klog_buf_len);

    if (n < 0) {

        perror("klogctl");

        return EXIT_FAILURE;