simple/prwtmp/prwtmp.c

char prwtmp_c_rcs_id[] = 
	"$Id: prwtmp.c,v 1.3 2016-07-05 19:13:09 hjp Exp $";
/*
 * prwtmp - print wtmp to stdout
 *
 * $Log: prwtmp.c,v $
 * Revision 1.3  2016-07-05 19:13:09  hjp
 * Adapt to modern linux utmp structure: microsecond timestamps, IPv6
 *
 * Revision 1.2  1998-05-28 16:18:21  hjp
 * use GNUmakerules/GNUmakevars for CC and INSTALL.
 * Bug fix: initial offset wasn't initialized
 * Bug fix: #include <unistd.h> and a cast (both needed for glibc2)
 *
 * Revision 1.1  1997/01/13 14:59:40  hjp
 * Checked into CVS.
 * Added -o and -s options.
 *
 */
#include <assert.h>
#include <errno.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <time.h>

#include <sys/types.h>
#include <unistd.h>
#include <utmp.h>

char *cmnd;

void usage(void) {
	fprintf(stderr, "Usage: %s [-o] [-s start] [file]\n", cmnd);
	exit(1);
}


/* The address is declared as a int32_t[], but it's really just an array
 * of bytes
 */

void print_addr(void *p, size_t sz) {
        uint8_t *pp = p;
        if (sz == 4) {
                /* assume ipv4 */
                char buf[16];
                snprintf(buf, sizeof(buf), "%d.%d.%d.%d", pp[0], pp[1], pp[2], pp[3]);
                printf("%-*s ", sizeof(buf), buf);
        } else {
                /* assume ipv6 */
                for (int i = 0; i < sz; i += 2) {
                        if (i > 0) printf(":");
                        printf("%02x%02x", pp[i], pp[i+1]);
                }
                printf(" ");
        }
}


int main (int argc, char **argv) {
	FILE *fp;
	struct utmp u;
	char *filename = WTMP_FILE;
	long off = 0;
	int print_offset = 0;
	int c;
	char *p;

	cmnd = argv[0];
	while ((c = getopt(argc, argv, "s:o")) != EOF) {
		switch(c) {
		case 's':
			off = strtoul(optarg, &p, 0);
			if (p == optarg || *p != '\0') usage();
			break;
		case 'o':
			print_offset = 1;
			break;
		case '?':
			usage();
		default:
			assert(0);
		}
	}

	if (argc > optind) filename = argv[optind];

	fp = fopen(filename, "rb");
	if (!fp) {
		fprintf(stderr, "%s: cannot open %s: %s\n",
			cmnd, filename, strerror(errno));
		exit(1);
	}
	if (fseek(fp, off, SEEK_SET) == -1) {
		fprintf(stderr, "%s: cannot seek to %ld on %s: %s\n",
			cmnd, off, filename, strerror(errno));
		exit(1);
	}
		
	while (fread(&u, (int)sizeof(u), 1, fp) == 1) {
		char tbuf[20];

		if (print_offset) printf ("%8ld: ", off);
		off += sizeof(u);

		strftime(tbuf, (int)sizeof(tbuf), "%Y-%m-%d %H:%M:%S",
		         localtime(&u.ut_time));
		printf("%s.%06d ", tbuf, (int)u.ut_tv.tv_usec);
		printf("%-*.*s ",
		       (int)sizeof(u.ut_user),
		       (int)sizeof(u.ut_user),
		       u.ut_user);
		printf("%-*.*s ",
		       (int)sizeof(u.ut_id),
		       (int)sizeof(u.ut_id),
		       u.ut_id);
		printf("%-*.*s ",
		       (int)sizeof(u.ut_line),
		       (int)sizeof(u.ut_line),
		       u.ut_line);
		printf("%5d ", (int)u.ut_pid); /* PID is typically < 30000 */
		printf("%5d ", (int)u.ut_type); /* short on HP-UX */
		printf("%5d ", (int)u.ut_exit.e_termination); /* short on HP-UX */
		printf("%5d ", (int)u.ut_exit.e_exit); /* short on HP-UX */
		printf("%-*.*s ",
		       (int)sizeof(u.ut_host),
		       (int)sizeof(u.ut_host),
		       u.ut_host);
		// printf("%08lx ", (unsigned long)u.ut_addr);
                print_addr(u.ut_addr_v6, sizeof(u.ut_addr_v6));
		printf("%10ld ", (long)u.ut_session); // either long or int32_t, so 10 digits should be enough
		printf("\n");
		
	}
	return 0;
}
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