/*
 * DF-2799 marker #1: a single `jail.list` read.  Uses the raw
 * __sysctl(202) path so it works with /usr/bin/sysctl busy or wedged.
 * Expected on the deadlocked kernel: NEVER returns (blocks in
 * sysctl_jail_list on jail_lock) -> `timeout N ./listonce` exits 124.
 * On a healthy/patched kernel: returns immediately, rc 0.
 */
#include <sys/sysctl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int
main(void)
{
	static char buf[1 << 18];
	size_t len = sizeof(buf);
	int name[3];
	size_t namelen = 0;

	/* jail.list */
	name[namelen++] = 1;		/* CTL_KERN */
	name[namelen++] = 33;		/* jail node OID (from mib lookup) */
	name[namelen++] = 1;		/* .list   — resolved below by name */

	/* do it by name to avoid hardcoding the mib numbers */
	if (sysctlbyname("jail.list", buf, &len, NULL, 0) < 0) {
		perror("sysctl jail.list");
		return (1);
	}
	printf("listonce: ok (%zu bytes)\n", len);
	return (0);
}