#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <rctl.h>
#include <err.h>
#include <errno.h>

int
main(int argc, char *argv[])
{
	int32_t sysconf_ncpus = (int32_t)sysconf(_SC_NPROCESSORS_ONLN);

	printf("ncpu = %d\n", sysconf_ncpus);

	rctlblk_t *rblks[] = {
		calloc(1, rctlblk_size()),
		calloc(1, rctlblk_size()),
	};

	/*
	 * As per resource_controls(5), the "zone.cpu-cap" resource control is
	 * "the percentage of a single CPU that can be used by all user threads
	 * in a zone, expressed as an integer."  That is, a value of 100 means
	 * one whole CPU on this system.  If there is no cap, or the cap is
	 * greater than the number of actual detected CPUs, we just use the CPU
	 * count value.
	 */
	uint64_t capval = 0;

	int flag = RCTL_FIRST;
	for (unsigned i = 0; ; i++) {
		int flag = i == 0 ? RCTL_FIRST : RCTL_NEXT;
		rctlblk_t *rblk = rblks[i % 2];
		rctlblk_t *rblkprev = rblks[(i + 1) % 2];

		if (getrctl("zone.cpu-cap", rblkprev, rblk, flag) != 0) {
			if (errno == ENOENT) {
				break;
			}
			err(1, "getrctl");
		}

		int s = 0;
		if (!(rctlblk_get_local_flags(rblk) & RCTL_LOCAL_MAXIMAL) &&
		    rctlblk_get_local_action(rblk, &s) == RCTL_LOCAL_DENY) {
			rctl_qty_t v = rctlblk_get_value(rblk);

			if (capval == 0 || capval > v) {
				capval = v;
			}
		}
	}

	if (capval == 0) {
		printf("uncapped, so %d CPUs\n", sysconf_ncpus);
	} else {
		int cap_ncpus = capval / 100;

		if (cap_ncpus > sysconf_ncpus) {
			printf("cap too large, so %d CPUs\n", sysconf_ncpus);
		} else {
			printf("capped, at %d CPUs\n", cap_ncpus);
		}
	}
}