/* gcc mem-hog.c -g -o mem-hog -Wall -Wextra */

#include <stdio.h>
#include <unistd.h>
#include <err.h>
#include <signal.h>
#include <fcntl.h>

#define UNUSED __attribute__ ((unused))
#define BUFFER_SIZE 1024

volatile int end;

void sighandler1(UNUSED int signo)
{
}

void sigint(UNUSED int signo)
{
	end = 1;
}

int page_cache_hog(void)
{
	int fd = -1;
	char buff[BUFFER_SIZE];
	char path[BUFFER_SIZE];
	int ret = 0;

	sprintf(path, "%s", "DATAFILE");
	fd = open(path, O_RDONLY);
	if (fd == -1) {
		warn("open %s failed", path);
		return -1;
	}

	while ((ret = read(fd, buff, sizeof(buff))) > 0);
	if (ret == -1)
		warn("read %s failed", path);

	close(fd);
	return ret;
}

int mem_hog(void)
{
	sigset_t sigset;
	int ret = 0;

	if (sigemptyset(&sigset) < 0)
		err(1, "sigemptyset()");
	sigsuspend(&sigset);

	while (!end) {
		ret = page_cache_hog();

		sigsuspend(&sigset);
	}

	return ret;
}

int main(UNUSED int argc, UNUSED char *argv[])
{
	struct sigaction sa1, sa2;

	sa1.sa_handler = sighandler1;
	if (sigemptyset(&sa1.sa_mask) < 0)
		err(1, "sigemptyset()");

	sa1.sa_flags = 0;
	if (sigaction(SIGUSR1, &sa1, NULL) < 0)
		err(1, "sigaction()");

	sa2.sa_handler = sigint;
	if (sigemptyset(&sa2.sa_mask) < 0)
		err(1, "sigemptyset()");

	sa2.sa_flags = 0;
	if (sigaction(SIGINT, &sa2, NULL) < 0)
		err(1, "sigaction()");

	return mem_hog();
}