#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <assert.h>
#include <fcntl.h>
#include <inttypes.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <pthread.h>

/*
 * Usage: rw_seq_cst_vs_drop_caches [-m] /mnt/lustre/file0 /mnt/lustre2/file0

 * Race reads of the same file on two client mounts vs writes and drop
 * caches to detect sequential consistency violations. Run
 * indefinately.  all abort() if a consistency violation is found in
 * which case the wait status ($?) will be 134.
*/

int mmap_mode;		/* -m flag */

static void usage(void)
{
	fprintf(stdout,
		"%s: rw_seq_cst_vs_drop_caches [-m] /mnt/lustre/file0 /mnt/lustre2/file0\n"
"	-m : use mmap to read/write file\n", __func__);
}

#define handle_error(msg)	\
	do { perror(msg); exit(EXIT_FAILURE); } while (0)

static int fd[2] = { -1, -1 };
/* u_max is total number of writes, which are time consumg because they are
 * contending with constant reads
 */
static uint64_t u, u_max = UINT64_MAX / 2;
static uint64_t v[2];
char *ptr;

static void *access_thread_start(void *unused)
{
	char *ptr2 = NULL;
	ssize_t rc;
	int i;

	if (mmap_mode) {
		ptr2 = mmap(NULL, sizeof(v[1]), PROT_READ,
			    MAP_PRIVATE | MAP_POPULATE, fd[1], 0);
		if (ptr2 == MAP_FAILED)
			handle_error("mmap");
	}

	do {
		for (i = 0; i < 2; i++) {
			if (mmap_mode) {
				memcpy(&v[i], i == 0 ? ptr : ptr2,
				       sizeof(v[i]));
			} else {
				rc = pread(fd[i], &v[i], sizeof(v[i]), 0);
				if (rc < 0 || rc != sizeof(v[i]))
					handle_error("pread");
			}
		}
	} while (v[0] <= v[1]);

	fprintf(stderr, "error: u = %"PRIu64", v = %"PRIu64", %"PRIu64"\n",
		u, v[0], v[1]);

	if (mmap_mode)
		munmap(ptr2, sizeof(v[i]));
	abort();
}

static char stderr_buf[4096];

int main(int argc, char *argv[])
{
	int drop_caches_fd = -1;
	pthread_t access_thread;
	struct stat st[2];
	ssize_t rc;
	int i, ch;

	setvbuf(stderr, stderr_buf, _IOLBF, sizeof(stderr_buf));

	while ((ch = getopt(argc, argv, "m")) >= 0) {
		switch (ch) {
		case 'm':
			mmap_mode = 1;
			break;
		default:
			usage();
			exit(EXIT_FAILURE);
		}
	}

	argc -= optind;
	argv += optind;

	if (argc != 2) {
		usage();
		exit(EXIT_FAILURE);
	}

	drop_caches_fd = open("/proc/sys/vm/drop_caches", O_WRONLY);
	assert(!(drop_caches_fd < 0));

	for (i = 0; i < 2; i++) {
		fd[i] = open(argv[i], O_RDWR|O_CREAT|O_TRUNC, 0666);
		if (fd[i] < 0)
			handle_error("open");

		rc = fstat(fd[i], &st[i]);
		if (rc < 0)
			handle_error("fstat");
	}

	/* file0 and file1 should be the same file on two different
	 * client mount points. */
	if (st[0].st_dev != st[1].st_dev ||
	    st[0].st_ino != st[1].st_ino) {
		fprintf(stderr, "file mismatch\n");
		exit(EXIT_FAILURE);
	}

	if (mmap_mode) {
		if (ftruncate(fd[0], sizeof(u)) < 0)
			handle_error("ftruncate");

		ptr = mmap(NULL, sizeof(u), PROT_READ|PROT_WRITE, MAP_SHARED,
			   fd[0], 0);
		if (ptr == MAP_FAILED)
			handle_error("mmap");
		memcpy(ptr, &u, sizeof(u));
	} else {
		rc = pwrite(fd[0], &u, sizeof(u), 0);
		if (rc < 0 || rc != sizeof(u))
			handle_error("pwrite");
	}

	rc = pthread_create(&access_thread, NULL, &access_thread_start, NULL);
	if (rc != 0)
		handle_error("pthread_create");

	for (u = 1; u <= u_max; u++) {
		if (mmap_mode) {
			memcpy(ptr, &u, sizeof(u));
		} else {
			rc = pwrite(fd[0], &u, sizeof(u), 0);
			if (rc < 0 || rc != sizeof(u))
				handle_error("pwrite");
		}

		rc = write(drop_caches_fd, "3\n", 2);
		if (rc < 0 || rc != 2)
			handle_error("drop caches");
	}

	rc = pthread_cancel(access_thread);
	if (rc != 0)
		handle_error("pthread_cancel");

	rc = pthread_join(access_thread, NULL);
	if (rc != 0)
		handle_error("pthread_join");

	if (mmap_mode)
		munmap(ptr, sizeof(u));

	return 0;
}