Updated reader userspace program

src/aarch64-linux-flush-dcache/my_shmem.c

@@ -263,7 +263,12 @@ static int my_shmem_fops_release(struct inode *inode, struct file *filp)
 	return 0;
 }
 
-// static int
+static int my_shmem_fops_fsync(
+	struct file *filp, loff_t bgn_off, loff_t end_off, int datasync)
+{
+	pr_info("[%s] Entered.\n", __func__);
+	
+}
 
 static const struct file_operations my_shmem_fops = {
 	.owner = THIS_MODULE,

src/aarch64-linux-flush-dcache/userspace/reader.c

@@ -0,0 +1,92 @@
+#include <stdbool.h>
+#include <stdatomic.h>
+#include <pthread.h>
+#include <time.h>
+#include <unistd.h>		// sysconf
+#include <stdio.h>		// printf
+#include <stdlib.h>		// exit
+#include <fcntl.h>		// O_READ
+#include <sys/mman.h>	// mmap
+#include <string.h>		// strlen
+#include <errno.h>		// errno
+
+#define eprintf(args...) fprintf(stderr, ##args)
+
+const char *DEVICE_PATH = "/dev/my_shmem";
+const struct timespec WAIT_DURATION = {
+	.tv_nsec = 100000000, // 0.1s
+	.tv_sec = 0,
+};
+
+static atomic_bool timeout;
+
+void *pthread_fn(void *);
+
+int main(int argc, char *argv[])
+{
+	const long PAGE_SIZE = sysconf(_SC_PAGESIZE);
+	if (PAGE_SIZE == -1) {
+		eprintf("Error retrieving page size: %d.\n", errno);
+		exit(EXIT_FAILURE);
+	}
+
+	// open device file w/ RW perms
+	FILE *fp = fopen(DEVICE_PATH, "r+");
+	if (!fp) {
+		eprintf("Error opening device %s: %d.\n", DEVICE_PATH, errno);
+		exit(EXIT_FAILURE);
+	}
+	int fd = fileno(fp);
+	if (fd == -1) {
+		eprintf("Error retrieving file descriptor: %d.\n", errno);
+		exit(EXIT_FAILURE);
+	}
+
+	// mmap device
+	void *buf = mmap(NULL, PAGE_SIZE * 2, PROT_READ,
+		MAP_SHARED, fd, 0);
+	if (!buf) {
+		eprintf("Error mmap-ing: %d.\n", errno);
+		exit(EXIT_FAILURE);
+	}
+
+	// Read from mmap-ed device
+	pthread_t thread_handle;
+	int ret_pth_create = pthread_create(
+		&thread_handle, NULL, &pthread_fn, buf);
+	if (ret_pth_create) {
+		eprintf("Error pthread_create: %d.\n", ret_pth_create);
+	}
+
+	// Sleep for some time, then inform exit.
+	nanosleep(&WAIT_DURATION, NULL);
+	atomic_store(&timeout, true);
+
+	// Join thread
+	pthread_join(thread_handle, NULL);
+
+	// Unmap device
+	munmap(buf, PAGE_SIZE * 2);
+
+	// Close device
+	fclose(fp);
+
+	printf("Finished!\n");
+	exit(EXIT_SUCCESS);
+}
+
+void *pthread_fn(void *mmap_buf) {
+	bool time_to_exit;
+	char readbuf[5];
+
+	for (;;) {
+		time_to_exit = atomic_load(&timeout);
+		if (time_to_exit) break;
+
+		memcpy(readbuf, mmap_buf, 4);
+		printf("Read 0x%x 0x%x 0x%x 0x%x.\n",
+			readbuf[0], readbuf[1], readbuf[2], readbuf[3]);
+	}
+
+	return NULL;
+}