update

Signed-off-by: Wenchao Hao <haowenchao@xiaomi.com>

demo.c

@@ -1,25 +1,51 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <string.h>
+
 
 #define MB_BYTES (1024*1024)
 
-int main(void)
+int main(int argc, char **argv)
 {
 	unsigned long *p;
+	unsigned long *m;
 	int i = 0;
-	int nr_mb;
-	int bytes;
 	int max;
 
-	printf("please specify how many memory to alloc\n");
-	scanf("%d", &nr_mb);
+	const char *file_path = argv[1];
+	int fd = open(file_path, O_RDONLY);
+	if (fd == -1) {
+		perror("open");
+		return 1;
+	}
 
-	bytes = nr_mb * MB_BYTES;
-	max = bytes / 8;
-	p = malloc(bytes);
+	struct stat sb;
+	if (fstat(fd, &sb) == -1) {
+		perror("fstat");
+		close(fd);
+		return 1;
+	}
+
+	size_t file_size = sb.st_size;
+
+	printf("%ld, %d Kb\n", file_size, file_size/1024);
+	void *mapped = mmap(NULL, file_size, PROT_READ, MAP_PRIVATE, fd, 0);
+	if (mapped == MAP_FAILED) {
+		perror("mmap");
+		close(fd);
+		return 1;
+	}
+	m = mapped;
+
+	max = file_size / 8;
+	p = malloc(file_size);
 
 	for (i = 0; i < max; i++)
-		*(p + i) = i;
+		*(p + i) = *(m + i);
 
 	while(1);