contrib: add mmap_test

Relates-to: #318

contrib/mmap_test/.gitignore

@@ -0,0 +1,2 @@
+/mmap_test
+/test.bin

contrib/mmap_test/Makefile

@@ -0,0 +1,6 @@
+mmap_test: Makefile *.c
+	gcc -Wall -Wextra -g -o mmap_test mmap_test.c
+
+.PHONY: format
+format:
+	clang-format --style=file -i *.c

contrib/mmap_test/mmap_test.c

@@ -0,0 +1,50 @@
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+/*
+HOW TO USE THIS:
+truncate -s 10G test.bin && ./mmap_test
+*/
+
+int main()
+{
+    int fd;
+    char* addr;
+    struct stat sb;
+
+    fd = open("test.bin", O_RDWR);
+    if (fd == -1) {
+        perror("open test.bin");
+        exit(1);
+    }
+
+    if (fstat(fd, &sb) == -1) {
+        perror("fstat");
+        exit(2);
+    }
+
+    addr = mmap(NULL, sb.st_size, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, 0);
+    if (addr == MAP_FAILED) {
+        perror("mmap");
+        exit(3);
+    }
+
+    printf("pid %d, mmap ok (%ld MiB)\n", getpid(), sb.st_size/1024/1024);
+
+    for(long i = 0; i < sb.st_size; i += 1024) {
+        volatile char x = addr[i];
+        x++;
+    }
+
+    printf("sleeping 1h\n");
+    sleep(3600);
+
+    munmap(addr, sb.st_size);
+    close(fd);
+
+    exit(0);
+}