add 01-02

src/01-02-mmap-file.md

@@ -1 +1,35 @@
 # Mmap file
+
+Creates a memory map of a file using mmap and simulates some non-sequential reads from the file. Using a memory map means you just index into a slice rather than dealing with seek to navigate a File.
+
+```zig
+    const file = try fs.cwd().createFile(filename, .{
+        .read = true,
+        .truncate = true,
+        .exclusive = false, // Set to true will ensure this file is created by us
+    });
+    defer file.close();
+
+    // Before mmap, we need to ensure file isn't empty
+    try file.setEndPos(file_size);
+
+    const md = try file.metadata();
+    print("File size: {d}\n", .{md.size()});
+
+    var ptr = try std.os.mmap(
+        null,
+        20,
+        std.os.PROT.READ | std.os.PROT.WRITE,
+        std.os.MAP.PRIVATE,
+        file.handle,
+        0,
+    );
+    defer std.os.munmap(ptr);
+
+    // Write file via mmap
+    std.mem.copyForwards(u8, ptr, "hello zig cookbook");
+
+    // Read file via mmap
+    print("File body: {s}", .{ptr});
+
+```