std: Add a few tests for mmap/munmap

lib/std/os/test.zig

@@ -256,3 +256,101 @@ test "memfd_create" {
     expect(bytes_read == 4);
     expect(mem.eql(u8, buf[0..4], "test"));
 }
+
+test "mmap" {
+    if (builtin.os == .windows)
+        return error.SkipZigTest;
+
+    // Simple mmap() call with non page-aligned size
+    {
+        const data = try os.mmap(
+            null,
+            1234,
+            os.PROT_READ | os.PROT_WRITE,
+            os.MAP_ANONYMOUS | os.MAP_PRIVATE,
+            -1,
+            0,
+        );
+        defer os.munmap(data);
+
+        testing.expectEqual(@as(usize, 1234), data.len);
+
+        // By definition the data returned by mmap is zero-filled
+        std.mem.set(u8, data[0 .. data.len - 1], 0x55);
+        testing.expect(mem.indexOfScalar(u8, data, 0).? == 1234 - 1);
+    }
+
+    const test_out_file = "os_tmp_test";
+    // Must be a multiple of 4096 so that the test works with mmap2
+    const alloc_size = 8 * 4096;
+
+    // Create a file used for testing mmap() calls with a file descriptor
+    {
+        const file = try fs.cwd().createFile(test_out_file, .{});
+        defer file.close();
+
+        var out_stream = file.outStream();
+        const stream = &out_stream.stream;
+
+        var i: u32 = 0;
+        while (i < alloc_size / @sizeOf(u32)) : (i += 1) {
+            try stream.writeIntNative(u32, i);
+        }
+    }
+
+    // Map the whole file
+    {
+        const file = try fs.cwd().createFile(test_out_file, .{
+            .read = true,
+            .truncate = false,
+        });
+        defer file.close();
+
+        const data = try os.mmap(
+            null,
+            alloc_size,
+            os.PROT_READ,
+            os.MAP_PRIVATE,
+            file.handle,
+            0,
+        );
+        defer os.munmap(data);
+
+        var mem_stream = io.SliceInStream.init(data);
+        const stream = &mem_stream.stream;
+
+        var i: u32 = 0;
+        while (i < alloc_size / @sizeOf(u32)) : (i += 1) {
+            testing.expectEqual(i, try stream.readIntNative(u32));
+        }
+    }
+
+    // Map the upper half of the file
+    {
+        const file = try fs.cwd().createFile(test_out_file, .{
+            .read = true,
+            .truncate = false,
+        });
+        defer file.close();
+
+        const data = try os.mmap(
+            null,
+            alloc_size,
+            os.PROT_READ,
+            os.MAP_PRIVATE,
+            file.handle,
+            alloc_size / 2,
+        );
+        defer os.munmap(data);
+
+        var mem_stream = io.SliceInStream.init(data);
+        const stream = &mem_stream.stream;
+
+        var i: u32 = alloc_size / 2 / @sizeOf(u32);
+        while (i < alloc_size / @sizeOf(u32)) : (i += 1) {
+            testing.expectEqual(i, try stream.readIntNative(u32));
+        }
+    }
+
+    try fs.cwd().deleteFile(test_out_file);
+}