Add an Ioctl() message to the File interface.

mojo/services/files/public/interfaces/file.mojom

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // TODO(vtl): notes to self:
 //  - file offsets, file positions, and file sizes are int64 (though positions
 //    and sizes must always be non-negative)
 //  - buffer size parameters (for read/write) are uint32
 
 module mojo.files;
@@ skipping 62 matching lines @@
 
   // TODO(vtl): What are the rules for reopening (w.r.t. changing mode/flags).
   // E.g., obviously can go from "read-write" to "read", but reverse? (probably
   // not), can remove "append"? (probably not?). Do we allow "truncate"?
   Reopen(File& file, uint32 open_flags) => (Error error);
 
   // TODO(vtl): probably should have access flags (but also exec?); how do these
   // relate to access mode?
   AsBuffer() => (Error error, handle<shared_buffer>? buffer);
 
+  // Special-file-specific control function, for device "files". |in| and |out|
+  // are dependent on |request|.
+  // TODO(vtl): Make a master list of request values somewhere.
+  Ioctl(uint32 request, array<uint32>? in_values)
+      => (Error error, array<uint32>? out_values);
+
   // TODO(vtl): Add a "watch"?
   // TODO(vtl): Add something analogous to fsync(2)?
 };