joyent/node — comment on commit 99757cbeb22d34c8365637988e16db07fc380ec8
File:  line 0
By bnoordhuis:

Right, @piscisaureus told me more or less the same.

> Are there any Unices that require r+ for futimes?

No. Opening the file in read-only mode is enough to update file attributes. Regular uid/gid access control still applies, of course.