What is the expected use case for Direct I/O using fscrypt? This isn't a problem which is unique to fscrypt, but one of the really unfortunate aspects of the DIO interface is the silent fallback to buffered I/O. We've lived with this because DIO goes back decades, and the original use case was to keep enterprise databases happy, and the rules around what is necessary for DIO to work was relatively well understood. But with fscrypt, there's going to be some additional requirements (e.g., using inline crypto) required or else DIO silently fall back to buffered I/O for encrypted files. Depending on the intended use case of DIO with fscrypt, this caveat might or might not be unfortunately surprising for applications. I wonder if we should have some kind of interface so we can more explicitly allow applications to query exactly what the requirements might be for a particular file vis-a-vis Direct I/O. What are the memory alignment requirements, what are the file offset alignment requirements, what are the write size requirements, for a particular file. - Ted
