[PATCHv8 2/6] block: use generic u16 for write hints

[Christoph Hellwig]

On Thu, Oct 17, 2024 at 09:09:33AM -0700, Keith Busch wrote:
> From: Keith Busch <kbusch at kernel.org>
> 
> This is still backwards compatible with lifetime hints. It just doesn't
> constrain the hints to that definition.

So in the end we'll end up with two uses of it - the existing 5
temperature hints and the new stream separation.  I think it
would be cleaner to make it a union, but I don't care that
strongly.

But we probably want a way to distinguish which one is supported.

E.g. for SCSI we set a net BLK_FEAT_WRITE_HINTS, for NVMe we'll set
BLK_FEAT_STREAM_SEPARATION.

Either way this should probably be the first patch in the series.