Re: [PATCH 2/2] iov_iter: optimise iter type checking

[Christoph Hellwig]

On Thu, Nov 19, 2020 at 03:29:43PM +0000, Pavel Begunkov wrote:
> The problem here is that iov_iter_is_*() helpers check types for
> equality, but all iterate_* helpers do bitwise ands. This confuses
> a compiler, so even if some cases were handled separately with
> iov_iter_is_*(), it can't eliminate and skip unreachable branches in
> following iterate*().

I think we need to kill the iov_iter_is_* helpers, renumber to not do
the pointless bitmask and just check for equality (might turn into a
bunch of nice switch statements actually).