clean up kernel_{read,write} & friends v2

[Al Viro]

On Thu, May 28, 2020 at 12:22:08PM -0700, Joe Perches wrote:

> Hard limits at 80 really don't work well, especially with
> some of the 25+ character length identifiers used today.

IMO any such identifier is a good reason for a warning.

The litmus test is actually very simple: how unpleasant would it be
to mention the identifiers while discussing the code over the phone?