Re: [PATCH v5 4/9] iov_iter: Add a function to extract a page list from an iterator

[Al Viro <viro@zeniv.linux.org.uk>]

On Thu, Jan 12, 2023 at 09:15:50PM +0000, Al Viro wrote:
> On Wed, Jan 11, 2023 at 02:28:05PM +0000, David Howells wrote:
> 
> > +ssize_t iov_iter_extract_pages(struct iov_iter *i,
> > +			       struct page ***pages,
> > +			       size_t maxsize,
> > +			       unsigned int maxpages,
> > +			       unsigned int gup_flags,
> > +			       size_t *offset0,
> > +			       unsigned int *cleanup_mode)
> 
> This cleanup_mode thing is wrong.  It's literally a trivial
> function of ->user_backed and ->data_source - we don't
> even need to look at the ->type.
> 
> Separate it into an inline helper and be done with that;
> don't carry it all over the place.
> 
> It's really "if not user-backed => 0, otherwise it's FOLL_PIN or FOLL_GET,
> depending upon the direction".

Seriously, it would be easier to follow that way; if you really insist upon
keeping these calling conventions, at least put the calculation in one place -
don't make readers to chase down into every sodding helper to check if they
do what you'd expect them to do.