Re: [PATCH v5 03/12] Turn fault_in_pages_{readable,writeable} into fault_in_{readable,writeable}

[Andreas Gruenbacher]

On Tue, Aug 3, 2021 at 10:57 PM Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> On Tue, Aug 03, 2021 at 09:18:09PM +0200, Andreas Gruenbacher wrote:
> > Turn fault_in_pages_{readable,writeable} into versions that return the number
> > of bytes faulted in instead of returning a non-zero value when any of the
> > requested pages couldn't be faulted in.  This supports the existing users that
> > require all pages to be faulted in, but also new users that are happy if any
> > pages can be faulted in.
> >
> > Neither of these functions is entirely trivial and it doesn't seem useful to
> > inline them, so move them to mm/gup.c.
> >
> > Rename the functions to fault_in_{readable,writeable} to make sure that code
> > that uses them can be fixed instead of breaking silently.
>
> Sigh...  We'd already discussed that; it's bloody pointless.  Making short
> fault-in return success - absolutely.  Reporting exact number of bytes is
> not going to be of any use to callers.

I'm not actually convinced that you're right about this. Let's see
what we'll end up with; we can always strip things down in the end.

Thanks,
Andreas