return an ERR_PTR from __filemap_get_folio v2

[Andrew Morton]

On Sat, 21 Jan 2023 07:57:48 +0100 Christoph Hellwig <hch at lst.de> wrote:

> __filemap_get_folio and its wrappers can return NULL for three different
> conditions, which in some cases requires the caller to reverse engineer
> the decision making.  This is fixed by returning an ERR_PTR instead of
> NULL and thus transporting the reason for the failure.  But to make
> that work we first need to ensure that no xa_value special case is
> returned and thus return the FGP_ENTRY flag.  It turns out that flag
> is barely used and can usually be deal with in a better way.
> 
> Note that the shmem patches in here are non-trivial and need some
> careful review and testing.

How are we going with the review and testing.  I assume that
we're now OK on the runtime testing front, but do you feel that
review has been adequate?

Thanks.