linux-ext4 - Re: return an ERR_PTR from __filemap_get

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Date:   Tue, 28 Mar 2023 16:04:33 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Hugh Dickins <hughd@...gle.com>, linux-afs@...ts.infradead.org,
        linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org,
        cluster-devel@...hat.com, linux-mm@...ck.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-nilfs@...r.kernel.org
Subject: Re: return an ERR_PTR from __filemap_get_folio v2

On Sat, 21 Jan 2023 07:57:48 +0100 Christoph Hellwig <hch@....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.