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From:   Ryusuke Konishi <konishi.ryusuke@gmail.com>
Date:   Wed, 18 Jan 2023 21:39:08 +0900
Message-ID: <CAKFNMomcjvUSh-nS1MqptYdiT-1frRsmHgx2mHBBm_588kprrQ@mail.gmail.com>
Subject: Re: [PATCH 9/9] mm: return an ERR_PTR from __filemap_get_folio
To:     Christoph Hellwig <hch@lst.de>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Hugh Dickins <hughd@google.com>, linux-afs@lists.infradead.org,
        linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org,
        cluster-devel@redhat.com, linux-mm@kvack.org,
        linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-nilfs@vger.kernel.org
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On Wed, Jan 18, 2023 at 7:41 PM Christoph Hellwig wrote:
>
> Instead of returning NULL for all errors, distinguish between:
>
>  - no entry found and not asked to allocated (-ENOENT)
>  - failed to allocate memory (-ENOMEM)
>  - would block (-EAGAIN)
>
> so that callers don't have to guess the error based on the passed
> in flags.
>
> Also pass through the error through the direct callers:

> filemap_get_folio, filemap_lock_folio filemap_grab_folio
> and filemap_get_incore_folio.

As for the comments describing the return values of these callers,
isn't it necessary to rewrite the value from NULL in case of errors ?

Regards,
Ryusuke Konishi