linux-kernel - Re: [PATCH 1/6] relay: allow the use of const callback structs

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Date:   Thu, 19 Nov 2020 08:11:20 +0000
From:   Christoph Hellwig <hch@...radead.org>
To:     Jani Nikula <jani.nikula@...el.com>
Cc:     linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
        linux-block@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        ath11k@...ts.infradead.org, ath10k@...ts.infradead.org,
        Kalle Valo <kvalo@...eaurora.org>,
        linux-wireless@...r.kernel.org,
        QCA ath9k Development <ath9k-devel@....qualcomm.com>
Subject: Re: [PATCH 1/6] relay: allow the use of const callback structs

> +/*
> + * rchan_callback wrappers. Call the callbacks if available, otherwise fall back
> + * to default behaviour.
> + */

This adds an overly long line.  That being said this behavior is pretty
normal for kernel APIs, so I'm not even sure we need it at all.

> +
> +/*
> + * subbuf_start() callback.
> + */

and this one is for sure completley useless.  Same for all the other
similar ones.

But taking one step back:  All instances implement create_buf_file
and remove_buf_file, which makes sense as that is the prime aim
of these methods.  So there is no point in making those optional.
subbuf_start_callback is overriden by two instances, so making that
optional totally makes sense.  buf_mapped and buf_unmapped are
never overriden, so they should be removed entirely.

More importantly there is no case that passes a NULL rchan_callbacks,
which makes complete sense as it wouldn't even create a file.  So
remove that case as well and just replace it with a sanity check in
relay_open().

Please also add a patch to mark all rchan_callbacks instances const
while you're at it.