linux-kernel - Re: [RFC PATCH v3 02/12] net: page_pool: create hooks for custom page providers

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Message-ID: <20231113171058.68973860@kernel.org>
Date:   Mon, 13 Nov 2023 17:10:58 -0500
From:   Jakub Kicinski <kuba@...nel.org>
To:     Mina Almasry <almasrymina@...gle.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        David Ahern <dsahern@...nel.org>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Jeroen de Borst <jeroendb@...gle.com>,
        Praveen Kaligineedi <pkaligineedi@...gle.com>
Subject: Re: [RFC PATCH v3 02/12] net: page_pool: create hooks for custom
 page providers

On Sun, 12 Nov 2023 19:28:52 -0800 Mina Almasry wrote:
> My issue with this is that if the driver doesn't support dmabuf then
> the driver will accidentally use the pp backed by the dmabuf, allocate
> a page from it, then call page_address() on it or something, and
> crash.
> 
> Currently I avoid that by having the driver be responsible for picking
> up the dmabuf from the netdev_rx_queue and giving it to the page pool.
> What would be the appropriate way to check for driver support in the
> netlink API? Perhaps adding something to ndo_features_check?

We need some form of capabilities. I was expecting to add that as part
of the queue API. Either a new field in struct net_device or in ndos.
I tend to put static driver caps of this nature into ops.
See for instance .supported_ring_params in ethtool ops.