linux-kernel - Re: [RFC v2 02/19] skbuff: pass a struct ubuf

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Date:   Tue, 11 Jan 2022 21:51:55 +0800
From:   Hao Xu <haoxu@...ux.alibaba.com>
To:     Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        David Ahern <dsahern@...nel.org>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [RFC v2 02/19] skbuff: pass a struct ubuf_info in msghdr

在 2021/12/21 下午11:35, Pavel Begunkov 写道:
> Instead of the net stack managing ubuf_info, allow to pass it in from
> outside in a struct msghdr (in-kernel structure), so io_uring can make
> use of it.
> 
> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> ---
Hi Pavel,
I've some confusions here since I have a lack of
network knowledge.
The first one is why do we make ubuf_info visible
for io_uring. Why not just follow the old MSG_ZEROCOPY
logic?

The second one, my understanding about the buffer
lifecycle is that the kernel side informs
the userspace by a cqe generated by the ubuf_info
callback that all the buffers attaching to the
same notifier is now free to use when all the data
is sent, then why is the flush in 13/19 needed as
it is at the submission period?

Regards,
Hao