netdev - Re: [PATCH for-6.1 0/3] fail io_uring zc with sockets not supporting it

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Date:   Fri, 21 Oct 2022 12:27:28 +0200
From:   Stefan Metzmacher <metze@...ba.org>
To:     Pavel Begunkov <asml.silence@...il.com>,
        Jens Axboe <axboe@...nel.dk>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "David S . Miller" <davem@...emloft.net>
Cc:     io-uring@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH for-6.1 0/3] fail io_uring zc with sockets not supporting
 it

Hi Pavel,

> Some sockets don't care about msghdr::ubuf_info and would execute the
> request by copying data. Such fallback behaviour was always a pain in
> my experience, so we'd rather want to fail such requests and have a more
> robust api in the future.
> 
> Mark struct socket that support it with a new SOCK_SUPPORT_ZC flag.
> I'm not entirely sure it's the best place for the flag but at least
> we don't have to do a bunch of extra dereferences in the hot path.

I'd give the flag another name that indicates msg_ubuf and
have a 2nd flag that can indicate support for SO_ZEROCOPY in sk_setsockopt()

The SO_ZEROCOPY version is also provided by AF_RDS.

metze