linux-kernel - Re: [PATCH net-next v5 3/9] net: devmem: Implement TX path

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Message-ID: <Z7yumPB749GdF26X@mini-arch>
Date: Mon, 24 Feb 2025 09:38:32 -0800
From: Stanislav Fomichev <stfomichev@...il.com>
To: Mina Almasry <almasrymina@...gle.com>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, virtualization@...ts.linux.dev,
	kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
	Donald Hunter <donald.hunter@...il.com>,
	Jakub Kicinski <kuba@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>, Jonathan Corbet <corbet@....net>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	Jeroen de Borst <jeroendb@...gle.com>,
	Harshitha Ramamurthy <hramamurthy@...gle.com>,
	Kuniyuki Iwashima <kuniyu@...zon.com>,
	Willem de Bruijn <willemb@...gle.com>,
	David Ahern <dsahern@...nel.org>,
	Neal Cardwell <ncardwell@...gle.com>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	Stefano Garzarella <sgarzare@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Shuah Khan <shuah@...nel.org>, sdf@...ichev.me,
	asml.silence@...il.com, dw@...idwei.uk,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Victor Nogueira <victor@...atatu.com>,
	Pedro Tammela <pctammela@...atatu.com>,
	Samiullah Khawaja <skhawaja@...gle.com>,
	Kaiyuan Zhang <kaiyuanz@...gle.com>
Subject: Re: [PATCH net-next v5 3/9] net: devmem: Implement TX path

On 02/22, Mina Almasry wrote:
> Augment dmabuf binding to be able to handle TX. Additional to all the RX
> binding, we also create tx_vec needed for the TX path.
> 
> Provide API for sendmsg to be able to send dmabufs bound to this device:
> 
> - Provide a new dmabuf_tx_cmsg which includes the dmabuf to send from.
> - MSG_ZEROCOPY with SCM_DEVMEM_DMABUF cmsg indicates send from dma-buf.
> 
> Devmem is uncopyable, so piggyback off the existing MSG_ZEROCOPY
> implementation, while disabling instances where MSG_ZEROCOPY falls back
> to copying.
> 
> We additionally pipe the binding down to the new
> zerocopy_fill_skb_from_devmem which fills a TX skb with net_iov netmems
> instead of the traditional page netmems.
> 
> We also special case skb_frag_dma_map to return the dma-address of these
> dmabuf net_iovs instead of attempting to map pages.
> 
> Based on work by Stanislav Fomichev <sdf@...ichev.me>. A lot of the meat
> of the implementation came from devmem TCP RFC v1[1], which included the
> TX path, but Stan did all the rebasing on top of netmem/net_iov.
> 
> Cc: Stanislav Fomichev <sdf@...ichev.me>
> Signed-off-by: Kaiyuan Zhang <kaiyuanz@...gle.com>
> Signed-off-by: Mina Almasry <almasrymina@...gle.com>

Acked-by: Stanislav Fomichev <sdf@...ichev.me>

(assuming Eric/Willem will also take a look at this)