On 5/2/25 1:47 PM, Paolo Abeni wrote:
On 4/29/25 5:26 AM, 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.
The TX path may release the dmabuf in a context where we cannot wait. This happens when the user unbinds a TX dmabuf while there are still references to its netmems in the TX path. In that case, the netmems will be put_netmem'd from a context where we can't unmap the dmabuf, Resolve this by making __net_devmem_dmabuf_binding_free schedule_work'd.
Based on work by Stanislav Fomichev sdf@fomichev.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@fomichev.me Signed-off-by: Kaiyuan Zhang kaiyuanz@google.com Signed-off-by: Mina Almasry almasrymina@google.com Acked-by: Stanislav Fomichev sdf@fomichev.me
I'm sorry for the late feedback. A bunch of things I did not notice before...
The rest LGTM, and my feedback here ranges from nit to corner-cases, so we are probably better off with a follow-up than with a repost, other opinions welcome!
/P