On 2/3/25 11:39 PM, 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@xxxxxxxxxxx>. 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@xxxxxxxxxxx>
> Signed-off-by: Kaiyuan Zhang <kaiyuanz@xxxxxxxxxx>
> Signed-off-by: Mina Almasry <almasrymina@xxxxxxxxxx>
Very minor nit: you unexpectedly leaved a lot of empty lines after the SoB.
[...]
@@ -240,13 +249,23 @@ net_devmem_bind_dmabuf(struct net_device *dev,
unsigned int dmabuf_fd,
> * binding can be much more flexible than that. We may be able to
> * allocate MTU sized chunks here. Leave that for future work...
> */
> - binding->chunk_pool =
> - gen_pool_create(PAGE_SHIFT, dev_to_node(&dev->dev));
> + binding->chunk_pool = gen_pool_create(PAGE_SHIFT,
> + dev_to_node(&dev->dev));
> if (!binding->chunk_pool) {
> err = -ENOMEM;
> goto err_unmap;
> }
>
> + if (direction == DMA_TO_DEVICE) {
> + binding->tx_vec = kvmalloc_array(dmabuf->size / PAGE_SIZE,
> + sizeof(struct net_iov *),
> + GFP_KERNEL);
> + if (!binding->tx_vec) {
> + err = -ENOMEM;
> + goto err_free_chunks;
It looks like the later error paths (in the for_each_sgtable_dma_sg()
loop) could happen even for 'direction == DMA_TO_DEVICE', so I guess an
additional error label is needed to clean tx_vec on such paths.
/P
