Re: [PATCH v7] virtio_net: support split header

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Sep 02, 2022 at 03:36:25PM +0800, Heng Qi wrote:
> We need to clarify that the purpose of header splitting is to make all payloads
> can be independently in a page, which is beneficial for the zerocopy
> implemented by the upper layer.

absolutely, pls add motivation.

> If the driver does not enforce that the buffers submitted to the receiveq MUST
> be composed of at least two descriptors, then header splitting will become meaningless,
> or the VIRTIO_NET_F_SPLIT_TRANSPORT_HEADER feature should not be negotiated at this time.
> 
> 
> Thanks.
> 
> 


This seems very narrow and unecessarily wasteful of descriptors.
What is wrong in this:

<header>...<padding>... <beginning of page><data>

seems to achieve the goal of data in a separate page without
using extra descriptors.

thus my proposal to replace the requirement of a separate
descriptor with an offset of data from beginning of
buffer that driver sets.


-- 
MST