RE: [RFC PATCH v7 01/19] Add a new structure for skb buffer from external.

Dong, Eddie
2010-06-23T08:09:40Z

> 3) As I have mentioned above, with this idea, netdev_alloc_skb() will
> allocate
> as usual, the data pointed by skb->data will be copied into the first
> guest buffer.
> That means we should reserve sufficient room in guest buffer. For PS
> mode
> supported driver (for example ixgbe), the room will be more than 128.
> After 128bytes,
> we will put the first frag data. Look into virtio-net.c the function
> page_to_skb()
> and receive_mergeable(), that means we should modify guest virtio-net
> driver to
> compute the offset as the parameter for skb_set_frag().
>
> How do you think about this? Attached is a patch to how to modify the
> guest driver.
> I reserve 512 bytes as an example, and transfer the header len of the
> skb in hdr->hdr_len.
>
Xiaohui & Herbert:
Mixing copy of head & 0-copy of bulk data imposes additional challange to find the guest buffer. The backend driver may be unable to find a spare guest buffer from virtqueue at that time which may block the receiving process then.
Can't we completely eliminate netdev_alloc_skb here? Assigning guest buffer at this time makes life much easier.
Thx, Eddie