According to Virtual I/O Spec:
When using legacy interfaces, transitional drivers which have not negotiated VIRTIO_F_ANY_LAYOUT MUST use a single descriptor for the struct virtio_net_hdr on both transmit and receive, with the network data in the following descriptors.
https://docs.oasis-open.org/virtio/virtio/v1.2/cs01/virtio-v1.2-cs01.html#x1-2280006 (Section 5.1.6.6)
Signed-off-by: Zhe Weng <wengzhe@xiaomi.com>
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