On Mon, Aug 12, 2024 at 8:15 PM Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
> BTW, Mina, the core should probably also check that XDP isn't installed
> before / while the netmem is bound to a queue.
Sorry if noob question, but what is the proper check for this? I tried
adding this to net_devmem_bind_dmabuf_to_queue():
if (xdp_rxq_info_is_reg(&rxq->xdp_rxq))
return -EEXIST;
But quickly found out that in netif_alloc_rx_queues() we initialize
all the rxq->xdp_rxq to state REGISTERED regardless whether xdp is
installed or not, so this check actually fails.
Worthy of note is that GVE holds an instance of xdp_rxq_info in
gve_rx_ring, and seems to use that for its xdp information, not the
one that hangs off of netdev_rx_queue in core.
Additionally, my understanding of XDP is limited, but why do we want
to disable it? My understanding is that XDP is a kernel bypass that
hands the data directly to userspace. In theory at least there should
be no issue binding dmabuf to a queue, then getting the data in the
queue via an XDP program instead of via TCP sockets or io uring. Is
there some fundamental reason why dmabuf and XDP are incompatible?
--
Thanks,
Mina
