Re: Expectations of an RX mbuf when using virtio PMD

[Oleksandr Nahnybida <oleksandrn@interfacemasters.com>]

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Hello Patrick,

You can use rte_net_get_ptype function directly if packet_type is
RTE_PTYPE_UNKNOWN.
Whether the packet_type value is set is PMD/NIC dependent.
i40e does this at the hardware level, virtio does this in software with
rte_net_get_ptype and only in the specific case.

Best regards,
Oleksandr

On Sun, Dec 8, 2024 at 12:49 AM Patrick Mahan <mahan@mahan.org> wrote:

> Hello All,
>
> Specifics:
>     DPDK Version: dpdk-stable-18.11.11
>     Linux Kernel: 4.19.87
>     Intel 64-bit architecture
>
> I am working on a code to support our socket based processes that need to
> run on
> our DPDK-enabled platform.  I am using the virtio_user exception path
> mechanism
> to support this and initial tests seem fine.
>
> However, I am seeing issues when we receive the packet from the virtio
> port, that
> the packet_type field is not set.
>
> In my code, I have setup my physical PMD (i40e) as etherdev 0 and etherdev
> 1 and
> have setup the virtual side with virtio as  etherdev 2 and etherdev 3.
>
> I am pairing this as etherdev 0 (physical) to etherdev 2 (virtio_user0) and
> etherdev 1 (physical) to etherdev 3 (virtio_user1).
>
> I am using the EAL function `rte_eal_hotplug_add()` as suggested in the
> documentation.
>
> I have added code in my dispatch function to generate a syslog(3) to print
> the
> contents of the packet_type field in the received mbuf.
>
> I then generate traffic to etherdev 1 from connected host and I am seeing
> the
> following:
>
> The inbound packet log shows -
>
> Dec  7 21:24:45 2024 pmahan-dpdk pktdaemon-eal[27614]: CPU 2 TID
> 1140607382984128: [pktdaemon.NOTICE]:
> pkt_dpdk::switch_q_pkts()[2][1=>3][Q=0]:
> mbuf packet type is 0x00000091
>
> So etherdev 1 packet (physical) has packet_type of 0x91 which translates to
>     RTE_PTYPE_L2_ETHER
>     RTE_PTYPE_L3_IPV4_EXT_UNKNOWN
>
> Which has been my experience for receiving packets from the physical PMD.
> However, now that I have added the virtio port, the return packet does not
> seemed
> to have this value set -
>
> Dec  7 21:24:45 2024 pmahan-dpdk pktdaemon-eal[27614]: CPU 2 TID
> 1140607382984128: [pktdaemon.NOTICE]:
> pkt_dpdk::switch_q_pkts()[2][3=>1][Q=0]:
> mbuf packet type is 0x00000000
>
> I have looked into virtio PMD code and see that there is a function to
> fill in
> the packet type called `virtio_rx_offload()` but it is only called if the
> hardware associated with the virtual queue supports offloading and then
> only if
> the `virtio_net_hdr` has no flags or its `gso_type` is not GSO_NONE.
>
> If I ignore the flags and just inject the packets directly, everything
> seems to
> work, but I have internal code that needs to know the basic ethernet type
> as well
> as the L3 options and I was hoping to rely on the packet_type of the mbuf
> instead
> of having to do packet groveling.
>
> Is this an "as designed" or am I missing something in the configuration?
>
> Thanks for any pointers,
>
> Patrick
>

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