Expectations of an RX mbuf when using virtio PMD

[Patrick Mahan]

On 12/7/24 3:58 PM, Oleksandr Nahnybida wrote:
> 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.
> 

Thanks for the suggestion, I guess I was spoiled by the PMD setting it for me 
that I expected it was a basic function of the PMD.

Thanks,

Patrick

> Best regards,
> Oleksandr
> 
> On Sun, Dec 8, 2024 at 12:49 AM Patrick Mahan <mahan at mahan.org 
> <mailto:mahan at 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
>