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* [dpdk-dev] [Bug 729] Bad mbuf chain handling in the memif driver resulting in truncated packets
@ 2021-06-10  9:51 bugzilla
  0 siblings, 0 replies; only message in thread
From: bugzilla @ 2021-06-10  9:51 UTC (permalink / raw)
  To: dev

https://bugs.dpdk.org/show_bug.cgi?id=729

            Bug ID: 729
           Summary: Bad mbuf chain handling in the memif driver resulting
                    in truncated packets
           Product: DPDK
           Version: unspecified
          Hardware: All
                OS: All
            Status: UNCONFIRMED
          Severity: normal
          Priority: Normal
         Component: ethdev
          Assignee: dev@dpdk.org
          Reporter: ivan4th@gmail.com
  Target Milestone: ---

In a couple of places in the memif driver [1][2] rte_pktmbuf_is_contiguous()
[3] is being used to check whether there are more mbufs in the chain when
sending packets. Problem is, rte_pktmbuf_is_contiguous() checks nb_segs in the
mbuf, which, as far as I understand, is only set to the number of segments in
the first mbuf in the chain. This results in truncated packets as usually,
nb_segs is 1 in the mbufs other than the first. Replacing
rte_pktmbuf_is_contiguous(mbuf) == 0 with mbuf->next != NULL fixes the issue.

The problem has been observed while trying to use TRex traffic generator with
VPP [4].

[1]
http://code.dpdk.org/dpdk/v21.05/source/drivers/net/memif/rte_eth_memif.c#L660

[2]
http://code.dpdk.org/dpdk/v21.05/source/drivers/net/memif/rte_eth_memif.c#L717

[3] http://code.dpdk.org/dpdk/v21.05/source/lib/mbuf/rte_mbuf.h#L1687

[4] https://github.com/cisco-system-traffic-generator/trex-core/issues/686

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