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    Subject[PATCH net-next v4 0/4] tun/tap: use kfree_skb_reason() to trace dropped skb
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    The commit c504e5c2f964 ("net: skb: introduce kfree_skb_reason()") has
    introduced the kfree_skb_reason() to help track the reason.

    The tun and tap are commonly used as virtio-net/vhost-net backend. This is to
    use kfree_skb_reason() to trace the dropped skb for those two drivers.

    Changed since v1:
    - I have renamed many of the reasons since v1. I make them as generic as
    possible so that they can be re-used by core networking and drivers.

    Changed since v2:
    - declare drop_reason as type "enum skb_drop_reason"
    - handle the drop in skb_list_walk_safe() case for tap driver, and
    kfree_skb_list_reason() is introduced

    Changed since v3 (only for PATCH 4/4):
    - rename to TAP_FILTER and TAP_TXFILTER
    - honor reverse xmas tree style declaration for 'drop_reason' in
    tun_net_xmit()


    The following reasons are introduced.

    - SKB_DROP_REASON_SKB_CSUM

    This is used whenever there is checksum error with sk_buff.

    - SKB_DROP_REASON_SKB_COPY_DATA

    The kernel may (zero) copy the data to or from sk_buff, e.g.,
    zerocopy_sg_from_iter(), skb_copy_datagram_from_iter() and
    skb_orphan_frags_rx(). This reason is for the copy related error.

    - SKB_DROP_REASON_SKB_GSO_SEG

    Any error reported when GSO processing the sk_buff. It is frequent to process
    sk_buff gso data and we introduce a new reason to handle that.

    - SKB_DROP_REASON_SKB_PULL
    - SKB_DROP_REASON_SKB_TRIM

    It is frequent to pull to sk_buff data or trim the sk_buff data.

    - SKB_DROP_REASON_DEV_HDR

    Any driver may report error if there is any error in the metadata on the DMA
    ring buffer.

    - SKB_DROP_REASON_DEV_READY

    The device is not ready/online or initialized to receive data.

    - SKB_DROP_REASON_FULL_RING

    Suggested by Eric Dumazet.

    - SKB_DROP_REASON_TAP_FILTER

    Suggested by Menglong Dong. For sk_buff dropped by (ebpf) filter directly
    attached to tun/tap, e.g., via TUNSETFILTEREBPF.

    - SKB_DROP_REASON_TAP_TXFILTER

    Suggested by Menglong Dong. For sk_buff dropped by tx filter implemented at
    tun/tap, e.g., check_filter()


    This is the output for TUN device.

    # cat /sys/kernel/debug/tracing/trace_pipe
    <idle>-0 [014] b.s3. 893.074829: kfree_skb: skbaddr=0000000013eea285 protocol=4 location=00000000036fe12c reason: FULL_RING
    vhost-4456-4469 [024] b..1. 893.230235: kfree_skb: skbaddr=0000000011eab049 protocol=2054 location=00000000036fe12c reason: FULL_RING
    arping-6811 [002] b..1. 893.235606: kfree_skb: skbaddr=000000000121f124 protocol=2054 location=00000000036fe12c reason: FULL_RING
    arping-6811 [002] b..1. 894.235682: kfree_skb: skbaddr=000000000121f124 protocol=2054 location=00000000036fe12c reason: FULL_RING
    vhost-4456-4469 [024] b..1. 894.291240: kfree_skb: skbaddr=00000000d093f0cd protocol=2054 location=00000000036fe12c reason: FULL_RING


    This is the output for TAP device.

    # cat /sys/kernel/debug/tracing/trace_pipe
    <idle>-0 [004] ..s1. 1584.564287: kfree_skb: skbaddr=00000000e0987862 protocol=0 location=00000000177d2c83 reason: NOT_SPECIFIED
    arping-9338 [018] ..s1. 1584.642082: kfree_skb: skbaddr=00000000856cd27d protocol=2054 location=00000000615812ac reason: FULL_RING
    arping-9338 [018] ..s1. 1585.642190: kfree_skb: skbaddr=00000000856cd27d protocol=2054 location=00000000615812ac reason: FULL_RING
    arping-9338 [018] ..s1. 1586.642271: kfree_skb: skbaddr=00000000856cd27d protocol=2054 location=00000000615812ac reason: FULL_RING
    arping-9338 [018] ..s1. 1587.642368: kfree_skb: skbaddr=00000000856cd27d protocol=2054 location=00000000615812ac reason: FULL_RING


    drivers/net/tap.c | 35 +++++++++++++++++++++++++----------
    drivers/net/tun.c | 38 ++++++++++++++++++++++++++++++--------
    include/linux/skbuff.h | 21 +++++++++++++++++++++
    include/trace/events/skb.h | 10 ++++++++++
    net/core/skbuff.c | 11 +++++++++--
    5 files changed, 95 insertions(+), 20 deletions(-)


    Thank you very much!

    Dongli Zhang


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