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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 -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 -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