Re: [PATCH net-next v3 2/4] net: tap: track dropped skb via kfree_skb_reason()

On 2/21/22 8:31 PM, Dongli Zhang wrote:

Hi David,

On 2/21/22 7:24 PM, David Ahern wrote:

quoted

On 2/20/22 10:34 PM, Dongli Zhang wrote:

quoted

The TAP can be used as vhost-net backend. E.g., the tap_handle_frame() is
the interface to forward the skb from TAP to vhost-net/virtio-net.

However, there are many "goto drop" in the TAP driver. Therefore, the
kfree_skb_reason() is involved at each "goto drop" to help userspace
ftrace/ebpf to track the reason for the loss of packets.

The below reasons are introduced:

- SKB_DROP_REASON_SKB_CSUM
- SKB_DROP_REASON_SKB_COPY_DATA
- SKB_DROP_REASON_SKB_GSO_SEG
- SKB_DROP_REASON_DEV_HDR
- SKB_DROP_REASON_FULL_RING

Cc: Joao Martins <redacted>
Cc: Joe Jin <redacted>
Signed-off-by: Dongli Zhang <redacted>
---
Changed since v1:
  - revise the reason name
Changed since v2:
  - declare drop_reason as type "enum skb_drop_reason"
  - handle the drop in skb_list_walk_safe() case

 drivers/net/tap.c          | 35 +++++++++++++++++++++++++----------
 include/linux/skbuff.h     |  9 +++++++++
 include/trace/events/skb.h |  5 +++++
 3 files changed, 39 insertions(+), 10 deletions(-)

couple of places where the new reason should be in reverse xmas order;
logic wise:

Reviewed-by: David Ahern <dsahern@kernel.org>

I will re-order the reasons in the same patch and re-send with your Reviewed-by
in the next version.

I have sent out v4 and I finally decide to not re-order reasons for this patch
as this may makes trouble for backport.

I will not follow the reverse xmas order here, as all existing variables are not
declared in reverse xmas order.

Thank you very much!

Dongli Zhang