netdev - Re: [PATCH net-next 00/10] drop_monitor: Capture dropped packets and metadata

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Date:   Thu, 8 Aug 2019 15:08:25 -0600
From:   David Ahern <dsahern@...il.com>
To:     Ido Schimmel <idosch@...sch.org>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, nhorman@...driver.com, jiri@...lanox.com,
        toke@...hat.com, roopa@...ulusnetworks.com,
        nikolay@...ulusnetworks.com, jakub.kicinski@...ronome.com,
        andy@...yhouse.net, f.fainelli@...il.com, andrew@...n.ch,
        vivien.didelot@...il.com, mlxsw@...lanox.com,
        Ido Schimmel <idosch@...lanox.com>
Subject: Re: [PATCH net-next 00/10] drop_monitor: Capture dropped packets and
 metadata

On 8/7/19 4:30 AM, Ido Schimmel wrote:
> Example usage with patched dropwatch [1] can be found here [2]. Example
> dissection of drop monitor netlink events with patched wireshark [3] can
> be found here [4]. I will submit both changes upstream after the kernel
> changes are accepted. Another change worth making is adding a dropmon
> pseudo interface to libpcap, similar to the nflog interface [5]. This
> will allow users to specifically listen on dropmon traffic instead of
> capturing all netlink packets via the nlmon netdev.

Nice work, Ido.

On top of your dropwatch changes I added the ability to print the
payload as hex. e.g.,

Issue Ctrl-C to stop monitoring
drop at: nf_hook_slow+0x59/0x98 (0xffffffff814ec532)
input port ifindex: 1
timestamp: Thu Aug  8 15:04:02 2019 360015026 nsec
length: 64
00 00 00 00 00 00 00 00  00 00 00 00 08 00 45 00      ........ ......E.
00 3c e7 50 40 00 40 06  55 69 7f 00 00 01 7f 00      .<.P@.@. Ui......
00 01 80 2c 30 39 74 b9  c7 4d 00 00 00 00 a0 02      ...,09t. .M......
ff d7 fe 30 00 00 02 04  ff d7 04 02 08 0a 53 79       ...0.... ......Sy
original length: 74


Seems like the skb protocol is also needed to properly parse the payload
- ie., to know it is an ethernet header, followed by ip and tcp.