Re: Legacy Linux kernel support

[Mario Rugiero via tcpdump-workers <tcpdump-workers () lists tcpdump org>]

> --- Begin Message ---
>
>
> From: Mario Rugiero <mrugiero () gmail com>
>
> Date: Wed, 1 Apr 2020 20:14:57 -0300
>
> OK, follow up.
> I haven't yet been able to test it, which is why I've been delaying
> writing about this,
> but these two commits[0][1], which according to these threads[2][3]
> are the ones fixing
> the timeout issue, have been applied to CentOS 7 default kernel,
> 3.10.0-1062.el7.
> It can also be seen by comparing vanilla 3.10[4] with the CentOS
> sources[5], diffing
> the files located at net/packet/af_packet.c.
> This *should* mean it works without the workaround. I'd like to try
> it, but I'm currently
> fighting with VirtualBox guest additions and in a metered connection
> (I have no home
> connection and my country is in quarantine), so I'm being rather
> careful on my data
> usage.
>
> Now, if this is deemed insufficient, I have a test in mind that I may
> as well have
> early feedback on, with the following setup:
> - libpcap with the workaround removed;
> - vanilla and CentOS' kernels alternated;
> - a 2MiB packet ring;
> - a 64kiB block size and snaplen;
> - timeout of 8ms;
> - injection to a virtual interface at 1 packet every 20ms;
> - a simple application that reads and do nothing on its peer.
>
> I think that should give as a buffer small enough and a frequency low enough to
> fill the buffer and result in observable packet loss.
>
> Does it make sense? Any suggestions or criticisms to the setup? Is it necessary?
>
> [0]: https://github.com/torvalds/linux/commit/da413eec729dae5dcb150e2eb34c5e7e5e4e1b49
> [1]: https://github.com/torvalds/linux/commit/41a50d621a321b4c15273cc1b5ed41437f4acdfb
> [2]: https://www.mail-archive.com/netdev () vger kernel org/msg163532.html
> [3]: https://www.mail-archive.com/search?l=netdev () vger kernel 
> org&q=subject:%22TPACKET_V3+timeout+bug%5C%3F%22&o=newest&f=1
> [4]: https://cdn.kernel.org/pub/linux/kernel/v3.x/linux-3.10.tar.xz
> [5]: http://vault.centos.org/7.7.1908/os/Source/SPackages/kernel-3.10.0-1062.el7.src.rpm
>
> --- End Message ---
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