From da76459dc21b5af2449af2d36eb95226cb186ce2 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 28 Apr 2024 11:35:11 +0200 Subject: Adding upstream version 2.6.12. Signed-off-by: Daniel Baumann --- dev/plug_qdisc/README | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 59 insertions(+) create mode 100644 dev/plug_qdisc/README (limited to 'dev/plug_qdisc/README') diff --git a/dev/plug_qdisc/README b/dev/plug_qdisc/README new file mode 100644 index 0000000..ccc9bd0 --- /dev/null +++ b/dev/plug_qdisc/README @@ -0,0 +1,59 @@ + ** Plug queueing disciplines ** + + The 'plug' qdisc type is not documented. It is even not supported + by traffic shaping tools like 'tc' from iproute2 package. + + Such qdiscs have already been used by Yelp engineers but outside + of haproxy with libnl-utils tools (especially nl-qdisc-* tools) + to implement a workaround and make haproxy reloads work. + + Indeed with such plug qdiscs coupled with iptables configurations + we are able to temporarily bufferize IP packets and to release them as + needed. So, they may be very useful to "synchronize" TCP sessions + or at higher level to put network applications in states approaching + the ones suspected to occur during bugs. Furthermore to be sure + to produce a correct bug fix, it may be useful to reproduce + as mush as needed such painful bugs. This is where plug qdiscs + may be useful. + + To have an idea about how to use plug qdisc on the command line I highly recommend to + read Willy Tarreau blog here: + + https://www.haproxy.com/blog/truly-seamless-reloads-with-haproxy-no-more-hacks/ + + which refers to this other one from Yelp: + + https://engineeringblog.yelp.com/2015/04/true-zero-downtime-haproxy-reloads.html + + The code found in plug_qdisc.c file already helped in fixing a painful bug hard to + fix because hard to reproduce. To use the API it exports this is quite easy: + + - First your program must call plug_disc_attach() to create if not already created + a plug qdisc and use it (must be done during your application own already existing + initializations). + Note that this function calls plug_qdisc_release_indefinite_buffer() so that to + release already buffered packets before you start your application, + + - then call plug_qdisc_plug_buffer() to start buffering packets incoming to your + plug qdisc. So they won't be delivered to your application, + + - then call plug_qdisc_release_indefinite_buffer() to stop buffering the packets + incoming to your plug qdisc and release those already buffered. + So, that to be deliver them to your application. + + This code is short and simple. But uses several libraries especially libnl-route module + part of libnl library. To compile haproxy and make it use the plug_qdisc.c code we had + to link it against several libnl3 library modules like that: + + -lnl-genl-3 -lnl-route-3 -lnl-3 -lnl-cli-3 + + + - Some references: + Libnl API documentation may be found here: + https://www.infradead.org/~tgr/libnl/doc/api/index.html + + Kernel sources: + http://elixir.free-electrons.com/linux/latest/source/net/sched/sch_plug.c + + Nice website about traffic shaping with queuing disciplines: + http://wiki.linuxwall.info/doku.php/en:ressources:dossiers:networking:traffic_control -- cgit v1.2.3