On 10/13/2015 5:35 PM, Hiren Panchasara wrote: > Author: hiren > Date: Wed Oct 14 00:35:37 2015 > New Revision: 289276 > URL: https://svnweb.freebsd.org/changeset/base/289276 > > Log: > There are times when it would be really nice to have a record of the last > few > packets and/or state transitions from each TCP socket. That would help with > narrowing down certain problems we see in the field that are hard to > reproduce > without understanding the history of how we got into a certain state. This > change provides just that. > > It saves copies of the last N packets in a list in the tcpcb. When the > tcpcb is > destroyed, the list is freed. I thought this was likely to be more > performance-friendly than saving copies of the tcpcb. Plus, with the > packets, > you should be able to reverse-engineer what happened to the tcpcb. > > To enable the feature, you will need to compile a kernel with the TCPPCAP > option. Even then, the feature defaults to being deactivated. You can > activate > it by setting a positive value for the number of captured packets. You can > do > that on either a global basis or on a per-socket basis (via a setsockopt > call). > > There is no way to get the packets out of the kernel other than using kmem > or > getting a coredump. I thought that would help some of the legal/privacy > concerns > regarding such a feature. However, it should be possible to add a future > effort > to export them in PCAP format. > > I tested this at low scale, and found that there were no mbuf leaks and the > peak > mbuf usage appeared to be unchanged with and without the feature. > > The main performance concern I can envision is the number of mbufs that > would be > used on systems with a large number of sockets. If you save five packets per > direction per socket and have 3,000 sockets, that will consume at least > 30,000 > mbufs just to keep these packets. I tried to reduce the concerns associated > with > this by limiting the number of clusters (not mbufs) that could be used for > this > feature. Again, in my testing, that appears to work correctly. > > Differential Revision: D3100
You're supposed to use the full URL here which will auto close the review. I also replied to the review with style findings just now. > Submitted by: Jonathan Looney <jlooney at juniper dot net> > Reviewed by: gnn, hiren -- Regards, Bryan Drewery
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