* Thibault, Daniel ([email protected]) wrote: > I was reading Michael Kerrisk's "Namespaces in operation" > (http://lwn.net/Articles/531114/), which explains most of the > namespace functionalities, and this brings to mind a number of > questions. > > Are trace paths namespace-ready? Per-PID traces are apparently not > much at risk since a process can join a PID namespace only upon its > creation (that is to say, PIDs are immutable). However, collisions > are still possible, such as if two user-space processes start > within the same one-second window in two sibling PID namespaces > such that they have the same virtual PID.
yes, this is a possible race indeed for per-PID tracing in UST, since I think we're using namespaced PIDs to identify programs. > > But what of per-UID traces? What happens to a trace in progress if > one or more processes switch user namespaces? nothing. > Presumably new > sub-directories would be created under "session-name/ust/uid/"? no. > What about the case where two processes run by two different users > (and thus being recorded under different uid subdirectories) switch > to private user namespaces which happen to both map to the same > numerical virtual uid? We need to make sure the second process > switch does not overwrite the trace files of the first (recall that > per-uid trace paths do not include timestamps like per-pid trace > paths do). Disambiguation between different PIDs requires the vpid context if you use per-UID buffers. > > Finally, in the case of a remote trace being received by the relay > daemon, could a network or UTS namespace switch of the traced > processes cause trouble? I suspect not, since the daemons at > either end of the connection are lttng-owned and would presumably > not undergo namespace switches themselves. I don't see it causing an issue. It might be good to try it out though. Thanks, Mathieu > > Daniel U. Thibault > Protection des systèmes et contremesures (PSC) | Systems Protection & > Countermeasures (SPC) > Cyber sécurité pour les missions essentielles (CME) | Mission Critical Cyber > Security (MCCS) > R & D pour la défense Canada - Valcartier (RDDC Valcartier) | Defence R&D > Canada - Valcartier (DRDC Valcartier) > 2459 route de la Bravoure > Québec QC G3J 1X5 > CANADA > Vox : (418) 844-4000 x4245 > Fax : (418) 844-4538 > NAC : 918V QSDJ <http://www.travelgis.com/map.asp?addr=918V%20QSDJ> > Gouvernement du Canada | Government of Canada > <http://www.valcartier.drdc-rddc.gc.ca/> > > _______________________________________________ > lttng-dev mailing list > [email protected] > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com _______________________________________________ lttng-dev mailing list [email protected] http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
