C/R minisummit notes (namespace naming)

Serge E. Hallyn serue at us.ibm.com
Fri Jul 25 12:34:58 PDT 2008

Quoting Daniel Lezcano (dlezcano at fr.ibm.com):
> Serge E. Hallyn wrote:
>> Quoting Eric W. Biederman (ebiederm at xmission.com):
>>> Currently we have three possibilities on how to name pid namespaces.
>>> - indirect via processes
>>> - pids
>>> - names in the filesystem
>>> We discussed this a bit in the hallway track and pids are look like the way
>>> to go. Pavel has a patch in progress to help sort this out.
>>> The practical problem we have today is that we need a way to wait for the network
>>> namespace in particular and namespaces in general to exit.
>>> At a first glance waitid(P_NS, <pid>,....) looks like a useful way to achieve
>>> this.  After looking at wait a bit more it really is fundamentally just an exit
>>> status reaper of zombies, that has the option of blocking when the zombies
>>> do not yet exist.  In any kind of event loop you would wait for SIGCHLD either
>>> as a signal or with signalfd.
>>> So how shall we wait for a namespace to exit?  My brainstorm tonight suggests
>>> inotify_add_watch(ifd, "/proc/ns/<pid>", IN_DELETE);
>>> Eric
>> I'm sorry, I'm still not quite clear on...
>> Why?
>> You care about when the tasks exit, and you care about when network
>> devices, for instance, need to be deleted (which you can presumably
>> get uevents for, when they get moved back into init_net_ns).
>> Why do you care when the struct net actually gets deleted?
> IMO, if we consider a container being an aggregation of different  
> namespaces, we should consider the container dies when all the  
> namespaces are dead.
> One good example is an application ran inside a container and doing a  
> bulk data writing over the network. When the application finish its last  
>  call to "send" it will exits. At this point, there is no more processes 
> running inside the container but we can not consider the container is 
> dead because there are still some pending datas in the socket to be 
> delivered to the peer.
> Eric will post a patch to automatically destroy the virtual devices when  
> the netns is destroyed, so there is no way to know if a network  
> namespace is dead or not as the uevent socket will not deliver an event  
> outside of the container.

My question remains: who cares?


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