Re: [RFC][PATCH] VPIDs: Virtualization of PIDs (OpenVZ approach)

[Kirill Korotaev <dev@openvz.org>]

> well, IMHO this approach lacks a few things which would
> be very useful in a mainline pid virtualization, which
> pretty much explains why it is relatively small
> 
>  - hierarchical structure (it's flat, only one level)
PID virtualization has nothing to do with containers and its structure. 
This VPID patch can be used both in environments with hierarchical and 
flat structure.
I mean that this VPID patch introduces some kind of abstraction, which 
means that global unique pid is not always what user sees. Thats it.
And kernel should not be modified in all places where access checks 
current->pid == allowed_pid are done. Global unique PIDs are preserved.

>  - a proper administration scheme
Can't catch what you mean. What kind of administration do you want for 
VPIDs? Do you have one for usual PIDs? It is assigned by kernel and 
that's it.

>  - a 'view' into the child pid spaces
it has. see proc patch.

>  - handling of inter context signalling
How is it related to inter context signalling???
virtualization of signaling is a separate task and has nothing to do 
with pids.

> and, more important, it does not deal with the existing
> issues and error cases, where references to pids, tasks,
> task groups and sessions aren't handled properly ...
1. if kernel has some errors, these errors should be fixed. 
Virtualization doesn't deal with it, doesn't solve such issues, doesn't 
make it worse. So what do you mean?
2. if kernel has some issues and error cases can you point them to me? I 
will be glad to fix it. Without pointing to the facts your words sound 
like a pure speculation. What issues? What error cases? Where task 
groups and sessiona aren't handled properly?

> I think that in real world virtualization scenarios
> with hundreds of namespaces those 'imprecisions' will 
> occasionally lead to very strange and random behaviour
> which in many cases will go completely unnoticed.
OpenVZ successfully works with >1000 VPSs on a single server.
What scenarios do you mean?
I see no arguments from your side except for some guesses.

> so I really prefer to cleanup the existing pid handling
> first, to avoid big surprises later ...
I'm not against pid handling cleanups, am I?
This can be done in parallel/before/after.

Kirill