[CRIU] [Q] cgroup roots rewritting

[Tycho Andersen]

On Tue, May 17, 2016 at 12:03:17AM +0300, Cyrill Gorcunov wrote:
> On Mon, May 16, 2016 at 02:57:48PM -0600, Tycho Andersen wrote:
> > > 
> > > And I dont understand why we change @from here. Imagine you have
> > > a several sets of controller all laying in cgroup 300. Then
> > > we need to change it to say 400, and once first match hit
> > > we change source 300 to 400 here and continue trying to
> > > compare with it. Which is wrong I this -- the strstartswith
> > > no longer match old '300' ones for the rest of the set.
> > > What I'm missing here?
> > 
> > I think we have to change the *from there, because if you don't you
> > end up with cg sets that have been rewritten, but CgroupDirEntrys
> > which haven't been.
> 
> Ah, could be indeed.
> 
> > 
> > I agree that the logic to change *from is wrong, though. Probably I
> > never noticed because there aren't usually very many cg sets :). I
> > think it should be that we still rewrite *from, but only at the very
> > end, once we have iterated through all the cg sets. Does that make
> > sense?
> 
> I think so. Anyway, I'm not yet sure I've a clear vision of how
> it should be at the end.
> 
> Yes, I use --cgroup-root optio for restore but I noticed even
> if I disable *from change the criu fails -- prepare_cgroup_sfd
> still uses old 300 prefix instead of new one 400, so restore
> fails because directories are in wrong place.
> 
> Gimme some more time to figure out where is the problem.
> I just wated to notify you as soon as possible that
> cgroup-root seems to be somehow weirdo in behaviour...

Yes :(. The code is a lot weird here. Let me know if you have any
questions or want help.

Tycho

> > 
> > > We hit a problem when been renaming suspended container --
> > > on restore we give it a new name (400) and criu can't
> > > move taks in nonexisting cgroup 300, which container
> > > had befor the renaming (of course in image all controllers
> > > and sets have old 300 in dirs and paths).
> > 
> > I suppose you are using --cgroup-root here?
> > 
> > Tycho
> > 
> > > Could you please elaborate which scenario this commit
> > > addresses? Actually the comment in code didn't help much :)
> > > 
> > > 	Cyrill
> > 
> 
> 	Cyrill