Re: [RFC][v7][PATCH 0/9] Implement clone2() system call

[Alexey Dobriyan <adobriyan@gmail.com>]

On Thu, Sep 24, 2009 at 01:35:56PM -0500, Serge E. Hallyn wrote:
> Quoting Alexey Dobriyan (adobriyan@gmail.com):
> > I don't like this even more.
> > 
> > Pid namespaces are hierarchical _and_ anonymous, so simply
> > set of numbers doesn't describe the final object.
> > 
> > struct pid isn't special, it's just another invariant if you like
> > as far as C/R is concerned, but system call is made special wrt pids.
> > 
> > What will be in an image? I hope "struct kstate_image_pid" with several
> 
> Sure pid namespaces are anonymous, but we will give each an 'objref'
> valid only for a checkpoint image, and store the relationship between
> pid namespaces based on those objrefs.  Basically the same way that user
> structs and hierarchical user namespaces are handled right now.

OK, that's certainly doable.

You're commiting yourself to creation of tasks in userspace if this goes in. :-\
Which can let you into putting wrong kind of relations into image.
IIRC, clone_flags were in image (still?), but tomorrow kernel will get
new way to acquire, say, uts_ns, which, in theory, can't be described by
a set of consecutive clones, so, you'll have to fixup something in kernel.

> > numbers and with references to such object from other places, so it
> > seems natural to do alloc_pid() with needed numbers and that attach new
> > shiny pid to where needed. But this clone_pid is only for task_struct's pids.