[Devel] Re: The issues for agreeing on a virtualization/namespaces implementation.

[Kyle Moffett]

On Feb 07, 2006, at 17:06, Eric W. Biederman wrote:
> I think I can boil the discussion down into some of the fundamental  
> questions that we are facing.
>
> Currently everyone seems to agree that we need something like my  
> namespace concept that isolates multiple resources.
>
> We need these for
> UIDS
> FILESYSTEM

I have one suggestion for this (it also covers capabilities to a  
certain extent).  Could we use the kernel credentials system to  
abstract away the concept of a single UID/GID?  We currently have  
uid, euid, gid, egid, groups, fsid.  I'm thinking that there would be  
virtualized UID tables to determine ownership of processes/SHM/etc.

Each process would have a (uid_container,uid) pair (or similar) as  
its "uid" and likewise for gid.  Then the ability to send signals to  
any given (uid_container,uid) or (gid_container,gid) pair would be  
given by keys in the kernel keyring indexed by the "uid_container"  
part and containing the "uid" part (or maybe just a pointer).

Likewise the filesystem access could be virtualized by using uid and  
gid keys in the kernel keyring indexed by vfsmount (Not superblock,  
so that it would be possible to have different UID representations on  
different mounts/parts of the same filesystem).

I'm guessing that the performance implications of the above would not  
be quite so nice, as it would put a lot of code in the fastpath, but  
I would guess that it might be possible to use the existing fields  
for processes without any virtualization needs.

Cheers,
Kyle Moffett

--
There is no way to make Linux robust with unreliable memory  
subsystems, sorry.  It would be like trying to make a human more  
robust with an unreliable O2 supply. Memory just has to work.
   -- Andi Kleen