[Devel] Re: semantics for namespace naming

[Sukadev Bhattiprolu]

Serge E. Hallyn [serue at us.ibm.com] wrote:
| Let's say we have a vserver, from which we start some jobs
| which we want to checkpoint/restart/migrate.  These are two
| of the usages we currently foresee for the namespaces, though
| I'd say it's safe to assume there will be more.
| 
| I'll want to be able to address the c/r jobs by some ID in
| order to checkpoint and kill them.  I'll also want to be
| able to address the entire vserver by some ID, in order to
| kill it.  In that case the c/r jobs should also be killed.
| So those jobs are known by at least two id's.

For your calculate_pi example below, are the two ids "calculate_pi"
and "/sergevserver/calculate_pi" (ie. are the two plus ids basically 
like relative and absolute pathnames or are they independent ?

And unrelated to the namespace naming - by "job" do you mean a single
process or can a job include multiple processes ? If it can include
multiple, can we checkpoint/restart/migrate just the job ? I am
thinking that we would need to migrate the entire vserver to
preserve process relationships - no ? 

| Furthermore, I may want two vservers on the same machine, both
| running a c/r job called 'calculate_pi'.
| 
| So we can look at this as a filesystem.  In the above scenario,
| we've got /sergesvserver, /sergesvserver/calculate_pi,
| /randomvserver, and /randomvserver/calculate_pi.  And, if
| user hallyn logs into /sergesvserver using pam_namespace.so,
| unsharing his mounts namespace to get a private /tmp and /home,
| then he ends up in /sergesvserver/unnamed1.  So each nsproxy
| has a node in the namespace id filesystem, with random names
| unless/until it is renamed to a more meaningful name.  This
| allows us to switch to a vserver by specifying the vserver's
| name (ln /sys/namespaces/vserver1 /proc/nsproxy or whatever
| semantics we end up using), kill an entire vserver recursively
| (rm -rf /sys/namespaces/vserver1), perhaps even checkpoint
| (tar jcf /tarballs/vserver1 /sys/namespaces/vserver1) and
| certainly rename (mv /sys/namespaces/unnamed1 /sys/namespaces/sergeprivhome).
| 
| One key observeration which I haven't made explicit is that you
| never actually leave a nsid ("container").  If you start under
| /vserver1, you will always be under /vserver1.  I don't know of
| any reason that would not be appropriate.  If I start a nested
| vserver from there, then to me it may be known as
| 'vserver_testme', while to the admin of the machine, it would be
| known as /vserver1/vserver_testme.
| 
| This makes one possible implementation of the container struct:
| 
| 	struct container {
| 		struct container *parent;
| 		char *name;
| 		struct nsproxy *nsproxy;
| 		struct list_head children;
| 	};
| 	struct nsproxy {
| 		...
| 		struct container *container;
| 	};
| 
| Plus of course relevant sysfs stuff.
| 
| -serge
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