20.08.2012 18:56, J. Bruce Fields пишет:
On Mon, Aug 20, 2012 at 03:05:49PM +0400, Stanislav Kinsbursky wrote:
16.08.2012 23:29, J. Bruce Fields пишет:
Looking back at this:
- adding the sv_lock looks like the right thing to do anyway
independent of containers, because svc_age_temp_xprts may
still be running.
- I'm increasingly unhappy about sharing rpc servers between
network namespaces. Everything would be easier to understand
if they were independent. Can we figure out how to do that?
Could you, please, elaborate on your your unhappiness?
It seems like you're having to do a lot of work on each individual rpc
server (callback server, lockd, etc.) to make per-net startup/shutdown
work. And then we still don't have it quite right (see the shutdown
races).)
In general whenever we have the opportunity to have entirely separate
data structures, I'd expect that to simplify things: it should eliminate
some locking and reference-counting issues.
Agreed. But current solution still looks like the easies way to me to implement
desired functionality.
I.e. I don't like it too. But the problem here, is that rpc server
is tied with kernel threads creation and destruction. And these
threads can be only a part of initial pid namespace (because we have
only one kthreadd). And we decided do not create new kernel thread
per container when were discussing the problem last time.
There really should be some way to create a kernel thread in a specific
namespace, shouldn't there?
Kthreads support in a container is rather a "political" problem, than an
implementation problem.
Currently, when you call kthread_create(), you add new job to kthreadd queue.
Kthreadd is unique, starts right after init and lives in global initial
environment. So, any kthread inherits namespaces from it.
Of course, we can start one kthread per environment and change it's root or even
network namespace in kthread function. But pid namespace of this kthread will
remain global.
It looks like not a big problem, when we shutdown kthread by some variable. But
what about killable nfsd kthreads?
1) We can't kill them from nested pid namespace.
2) How we will differ nfsd kthreads in initial pid namespace?
In OpenVZ we have kthreadd per pid hamespace and it allows us to create kthreads
(and thus services) per pid namespace.
Until we have that, could the threads be taught to fix their namespace
on startup?
Unfortunately, changing of pid namespace for kthreads doesn't look like an easy
trick.
--b.
--
Best regards,
Stanislav Kinsbursky
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