[Devel] [RFC] Containers infrastructure problems

[Pavel Emelianov]

Hi.

I'm trying to implement RSS accounting via containers and
I have some difficulties and proposals.

1. Fork

container_fork() is placed before new task obtains its
new mm_struct, files_struct, signal_struct etc. Isn't it
better to move container fork at the place where newly
created task it fully initialized to give controller
possibility to work with new mm, signals etc?

2. Early container usage

Consider the following code:

  struct my_container *cnt;

  cnt = my_cnt_from_cont(task_container(current, &my_subsys));

the problem is that when it is used before I register my
rss subsystem in initcall task_container returns me
dummytop container which is not my_container actually :(

I've workarounded this issue with

static int rss_create(struct container_subsys *ss,
                   struct container *cont)
{
       struct rss_container *rss;

       rss = kzalloc(sizeof(struct rss_container), GFP_KERNEL);
       if (rss == NULL)
               return -ENOMEM;

       ...
       cont->subsys[rss_subsys.subsys_id] = &rss->css;
       return 0;
}

static struct rss_container init_rss_container;

static __init int rss_create_early(struct container_subsys *ss,
                struct container *cont)
{
       struct rss_container *rss;

       rss = &init_rss_container;
       ...
       cont->subsys[rss_subsys.subsys_id] = &rss->css;
       ss->create = rss_create;
       return 0;
}

static struct container_subsys rss_subsys = {
        .name = "rss",
        .create = rss_create_early,
};

void __init container_rss_init_early(void)
{
        container_register_subsys(&rss_subsys);
}

and call container_rss_init_early() from container_init_early()
but this is probably not what we want.

I believe that we need some early container initialization
implemented in a generic way. What do you think?

Thanks,
Pavel.