Quoting Alexey Dobriyan (adobriyan@xxxxxxxxx):
> On Thu, Feb 26, 2009 at 06:57:55PM +0300, Alexey Dobriyan wrote:
> > On Thu, Feb 12, 2009 at 03:04:05PM -0800, Dave Hansen wrote:
> > > dave@nimitz:~/kernels/linux-2.6-openvz$ git diff v2.6.27.10... kernel/cpt/ | diffstat
>
> > > 47 files changed, 20702 insertions(+)
> > >
> > > One important thing that leaves out is the interaction that this code
> > > has with the rest of the kernel. That's critically important when
> > > considering long-term maintenance, and I'd be curious how the OpenVZ
> > > folks view it.
> >
> > OpenVZ as-is in some cases wants some functions to be made global
> > (and if C/R code will be modular, exported). Or probably several
> > iterators added.
> >
> > But it's negligible amount of changes compared to main code.
>
> Here is what C/R code wants from pid allocator.
Yup. Agreed. That is exactly what I would have thought it would look
like. We may have found the first bit of helper code we can all agree
on for c/r? :)
Eric may disagree as he wanted to play games with
/proc/sys/kernel/pid_max, but that seems hard to pull off for nested
pid namespaces.
thanks,
-serge
> With the introduction of hierarchical PID namespaces, struct pid can
> have not one but many numbers -- tuple (pid_0, pid_1, ..., pid_N),
> where pid_i is pid number in pid_ns which has level i.
>
> Now root pid_ns of container has level n -- numbers from level n to N
> inclusively should be dumped and restored.
>
> During struct pid creation first n-1 numbers can be anything, because the're
> outside of pid_ns, but the rest should be the same.
>
> Code will be ifdeffed and commented, but anyhow, this is an example of
> change C/R will require from the rest of the kernel.
>
>
>
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
> @@ -182,6 +182,34 @@ static int alloc_pidmap(struct pid_namespace *pid_ns)
> return -1;
> }
>
> +static int set_pidmap(struct pid_namespace *pid_ns, pid_t pid)
> +{
> + int offset;
> + struct pidmap *map;
> +
> + offset = pid & BITS_PER_PAGE_MASK;
> + map = &pid_ns->pidmap[pid/BITS_PER_PAGE];
> + if (unlikely(!map->page)) {
> + void *page = kzalloc(PAGE_SIZE, GFP_KERNEL);
> + /*
> + * Free the page if someone raced with us
> + * installing it:
> + */
> + spin_lock_irq(&pidmap_lock);
> + if (map->page)
> + kfree(page);
> + else
> + map->page = page;
> + spin_unlock_irq(&pidmap_lock);
> + if (unlikely(!map->page))
> + return -ENOMEM;
> + }
> + if (test_and_set_bit(offset, map->page))
> + return -EBUSY;
> + atomic_dec(&map->nr_free);
> + return pid;
> +}
> +
> int next_pidmap(struct pid_namespace *pid_ns, int last)
> {
> int offset;
> @@ -239,7 +267,7 @@ void free_pid(struct pid *pid)
> call_rcu(&pid->rcu, delayed_put_pid);
> }
>
> -struct pid *alloc_pid(struct pid_namespace *ns)
> +struct pid *alloc_pid(struct pid_namespace *ns, int *cr_nr, unsigned int cr_level)
> {
> struct pid *pid;
> enum pid_type type;
> @@ -253,7 +281,10 @@ struct pid *alloc_pid(struct pid_namespace *ns)
>
> tmp = ns;
> for (i = ns->level; i >= 0; i--) {
> - nr = alloc_pidmap(tmp);
> + if (cr_nr && ns->level - i <= cr_level)
> + nr = set_pidmap(tmp, cr_nr[ns->level - i]);
> + else
> + nr = alloc_pidmap(tmp);
> if (nr < 0)
> goto out_free;
>
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