Hello, Eric.
On 03/31/2010 06:39 PM, Eric W. Biederman wrote:
> Let me try a happy median between overwhelming and too little
> information by giving you some experts, and a bit of overview.
>
> (Ugh after have writing this I certainly will agree that we
> have some many layers in the device model that they become
> obfuscating abstractions).
Yeah, exactly, and this patchset is pushing it further with no
documentation and indirections to high heavens. As someone who
doesn't have much experience with namespaces, I can't make much sense
of this patchset and it obfuscates the whole kobject thing more and
that's a bad direction to be heading toward.
> Looking through my code there are 3 types of callbacks.
> - Callbacks to the namespace type of a children.
> .child_ns_type
Can you please also explain the relationships among kobjects, ns_types
and NSes?
> - Callbacks to find the namespace of a kobject.
> .namespace
> - Callbacks on the a namespace type to find the namespace
> of a particular context.
> .current_ns
> .initial_ns (not used in my patchset)
> .netlink_ns (not used in my patchset)
>
> In a world of weird explicitness I expect .child_ns_type and
> .namespace could be made to go away by pushing through explicit
> ns_type, and namespace parameters everywhere. But that seems
> like an awful lot of unnecessary code churn and bloat with
> the only real advantage being that we have an abstraction
> stored explicit at each layer.
* How much churn would it be? I would be willing to trade quite a bit
if the following can go away. The sheer amount of indirection there
scares me a lot.
struct kobj_type {
...
const struct kobj_ns_type_operations *(*child_ns_type)(struct kobject *kobj);
...
};
* Is it necessary to teach kobject layer the concept of namespaces?
Wouldn't it be possible to let kobject and sysfs deal with tags and
make namespaces use them?
> static int kobj_bcast_filter(struct sock *dest_sk, struct sk_buff *skb, void *data)
> {
> struct kobject *kobj = data;
> const struct kobj_ns_type_operations *ops;
>
> ops = kobj_ns_ops(kobj);
> if (ops) {
> const void *sock_ns, *ns;
> ns = kobj->ktype->namespace(kobj);
> sock_ns = ops->netlink_ns(dsk);
> return sock_ns != ns;
> }
>
> return 0;
> }
>
> initial_ns is used to figure out what the initial/default
> namespace is for a class of namespaces. We only report
> with /sbin/hotplug events in the initial network namespace.
> At least for now.
>
> static int kobj_usermode_filter(struct kobject *kobj)
> {
> const struct kobj_ns_type_operations *ops;
>
> ops = kobj_ns_ops(kobj);
> if (ops) {
> const void *init_ns, *ns;
> ns = kobj->ktype->namespace(kobj);
> init_ns = ops->initial_ns();
> return ns != init_ns;
> }
>
> return 0;
> }
I can understand you would need two different ways of establishing the
accessor depending on the mode of access (file IO or netlink) but can
initial_ns ever be dynamic? Can't it just be void *inital_ns instead
of a callback?
Thanks.
--
tejun
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