Re: [patch 1/4] Network namespaces: cleanup of dev_base list use

Andrey Savochkin
2006-06-26T15:42:08Z

Hi Eric,

On Mon, Jun 26, 2006 at 09:13:52AM -0600, Eric W. Biederman wrote:
> Andrey Savochkin <saw@swsoft.com> writes:
>
> > Cleanup of dev_base list use, with the aim to make device list per-namespace.
> > In almost every occasion, use of dev_base variable and dev->next pointer
> > could be easily replaced by for_each_netdev loop.
> > A few most complicated places were converted to using
> > first_netdev()/next_netdev().
>
> As a proof of concept patch this is ok.
>
> As a real world patch this is much too big, which prevents review.
> Plus it takes a few actions that are more than replace just
> iterators through the device list.

dev_base list is historically not the cleanest part of Linux networking.
I've still spotted a place where the first device in dev_base list is assumed
to be loopback. In early days we had more, now only one place or two...

>
> In addition I suspect several if not all of these iterators
> can be replaced with the an appropriate helper function.
>
> The normal structure for a patch like this would be to
> introduce the new helper function. for_each_netdev.
> And then to replace all of the users while cc'ing the
> maintainers of those drivers. With each different
> driver being a different patch.
>
> There is another topic for discussion in this patch as well.
> How much of the context should be implicit and how much
> should be explicit.
>
> If the changes from netchannels had already been implemented, and all of
> the network processing was happening in a process context then I would
> trivially agree that implicit would be the way to go.

Why would we want all network processing happen in a process context?

>
> However short of always having code always execute in the proper
> context I'm not comfortable with implicit parameters to functions.
> Not that this the contents of this patch should address this but the
> later patches should.

We just have too many layers in networking code, and FIB/routing
illustrates it well.

>
> When I went through this, my patchset just added an explicit
> continue if the devices was not in the appropriate namespace.
> I actually prefer the multiple list implementation but at
> the same time I think it is harder to get a clean implementation
> out of it.

Certainly, dev_base list reorganization is not the crucial point in network
namespaces. But it has to be done some way or other.
If people vote for a single list with skipping devices from a wrong
namespace, it's fine with me, I can re-make this patch.

I personally prefer per-namespace device list since we have too many places
in the kernel where this list is walked in a linear fashion,
and with many namespaces this list may become quite long.

Regards

Andrey