Re: [patch 1/2] fork_connector: add a fork connector

Ram
2005-03-22T19:18:56Z

On Tue, 2005-03-22 at 11:22, Evgeniy Polyakov wrote:
> On Tue, 22 Mar 2005 10:26:19 -0800
> Ram <linuxram@us.ibm.com> wrote:
>
> > On Mon, 2005-03-21 at 23:07, Guillaume Thouvenin wrote:
> > > On Mon, 2005-03-21 at 12:52 -0800, Ram wrote:
> > > > If a bunch of applications are listening for fork events,
> > > > your patch allows any application to turn off the
> > > > fork event notification? Is this the right behavior?
> > >
> > > Yes it is. The main management is done by application so, if several
> > > applications are listening for fork events you need to choose which one
> > > will turn off the fork connector.
> > >
> > > I want to keep this turn on/off mechanism simple but if it's needed I
> > > can manage the variable "cn_fork_enable" as a counter. Thus the callback
> > > could be something like:
> > >
> > > static void cn_fork_callback(void *data)
> > > {
> > > int start;
> > > struct cn_msg *msg = (struct cn_msg *)data;
> > >
> > > if (cn_already_initialized && (msg->len == sizeof(cn_fork_enable))) {
> > > memcpy(&start, msg->data, sizeof(cn_fork_enable));
> > > if (start)
> > > cn_fork_enable++;
> > > else
> > > cn_fork_enable > 0 ? cn_fork_enable-- : 0;
> > > }
> > > }
> >
> > I think a better way is:
> >
> > Providing a different connector channel called the administrator
> > channel which can be used only by a super-user, and gives you
> > the ability to switch on or off any connector channel including the
> > fork-connector channel.
>
> Only super-user can bind netlink socket to multicast group.

ok. I did not realize that.

>
> > For lack of better term I am using the word 'channel' to mean
> > something that carries events of particular type through the
> > connector-infrastructure.
>
> I still do not see why it is needed.
> Super-user can run ip command and turn network interface off
> not waiting while apache or named exits or unbind.
>
> In theory I can create some kind of userspace registration mechanism,
> when userspace application reports it's pid to the connector,
> and then it sends data to the specified pids, but does not
> allow controlling from userspace.
> But I really do not think it is a good idea to permit
> non-priviledged userspace processes to know about deep
> kernel internals through connector's messages.

Yes. non-priviledged userspace processes should not know
any deep kernel internals through connector events.

I think what I am driving at is, an application that is critically
dependent on the fork-notification, suddenly stops receiving such
notification because some other application has switched off the
service without its notice.

the reason I am concerned is I am planning to feed this fork-events
to my in-kernel module. Side note: I would really like support for
in-kernel listners through connector infrastructure.

RP

>
> > RP
> >
> >
> > >
> > >
> > > What do you think about this implementation?
> > >
> > > Guillaume
> > >
>
>
> Evgeniy Polyakov
>
> Only failure makes us experts. -- Theo de Raadt