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

[Jay Lan <jlan@engr.sgi.com>]

Ram wrote:
> 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.

Listners in the kernel? Sound like a PAGG thing again!

Guillaume's stuff was originally an in-kernel module. CSA/Job
are kernel modules also. We all use hook management feature of PAGG,
which offer event notification to other kernel components.

Guillaume moved to connector approach and i am moving to that
direction too because Andrew likes to see in-kernel modules moved
to user space.

It is kind of funny to see someone trying to get a notification
through a connector and then feed it back to the kernel! This
does not sound right to me!

- jay

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

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