Re: [patch] kernel events layer

[Robert Love <rml@ximian.com>]

On Sat, 2004-07-24 at 10:54 -0700, Deepak Saxena wrote:

> Oh ok, that makes much more sense now. "arch/kerne/cpu" is the
> name of the file, from which that message came.

Yah.  It is pretty simple and it gives us a unique name without imposing
any naming policy.

I have, however, been thinking about using kobject paths. ;-)  I
actually like the idea now, but I do not think we can get a kobject for
most of the stuff we need, unfortunately.  Also, we need the kobject
name to be unique.  This is an interesting concept to keep in mind,
though.

> I think we agree.  So are there some existing docs that you/Ximian has 
> on reccomended usage and object naming? I didn't see anything on 
> freedesktop.org.  That's where a lot of my questions are coming from. We 
> have this really simple events system, but how do we expect it to be used
> in the kernel.

No, we don't have any usage recommendations.  Going forward, this is
something we all need to work on and agree with.

All I want is a way to get events to user-space asynchronously without
any hacks.  This fits the bill nicely.  ;-)

That said, I do have some basic ideas about usage.  I see two main uses,
asynchronous events (such as, filesystem mounted) and the more specific
case of errors (such as device failure).

Criteria for adding the event would be that user-space needs to know
about it, and would normally have to poll to get the information.  If
the event is so non-important that right now no one even knows about it
or cares about it, it may not be worth adding.

But let's look at filesystem mounted, since many user-space applications
are interested in this.  Right now, they poll /proc/mtab every few
seconds, parse it, and look for changes.  Gross, right?

So we can create an event in fs/mount.c, say "/org/kernel/fs/mount" with
the signal "change".  The payload could be a simple "mounted" and
"unmounted" or the exact details on what was mounted or unmounted or
even nothing.  I'd prefer to give no information and just have the event
cause a re-read of /proc/mtab.  But whatever.

So we want up with, in do_mount,

	send_kevent (KEVENT_FS, "/org/kernel/fs/mount",
		     "change", "mounted");

Or similar.

	Robert Love