Re: split kobject creation and hotplug event generation

[Kay Sievers <kay.sievers@vrfy.org>]

On Mon, Feb 28, 2005 at 11:46:42AM -0800, Greg KH wrote:
> On Sat, Feb 26, 2005 at 06:53:16AM +0100, Kay Sievers wrote:
> > This splits the implicit generation of a hotplug events from
> > kobject_add() and kobject_del(), to give the user of of these
> > functions control over the time the event is created.
> > 
> > The kobject_register() and unregister functions still have the same
> > behavior and emit the events by themselves.
> > 
> > The class, block and device core is changed now to emit the hotplug
> > event _after_ the "dev" file, the "device" symlink and the default
> > attributes are created. This will save udev from spinning in a stat() loop
> > to wait for the files to appear, which is expensive if we have a lot of
> > concurrent events.
> 
> So, does this solve the issue that everyone has been complaining about
> for years with the hotplug event happening before the sysfs files are
> present?

I expect most of them, yes. It is not a guarantee, cause drivers can and will
create attributes at any time. :) But the most interesting default ones, that
people tend to expect at event time will be there _before_ the event happens.

To get this for the whole system and not only the class+block core, a few remainig
places that use kobject_register() need to be changed to use kobject_add(), but
that is a trivial change and nice too, cause it cleans up some error pathes, where
a device needs to be unregistered in the same function and it emits two completely
useless events for that.

> And if we add this, can we pretty much get rid of all of the
> wait_for_sysfs like logic in udev?

Yes, that was the motivation to do this. With all the hotplug env vars
we have now, we can throw out all the compiled-in lists and if some crazy
devices still need to wait, we can add something to udev's rule logic, that a
configured rule will wait for that file to show up.

Thanks,
Kay