Re: event sequencing

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

On Fri, 2005-02-25 at 11:18 -0500, Jon Smirl wrote:
>I working on adding hotplug monitor change detection code to some
>framebuffer drivers. I having trouble with event sequencing.

Oh, back to the original question and sorry for all that noise. :)

>In my probe function I do a class_simple_device_add() to create the
>class entry. Later in the probe function I do
>kobject_hotplug(&info->class_device->kobj, KOBJ_MOUNT); to indicate a
>monitor change.
>
>I'm receiving the MOUNT event before the ADD one. How can I control the order?
>
>Even in cases where MOUNT comes after ADD udev has not built my device
>nodes yet. My MOUNT app needs to use the device node. This is my
>bigger problem.

The event for the fb device needs to create a device node and therefore
takes longer than the mount event which seems to happen at the same
time. That's the reason for the unpredictable order, which can happen
anytime with "normal" hotplug.

But all events sent through the kobject_hotplug have kernel created
sequence numbers and udevd reorders the events to be executed in the
right order.
All events belonging to a device will be executed one after the other if
udevd recognizes a dependency, which is: the same devpath, a parent
device or a physical device behind it.

To solve all known kind of timing problems, we changed udev to be able
to take over the whole hotplug event and give the "normal" hotplug
scripts the same sane timing we need to have for udev to work properly.

udev versions later than 047 recognize if /proc/sys/kernel/hotplug is set
to /sbin/udevsend and then handle the hotplug scripts too.

> I'm using RH FC3 but this needs to work on all distributions when finished.

Fedora-Devel has already switched to "managed hotplug events" and the whole
system depends on udevd to handle hotplug.d/. Your should not see this
problem there.

Kay



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