Re: about split the udev

[Greg KH <greg@kroah.com>]

On Tue, Jan 13, 2004 at 07:05:26PM +0000, Tristan Wibberley wrote:
> Greg KH wrote:
> 
> | I am talking about udev splitting into 2 pieces:
> | 	udev - called the same way udev is called today.
> | 	       creates a tiny message queue message based on the hotplug
> | 	       event and then exits.  This can probably be done in under
> | 	       6Kb of binary code.
> | 	udevd - receives the udev message queue messages.  Orders them
> | 		in the proper order (based on the SEQ_NUM from the
> | 		hotplug event), and then acts on them.  Size should be
> | 		about what we have today for the udev binary 50Kb or so.
> |
> | We need to do this in order to properly handle out of order hotplug
> | events.
> 
> Will that solve the problem? If udevd keeps up with the messages, and
> the udev that supplies the second message pre-empts the one that
> provides the first, will udevd process the second message because it
> doesn't know that there is an earlier one about to come in?
> 
> If udevd waits for contiguous SEQ_NUMs to ensure this doesn't happen,
> then a dead/locked-up udev will freeze everything (udevd won't know
> which of the events it has should wait until after the unknown one). I
> think a different solution is required.

No, udev will have to peek at future messages to see if we got them out
of order, and re-order them.  And a time-out will have to be in place in
case we somehow lose one entirely.

thanks,

greg k-h


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