Re: udevstart v udevtrigger

[Rich Turner <rich@storix.com>]

what would be the effects of running udevtrigger on a system running a kernel 
prior to 2.6.15?

will it fail and return a non-zero return code? will it lock up the kernel?

if running udevtrigger on a pre-2.6.15 kernel causes bad things then i will 
need to do some kernel level checking before running it.

On Thursday 13 July 2006 16:59, Kay Sievers wrote:
> On Thu, 2006-07-13 at 15:06 -0700, Rich Turner wrote:
> > we use udev when we perform a bare-metal restore of a system from a
> > backup (if the system that we created boot media from has it available).
> > we use udev to create device nodes in our boot media environment only.
> > once the system is rebuilt then the system's original udev support is
> > used.
> >
> > our only support requirement is that the system is running kernel 2.4 or
> > later. granted udev requires 2.6 so those systems are the only ones we
> > are discussing.
> >
> > in short:
> > we create the system installation boot media and include the following
> > udev-related files on the media:
> > udev
> > udevstart
> > udevd (only if udev is not available and there is udevstart)
> > /etc/udev/*
> >
> > we use udev by running udevstart if we have udev command. or we start
> > udevd if we do not have the udev command and then run udevstart. this is
> > creating all necessary device nodes.
> >
> > i have not tested this yet, but my thoughts are to add udevtrigger to the
> > boot media. then if there is not a udevstart command create a link
> > udevstart->udevtrigger. that way i will not have to make changes
> > everywhere else in the software where i do run udevstart.
> >
> > i guess the question is can i treat udevstart and udevtrigger as the same
> > command?
> >
> > will udevtrigger provide me with the same results as udevstart?
>
> Udevstart, just creates devices nodes and runs completely serialized, it
> will return when all currently known kernel devices are found and all
> device nodes are created. It will not cause a coldplug run or trigger
> kernel module loads for events that got lost during boot.
>
> Udevtrigger, just asks the kernel to emit all events for all devices
> again. Everything runs in parallel, also events to load kerenl modules
> are generated. Everything, including device node creation, runs
> asynchronously. If needed, you have to wait until the kernel has sent
> all events and udev is finished handling the events. That's what
> udevsettle is used for.
>
> Udevstart will hang, if one rule execution blocks, udevtrigger will not
> block the whole process.
>
> Udevtrigger replaced the coldplug logic from the old hotplug package,
> udevstart can't do any coldplug. Udevtrigger needs at least kernel
> 2.6.15.
>
> Udevstart and the udev binary are no longer installed by default on
> recent systems.
>
> Kay

-- 
Rich Turner
Storix, Inc.
619-543-0200 x113


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