Re: udevstart v udevtrigger

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

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



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