Udev and initscripts

Udev and initscripts

[Alexander E. Patrakov]

It has been stated many times that scripts that should run after device 
is available should live in /etc/dev.d directory. However, I have 
trouble following this. The recommendation works perfectly when one has 
to wait for creation of a single device, but it is difficult or 
impossible to implement when waiting for many unknown devices.

The problem is that Linux From Scratch needs an initscript with the 
following properties:

1) it should read a file "/etc/sysconfig/modules" (aka "/etc/modules" in 
Debian). All modules listed there by the user should be modprobed into 
the kernel.

2) The next initscript should be able to assume that all devices it 
needs are already there.

How do I implement (2), i.e., wait for creation of all devices that can 
be created by a user-specified list of modules?

Just doing nothing does not work, as illustrated by the following example:

[root in ~]# modprobe nbd ; ( ls /dev/nbd* | wc -l ) ; sleep 1 ; \
( ls /dev/nbd* | wc -l )
     113
     128

-- 
Alexander E. Patrakov


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Re: Udev and initscripts

[Kevin P. Fleming]

Alexander E. Patrakov wrote:

> The problem is that Linux From Scratch needs an initscript with the 
> following properties:
> 
> 1) it should read a file "/etc/sysconfig/modules" (aka "/etc/modules" in 
> Debian). All modules listed there by the user should be modprobed into 
> the kernel.
> 
> 2) The next initscript should be able to assume that all devices it 
> needs are already there.

I believe this is the real source of the problem; if you are going to 
support hotplug, then you really have to support it properly. That means 
that instead of having an initscript wait for devices to appear, the 
actions that initscript would do upon the device appearance should be 
done by a hotplug script.

If the initscript really does need to wait until the devices appear, 
then you'll need to have a hotplug script that is invoked when the 
device(s) are created that creates some type of "flag" file that the 
initscript can wait for. However, this approach is fraught with 
problems, like the fact that the initscript will wait forever if the 
device just happens to not be attached to the system during this boot, 
or the device is not responding, etc.


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