HotPlug and Udev Questions

Dan McGhee beesnees at grm.net
Thu Jun 30 18:01:49 PDT 2005


Although most of my questions concern post_LFS issues, I'm posting here 
because the discussion of modules and devices is in LFS-6.0.  If my 
questions are not appropriate for this list, I'll transfer them to BLFS.

My printer, which prints "randomly" and my desire to have my new digital 
camera work with GIMP caused me to start researching hotplug.  (BEGIN 
OFF TOPIC  The ghoto2 Users' Manual has a great discussion of 
permissions and configurations for usb.  END OFF TOPIC)  My research 
ultimately lead to Section 7.4 of the LFS Manual.  In particular, 
Section 7.4.3, "Handling Hotpluggable/Dynamic Devices, p. 244, says:

If the driver of the just plugged in device is available as a module but 
currently unloaded, then attaching the device to the system will only 
cause the kernel's bus driver to generate a hotplug event that notifies 
userspace of the new device connection and it not being attached to a 
driver.  In effect, nothing happens and the device itself is not usable yet.

My first question is this.  If I have udev set up as a result of the 
bootscripts, do I also need to install hotplug to get my printer to 
work--its drivers are completely modular?  Will this also apply to my 
digital camera whose drivers are supplied by gphoto2?  And ultimately 
also apply to my scanner whose drivers are in SANE?  (Yes, Declan, 
there's a pun in there :) )

In looking at the documentation at http://linux-hotplug.sourceforge.net 
and the LFS/BLFS hints for modules and hotplugging, I used some of the 
commands to see if the software was properly installed.  Instead of

</sbin/hotplug>

'cat /proc/sys/kernel/hotplug' gave me

</sbin/udevsend>

If I install the hotplug package from SourceForge, will /proc point to 
the right binary?  What is the purpose of 'udevsend'?  If I'm correct 
about the side-by-side operation of udev and hotplug, is it correct to 
assume that I need do nothing to udev as far as the boot sequence is 
concerned?

Lastly, has anyone identified any "traps" in which this path will 
ensnare me?

Thanks for reading this and thanks for any input.

Dan



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