Ozan Türkyılmaz wrote:
26.01.2010 17:42, Greg KH yazmış:
On Sun, Jan 24, 2010 at 10:49:24AM +0530, Joel Fernandes wrote:
Hi Peter,
Thanks for your message.
Actually I'm interested in how modprobe autoloads modules based on the
modalias files in sysfs. I read this in Greg KH's great book - Linux
Kernel
in a Nutshell and I've been wondering how the modules would get
loaded if
they had to be loaded in the first place to have the device->module
list to
exist.
modprobe is "smart" and knows what modules support what devices based on
the cache it creates when you run 'depmod' when a new kernel is
installed.
is it possible to get that information (what module determines what
driver) from modprobe.
(sorry for the problem Greg KH. i hit the wrong button)
Hi,
modinfo should give you all the information you need.
For example:
- modinfo my_module
filename: ./my_module.ko
license: GPL
srcversion: 00C7B5EE66E00EC3C91D3D9
alias: usb:v0EA0p2168d*dc*dsc*dp*ic*isc*ip*
depends: usbcore
vermagic: 2.6.24-19-generic SMP mod_unload 586
alias field indicate alias for this module (based on usb_device_id table
in source file).
When you execute "depmod -a" the following line is added to
/lib/modules/<kernel name>/modules.alias:
alias usb:v0EA0p2168d*dc*dsc*dp*ic*isc*ip* my_module
where:
v idVendor
p idProduct
d bcdDevice
dc bDeviceClass
dsc bDeviceSubClass
dp bDeviceProtocol
ic bInterfaceClass
isc bInterfaceSubClass
ip bInterfaceProtocol
This line says that if I do:
modprobe usb:v0EA0p2168[remaining fields filled with whatever we like]
so in practice I can do:
modprobe usb:v0EA0p2168d0200dc00dsc00dp00ic08isc06ip50
to load my_module.
NOTE: in this example I used USB sub-system but all this applies to
other sub-systems(PCI, PCMCIA, ...),
vendor and product id are fictitious.
All this stuff is here to allow udev do the right thing.
For example you can add the following line to
/etc/udev/rules.d/90-modprobe.rules:
ENV{MODALIAS}=="?*", RUN+="/sbin/modprobe -Q $env{MODALIAS}"
so udev load the right module when you plug in the device.
You can check it by issuing the following command:
udevmonitor -e | grep MODALIAS
then when you plug the device you get:
MODALIAS=usb:v0EA0p2168d0200dc00dsc00dp00ic08isc06ip50
hope this helps
regards
Luca
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