udev & modalias files

Greg KH greg at kroah.com
Fri Jun 3 14:48:51 EDT 2016

On Fri, Jun 03, 2016 at 10:02:02PM +0530, Muni Sekhar wrote:
> Hi,
> I see lot of modalias files under /sys directory.
> For e.g:
> # cat /sys/devices/pci0000:00/0000:00:1c.0/0000:02:00.0/modalias
> pci:v00001556d00005555sv00004000sd00000000bc08sc05i01
> I would like to know which part of the kernel module creates sysfs
> modalias file?

The kernel bus code for the device that the bus is on creates this.  For
this example, the PCI bus code does this work.

> How does udev load modules dynamically when a new device is added?

The book, "Linux Device Drivers, version 3", free online, has a whole
section on this, I suggest reading it.

> Where should I look for default udev rules?

In the udev or systemd package on your machine.  Specific ways to do
this depends on your distro.

greg k-h

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