[Buildroot] Linux kernel module is not running anymore when switching from mdev to udev

[Buildroot] Linux kernel module is not running anymore when switching from mdev to udev

[Lucas De Marchi]

Hi Frank,

On Wed, Mar 5, 2014 at 5:49 AM, Frank Ihle <frank.ihle@hs-offenburg.de> wrote:
> Hi everyone,
>
> there is this problem, that I searched the Internet
> for its solution but without success. Here's what it's about, I hope
> someone can give me a hint:
>
>
>
>         I'm using Buildroot 2013.10 to generate my Linux 2.6.39 Images, with the following Kernel  module:
>
>
>
>   void GPIO_LED(void) {
>
>   printk(" GPIO: set PC8: '0');
>
>   at91_set_gpio_value(AT91_PIN_PC8, 1);
>
>
>   }
>
>
>   int init_module(void) {
>
>   GPIO_LED();   return 0;
>
>
>   }
>
>
>   MODULE_LICENSE("GPL");
>
>
>
> When using it with mdev device management. everything works just
> fine. But using it with a udev device management, while executing insmod

I don't see how udev could be related to your problem. Maybe just how
the dependencies were chosen...


>
>
>
>   insmod /usr/modules/measurement_gpio.ko
>
>
>
> the following message appeared:
>
>
>
>   insmod: can't insert '/usr/modules/measurement_gpio.ko': invalid
>   module format
>
>
>
> Every setting stayed the same (especially the kernel version) but the
>  device management changes during this test, so actually the module
> should be fine. Building the kernel to be able for loading modules for
> multiple versions didn't solve it, neither the option "force module
> loading"
>
>
> The way I build my module is:
>
>
> with Buildroot I'm generating an Image, on the way a Linux 2.6.39 is installed.Afterwards I'm compiling the kernel module with the path to the Linux 2.6.39, that Buildroot has downloaded.When the module is created I'm putting it into a fs-overlay directory, so it will be included into the image on next build.I hit another "make" on Buildroot and i got everything together and a bootable image.
>
>
> I change nothing, that's why it confuses me even more
>
>
> How can this be and how to solve it?

I successfully built an image with buildroot using systemd/udev/kmod
some days ago. And inserting modules work fine. If it was a more
recent kernel I'd say it's because you enabled module signature and
your out-of-tree module isn't signed.  But it doesn't look like this.

CC'ing buildroot's ML to see if they have a clue.

>
> Kind Regards,
> Frank
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-- 

Lucas De Marchi

[Buildroot] Linux kernel module is not running anymore when switching from mdev to udev

[Thomas Petazzoni]

Frank,

On Fri, 7 Mar 2014 01:08:36 -0300, Lucas De Marchi wrote:

> > there is this problem, that I searched the Internet
> > for its solution but without success. Here's what it's about, I hope
> > someone can give me a hint:
> >
> >
> >
> >         I'm using Buildroot 2013.10 to generate my Linux 2.6.39 Images, with the following Kernel  module:
> >
> >
> >
> >   void GPIO_LED(void) {
> >
> >   printk(" GPIO: set PC8: '0');
> >
> >   at91_set_gpio_value(AT91_PIN_PC8, 1);
> >
> >
> >   }
> >
> >
> >   int init_module(void) {
> >
> >   GPIO_LED();   return 0;
> >
> >
> >   }
> >
> >
> >   MODULE_LICENSE("GPL");
> >
> >
> >
> > When using it with mdev device management. everything works just
> > fine. But using it with a udev device management, while executing insmod
> 
> I don't see how udev could be related to your problem. Maybe just how
> the dependencies were chosen...

I agree: the kernel module shown by Frank only toggle a GPIO, and does
not expose any device in /dev or anything that would involve udev or
mdev.

> > the following message appeared:
> >
> >   insmod: can't insert '/usr/modules/measurement_gpio.ko': invalid
> >   module format

Are you sure you have built your module correctly, against the right
version of the kernel headers that match the kernel you're running?

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com