In section 08, how to configure kernel after making changes?

amoghmc

In section 8: writing your first patch,
I made the change to the uvc_driver.c by adding the following line

pr_info("I changed uvcvideo driver in the Linux Kernel\n");

Now how do I configure the module CONFIG_USB_VIDEO_CLASS=y?
I manually changed the line in .config from 'm' to 'y' and recompiled the kernel using:
make -j3 all

But I don't see the change in dmesg and now I am stuck in this part.

exlud

Sorry I didn't know other alternative, but really not suggest to edit .config file directly, as the file itself said, "Automatically generated file; DO NOT EDIT."

You can search by / in the menu, for example, /USB_VIDEO_CLASS says the dependency tree
--Device Drivers
--MEDIA_SUPPORT
--MEDIA_USB_SUPPORT
--USB_VIDEO_CLASS
So in this case, single change of USB_VIDEO_CLASS expect to work. But in general case, change(especially add) a single entry in .config file may leave it's dependency wild.

By the way, y (built-in to kernel image) and m (build as a module) controls how to build the module into the new image. But sudo modprobe uvcvideo searches modules in the current operating system, I guess that's why it works after reboot.
Have you tried to insmod after make (set it as m), hope it can save you from an extra reboot.

amoghmc

Edit: After make -j3 I followed the rest of the instructions:

sudo make modules_install install
sudo modprobe uvcvideo
dmesg | less | grep "changed"

And I dint see any result!

amoghmc

Update: It seems to work ONLY IF I reboot my system but the course material says I don't need to reboot. Please tell me where I went wrong with my commands? This is the list of commands I executed:

1. vim .config # to change CONFIG_USB_VIDEO_CLASS from 'm' to 'y'
2. make -j6
3. sudo make modules_install install
4. sudo modprobe uvcvideo
5. dmesg | less | grep "changed" # didn't work
6. sudo reboot
7. dmesg | less | grep "changed" # works now!

Where did I go wrong?

exlud

@amoghmc said:
In section 8: writing your first patch,
I made the change to the uvc_driver.c by adding the following line

pr_info("I changed uvcvideo driver in the Linux Kernel\n");

Now how do I configure the module CONFIG_USB_VIDEO_CLASS=y?

I would try make menuconfig

I manually changed the line in .config from 'm' to 'y' and recompiled the kernel using:

Suggest not to do that way,
reason 1: change .config file directly may leave some dependencies untouched.
reason 2: change from m to y has nothing to do with this issue.

make -j3 all

after this, you will have a ko file named like uvc.ko, insmod that ko

But I don't see the change in dmesg and now I am stuck in this part.

amoghmc

@exlud
Is there an alternate way to configure modules? make menuconfig overwhelms with me with too many options, which is why I manually edited .config. Considering I only wanted to make a single change.

viveky120

Hi amoghmc,
Changing .config file manually is not a good idea. You may miss dependencies (if any).

pitaking

Hey, I just encountered the same thing.

All you have to do it update grub and boot into the "dirty" version.

I realized that after running ll /boot and noticing that the most up to date image has no longer the original name.

Simply put: you have to boot into the most up to date version of your Kernel: