5.12.3. Creating the Patch

Two methods exist by which you can create the patch: devtool and Quilt. For kernel patches, the Git workflow is more appropriate. This section assumes the Git workflow and shows the steps specific to this example.

  1. Change the working directory: Change to where the kernel source code is before making your edits to the calibrate.c file:

         $ cd ~/poky/build/tmp/work/qemux86-poky-linux/linux-yocto-${PV}-${PR}/linux
                            

    Because you are working in an established Git repository, you must be in this directory in order to commit your changes and create the patch file.

    Note

    The PV and PR variables represent the version and revision for the linux-yocto recipe. The PV variable includes the Git meta and machine hashes, which make the directory name longer than you might expect.
  2. Edit the source file: Edit the init/calibrate.c file to have the following changes:

         void calibrate_delay(void)
         {
             unsigned long lpj;
             static bool printed;
             int this_cpu = smp_processor_id();
    
             printk("*************************************\n");
             printk("*                                   *\n");
             printk("*        HELLO YOCTO KERNEL         *\n");
             printk("*                                   *\n");
             printk("*************************************\n");
    
         	if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
                   .
                   .
                   .
                            
  3. Stage and commit your changes: These Git commands display the modified file, stage it, and then commit the file:

         $ git status
         $ git add init/calibrate.c
         $ git commit -m "calibrate: Add printk example"
                            
  4. Generate the patch file: This Git command creates the a patch file named 0001-calibrate-Add-printk-example.patch in the current directory.

         $ git format-patch -1