workflows: bootlinux: add clean builds configuration option

Add CONFIG_BOOTLINUX_CLEAN_BEFORE_BUILD option to enable clean builds
for both fragment and monolithic configurations via configurable
mrproper execution.

Changes:
- Add CONFIG_BOOTLINUX_CLEAN_BEFORE_BUILD Kconfig option (default: n)
- Add global mrproper task in config.yml for non-9P builds
- Add mrproper task in 9P build workflow for localhost builds
- Conditional execution based on bootlinux_clean_before_build variable

This provides deterministic builds when needed while preserving
incremental build performance by default. The mrproper task runs
before configuration to ensure pristine source state.

Features:
- Works with both monolithic and fragment configurations
- Separate handling for 9P vs target builds
- Clear documentation of trade-offs (clean vs incremental builds)
- Maintains existing workflow compatibility

Generated-by: Claude AI
Signed-off-by: Daniel Gomez <[email protected]>

Author: dkruces

playbooks/roles/bootlinux/tasks/build/9p.yml

@@ -109,6 +109,15 @@
       $ {{ ansible_callback_diy.result.output.cmd | join(' ') }}
       {{ ansible_callback_diy.result.output.stdout | default('') }}
 
+- name: Clean kernel source before configuration (make mrproper) on the control node
+  community.general.make:
+    chdir: "{{ bootlinux_9p_host_path }}"
+    target: "mrproper"
+  when: bootlinux_clean_before_build|default(false)|bool
+  run_once: true
+  delegate_to: localhost
+  tags: ["build-linux"]
+
 - name: Copy configuration for Linux {{ target_linux_tree }} on the control node
   ansible.builtin.template:
     src: "{{ linux_config }}"

playbooks/roles/bootlinux/tasks/config.yml

@@ -31,6 +31,14 @@
   when:
     - linux_next_configs.matched > 0
 
+- name: Clean kernel source before configuration (make mrproper) for non-9P builds
+  community.general.make:
+    chdir: "{{ target_linux_dir_path }}"
+    target: "mrproper"
+  when:
+    - bootlinux_clean_before_build|default(false)|bool
+    - not bootlinux_9p|bool
+
 - name: Set the .config file for building the test kernel
   ansible.builtin.set_fact:
     linux_config: "{{ item | basename }}"

workflows/linux/Kconfig

@@ -188,6 +188,28 @@ config BOOTLINUX_REPRODUCIBLE_BUILDS
 	  Recommended for CI/CD environments and when build reproducibility
 	  is required. Compatible with both GCC and Clang toolchains.
 
+config BOOTLINUX_CLEAN_BEFORE_BUILD
+	bool "Clean kernel source before building (make mrproper)"
+	output yaml
+	default n
+	help
+	  If enabled, run 'make mrproper' before kernel configuration and
+	  building. This ensures a completely clean build from pristine
+	  source code by removing all configuration files, build artifacts,
+	  and generated files.
+
+	  Enable this for:
+	  - Deterministic, reproducible builds
+	  - Debugging configuration issues
+	  - Ensuring no stale artifacts interfere
+
+	  Disable this for:
+	  - Faster incremental builds during development
+	  - Preserving existing .config when not using fragments
+
+	  Note: This adds significant build time as all objects must be
+	  rebuilt from scratch.
+
 menu "ccache configuration"
 
 config BOOTLINUX_CCACHE