Add support for developer config snippets

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

Makefile

@@ -9,8 +9,10 @@ O    ?= output
 # otherwise treat it as relative to ./buildroot.
 override O := $(if $(filter /%,$O),$O,$(CURDIR)/$O)
 
-config := $(O)/.config
+config      := $(O)/.config
-bmake   = $(MAKE) -C buildroot O=$(O) $1
+bmake        = $(MAKE) -C buildroot O=$(O) $1
+SNIPPETS_DIR := $(CURDIR)/configs/snippets
+MERGE_CONFIG := $(CURDIR)/buildroot/support/kconfig/merge_config.sh
 
 
 all: $(config) buildroot/Makefile
@@ -26,6 +28,23 @@ $(config):
 	@echo "'make <board>_defconfig' before building an image."
 	@exit 1
 
+apply-%: $(SNIPPETS_DIR)/%.conf | $(config)
+	@KCONFIG_CONFIG=$(config) $(MERGE_CONFIG) -m $(config) $<
+	@+$(call bmake,olddefconfig)
+	@echo "Applied snippet: $<"
+
+list-snippets:
+	@echo "Available snippets (use 'make apply-<name>'):"
+	@ls $(SNIPPETS_DIR)/*.conf 2>/dev/null | sed 's|.*/||; s|\.conf$$||; s|^|  |'
+
+dev: | $(config)
+	@for s in $(SNIPPETS_DIR)/*.conf; do \
+		KCONFIG_CONFIG=$(config) $(MERGE_CONFIG) -m $(config) $$s; \
+		echo "Applied snippet: $$s"; \
+	done
+	@+$(call bmake,olddefconfig)
+	@+$(call bmake,all)
+
 %: | buildroot/Makefile
 	@+$(call bmake,$@)
 
@@ -44,4 +63,4 @@ test:
 buildroot/Makefile:
 	@git submodule update --init
 
-.PHONY: all check coverity dep test cyclonedx
+.PHONY: all check coverity dep test cyclonedx list-snippets dev

configs/snippets/dev.conf

@@ -0,0 +1 @@
+BR2_TARGET_ENABLE_ROOT_LOGIN=y

configs/snippets/ext4.conf

@@ -0,0 +1,3 @@
+BR2_TARGET_ROOTFS_EXT2=y
+BR2_TARGET_ROOTFS_EXT2_4=y
+BR2_TARGET_ROOTFS_EXT2_SIZE="512M"

doc/developers-guide.md

@@ -7,12 +7,12 @@ account, which is created based on credentials found in the VPD area --
 for Qemu devices this is emulated using `qemu_fw_cfg`.
 
 For developers this can be quite frustrating to be blocked from logging
-in to debug the system.  So we recommend enabling the `root` account in
+in to debug the system.  The quickest way to enable root login is to
-the Buildroot `make menuconfig` system.
+apply the `dev` configuration snippet:
 
-    make menuconfig
+    make apply-dev
-         -> System configuration
+
-            -> [*]Enable root login with password
+See [Configuration Snippets](#configuration-snippets) for more details.
 
 > [!IMPORTANT]
 > Please see the [Contributing](#contributing) section, below, for
@@ -166,6 +166,36 @@ on Buildroot to finalize the target filesystem and generate the images.
 The final `run` argument is explained below.
 
 
+### Configuration Snippets
+
+Infix ships a set of Kconfig fragments in `configs/snippets/` that can
+be merged into your active `.config` on demand.  This avoids polluting
+defconfigs with settings that are only useful during development.
+
+To see what snippets are available:
+
+    make list-snippets
+
+To apply a single snippet to the current output directory:
+
+    make apply-dev          # enable root login
+    make apply-ext4         # build an ext4 rootfs (needed for boards
+                            # whose bootloader lacks squashfs support,
+                            # e.g. Marvell ESPRESSObin)
+
+The `apply-*` targets require an existing `.config` (i.e. you must have
+already run a `make <board>_defconfig`).  The snippet is merged using
+Buildroot's `merge_config.sh`, so it behaves like `make menuconfig`:
+unrelated settings are preserved, conflicting ones are overridden.
+
+To apply **all** snippets at once and then build:
+
+    make dev
+
+This is the recommended one-shot command for setting up a development
+build from a freshly selected defconfig.
+
+
 ### YANG Model
 
 When making changes to the `confd` and `statd` services, you will often

test/case/repo/defconfig.sh

@@ -1,4 +1,6 @@
 #!/bin/sh
+# Verify all config/*_defconfig files, skipping any subdirectories,
+# e.g., developer snippets not used in official builds.
 
 SCRIPT_PATH="$(dirname "$(readlink -f "$0")")"
 CONFIGS="$SCRIPT_PATH/../../../configs"
@@ -47,6 +49,7 @@ check()
     done
 }
 
-check "$CONFIGS"/* || exit 1
+# shellcheck disable=SC2046
+check $(find "$CONFIGS" -maxdepth 1 -type f | LC_ALL=C sort) || exit 1
 
 exit 0