Merge pull request #2042 from tych0/kernel-config-docs

Kernel config project docs

projects/kernel-config/Dockerfile

@@ -23,7 +23,14 @@ RUN set -e && for patch in /patches/*.patch; do \
         patch -p1 < "$patch"; \
     done
 
-RUN /config/makeconfig.sh ${ARCH} ${KERNEL_SERIES}
+RUN \
+  if [ -n "${DEBUG}" ]; then dbg=kernel_config.debug; else dbg=; fi && \
+  /config/makeconfig.sh \
+    kernel_config.base \
+    "kernel_config.${ARCH}" \
+    "kernel_config.${ARCH}.${KERNEL_SERIES}" \
+    "kernel_config.${KERNEL_SERIES}" \
+    "$dbg"
 RUN /config/check-kernel-config.sh /linux/.config
 
 RUN mkdir /out

projects/kernel-config/Makefile

@@ -12,7 +12,7 @@
 HASH?=$(shell git ls-tree HEAD -- ../$(notdir $(CURDIR)) | awk '{print $$3}')
 # Name on Hub
 IMAGE:=kernel
-ARCH?=$(shell if [ "$$(arch)" = "x86_64" ]]; then echo x86; else $$(arch); fi)
+ARCH?=x86_64
 
 .PHONY: check tag push sign
 # Targets:

projects/kernel-config/README.md

@@ -0,0 +1,38 @@
+## kernel config project
+
+The intent of the kernel config project is to demonstrate a better way to
+handle kernel config. Specifically:
+
+* support for arch and version specific config
+* make diffs as readable as possible
+* ensure that all of our config settings are kept after oldconfig
+
+We achieve the goals by:
+
+* having version-specific config in separate files, which are automatically
+  merged
+* only keeping track of visible symbols, only keeping track of a delta from
+  defconfig, and keeping symbols sorted alphabetically
+* checking after a `make oldconfig` in the kernel, that all of our symbols are
+  set as we want them to be
+
+The bulk of this work happens in makeconfig.sh, which merges the configs (and
+checks that the resulting config is okay).
+
+One important piece is generating a kernel config for a new version. There are
+a few cases:
+
+* A new kconfig symbol is introduced that we want to set a non-default value
+  of: in this case, we introduce a new `kernel_config.${VERSION}` file, and set
+  the value to what we want to set it to
+* A config symbol that was no-default before become the default: in this case,
+  we would move the non-default setting to version specific files for all of
+  the other versions, and not set anything for this new kernel, since what we
+  want is now the default.
+* A symbol we want to set is removed (or renamed), similar to the above, we
+  simply move the old symbol name to version specific files for older kernels
+  and put the new symbol name (if it exists) in the new version specific file
+
+When dropping support for an old kernel version, we just delete that version
+specific file, and promote any option that is present in all other versions to
+the common config file.

projects/kernel-config/kernel_config.debug

@@ -24,3 +24,4 @@ CONFIG_KGDB_SERIAL_CONSOLE=y
 CONFIG_KGDBOC=y
 CONFIG_DEBUG_RODATA_TEST=y
 CONFIG_DEBUG_WX=y
+# CONFIG_PANIC_ON_OOPS is not set

projects/kernel-config/makeconfig.sh

@@ -2,10 +2,6 @@
 
 set -e
 
-ARCH=$1
-KERNEL_SERIES=$2
-DEBUG=$3
-
 cd /linux && make defconfig
 
 function merge_config()
@@ -32,15 +28,9 @@ function merge_config()
 
 cd /linux && make defconfig && make oldconfig
 
-merge_config "/config/kernel_config.base"
-merge_config "/config/kernel_config.${ARCH}"
-merge_config "/config/kernel_config.${KERNEL_SERIES}"
-merge_config "/config/kernel_config.${ARCH}.${KERNEL_SERIES}"
-
-if [ -n "${DEBUG}" ]; then
-    sed -i sed -i 's/CONFIG_PANIC_ON_OOPS=y/# CONFIG_PANIC_ON_OOPS is not set/' /linux/arch/x86/configs/x86_64_defconfig
-    append_config "/config/kernel_config.debug"
-fi
+for config in "$@"; do
+  merge_config "$config"
+done
 
 cd /linux && make oldconfig
 
@@ -51,7 +41,9 @@ function check_config()
     if [ ! -f "$1" ]; then return; fi
 
     while read line; do
-      if [ -n "${DEBUG}" ] && [ "$line" == "CONFIG_PANIC_ON_OOPS=y" ]; then continue; fi
+      # CONFIG_PANIC_ON_OOPS is special, and set both ways, depending on
+      # whether DEBUG is set or not.
+      if [ "$line" == *"CONFIG_PANIC_ON_OOPS"* ]; then continue; fi
       value="$(grep "^${line}$" /linux/.config || true)"
 
       # It's okay to for the merging script to have simply not listed values we
@@ -67,10 +59,6 @@ function check_config()
     done < $1
 }
 
-check_config "/config/kernel_config.base"
-check_config "/config/kernel_config.${ARCH}"
-check_config "/config/kernel_config.${KERNEL_SERIES}"
-check_config "/config/kernel_config.${ARCH}.${KERNEL_SERIES}"
-if [ -n "${DEBUG}" ]; then
-    check_config "/config/kernel_config.debug"
-fi
+for config in "$@"; do
+  check_config "$config"
+done