document using musl

conf/local.conf

@@ -57,3 +57,6 @@ ENABLE_UART = "1"
 #VIRTUAL-RUNTIME_init_manager = "busybox"
 #VIRTUAL-RUNTIME_dev_manager = "busybox-mdev"
 #VIRTUAL-RUNTIME_login_manager = "busybox"
+
+# Uncomment the following to enable musl libc
+#TCLIBC = "musl"

docs/README.md

@@ -12,6 +12,13 @@ included for some of them below.
 * [BeagleBone -- todo]()
 * [ODroid-C2 -- todo]()
 
+## Image Configuration
+
+OpenEmbedded supports a wide range of technology choices. Some of these are documented
+below.
+
+* [libc/init system](libc-init.md)
+
 ## Design Choices
 
 * [Superproject Management](superproject-management.md)

docs/init-system.md → docs/libc-init.md

@@ -1,4 +1,4 @@
-# Init System
+# libc and init system selection
 
 ## Systemd
 
@@ -25,11 +25,21 @@ VIRTUAL-RUNTIME_dev_manager = "busybox-mdev"
 VIRTUAL-RUNTIME_login_manager = "busybox"
 ```
 
-## Comparison of disk spaced used by init systems
+## Libc selection
 
-Systemd takes considerably more space than SysVinit. With a rPI2 build, the following
-are the rootfs sizes for core-image-minimal:
+glibc is the default libc, but musl can also be used by setting the following in
+local.conf:
 
+```
+TCLIBC = "musl"
+```
+
+## Comparison of disk spaced used
+
+* Musl + Busybox init/dev/login
+  * space used in ext4 filesystem on running system using df: 1.9MB
+  * adding sizes of files in image from buildhistory: 1.5MB
+  * number of files in image: 595
 * Busybox init/dev/login
   * space used in ext4 filesystem on running system using df: 3.5MB
   * adding sizes of files in image from buildhistory: 3.1MB
@@ -42,3 +52,7 @@ are the rootfs sizes for core-image-minimal:
   * space used in ext4 filesystem on running system using df: 33.2MB
   * adding sizes of files in image from buildhistory: 22MB
   * number of files in image: 1,806
+
+The space on disc used by a systemd image is much larger than adding the size of
+the files in the image. We're not sure why this is -- perhaps there is filesystem
+overhead for small files.