[build] Allow for named configurations at build time

Allow named configurations to be specified via the CONFIG=... build
parameter.  For headers in config/*.h which support named
configurations, the following files will be included when building
with CONFIG=<name>:

  - config/defaults/<platform>.h (e.g. config/defaults/pcbios.h)

  - config/<header>.h

  - config/<name>/<header>.h (only if the directory config/<name> exists)

  - config/local/<header>.h (autocreated if necessary)

  - config/local/<name>/<header>.h (autocreated if necessary)

This mechanism allows for predefined named configurations to be
checked in to the source tree, as a directory config/<name> containing
all of the required header files.

The mechanism also allows for users to define multiple local
configurations, by creating header files in the directory
config/local/<name>.

Note that the config/*.h files which are used only to configure
internal iPXE APIs (e.g. config/ioapi.h) cannot be modified via a
named configuration.  This avoids rebuilding the entire iPXE codebase
whenever switching to a different named configuration.

Inspired-by: Robin Smidsrød <robin@smidsrod.no>
Tested-by: Robin Smidsrød <robin@smidsrod.no>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/config/general.h b/src/config/general.h
index 72cfc3b86..539203457 100644
--- a/src/config/general.h
+++ b/src/config/general.h
@@ -182,6 +182,9 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #undef	GDBUDP			/* Remote GDB debugging over UDP
 				 * (both may be set) */
 
+#include <config/named.h>
+#include NAMED_CONFIG(general.h)
 #include <config/local/general.h>
+#include LOCAL_NAMED_CONFIG(general.h)
 
 #endif /* CONFIG_GENERAL_H */