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Diffstat (limited to 'Documentation/smart-config.txt')
| -rw-r--r-- | Documentation/smart-config.txt | 98 |
1 files changed, 0 insertions, 98 deletions
diff --git a/Documentation/smart-config.txt b/Documentation/smart-config.txt deleted file mode 100644 index 8467447..0000000 --- a/Documentation/smart-config.txt +++ /dev/null @@ -1,98 +0,0 @@ -Smart CONFIG_* Dependencies -1 August 1999 - -Michael Chastain <mec@shout.net> -Werner Almesberger <almesber@lrc.di.epfl.ch> -Martin von Loewis <martin@mira.isdn.cs.tu-berlin.de> - -Here is the problem: - - Suppose that drivers/net/foo.c has the following lines: - - #include <linux/config.h> - - ... - - #ifdef CONFIG_FOO_AUTOFROB - /* Code for auto-frobbing */ - #else - /* Manual frobbing only */ - #endif - - ... - - #ifdef CONFIG_FOO_MODEL_TWO - /* Code for model two */ - #endif - - Now suppose the user (the person building kernels) reconfigures the - kernel to change some unrelated setting. This will regenerate the - file include/linux/autoconf.h, which will cause include/linux/config.h - to be out of date, which will cause drivers/net/foo.c to be recompiled. - - Most kernel sources, perhaps 80% of them, have at least one CONFIG_* - dependency somewhere. So changing _any_ CONFIG_* setting requires - almost _all_ of the kernel to be recompiled. - -Here is the solution: - - We've made the dependency generator, mkdep.c, smarter. Instead of - generating this dependency: - - drivers/net/foo.c: include/linux/config.h - - It now generates these dependencies: - - drivers/net/foo.c: \ - include/config/foo/autofrob.h \ - include/config/foo/model/two.h - - So drivers/net/foo.c depends only on the CONFIG_* lines that - it actually uses. - - A new program, split-include.c, runs at the beginning of - compilation (make bzImage or make zImage). split-include reads - include/linux/autoconf.h and updates the include/config/ tree, - writing one file per option. It updates only the files for options - that have changed. - -Flag Dependencies - - Martin Von Loewis contributed another feature to this patch: - 'flag dependencies'. The idea is that a .o file depends on - the compilation flags used to build it. The file foo.o has - its flags stored in .flags.foo.o. - - Suppose the user changes the foo driver from resident to modular. - 'make' will notice that the current foo.o was not compiled with - -DMODULE and will recompile foo.c. - - All .o files made from C source have flag dependencies. So do .o - files made with ld, and .a files made with ar. However, .o files - made from assembly source do not have flag dependencies (nobody - needs this yet, but it would be good to fix). - -Per-source-file Flags - - Flag dependencies also work with per-source-file flags. - You can specify compilation flags for individual source files - like this: - - CFLAGS_foo.o = -DSPECIAL_FOO_DEFINE - - This helps clean up drivers/net/Makefile, drivers/scsi/Makefile, - and several other Makefiles. - -Credit - - Werner Almesberger had the original idea and wrote the first - version of this patch. - - Michael Chastain picked it up and continued development. He is - now the principal author and maintainer. Please report any bugs - to him. - - Martin von Loewis wrote flag dependencies, with some modifications - by Michael Chastain. - - Thanks to all of the beta testers. |
