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+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+    to be out of date, which will cause drivers/net/foo.c to be recompiled.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.
+
+    mkdep.c no longer generates warning messages for missing or unneeded
+    <linux/config.h> lines.  The new top-level target 'make checkconfig'
+    checks for these problems.
+
+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.