scripts/tags.sh: choose which directories to exclude from being indexed

It's common for drivers that share same physical components to also
duplicate source code (or at least portions of it). A good example is
both drivers/gpu/drm/amdgpu/* and drivers/gpu/drm/radeon/* have a header
file called atombios.h.

While their contents aren't the same, a lot of their structs have
the exact same names which makes navigating through the code base a bit
messy as cscope will show up 'references' across drivers which aren't
exactly correct.

Add IGNORE_DIRS variable, which specifies which directories
to be ignored from indexing.

Example:
        make ARCH=x86 IGNORE_DIRS="drivers/gpu/drm/radeon tools" cscope

Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Reviewed-by: Vipin Sharma <vipinsh@google.com>
Link: https://lore.kernel.org/r/Y5jf59VCL/HAt60q@mail.google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/kbuild/kbuild.rst

@@ -278,6 +278,13 @@ To get all available archs you can also specify all. E.g.::
 
     $ make ALLSOURCE_ARCHS=all tags
 
+IGNORE_DIRS
+-----------
+For tags/TAGS/cscope targets, you can choose which directories won't
+be included in the databases, separated by blank space. E.g.::
+
+    $ make IGNORE_DIRS="drivers/gpu/drm/radeon tools" cscope
+
 KBUILD_BUILD_TIMESTAMP
 ----------------------
 Setting this to a date string overrides the timestamp used in the

scripts/tags.sh

@@ -17,6 +17,13 @@ ignore="$(echo "$RCS_FIND_IGNORE" | sed 's|\\||g' )"
 # tags and cscope files should also ignore MODVERSION *.mod.c files
 ignore="$ignore ( -name *.mod.c ) -prune -o"
 
+# ignore arbitrary directories
+if [ -n "${IGNORE_DIRS}" ]; then
+	for i in ${IGNORE_DIRS}; do
+		ignore="${ignore} ( -path $i ) -prune -o"
+	done
+fi
+
 # Use make KBUILD_ABS_SRCTREE=1 {tags|cscope}
 # to force full paths for a non-O= build
 if [ "${srctree}" = "." -o -z "${srctree}" ]; then