[PATCH v3 RESEND] scripts/tags.sh: choose which directories to exclude from being indexed

[Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>]

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>
---
Changelog:

- v3: change commit message wording and rst syntax (Req Bagas Sanjaya)
      change makefile variable scope to global, use blank space
      separator and change variable name to IGNORE_DIRS.
      (Req: Vipin Sharma)
- v2: change approach to include everything unless specified by the 
  IGNOREDIRS variable: (Req: Vipin Sharma)
- v1: https://lore.kernel.org/lkml/Y5OKDvbGk4Kro6MK@mail.google.com/

Additional notes (if relevant):
- Patch v3 was reviewed-by Vipin Sharma here:
  https://lore.kernel.org/lkml/CAHVum0eNp5Dup_KyrS2N0zu5TfrtcCxphRnLuBFZa5PxahVg7A@mail.gmail.com/
---
 Documentation/kbuild/kbuild.rst | 7 +++++++
 scripts/tags.sh                 | 7 +++++++
 2 files changed, 14 insertions(+)

diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst
index 08f575e6236c..5202186728b4 100644
--- a/Documentation/kbuild/kbuild.rst
+++ b/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
diff --git a/scripts/tags.sh b/scripts/tags.sh
index e137cf15aae9..1ad45f17179a 100755
--- a/scripts/tags.sh
+++ b/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
-- 
2.38.1