[PATCH net-next 3/4] tools: ynl: stop find_kernel_root() spinning at the filesystem root

[Taylor Bates <tmbates12@gmail.com>]

In the current pyynl tooling, the find_kernel_root() function
contains a loop that climbs up the directory tree relative to the
spec file until it finds a MAINTAINERS file. If ynl_gen_c.py is run
in-tree it terminates properly in the root of the kernel tree.

The relative directory returned is then used to build the provenance
comment. The path of the root directory that it terminates at is
thrown away immediately at the call site:

  _, spec_kernel = find_kernel_root(args.spec)

However, if it is run out-of-tree and does not find a MAINTAINERS
file in any of the directories, find_kernel_root() reaches "/".
Since os.path.dirname() is idempotent at "/", the while True: has no
exit.

This can be reproduced on today's tree if the specs are copied to
a directory outside of the kernel tree:

  mkdir -p /tmp/ynl-oot/specs
  cp Documentation/netlink/netlink-raw.yaml /tmp/ynl-oot/
  cp Documentation/netlink/specs/rt-link.yaml /tmp/ynl-oot/specs/
  tools/net/ynl/pyynl/ynl_gen_c.py --spec /tmp/ynl-oot/specs/rt-link.yaml \
      --mode uapi --header

The fallback implemented in this patch still
provides a usable output:

  /* Do not edit directly, auto-generated from: */
  /*	tmp/ynl-oot/specs/rt-link.yaml */

Fixes: be5bea1cc0bf ("net: add basic C code generators for Netlink")
Signed-off-by: Taylor Bates <tmbates12@gmail.com>
---
 tools/net/ynl/pyynl/ynl_gen_c.py | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/net/ynl/pyynl/ynl_gen_c.py b/tools/net/ynl/pyynl/ynl_gen_c.py
index 2b3483db1b60..1c422141d2d7 100755
--- a/tools/net/ynl/pyynl/ynl_gen_c.py
+++ b/tools/net/ynl/pyynl/ynl_gen_c.py
@@ -3449,7 +3449,12 @@ def find_kernel_root(full_path):
     sub_path = ''
     while True:
         sub_path = os.path.join(os.path.basename(full_path), sub_path)
-        full_path = os.path.dirname(full_path)
+        parent = os.path.dirname(full_path)
+        if parent == full_path:
+            # Reached the filesystem root without finding a kernel tree, fall
+            # back to the path given.
+            return None, sub_path[:-1]
+        full_path = parent
         maintainers = os.path.join(full_path, "MAINTAINERS")
         if os.path.exists(maintainers):
             return full_path, sub_path[:-1]

-- 
2.55.0