CI: check the coding style of bpf programs

The project, as stated in CONTRIBUTING have a strong preference for
the Linux kernel coding style.
This patch enforces it by adding automatic checks in the CI for bpf
sources.
The patch uses and import the current checkpatch.pl and its
requirement spelling.txt.

Signed-off-by: Paolo Valerio <[email protected]>

.cirrus.yml

@@ -20,7 +20,23 @@ unittest_task:
     image: rust:bookworm
   build_script: make V=1 CARGO_OPTS=--verbose
   test_script: make test V=1 CARGO_OPTS=--verbose
-  check_script:
+  ebpf_style_script: |
+    # same as checkpatch for git output
+    # this will also makes perl happy.
+    export LANGUAGE=en_US.UTF-8; export LC_ALL=en_US.UTF-8
+    git remote update origin
+    cirrus_base=$(git merge-base origin/$CIRRUS_BASE_BRANCH HEAD)
+    COMMIT_RANGE=$(git rev-list ${cirrus_base}..HEAD --reverse)
+    for commit in $COMMIT_RANGE; do
+        pretty_commit=$(git -P show -s --format="%h (\"%s\")" --abbrev=12 ${commit})
+        echo "Commit ${pretty_commit}"
+        printf -- '-%0.s' $(seq 1 ${#pretty_commit})
+        echo "-------"
+        git show --format=email ${commit} -- '*/bpf/*' | ./tools/checkpatch.pl --no-tree --ignore=SPDX_LICENSE_TAG,FILE_PATH_CHANGES,EMAIL_SUBJECT,VOLATILE -q || { restyle=1 ; true ; }
+        echo
+    done
+    [ -z "${restyle}" ]
+  rust_check_script:
     - cargo fmt --check
     - cargo clippy -- -D warnings
 

.gitattributes

@@ -1,3 +1,6 @@
 vmlinux.h linguist-vendored
 **/bpf_sys/include/linux/*.h linguist-vendored
 *_uapi.rs linguist-vendored
+tools/checkpatch.pl linguist-vendored
+tools/spelling.txt linguist-vendored
+tools/const_structs.checkpatch linguist-vendored

docs/CONTRIBUTING.md

@@ -84,12 +84,13 @@ and/or [help wanted](https://github.com/retis-org/retis/issues?q=is%3Aissue+is%3
 
 ### Coding style
 
-We strictly follow the Rust coding style as enforced by `rustfmt` and have a
-strong preference for the
-[Linux kernel](https://www.kernel.org/doc/html/latest/process/coding-style.html)
-and particularly its
+We strictly follow the Rust coding style as enforced by `rustfmt` and we also adhere the
+[Linux kernel](https://www.kernel.org/doc/html/latest/process/coding-style.html) coding style
+as enforced by `checkpatch.pl` and particularly its
 [networking](https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html#multi-line-comments)
-flavor coding style for the BPF parts.
+flavor for the BPF parts. `checkpatch.pl` can generate false
+positives, and in such case the formerly described coding style rules
+take precedence over its suggestions.
 
 ### Events and Rust bindings