Only check DCO on the author's commits

dco_verify_white_list.txt

@@ -0,0 +1 @@
+58da8ae48f274c3c602fe03eb7675b09d23340af

support/bootstrap

@@ -52,6 +52,11 @@ if [ ! -e "${HOOKS_DIR}/prepare-commit-msg" ]; then
   ln -sf "${HOOKS_DIR_RELPATH}/hooks/prepare-commit-msg" "${HOOKS_DIR}/prepare-commit-msg"
 fi
 
+if [ ! -e "${HOOKS_DIR}/commit-msg" ]; then
+  echo "Installing hook 'commit-msg'"
+  ln -sf "${HOOKS_DIR_RELPATH}/hooks/commit-msg" "${HOOKS_DIR}/commit-msg"
+fi
+
 if [ ! -e "${HOOKS_DIR}/pre-push" ]; then
   echo "Installing hook 'pre-push'"
   ln -sf "${HOOKS_DIR_RELPATH}/hooks/pre-push" "${HOOKS_DIR}/pre-push"

support/hooks/commit-msg

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+#
+# A git commit hook that check the DCO signoff.
+#
+# To enable this hook, run `bootstrap`, or run the following from the root of
+# the repo. (Note that `bootstrap` will correctly install this even if this code
+# is located in a submodule, while the following won't.)
+#
+# $ ln -s ../../support/hooks/commit-msg .git/hooks/commit-msg
+
+COMMIT_MESSAGE_FILE="$1"
+SIGNOFF="Signed-off-by:"
+
+# Check for DCO signoff message. If one doesn't exist, warn the user.
+if ! grep -qs "^$SIGNOFF" "$COMMIT_MESSAGE_FILE"; then
+  echo -e "The commit doesn't have DCO signoff. Please ensure install the git hooks by './support/bootstrap'"
+  exit 1
+fi

support/hooks/pre-push

@@ -32,22 +32,6 @@ do
       RANGE="$REMOTE_SHA..$LOCAL_SHA"
     fi
 
-    # Verify DCO signoff. We do this before the format checker, since it has
-    # some probability of failing spuriously, while this check never should.
-    #
-    # In general, we can't assume that the commits are signed off by author
-    # pushing, so we settle for just checking that there is a signoff at all.
-    SIGNED_OFF=$(git rev-list --no-merges --grep "^Signed-off-by: " "$RANGE")
-    NOT_SIGNED_OFF=$(git rev-list --no-merges "$RANGE" | grep -Fxv "$SIGNED_OFF")
-    if [ -n "$NOT_SIGNED_OFF" ]
-    then
-      echo >&2 "ERROR: The following commits do not have DCO signoff:"
-      while read -r commit; do
-        echo "  $(git log --pretty=oneline --abbrev-commit -n 1 "$commit")"
-      done <<< "$NOT_SIGNED_OFF"
-      exit 1
-    fi
-
     # NOTE: The `tools` directory will be the same relative to the support
     # directory, independent of whether we're in a submodule, so no need to use
     # our `relpath` helper.