sync: improve sync script to handle common issues

Few recurring issues are fixed.
1. When there are patches in bpf tree that hasn't been synced yet, but bpf was
   already merged into bpf-next, merged patches would be applied twice,
   causing failures, requiring manual resolution. Now this is handled smarter
   and shouldn't happen.
2. When synced libbpf repo contains fixes from bpf that weren't yet merged
   into bpf-next, those bpf tree changes would cause inconsistency against
   bpf-next tree state. That's expected and usually is pretty easy for human
   to discard during consistency check, but is hard for automation. So instead
   of failing at the very end, ask human whether discrepancies look good.
3. If sync script detected no new patches needed syncing, it previously didn't
   restore linux repo state back. Fixed.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>

scripts/sync-kernel.sh

@@ -6,7 +6,6 @@ usage () {
 	echo "Set BPF_NEXT_BASELINE to override bpf-next tree commit, otherwise read from <libbpf-repo>/CHECKPOINT-COMMIT."
 	echo "Set BPF_BASELINE to override bpf tree commit, otherwise read from <libbpf-repo>/BPF-CHECKPOINT-COMMIT."
 	echo "Set MANUAL_MODE to 1 to manually control every cherry-picked commits."
-	echo "Set IGNORE_CONSISTENCY to 1 to ignore failed contents consistency check."
 	exit 1
 }
 
@@ -137,6 +136,7 @@ cherry_pick_commits()
 			echo "Warning! Cherry-picking '${desc} failed, checking if it's non-libbpf files causing problems..."
 			libbpf_conflict_cnt=$(git diff --name-only --diff-filter=U -- ${LIBBPF_PATHS[@]} | wc -l)
 			conflict_cnt=$(git diff --name-only | wc -l)
+			prompt_resolution=1
 
 			if ((${libbpf_conflict_cnt} == 0)); then
 				echo "Looks like only non-libbpf files have conflicts, ignoring..."
@@ -152,15 +152,37 @@ cherry_pick_commits()
 					echo "Error! That still failed! Please resolve manually."
 				else
 					echo "Success! All cherry-pick conflicts were resolved for '${desc}'!"
-					continue
+					prompt_resolution=0
 				fi
 			fi
 
-			read -p "Error! Cherry-picking '${desc}' failed, please fix manually and press <return> to proceed..."
+			if ((${prompt_resolution} == 1)); then
+				read -p "Error! Cherry-picking '${desc}' failed, please fix manually and press <return> to proceed..."
+			fi
 		fi
+		# Append signature of just cherry-picked commit to avoid
+		# potentially cherry-picking the same commit twice later when
+		# processing bpf tree commits. At this point we don't know yet
+		# the final commit sha in libbpf repo, so we record Linux SHA
+		# instead as LINUX_<sha>.
+		echo LINUX_$(git log --pretty='%h' -n1) "${signature}" >> ${TMP_DIR}/libbpf_commits.txt
 	done
 }
 
+cleanup()
+{
+	echo "Cleaning up..."
+	rm -r ${TMP_DIR}
+	cd_to ${LINUX_REPO}
+	git checkout ${TIP_SYM_REF}
+	git branch -D ${BASELINE_TAG} ${TIP_TAG} ${BPF_BASELINE_TAG} ${BPF_TIP_TAG} \
+		      ${SQUASH_BASE_TAG} ${SQUASH_TIP_TAG} ${VIEW_TAG} || true
+
+	cd_to .
+	echo "DONE."
+}
+
+
 cd_to ${LIBBPF_REPO}
 GITHUB_ABS_DIR=$(pwd)
 echo "Dumping existing libbpf commit signatures..."
@@ -226,6 +248,7 @@ FILTER_BRANCH_SQUELCH_WARNING=1 git filter-branch --prune-empty -f --subdirector
 COMMIT_CNT=$(git rev-list --count ${SQUASH_BASE_TAG}..${SQUASH_TIP_TAG})
 if ((${COMMIT_CNT} <= 0)); then
     echo "No new changes to apply, we are done!"
+    cleanup
     exit 2
 fi
 
@@ -304,19 +327,17 @@ done
 if ((${CONSISTENT} == 1)); then
 	echo "Great! Content is identical!"
 else
-	echo "Unfortunately, there are consistency problems!"
-	if ((${IGNORE_CONSISTENCY-0} != 1)); then
-		exit 4
-	fi
+	ignore_inconsistency=n
+	echo "Unfortunately, there are some inconsistencies, please double check."
+	read -p "Does everything look good? [y/N]: " ignore_inconsistency
+	case "${ignore_inconsistency}" in
+		"y" | "Y")
+			echo "Ok, proceeding..."
+			;;
+		*)
+			echo "Oops, exiting with error..."
+			exit 4
+	esac
 fi
 
-echo "Cleaning up..."
-rm -r ${TMP_DIR}
-cd_to ${LINUX_REPO}
-git checkout ${TIP_SYM_REF}
-git branch -D ${BASELINE_TAG} ${TIP_TAG} ${BPF_BASELINE_TAG} ${BPF_TIP_TAG} \
-	      ${SQUASH_BASE_TAG} ${SQUASH_TIP_TAG} ${VIEW_TAG}
-
-cd_to .
-echo "DONE."
-
+cleanup