mirror: Add .mailmap to the repository, sync with kernel's

Add a script to grep for the relevant entries in the .mailmap file of
the kernel repository, and use it to build a .mailmap file for the
mirror repo.

Signed-off-by: Quentin Monnet <[email protected]>

.mailmap

@@ -0,0 +1,5 @@
+Changbin Du <[email protected]> <[email protected]>
+Geliang Tang <[email protected]> <[email protected]>
+Herbert Xu <[email protected]>
+Maxim Mikityanskiy <[email protected]> <[email protected]>
+Quentin Monnet <[email protected]> <[email protected]>

scripts/mailmap-update.sh

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+
+set -eu
+
+usage () {
+    echo "USAGE: ./update-mailmap.sh <bpftool-repo> <linux-repo>"
+    exit 1
+}
+
+BPFTOOL_REPO=${1-""}
+LINUX_REPO=${2-""}
+
+if [ -z "${BPFTOOL_REPO}" ] || [ -z "${LINUX_REPO}" ]; then
+    echo "Error: bpftool or linux repos are not specified"
+    usage
+fi
+
+BPFTOOL_MAILMAP="${BPFTOOL_REPO}/.mailmap"
+LINUX_MAILMAP="${LINUX_REPO}/.mailmap"
+
+tmpfile="$(mktemp)"
+cleanup() {
+    rm -f "${tmpfile}"
+}
+trap cleanup EXIT
+
+grep_lines() {
+    local pattern="$1"
+    local file="$2"
+    grep "${pattern}" "${file}" || true
+}
+
+while read -r email; do
+    grep_lines "${email}$" "${LINUX_MAILMAP}" >> "${tmpfile}"
+done < <(git log --format='<%ae>' | sort -u)
+
+sort -u "${tmpfile}" > "${BPFTOOL_MAILMAP}"