sync: Sync .mailmap entries

The kernel repository has a .mailmap file to remap author names and
email addresses to their desired format in Git logs (for details, see
gitmailmap documentation [0]). Alas, this is only visible for author
information when looking at the logs locally, as GitHub does not support
mailmaps at the moment [1].

This commit adds a .mailmap file for libbpf, automatically generated
from the kernel's version. The script to generate the .mailmap is added,
too: it works by grepping email addresses from authors in the
repository, and collecting all lines ending with this address in the
kernel's .mailmap - in other words, all lines where this address is used
as a pattern for a remapping.

To keep the .mailmap up-to-date, add a call to the script to
sync-kernel.sh.

[0] https://git-scm.com/docs/gitmailmap
[1] https://github.com/orgs/community/discussions/22518

Signed-off-by: Quentin Monnet <qmo@kernel.org>

scripts/mailmap-update.sh

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+
+set -eu
+
+usage () {
+    echo "USAGE: ./mailmap-update.sh <libbpf-repo> <linux-repo>"
+    exit 1
+}
+
+LIBBPF_REPO="${1-""}"
+LINUX_REPO="${2-""}"
+
+if [ -z "${LIBBPF_REPO}" ] || [ -z "${LINUX_REPO}" ]; then
+    echo "Error: libbpf or linux repos are not specified"
+    usage
+fi
+
+LIBBPF_MAILMAP="${LIBBPF_REPO}/.mailmap"
+LINUX_MAILMAP="${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}" > "${LIBBPF_MAILMAP}"

scripts/sync-kernel.sh

@@ -352,4 +352,10 @@ else
 	esac
 fi
 
+echo "Regenerating .mailmap..."
+cd_to "${LINUX_REPO}"
+git checkout "${TIP_SYM_REF}"
+cd_to "${LIBBPF_REPO}"
+"${LIBBPF_REPO}"/scripts/mailmap-update.sh "${LIBBPF_REPO}" "${LINUX_REPO}"
+
 cleanup