Rename travis-ci/ directory to ci/

We are no longer using Travis. As such, we should move away from a lot
of CI functionality located in a folder called travis-ci/. This change
renames the travis-ci/ directory to the more generic ci/.
To preserve backwards compatibility until all "consumers" have
transitioned, we add a symbolic link called travis-ci back. It will be
removed in the near term future.

Signed-off-by: Daniel Müller <deso@posteo.net>

ci/rootfs/mkrootfs_debian.sh

@@ -0,0 +1,52 @@
+#!/bin/bash
+# This script builds a Debian root filesystem image for testing libbpf in a
+# virtual machine. Requires debootstrap >= 1.0.95 and zstd.
+
+# Use e.g. ./mkrootfs_debian.sh --arch=s390x to generate a rootfs for a
+# foreign architecture. Requires configured binfmt_misc, e.g. using
+# Debian/Ubuntu's qemu-user-binfmt package or
+# https://github.com/multiarch/qemu-user-static.
+
+set -e -u -x -o pipefail
+
+# Check whether we are root now in order to avoid confusing errors later.
+if [ "$(id -u)" != 0 ]; then
+	echo "$0 must run as root" >&2
+	exit 1
+fi
+
+# Create a working directory and schedule its deletion.
+root=$(mktemp -d -p "$PWD")
+trap 'rm -r "$root"' EXIT
+
+# Install packages.
+packages=(
+	binutils
+	busybox
+	elfutils
+	ethtool
+	iproute2
+	iptables
+	libcap2
+	libelf1
+	strace
+	zlib1g
+)
+packages=$(IFS=, && echo "${packages[*]}")
+debootstrap --include="$packages" --variant=minbase "$@" bookworm "$root"
+
+# Remove the init scripts (tests use their own). Also remove various
+# unnecessary files in order to save space.
+rm -rf \
+	"$root"/etc/rcS.d \
+	"$root"/usr/share/{doc,info,locale,man,zoneinfo} \
+	"$root"/var/cache/apt/archives/* \
+	"$root"/var/lib/apt/lists/*
+
+# Apply common tweaks.
+"$(dirname "$0")"/mkrootfs_tweak.sh "$root"
+
+# Save the result.
+name="libbpf-vmtest-rootfs-$(date +%Y.%m.%d).tar.zst"
+rm -f "$name"
+tar -C "$root" -c . | zstd -T0 -19 -o "$name"