ci: Add rootfs export script

Implement new script for container->rootfs extraction.

v2 (Valentine)
 * Adapt script for direct execution in test-* containers through
   ci-templates

Signed-off-by: Guilherme Gallo <guilherme.gallo@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34451>

.gitlab-ci/container/fdo_cntr_export.sh

@@ -0,0 +1,72 @@
+#!/usr/bin/env bash
+
+# This script exports the container image to a rootfs tarball and uploads it to
+# S3.
+#
+# Usage:
+#
+#   ./fdo_cntr_export.sh <container-image-url>
+#
+# The container image URL is the URL of the container image to export. It can be
+# a local path or a remote URL.
+
+# Example:
+# ./fdo_cntr_export.sh registry.freedesktop.org/mesa/mesa/debian/x86_64_test-android:tag
+
+# When changing this file, you need to bump the following
+# .gitlab-ci/image-tags.yml tags:
+# DEBIAN_TEST_GL_TAG
+# DEBIAN_TEST_VK_TAG
+
+set -eux -o pipefail
+
+: "${CONTAINER:=$1}"
+IMAGE_URL="${CONTAINER}"
+readonly IMAGE_URL
+
+container=$(buildah from "$IMAGE_URL")
+readonly container
+readonly ROOTFSTAR=lava-rootfs.tar.zst
+touch "$ROOTFSTAR"
+
+buildah copy "$container" ".gitlab-ci/container/setup-rootfs.sh" /root/setup-rootfs.sh
+
+# Using --isolation chroot to ensure proper execution in CI/CD environments
+buildah run --isolation chroot "$container" -- /root/setup-rootfs.sh
+
+buildah_export() {
+    # Mount the volume
+    mountpoint=$(buildah mount "$1")
+
+    if [ ! -d "$mountpoint" ]; then
+        echo "Mount point not found: $mountpoint" >/dev/stderr
+        exit 1
+    fi
+
+    # Compress to zstd
+    ZSTD_CLEVEL=10 tar -C "$mountpoint" -I zstd -cf "$2" .
+}
+
+# When hacking on it locally, the script might not be executed as root.
+# In CI it's always root.
+if (($(id -u) != 0)); then
+    # Run unshare for rootless envs
+    buildah unshare -- bash -c "$(declare -f buildah_export); buildah_export '$container' '$ROOTFSTAR'"
+else
+    # Run directly
+    buildah_export "$container" "$ROOTFSTAR"
+fi
+
+# Unmount the container
+buildah umount "$container"
+
+# Remove the container
+buildah rm "$container"
+
+# Upload the rootfs tarball to S3.
+# The URL format matches the registry format, and LAVA_DISTRIBUTION_TAG is
+# used later to match this URL.
+curl --fail --retry-connrefused --retry 4 --retry-delay 30 \
+  --header "Authorization: Bearer $(cat "${S3_JWT_FILE}")" \
+  -X PUT --form file=@"$ROOTFSTAR" \
+  "https://${S3_HOST}/${S3_KERNEL_BUCKET}/${CI_PROJECT_PATH}/${CI_JOB_NAME}:${FDO_DISTRIBUTION_TAG}"