app-emulation/docker: improve postinst message

Package-Manager: Portage-3.0.9, Repoman-3.0.2
Signed-off-by: Georgy Yakovlev <[email protected]>

app-emulation/docker/docker-19.03.13-r2.ebuild

@@ -302,15 +302,32 @@ pkg_postinst() {
 
 	elog
 	elog "To use Docker, the Docker daemon must be running as root. To automatically"
-	elog "start the Docker daemon at boot, add Docker to the default runlevel:"
-	elog "  rc-update add docker default"
-	elog "Similarly for systemd:"
-	elog "  systemctl enable docker.service"
+	elog "start the Docker daemon at boot:"
+	if systemd_is_booted || has_version sys-apps/systemd; then
+		elog "  systemctl enable docker.service"
+	else
+		elog "  rc-update add docker default"
+	fi
 	elog
 	elog "To use Docker as a non-root user, add yourself to the 'docker' group:"
-	elog "  usermod -aG docker youruser"
+	elog '  usermod -aG docker <youruser>'
 	elog
 
-	elog " Devicemapper storage driver has been deprecated"
-	elog " It will be removed in a future release"
+	if use device-mapper; then
+		elog " Devicemapper storage driver has been deprecated"
+		elog " It will be removed in a future release"
+		elog
+	fi
+
+	if use overlay; then
+		elog " Overlay storage driver/USEflag has been deprecated"
+		elog " in favor of overlay2 (enabled unconditionally)"
+		elog
+	fi
+
+	if has_version sys-fs/zfs; then
+		elog " ZFS storage driver is available"
+		elog " Check https://docs.docker.com/storage/storagedriver/zfs-driver for more info"
+		elog
+	fi
 }