assemblers: add org.osbuild.rawfs

This assembler outputs an image file which only contains the file
system.

assemblers/org.osbuild.rawfs

@@ -0,0 +1,48 @@
+#!/usr/bin/python3
+
+import contextlib
+import json
+import os
+import socket
+import subprocess
+import sys
+import osbuild.remoteloop as remoteloop
+
+
+@contextlib.contextmanager
+def mount(source, dest, *options):
+    os.makedirs(dest, 0o755, True)
+    subprocess.run(["mount", *options, source, dest], check=True)
+    try:
+        yield
+    finally:
+        subprocess.run(["umount", "-R", dest], check=True)
+
+
+def main(tree, output_dir, options, loop_client):
+    filename = options["filename"]
+    root_fs_uuid = options["root_fs_uuid"]
+    size = options["size"]
+
+    image = f"/var/tmp/osbuild-image.raw"
+    mountpoint = f"/tmp/osbuild-mnt"
+
+    subprocess.run(["truncate", "--size", str(size), image], check=True)
+    subprocess.run(["mkfs.ext4", "-U", root_fs_uuid, image], input="y", encoding='utf-8', check=True)
+
+    # Copy the tree into the target image
+    with loop_client.device(image) as loop, mount(loop, mountpoint):
+        subprocess.run(["cp", "-a", f"{tree}/.", mountpoint], check=True)
+
+    subprocess.run(["mv", image, f"{output_dir}/{filename}"], check=True)
+
+
+if __name__ == '__main__':
+    args = json.load(sys.stdin)
+
+    with socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM) as sock:
+        sock.setsockopt(socket.SOL_SOCKET, socket.SO_PASSCRED, 1)
+        sock.connect("/run/osbuild/api/remoteloop")
+        r = main(args["tree"], args["output_dir"], args["options"], remoteloop.LoopClient(sock))
+
+    sys.exit(r)