Handle attaching loop devices instead of handing it to mount

* So that we can pass extra loop options like Direct I/O
* To workaround an issue with loop device files not getting
automatically created

rawfile_servicer.py

@@ -4,6 +4,7 @@ from google.protobuf.wrappers_pb2 import BoolValue
 import rawfile_util
 from csi import csi_pb2, csi_pb2_grpc
 from orchestrator.k8s import volume_to_node, run_on_node
+from rawfile_util import attach_loop
 from remote import init_rawfile, scrub
 from util import log_grpc_request, run
 
@@ -48,7 +49,8 @@ class RawFileNodeServicer(csi_pb2_grpc.NodeServicer):
     def NodePublishVolume(self, request, context):
         mount_path = request.target_path
         img_file = rawfile_util.img_file(request.volume_id)
-        run(f"mount {img_file} {mount_path}")
+        loop_file = attach_loop(img_file)
+        run(f"mount {loop_file} {mount_path}")
         return csi_pb2.NodePublishVolumeResponse()
 
     @log_grpc_request

rawfile_util.py

@@ -2,6 +2,7 @@ import json
 from pathlib import Path
 
 from consts import DATA_DIR
+from util import run, run_out
 
 
 def img_dir(volume_id):
@@ -28,3 +29,27 @@ def patch_metadata(volume_id, obj):
     new_data = {**old_data, **obj}
     meta_file(volume_id).write_text(json.dumps(new_data))
     return new_data
+
+
+def attached_loops(file: str) -> [str]:
+    out = run_out(f"losetup -j {file}").stdout.decode()
+    lines = out.splitlines()
+    devs = [line.split(":", 1)[0] for line in lines]
+    return devs
+
+
+def attach_loop(file) -> str:
+    def next_loop():
+        loop_file = run_out(f"losetup -f").stdout.decode().strip()
+        if not Path(loop_file).exists():
+            pfx_len = len("/dev/loop")
+            loop_dev_id = loop_file[pfx_len:]
+            run(f"mknod {loop_file} b 7 {loop_dev_id}")
+        return loop_file
+
+    while True:
+        devs = attached_loops(file)
+        if len(devs) > 0:
+            return devs[0]
+        next_loop()
+        run(f"losetup -f {file}")

util.py

@@ -39,6 +39,11 @@ def run(cmd):
     return subprocess.run(cmd, shell=True, check=True)
 
 
+def run_out(cmd: str):
+    p = subprocess.run(cmd, shell=True, capture_output=True)
+    return p
+
+
 class remote_fn(object):
     def __init__(self, fn):
         self.fn = fn