fix: avoid duplicate capacity reservation for hardlinks

src/archive_clients/jobs.py

@@ -5,11 +5,12 @@ from __future__ import annotations
 import hashlib
 import json
 import shutil
+import stat
 import threading
 import time
 import uuid
 from pathlib import Path, PurePosixPath
-from typing import Callable
+from typing import Callable, Iterable
 
 from archive_clients.protocol import decode_message, encode_message
 from archive_clients.eviction import (
@@ -541,15 +542,29 @@ class ClientJobExecutor:
             sha256_hex=hashlib.sha256(resource.metainfo_bytes).hexdigest(),
         )
         del artifact
+        route_root = self.route_path(definition.transfer.route_id)
+        # Staging is normally zero-copy when qB's data root and the paired
+        # Syncthing route share a filesystem.  Do not reserve the complete
+        # logical payload in that case: FileMaterializer will use link(2),
+        # which consumes only directory/inode metadata.  Retain the metainfo
+        # allowance and reserve, and account for any source files that really
+        # must fall back to a data-copy path.
         self._require_space(
-            self.route_path(definition.transfer.route_id),
-            definition.transfer.transfer_delta_logical_bytes
+            route_root,
+            self._copy_required_bytes(
+                self.qb_root,
+                route_root,
+                (
+                    (entry.target_canonical_path, entry.logical_bytes)
+                    for entry in manifest.files
+                ),
+            )
             + len(resource.metainfo_bytes),
         )
         stage_transfer(
             manifest,
             source_root=self.qb_root,
-            sync_root=self.route_path(definition.transfer.route_id),
+            sync_root=route_root,
             store=self.store,
             artifact_sources={"metainfo/source.torrent": metainfo_path},
             sparse_supported=self.sparse_supported,
@@ -607,9 +622,18 @@ class ClientJobExecutor:
                 "target materialization was sent to the wrong client"
             )
         published = load_published_transfer(self._job_directory(definition))
+        # The target can likewise hardlink an arrived Syncthing payload into
+        # qB's content root when those directories share a filesystem.
         self._require_space(
             self.qb_root,
-            definition.transfer.transfer_delta_logical_bytes,
+            self._copy_required_bytes(
+                published.job_directory,
+                self.qb_root,
+                (
+                    (entry.payload_relative_path, entry.logical_bytes)
+                    for entry in published.manifest.files
+                ),
+            ),
         )
         info_hash = _info_hash(definition)
         resource = self.qbittorrent.get_resource(info_hash)
@@ -843,6 +867,36 @@ class ClientJobExecutor:
                 f"{required} bytes required including reserve"
             )
 
+    @staticmethod
+    def _copy_required_bytes(
+        source_root: Path,
+        destination_root: Path,
+        files: Iterable[tuple[str, int]],
+    ) -> int:
+        """Return logical bytes that cannot be materialized by hardlink.
+
+        A hardlink is possible only for regular files on the destination
+        filesystem.  Conservatively charge a file when it cannot be inspected;
+        the normal materializer will then provide the precise integrity error.
+        """
+
+        destination_device = destination_root.stat().st_dev
+        required = 0
+        for relative_path, logical_bytes in files:
+            relative = PurePosixPath(relative_path)
+            source = source_root.joinpath(*relative.parts)
+            try:
+                metadata = source.stat(follow_symlinks=False)
+            except OSError:
+                required += logical_bytes
+                continue
+            if (
+                not stat.S_ISREG(metadata.st_mode)
+                or metadata.st_dev != destination_device
+            ):
+                required += logical_bytes
+        return required
+
     def _observer(
         self, definition: job_pb2.JobDefinition
     ) -> SyncthingTransferObserver: