From 3bda2f10d96cbfe626d2024ef96c53ad4a6e0fa9 Mon Sep 17 00:00:00 2001
From: Thomas Waldmann <tw@waldmann-edv.de>
Date: Thu, 4 Dec 2025 23:32:05 +0100
Subject: [PATCH] HardLinkManager: allow NoneType for contentless hardlinks,
 see #9208

Some hardlinks have content and thus a chunks list,
but e.g. block or char device hardlinks do not have a chunks list.
---
 src/borg/helpers/fs.py | 2 +-
 src/borg/upgrade.py    | 4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/borg/helpers/fs.py b/src/borg/helpers/fs.py
index 07c263054..66e1ecdfb 100644
--- a/src/borg/helpers/fs.py
+++ b/src/borg/helpers/fs.py
@@ -346,7 +346,7 @@ class HardLinkManager:
     def __init__(self, *, id_type, info_type):
         self._map = {}
         self.id_type = id_type
-        self.info_type = info_type
+        self.info_type = info_type  # can be a single type or a tuple of types
 
     def borg1_hardlinkable(self, mode):  # legacy
         return stat.S_ISREG(mode) or stat.S_ISBLK(mode) or stat.S_ISCHR(mode) or stat.S_ISFIFO(mode)
diff --git a/src/borg/upgrade.py b/src/borg/upgrade.py
index 35d968837..9f6f653f0 100644
--- a/src/borg/upgrade.py
+++ b/src/borg/upgrade.py
@@ -1,4 +1,5 @@
 from struct import Struct
+from types import NoneType
 
 from .constants import REQUIRED_ITEM_KEYS, CH_BUZHASH
 from .compress import ZLIB, ZLIB_legacy, ObfuscateSize
@@ -53,7 +54,8 @@ class UpgraderFrom12To20:
 
     def new_archive(self, *, archive):
         self.archive = archive
-        self.hlm = HardLinkManager(id_type=bytes, info_type=list)  # hlid -> chunks_correct
+        # hlid -> chunks_correct list (or None, for contentless hardlinks)
+        self.hlm = HardLinkManager(id_type=bytes, info_type=(list, NoneType))
 
     def upgrade_item(self, *, item):
         """Upgrades the item as needed and removes legacy data."""