xattr: document fakeroot xattr as Linux-only, add missing fakeroot skip on FreeBSD, fixes #9394

src/borg/testsuite/platform/freebsd_test.py

@@ -2,10 +2,10 @@ import os
 import tempfile
 
 from ...platform import acl_get, acl_set
-from .platform_test import skipif_not_freebsd, skipif_acls_not_working
+from .platform_test import skipif_not_freebsd, skipif_fakeroot_detected, skipif_acls_not_working
 
 # set module-level skips
-pytestmark = [skipif_not_freebsd]
+pytestmark = [skipif_not_freebsd, skipif_fakeroot_detected]
 
 
 ACCESS_ACL = """\

src/borg/testsuite/xattr_test.py

@@ -3,7 +3,7 @@ import os
 import pytest
 
 from ..platform.xattr import buffer, split_lstring
-from ..xattr import is_enabled, getxattr, setxattr, listxattr
+from ..xattr import is_enabled, getxattr, setxattr, listxattr, XATTR_FAKEROOT
 from ..platformflags import is_linux
 
 
@@ -82,3 +82,11 @@ def test_getxattr_buffer_growth(tempfile_symlink):
 )
 def test_split_lstring(lstring, expected):
     assert split_lstring(lstring) == expected
+
+
+def test_xattr_fakeroot_flag():
+    """XATTR_FAKEROOT must be False when not on Linux or when fakeroot is not active."""
+    if not is_linux:
+        assert XATTR_FAKEROOT is False
+    if "FAKEROOTKEY" not in os.environ:
+        assert XATTR_FAKEROOT is False

src/borg/xattr.py

@@ -19,8 +19,9 @@ from .platform import listxattr, getxattr, setxattr, ENOATTR
 
 # If we are running with fakeroot on Linux, then use the xattr functions of fakeroot. This is needed by
 # the 'test_extract_capabilities' test, but also allows xattrs to work with fakeroot on Linux in normal use.
-# TODO: Check whether fakeroot supports xattrs on all platforms supported below.
-# TODO: If that's the case then we can make Borg fakeroot-xattr-compatible on these as well.
+# Note: fakeroot xattr support is Linux-only. fakeroot only wraps the Linux-style setxattr/getxattr API,
+# but FreeBSD/NetBSD use the extattr_* API instead, so fakeroot never intercepts xattr calls there.
+# On macOS, fakeroot explicitly disables xattr wrapping due to prototype incompatibilities.
 XATTR_FAKEROOT = False
 if sys.platform.startswith("linux"):
     LD_PRELOAD = os.environ.get("LD_PRELOAD", "")