utils.py: safe_link(): Copy if hardlink creation is not permitted

By default, Linux doesn't allow creating hardlinks to read-only files of
other users since Linux 3.6 (see /proc/sys/fs/protected_hardlinks).

This fixes staging when buildbox-casd is running as a separate user and
the traditional bubblewrap sandboxing backend is used. This combination
is not recommended, however, it's triggered in CI by docker images that
run buildbox-casd as a separate user and a few test cases that override
BST_FORCE_SANDBOX.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/buildstream/utils.py b/src/buildstream/utils.py
index 5009be338..b6716a29d 100644
--- a/src/buildstream/utils.py
+++ b/src/buildstream/utils.py
@@ -326,7 +326,7 @@ def safe_link(src: str, dest: str, *, result: Optional[FileListResult] = None, _
         if e.errno == errno.EEXIST and not _unlink:
             # Target exists already, unlink and try again
             safe_link(src, dest, result=result, _unlink=True)
-        elif e.errno == errno.EXDEV:
+        elif e.errno == errno.EXDEV or e.errno == errno.EPERM:
             safe_copy(src, dest)
         else:
             raise UtilError("Failed to link '{} -> {}': {}".format(src, dest, e)) from e