monkeypatch os.link (commaai#23480)

common/file_helpers.py

@@ -81,13 +81,25 @@ def _get_fileobject():
     return writer.get_fileobject(dir=temp_dir)
   return _get_fileobject
 
+def monkeypatch_os_link():
+  # This is neccesary on EON/C2, where os.link is patched out of python
+  if not hasattr(os, 'link'):
+    from cffi import FFI
+    ffi = FFI()
+    ffi.cdef("int link(const char *oldpath, const char *newpath);")
+    libc = ffi.dlopen(None)
+
+    def link(src, dest):
+      return libc.link(src.encode(), dest.encode())
+    os.link = link
 
 def atomic_write_on_fs_tmp(path, **kwargs):
   """Creates an atomic writer using a temporary file in a temporary directory
      on the same filesystem as path.
   """
   # TODO(mgraczyk): This use of AtomicWriter relies on implementation details to set the temp
   #                 directory.
+  monkeypatch_os_link()
   writer = AtomicWriter(path, **kwargs)
   return writer._open(_get_fileobject_func(writer, get_tmpdir_on_same_filesystem(path)))
 
@@ -96,5 +108,6 @@ def atomic_write_in_dir(path, **kwargs):
   """Creates an atomic writer using a temporary file in the same directory
      as the destination file.
   """
+  monkeypatch_os_link()
   writer = AtomicWriter(path, **kwargs)
   return writer._open(_get_fileobject_func(writer, os.path.dirname(path)))