Take a look at the source. It seems like the only thing they are doing is setting FILE_ATTRIBUTE_READONLY based on whether the file is writeable or not.
if (flags & _O_CREAT) {
if (!((req->mode & ~current_umask) & _S_IWRITE)) {
attributes |= FILE_ATTRIBUTE_READONLY;
}
}
The notes on fs.chmod are interesting as well.
/* Todo: st_mode should probably always be 0666 for everyone. We might also
* want to report 0777 if the file is a .exe or a directory.
*
* Currently it's based on whether the 'readonly' attribute is set, which
* makes little sense because the semantics are so different: the 'read-only'
* flag is just a way for a user to protect against accidental deleteion, and
* serves no security purpose. Windows uses ACLs for that.
*
* Also people now use uv_fs_chmod() to take away the writable bit for good
* reasons. Windows however just makes the file read-only, which makes it
* impossible to delete the file afterwards, since read-only files can't be
* deleted.
*
* IOW it's all just a clusterfuck and we should think of something that
* makes slighty more sense.
*
* And uv_fs_chmod should probably just fail on windows or be a total no-op.
* There's nothing sensible it can do anyway.
*/