def do_symlink_kernsrc(d):
    s = d.getVar("S")
    kernsrc = d.getVar("STAGING_KERNEL_DIR")
    if s != kernsrc:
        bb.utils.mkdirhier(kernsrc)
        bb.utils.remove(kernsrc, recurse=True)
        if s[-1] == '/':
            # drop trailing slash, so that os.symlink(kernsrc, s) doesn't use s as
            # directory name and fail
            s = s[:-1]
        if d.getVar("EXTERNALSRC"):
            # With EXTERNALSRC S will not be wiped so we can symlink to it
            os.symlink(s, kernsrc)
        else:
            import shutil
            shutil.move(s, kernsrc)
            os.symlink(kernsrc, s)

do_symlink_kernsrc(d)