Function mbedtls_x509_csr_parse_file 

pub unsafe extern "C" fn mbedtls_x509_csr_parse_file(
    csr: *mut mbedtls_x509_csr,
    path: *const c_char,
) -> c_int

\brief Load a Certificate Signing Request (CSR)

\note See notes for \c mbedtls_x509_csr_parse()

\param csr CSR context to fill \param path filename to read the CSR from

\return 0 if successful, or a specific X509 or PEM error code