Function mbedtls_x509write_csr_pem 

pub unsafe extern "C" fn mbedtls_x509write_csr_pem(
    ctx: *mut mbedtls_x509write_csr,
    buf: *mut c_uchar,
    size: usize,
    f_rng: mbedtls_f_rng_t,
    p_rng: *mut c_void,
) -> c_int

\brief Write a CSR (Certificate Signing Request) to a PEM string

\param ctx CSR to write away \param buf buffer to write to \param size size of the buffer \param f_rng RNG function. This must not be \c NULL. \param p_rng RNG parameter

\return 0 if successful, or a specific error code

\note \p f_rng is used for the signature operation.