How to get MTU of an dpdk interface?

[JakkuSakura]

I'm built an async high level network stack that supports websocket based on capsule(customized, runtime independent)/rawsocket and smoltcp.
Currently the mtu of rawsocket is fetched by pnet, mtu of dpdk device is hard coded. I would like to play around jumbo frames with multiple interfaces at the same time.
This requires getting MTU of a dpdk interface.
How to get MTU of an dpdk interface?

I can use ip a to get ena devices' MTU, but not igb_uio.

[JakkuSakura]

Okay, I got it. Unfunately port_id is not publicly visible

impl PortQueue {
    pub fn get_mtu(&self) -> std::io::Result<u16> {
        let mut result = MaybeUninit::uninit();
        unsafe {
            let errno = ffi::rte_eth_dev_get_mtu(self.port_id.raw(), result.as_mut_ptr());
            if errno == 0 {
                Ok(result.assume_init())
            } else {
                Err(std::io::Error::from_raw_os_error(errno))
            }
        }
    }
}

[harry-van-haaren]

Hi @qiujiangkun, (I'm a capsule noobie, but know a little about DPDK.. so this answer is mostly from DPDK knowledge.)

Indeed the rte_eth_dev_get_mtu function will get the MTU for the device, however I believe there is a limitation in Capsule at the moment that "multi-segment mbufs" are not supported, which means that the maximum size of any single frame must fit into the DPDK mbuf size (controlled by RTE_MBUF_DEFAULT_DATAROOM).

This is documented in the capsule source in mbuf.rs here; https://github.com/capsule-rs/capsule/blob/master/core/src/dpdk/mbuf.rs#L104

Hope this helps, -Harry