Function ancillary_space 

pub const fn ancillary_space<T>() -> usize
where
    T: AncillaryData,

Available on crate features io and ancillary only.

Returns the buffer size required to hold one ancillary message carrying a value of type T.

This is the platform-appropriate equivalent of CMSG_SPACE(T::SIZE) on Unix or WSA_CMSG_SPACE(T::SIZE) on Windows, and can be used as a const generic argument for AncillaryBuf.