Constant ZXIO_SOCKET_MARK_SO_MARK 

pub const ZXIO_SOCKET_MARK_SO_MARK: u8 = ZXIO_SOCKET_MARK_DOMAIN_1; // 1u8

Linux marks aren’t compatible with Fuchsia marks, we store the SO_MARK value in the fuchsia ZXIO_SOCKET_MARK_DOMAIN_1. If a mark in this domain is absent, it will be reported to starnix applications as a 0 since that is the default mark value on Linux.