We have multiple reports of Linux systems that might:

1. Pass our GSO support check at runtime
   

   quinn/quinn-udp/src/unix.rs

   Lines 823 to 825 in 93b6d01

   	/// Checks whether GSO support is available by checking the kernel version followed by setting
   	/// the UDP_SEGMENT option on a socket
   	pub(crate) fn max_gso_segments() -> usize {

2. But then fail with EIO on the first GSO sendmsg
   

   quinn/quinn-udp/src/unix.rs

   Lines 345 to 349 in 93b6d01

   	// Some network adapters and drivers do not support GSO. Unfortunately, Linux
   	// offers no easy way for us to detect this short of an EIO or sometimes EINVAL
   	// when we try to actually send datagrams using it.
   	#[cfg(any(target_os = "linux", target_os = "android"))]
   	if let Some(libc::EIO) | Some(libc::EINVAL) = e.raw_os_error() {

Reports:

• Disable GSO after encountering EIO on send, redux #1210
• https://bugzilla.mozilla.org/show_bug.cgi?id=1989895

Currently quinn-udp simply returns an error.

Instead, quinn-udp could attempt sending each segment individually.

Note that we already do a retry on other errors:

I am planning to land a hot-fix in Firefox for now, Relying on the QUIC layer to resend. relying on our QUIC state machine adds unnecessary delays.

Documenting this optimization here. I am not sure I will get to it any time soon.