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#487 Add ways to set Path Discovery MTU for Linux on a Socket. #515

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@darnuria darnuria commented Jun 9, 2024

Hello first contribution here! It may need some careful review since MTU management is a bit complicated and not so portable.

Add ways to set Path Discovery MTU for Linux on a Socket. (it may not work on freebsd EDIT: CI confirmed it! but may work on Windows subsystem and winsock: https://learn.microsoft.com/en-us/windows/win32/winsock/ipproto-ip-socket-options.

This contribution use setsocketops to configure Dont Fragment (DF) bit and OS
behavior related to PMTU.

It introduce PathMtuDiscoveringMode enum to manage it rust-way and 4 functions
respectively for ipv4/v6 and set/get.

Omit and Interface exist but are not widely documented.

Initially It started by preparing a PR for the patch purposed here: #487

Context: Why it can be needed in a rust library? Some protocols such as DNS in UDP or traceroute needs to manage the MTU on a socket level.

Exemples:

This contribution use setsocketops to configure Dont Fragment (DF) bit and OS
behavior related to PMTU.

It introduce PathMtuDiscoveringMode enum to manage it rust-way and 4 functions
respectively for ipv4/v6 and set/get.

Omit and Interface exist but are not widely documented.
src/sys/unix.rs Outdated
#[cfg_attr(docsrs, doc(cfg(all(feature = "all", target_os = "linux"))))]
#[repr(C)]
#[derive(Debug)]
pub enum PathMtuDiscoveringMode {
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I'm not sure about this enum.

Maybe it's better as a type alias with constants for the options? This way we don't have to do the conversion and we don't have to deal with the case where the kernel returns a value we don't support yet.

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Ok I agree, I may do a patch to the linux man page since some are not explicitly documented outside of the in.h/in6.h

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Maybe it's better as a type alias with constants for the options? This way we don't have to do the conversion and we don't have to deal with the case where the kernel returns a value we don't support yet.

I reused the pattern used for Type and Protocol code tell me if wasn't the best move. :)

src/sys/unix.rs Outdated Show resolved Hide resolved
@darnuria
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Hello, thanks for the review, will do the changes today.

darnuria and others added 4 commits June 19, 2024 14:28
I reused the pattern used elsewhere to have handful short hands documented,
while yet permiting futur constant not exposed in the lib.

Also expose MtuDiscovering Mode types..

#[cfg(all(feature = "all", target_os = "linux"))]
#[cfg_attr(docsrs, doc(cfg(all(feature = "all", target_os = "linux"))))]
impl PathMtuDiscoveringModeV6 {
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It involve some code duplication alas but it's code that... never change except for adding new mode since API don't change for Linux.

@darnuria darnuria marked this pull request as ready for review June 19, 2024 19:21
@Thomasdezeeuw
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Sorry @darnuria I didn't have time to review this last weekend and I don't think I'll have time the next two weeks either, so it's going to take a little while.

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2 participants