move AF_XDP structs and constants to linux/mod.rs

[arctic-alpaca]

Description

As discussed in #3956, the AF_XDP structs and constants are all uapi and as such should go into src/unix/linux_like/linux/mod.rs. This PR moves all AF_XDP structs and constants there.

The _v1 versions are for backwards compatibility with older kernel versions. With v1.0, they could probably be removed, since the newer versions will work (with new fields not being taken into account by the kernel). If that is desirable, I can crate a follow-up PR to remove them or remove them here.

Sources

• All structs and constants not explicitly listed are defined in if_xdp.h.
• xdp_ring_offset_v1 & xdp_mmap_offsets_v1 in xsk.h.
• xdp_umem_reg_v1 & xdp_statistics_v1 in xsk.c.

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are
  included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI

I could not test the the changes locally due to the error described in #3865 (comment)

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[tgross35]

Thanks!

If the _v1 structs aren't intended to be used anymore, could you mark them as deprecated here? Then this can go to 0.2, and they can be removed in a separate PR that only goes to main.

[arctic-alpaca]

If the CI failure is related to the changes, I cannot tell what caused it.

[tgross35]

Slight rewording to suggest an alternative, and to rewrap to 100 characters. Could you update the others as well?

Suggested change

	note = "We consider removing this as the newer version of this struct will work with older kernel versions. If you're using it, please comment on https://github.com/rust-lang/libc/issues/4168"
	note = "Use `xdp_ring_offset` instead, which will still work with old kernel versions. If \
	you still need this version, please comment at \
	https://github.com/rust-lang/libc/issues/4168"

After this please squash and we should be able to merge.

[tgross35]

Nah CI is just Android getting stuck, that happens for some reason

[arctic-alpaca]

I just realized that I made a mistake with the deprecation. The older versions might be used to check sizes for when another version gets added. Basically checking the length the kernel returns against foo_v1, foo_v2 and if it's larger than both, going with foo. Currently there are no _v2 structs, but that's only the case because of the bug mentioned in #3956. So while the up-to-date structs would work, there would be no way to check which version the kernel used if/when _v2 versions get added.

I'm not sure whether you would prefer to keep them in, or to only support the latest version of the Linux Kernel.

Sorry for getting this wrong. If it's fine for you, I'd remove the deprecation info and close the issue so that this PR only contains the move to the src/unix/linux_like/linux/mod.rs file.

[tgross35]

I think I need to double check what the kernel headers/docs say to get a better understanding. Feel free to drop deprecation from this PR, we can revisit later.

[arctic-alpaca]

Thanks, sorry again for the trouble.

[tgross35]

No trouble at all :)