Changing xdp_umem_reg definition

[tgross35]

Linux 6.12 added a new field to xdp_umem_reg, tx_metadata_len (patch). We have a PR to add this field to libc at rust-lang/libc#3956, and based on an informal search it seems like rustix might be about the only crate making use of this type currently. Is there any way we could add this field to libc without breaking things for rustix?

Considering this is a break in uapi I think we probably have some leeway making a breaking change on our end too, but I want to be sure it won't cause a build failure for everyone using rustix.

[arctic-alpaca]

For some added context, #1061 is currently blocked on the update of xdp_umem_reg in libc.

[sunfishcode]

From looking at the code, it doesn't look like anything will break for rustix's users if libc makes that change. Rustix doesn't use xdp_umem_reg directly for anything; it have its own XdpUmemReg. And the only thing rustix does with it is pass it to setsockopt, where a pointer and length are passed, so the kernel will only fill in the fields that rustix is expecting.

[tgross35]

Thanks for confirming! Guess we are all set then, the update should be in the next release.