Hi, I hope this is the correct way to ask about this issue, I haven't used the kernel mailing list before. Between different compilations of an AF_XDP project, I encountered "random" EINVAL errors when calling setsockopt XDP_UMEM_REG with the same parameter. I think this might be caused by this patch: https://lore.kernel.org/all/20231127190319.1190813-2-sdf@xxxxxxxxxx/ It added "tx_metadata_len" to the "xdp_umem_reg" struct. In the "xsk_setsockopt" code in xdp/xsk.c, the provided "optlen" is checked against the length of "xdp_umem_reg_v2" and "xdp_umem_reg" to check which version of "xdp_umem_reg", the user supplied. At least on my machine (x86_64, Fedora 40, 6.9.7), these two structs have the same size (32 bytes) due to the compiler adding padding to "xdp_umem_reg_v2". This means if the user supplies "xdp_umem_reg_v2", it is falsely treated as "xdp_umem_reg". I'm not sure whether there is some implicit struct packing happening or whether this is indeed a bug. Best regards, Julian
