Support for syscalls required for AF_XDP

[arctic-alpaca]

Hi,

I'm experimenting with AF_XDP and would love to use rustix instead of libc. For the BPF side of things, I use aya, so only the non-BPF related syscalls remain. Some syscalls are already supported like mmap and socket but others would need to be implemented or expanded/modified. I created a list of missing syscalls, constants and structs. Most of the syscalls, etc were added in 4.18 with some additions and modifications in later kernel versions.

Syscalls:

• setsockopt
  • setsockopt(fd, SOL_XDP, XDP_UMEM_REG, umem_reg, sizeof(umem_reg)), umem_reg see structs
  • setsockopt(fs, SOL_XDP, XDP_UMEM_FILL_RING, fill_size, sizeof(fill_size)), fill_size = u32 (https://github.com/torvalds/linux/blob/v6.6/net/xdp/xsk.c#L944)
  • setsockopt(fs, SOL_XDP, XDP_UMEM_COMPLETION_RING, comp_size, sizeof(comp_size)), comp_size = u32
  • setsockopt(fs, SOL_XDP, XDP_RX_RING, rx_size, sizeof(rx_size)), rx_size = u32
  • setsockopt(fs, SOL_XDP, XDP_TX_RING, tx_size, sizeof(tx_size)) tx_size = u32
• getsockopt
  • getsockopt(fd, SOL_XDP, XDP_MMAP_OFFSETS, *xdp_mmap_offsets, &optlen), xdp_mmap_offsets see structs
  • getsockopt(fd, SOL_XDP, XDP_STATISTICS, *xdp_statistics, &optlen), xdp_statistics see structs
  • getsockopt(fd, SOL_XDP, XDP_OPTIONS, *xdp_options, &optlen), xdp_options see structs
• bind
  • bind(fd, *sockaddr_xdp, sizeof(sockaddr_xdp)), sockaddr_xdp see structs, bind with various addresses is already supported but not with sockaddr_xdp
• if_indextoname
• if_nametoindex (optional)

Constants:

• AF_XDP
• PF_XDP same as AF_XDP
• SOL_XDP
• XDP socket options
• XDP offsets
• sockaddr_xdp map flags
• xsk_umem_config flags
• XDP_RING flags
• xdp_options flags
• masks for unaligned chunks mode
• xdp_desc options

Structs:

• sockaddr_xdp, used by bind(fd, *sockaddr_xdp, sizeof(sockaddr_xdp))
• xdp_ring_offset / xdp_ring_offset_v1, used in xdp_mmap_offsets
• xdp_mmap_offsets / xdp_mmap_offsets_v1, used by getsockopt(...,XDP_MMAP_OFFSETS,...)
• xdp_umem_reg / umem_reg_v1 used by setsockopt(...,XDP_UMEM_REG,...)
• xdp_desc, used by mmap as sizeof(xdp_desc) for XDP_PGOFF_{RX,TX}_RING
• xdp_statistics / xdp_statistics_v1, used by getsockopt(...,XDP_STATISTICS,...)
• xdp_options, used by getsockopt(...,XDP_OPTIONS,...)

If this is something you are interested in adding, I'd be happy to work on PR(s) to implement it but I would require some guidance:

• Some syscall parameters/returns come in two versions, how should this be implemented?
• Should kernel versions required for syscalls be listed?
• I'm unsure how testing can be done for things like setsockopt as I don't think there is a syscall to check their result.
• For {get,set}sockopt and bind I can orient myself at already existing syscalls in rustix but for if_indextoname and if_nametoindex, I'm unsure how to implement them.

[arctic-alpaca]

With #946 and #972 merged, this is completed.