Struct SubmitRing 

#[repr(C)]
pub struct SubmitRing {
    pub submit_head: u32,
    pub submit_tail: u32,
    pub complete_head: u32,
    pub complete_tail: u32,
    pub _pad: [u8; 48],
}

Shared-memory ring buffer mapped into both kernel and domain.

This struct defines the memory layout. The actual ring is initialized by the kernel and mapped at RING_VADDR in the domain’s address space.

Synchronization protocol:

1. Domain writes entries, advances submit_head (Release)
2. Domain calls SYS_SUBMIT
3. Kernel reads entries from submit_tail to submit_head (Acquire)
4. Kernel writes completions, advances complete_head (Release)
5. Domain reads completions from complete_tail to complete_head (Acquire)

Fields

submit_head: u32

Next slot for userspace to write (producer).

submit_tail: u32

Next slot for kernel to process (consumer).

complete_head: u32

Next completion slot for kernel to write (producer).

complete_tail: u32

Next completion slot for userspace to read (consumer).

_pad: [u8; 48]

Padding to cache-line boundary.