add virtio queue struct and flag

src/virtio/queue.rs

@@ -1,5 +1,6 @@
 use super::header::VirtioHeader;
 use super::Error;
+use bitflags::bitflags;
 
 pub const MAX_QUEUE_SIZE: usize = 32768;
 
@@ -29,3 +30,58 @@ impl VirtioQueue {
         Ok(Self { idx, size })
     }
 }
+
+struct Descriptor {
+    /// Address
+    addr: u64,
+    /// Length
+    len: u32,
+    /// The flags
+    flags: DescriptorFlag,
+    /// Next field if flags & NEXT
+    next: u16,
+}
+
+bitflags! {
+    pub struct DescriptorFlag: u16 {
+        /// Marks a buffer as continuing via the next field.
+        const NEXT = 1;
+        /// Marks a buffer as device write-only.
+        const WRITE = 2;
+        /// The buffer contains a list of buffer descriptors.
+        const INDIRECT = 4;
+    }
+}
+
+struct AvailRing {
+    flags: AvailRingFlag,
+    idx: u16,
+    ring: [u16; 32],
+    used_event: u16,
+}
+
+bitflags! {
+    pub struct AvailRingFlag: u16 {
+        const NO_INTERRUPT = 1;
+    }
+}
+
+struct UsedRing {
+    flags: UsedRingFlag,
+    idx: u16,
+    used_ring: [UsedElem; 32],
+    avail_event: u16,
+}
+
+struct UsedElem {
+    /// Index of start of used descriptor chain.
+    id: u32,
+    /// Total length of the descriptor chain which was used
+    len: u32,
+}
+
+bitflags! {
+    pub struct UsedRingFlag: u16 {
+        const NO_NOTIFY = 1;
+    }
+}