improve: add load_next_descriptor

Add load_next_descriptor and use it in load_descriptor_chain.

Signed-off-by: ihciah <[email protected]>

Author: ihciah

src/vmm/src/devices/virtio/iovec.rs

@@ -57,12 +57,11 @@ impl IoVecBuffer {
     /// The descriptor chain cannot be referencing the same memory location as another chain
     pub unsafe fn load_descriptor_chain(
         &mut self,
-        head: DescriptorChain,
+        mut desc: DescriptorChain,
     ) -> Result<(), IoVecError> {
         self.clear();
 
-        let mut next_descriptor = Some(head);
-        while let Some(desc) = next_descriptor {
+        loop {
             if desc.is_write_only() {
                 return Err(IoVecError::WriteOnlyDescriptor);
             }
@@ -85,7 +84,9 @@ impl IoVecBuffer {
                 .checked_add(desc.len)
                 .ok_or(IoVecError::OverflowedDescriptor)?;
 
-            next_descriptor = desc.next_descriptor();
+            if desc.load_next_descriptor().is_none() {
+                break;
+            }
         }
 
         Ok(())

src/vmm/src/devices/virtio/queue.rs

@@ -176,6 +176,41 @@ impl<'a, M: GuestMemory> DescriptorChain<'a, M> {
             None
         }
     }
+
+    /// Load the next descriptor in this descriptor chain.
+    /// If none is available, return None.
+    pub fn load_next_descriptor(&mut self) -> Option<()> {
+        if !self.has_next() {
+            return None;
+        }
+        if self.next >= self.queue_size {
+            return None;
+        }
+
+        let desc_head = self.desc_table.unchecked_add(u64::from(self.next) * 16);
+        let desc = match self.mem.load_obj::<Descriptor>(desc_head) {
+            Ok(ret) => ret,
+            Err(err) => {
+                error!(
+                    "Failed to read virtio descriptor from memory at address {:#x}: {}",
+                    desc_head.0, err
+                );
+                return None;
+            }
+        };
+        self.index = self.next;
+        self.addr = GuestAddress(desc.addr);
+        self.len = desc.len;
+        self.flags = desc.flags;
+        self.next = desc.next;
+        self.ttl -= 1;
+
+        if !self.is_valid() {
+            return None;
+        }
+
+        Some(())
+    }
 }
 
 #[derive(Debug)]