pre-fill the tx ring with bogus empty packets

overlay/virtqueue/descriptor_table.go

@@ -168,12 +168,12 @@ func (dt *DescriptorTable) releaseBuffers() error {
 	return nil
 }
 
-func (dt *DescriptorTable) CreateDescriptorForOutputs() (uint16, error) {
+func (dt *DescriptorTable) CreateDescriptorForOutputs() (uint16, uint32, error) {
 	//todo just fill the damn table
 	// Do we still have enough free descriptors?
 
 	if 1 > dt.freeNum {
-		return 0, ErrNotEnoughFreeDescriptors
+		return 0, 0, ErrNotEnoughFreeDescriptors
 	}
 
 	// Above validation ensured that there is at least one free descriptor, so
@@ -216,7 +216,7 @@ func (dt *DescriptorTable) CreateDescriptorForOutputs() (uint16, error) {
 		dt.descriptors[dt.freeHeadIndex].next = next
 	}
 
-	return head, nil
+	return head, desc.length, nil
 }
 
 func (dt *DescriptorTable) createDescriptorForInputs() (uint16, error) {

overlay/virtqueue/split_virtqueue.go

@@ -301,7 +301,6 @@ func (sq *SplitQueue) BlockAndGetHeadsCapped(ctx context.Context, maxToTake int)
 // and any further calls to [SplitQueue.OfferDescriptorChain] will stall.
 
 func (sq *SplitQueue) OfferInDescriptorChains() (uint16, error) {
-	// Create a descriptor chain for the given buffers.
 	var (
 		head uint16
 		err  error
@@ -350,18 +349,6 @@ func (sq *SplitQueue) SetDescSize(head uint16, sz int) {
 	sq.descriptorTable.descriptors[int(head)].length = uint32(sz)
 }
 
-func (sq *SplitQueue) OfferDescriptor(chain uint16, kick bool) error {
-	// Make the descriptor chain available to the device.
-	sq.availableRing.offerSingle(chain)
-
-	// Notify the device to make it process the updated available ring.
-	if kick {
-		return sq.Kick()
-	}
-
-	return nil
-}
-
 func (sq *SplitQueue) OfferDescriptorChains(chains []uint16, kick bool) error {
 	// Make the descriptor chain available to the device.
 	sq.availableRing.offer(chains)

overlay/virtqueue/used_ring.go

@@ -153,11 +153,7 @@ func (r *UsedRing) takeOne() (UsedElement, bool) {
 }
 
 // InitOfferSingle is only used to pre-fill the used queue at startup, and should not be used if the device is running!
-func (r *UsedRing) InitOfferSingle(x uint16, size int) {
-	//always called under lock
-	//r.mu.Lock()
-	//defer r.mu.Unlock()
-
+func (r *UsedRing) InitOfferSingle(x uint16, size uint32) {
 	offset := 0
 	// Add descriptor chain heads to the ring.
 
@@ -166,10 +162,8 @@ func (r *UsedRing) InitOfferSingle(x uint16, size int) {
 	// size) is always a power of 2 and smaller than the highest possible
 	// 16-bit value.
 	insertIndex := int(*r.ringIndex+uint16(offset)) % len(r.ring)
-	r.ring[insertIndex] = UsedElement{
-		DescriptorIndex: uint32(x),
-		Length:          uint32(size),
-	}
+	r.ring[insertIndex].DescriptorIndex = uint32(x)
+	r.ring[insertIndex].Length = size
 
 	// Increase the ring index by the number of descriptor chains added to the ring.
 	*r.ringIndex += 1