vhost

overlay/virtqueue/descriptor.go

@@ -0,0 +1,43 @@
+package virtqueue
+
+// descriptorFlag is a flag that describes a [Descriptor].
+type descriptorFlag uint16
+
+const (
+	// descriptorFlagHasNext marks a descriptor chain as continuing via the next
+	// field.
+	descriptorFlagHasNext descriptorFlag = 1 << iota
+	// descriptorFlagWritable marks a buffer as device write-only (otherwise
+	// device read-only).
+	descriptorFlagWritable
+	// descriptorFlagIndirect means the buffer contains a list of buffer
+	// descriptors to provide an additional layer of indirection.
+	// Only allowed when the [virtio.FeatureIndirectDescriptors] feature was
+	// negotiated.
+	descriptorFlagIndirect
+)
+
+// descriptorSize is the number of bytes needed to store a [Descriptor] in
+// memory.
+const descriptorSize = 16
+
+// Descriptor describes (a part of) a buffer which is either read-only for the
+// device or write-only for the device (depending on [descriptorFlagWritable]).
+// Multiple descriptors can be chained to produce a "descriptor chain" that can
+// contain both device-readable and device-writable buffers. Device-readable
+// descriptors always come first in a chain. A single, large buffer may be
+// split up by chaining multiple similar descriptors that reference different
+// memory pages. This is required, because buffers may exceed a single page size
+// and the memory accessed by the device is expected to be continuous.
+type Descriptor struct {
+	// address is the address to the continuous memory holding the data for this
+	// descriptor.
+	address uintptr
+	// length is the amount of bytes stored at address.
+	length uint32
+	// flags that describe this descriptor.
+	flags descriptorFlag
+	// next contains the index of the next descriptor continuing this descriptor
+	// chain when the [descriptorFlagHasNext] flag is set.
+	next uint16
+}