[go-marshal] Add dynamic tag in go_marshal.

This makes it easier to implement dynamically sized types in go-marshal. You
really only need to implement MarshalBytes, UnmarshalBytes and SizeBytes to
implement the entire interface.

By using the `dynamic` tag, the autogenerator will generate the rest of the
methods for us.

This change also simplifies how KernelIPTGetEntries implements Marshallable
using the newly added utility.

PiperOrigin-RevId: 356397114

1 files changed, 35 insertions, 0 deletions

diff --git a/tools/go_marshal/test/test.go b/tools/go_marshal/test/test.go
index e7e3ed74a..b8eb989d9 100644
--- a/tools/go_marshal/test/test.go
+++ b/tools/go_marshal/test/test.go
@@ -16,6 +16,8 @@
 package test
 
 import (
+	"gvisor.dev/gvisor/pkg/marshal/primitive"
+
 	// We're intentionally using a package name alias here even though it's not
 	// necessary to test the code generator's ability to handle package aliases.
 	ex "gvisor.dev/gvisor/tools/go_marshal/test/external"
@@ -198,3 +200,36 @@ type Type11 struct {
 	ex.External
 	y int64
 }
+
+// Type12Dynamic is a dynamically sized struct which depends on the autogenerator
+// to generate some Marshallable methods for it.
+//
+// +marshal dynamic
+type Type12Dynamic struct {
+	X primitive.Int64
+	Y []primitive.Int64
+}
+
+// SizeBytes implements marshal.Marshallable.SizeBytes.
+func (t *Type12Dynamic) SizeBytes() int {
+	return (len(t.Y) * 8) + t.X.SizeBytes()
+}
+
+// MarshalBytes implements marshal.Marshallable.MarshalBytes.
+func (t *Type12Dynamic) MarshalBytes(dst []byte) {
+	t.X.MarshalBytes(dst)
+	dst = dst[t.X.SizeBytes():]
+	for i, x := range t.Y {
+		x.MarshalBytes(dst[i*8 : (i+1)*8])
+	}
+}
+
+// UnmarshalBytes implements marshal.Marshallable.UnmarshalBytes.
+func (t *Type12Dynamic) UnmarshalBytes(src []byte) {
+	t.X.UnmarshalBytes(src)
+	for i := t.X.SizeBytes(); i < len(src); i += 8 {
+		var x primitive.Int64
+		x.UnmarshalBytes(src[i:])
+		t.Y = append(t.Y, x)
+	}
+}