Remove bytes read/written from marshal.Marshallable API.

Users of the API only care about whether the copy in/out succeeds in
their entirety, which is already signalled by the returned error.

PiperOrigin-RevId: 296297843

pkg/sentry/kernel/rseq.go

@@ -304,7 +304,7 @@ func (t *Task) rseqAddrInterrupt() {
 	}
 
 	var cs linux.RSeqCriticalSection
-	if _, err := cs.CopyIn(t, critAddr); err != nil {
+	if err := cs.CopyIn(t, critAddr); err != nil {
 		t.Debugf("Failed to copy critical section from %#x for rseq: %v", critAddr, err)
 		t.forceSignal(linux.SIGSEGV, false /* unconditional */)
 		t.SendSignal(SignalInfoPriv(linux.SIGSEGV))

pkg/sentry/syscalls/linux/sys_stat.go

@@ -131,8 +131,7 @@ func stat(t *kernel.Task, d *fs.Dirent, dirPath bool, statAddr usermem.Addr) err
 		return err
 	}
 	s := statFromAttrs(t, d.Inode.StableAttr, uattr)
-	_, err = s.CopyOut(t, statAddr)
-	return err
+	return s.CopyOut(t, statAddr)
 }
 
 // fstat implements fstat for the given *fs.File.
@@ -142,8 +141,7 @@ func fstat(t *kernel.Task, f *fs.File, statAddr usermem.Addr) error {
 		return err
 	}
 	s := statFromAttrs(t, f.Dirent.Inode.StableAttr, uattr)
-	_, err = s.CopyOut(t, statAddr)
-	return err
+	return s.CopyOut(t, statAddr)
 }
 
 // Statx implements linux syscall statx(2).

tools/go_marshal/gomarshal/generator_interfaces.go

@@ -507,13 +507,14 @@ func (g *interfaceGenerator) emitMarshallable() {
 	g.emit("// CopyOut implements marshal.Marshallable.CopyOut.\n")
 	g.recordUsedImport("marshal")
 	g.recordUsedImport("usermem")
-	g.emit("func (%s *%s) CopyOut(task marshal.Task, addr usermem.Addr) (int, error) {\n", g.r, g.typeName())
+	g.emit("func (%s *%s) CopyOut(task marshal.Task, addr usermem.Addr) error {\n", g.r, g.typeName())
 	g.inIndent(func() {
 		fallback := func() {
 			g.emit("// Type %s doesn't have a packed layout in memory, fall back to MarshalBytes.\n", g.typeName())
 			g.emit("buf := task.CopyScratchBuffer(%s.SizeBytes())\n", g.r)
 			g.emit("%s.MarshalBytes(buf)\n", g.r)
-			g.emit("return task.CopyOutBytes(addr, buf)\n")
+			g.emit("_, err := task.CopyOutBytes(addr, buf)\n")
+			g.emit("return err\n")
 		}
 		if thisPacked {
 			g.recordUsedImport("reflect")
@@ -539,11 +540,11 @@ func (g *interfaceGenerator) emitMarshallable() {
 			g.emit("hdr.Len = %s.SizeBytes()\n", g.r)
 			g.emit("hdr.Cap = %s.SizeBytes()\n\n", g.r)
 
-			g.emit("len, err := task.CopyOutBytes(addr, buf)\n")
+			g.emit("_, err := task.CopyOutBytes(addr, buf)\n")
 			g.emit("// Since we bypassed the compiler's escape analysis, indicate that %s\n", g.r)
 			g.emit("// must live until after the CopyOutBytes.\n")
 			g.emit("runtime.KeepAlive(%s)\n", g.r)
-			g.emit("return len, err\n")
+			g.emit("return err\n")
 		} else {
 			fallback()
 		}
@@ -553,20 +554,20 @@ func (g *interfaceGenerator) emitMarshallable() {
 	g.emit("// CopyIn implements marshal.Marshallable.CopyIn.\n")
 	g.recordUsedImport("marshal")
 	g.recordUsedImport("usermem")
-	g.emit("func (%s *%s) CopyIn(task marshal.Task, addr usermem.Addr) (int, error) {\n", g.r, g.typeName())
+	g.emit("func (%s *%s) CopyIn(task marshal.Task, addr usermem.Addr) error {\n", g.r, g.typeName())
 	g.inIndent(func() {
 		fallback := func() {
 			g.emit("// Type %s doesn't have a packed layout in memory, fall back to UnmarshalBytes.\n", g.typeName())
 			g.emit("buf := task.CopyScratchBuffer(%s.SizeBytes())\n", g.r)
-			g.emit("n, err := task.CopyInBytes(addr, buf)\n")
+			g.emit("_, err := task.CopyInBytes(addr, buf)\n")
 			g.emit("if err != nil {\n")
 			g.inIndent(func() {
-				g.emit("return n, err\n")
+				g.emit("return err\n")
 			})
 			g.emit("}\n")
 
 			g.emit("%s.UnmarshalBytes(buf)\n", g.r)
-			g.emit("return n, nil\n")
+			g.emit("return nil\n")
 		}
 		if thisPacked {
 			g.recordUsedImport("reflect")
@@ -592,11 +593,11 @@ func (g *interfaceGenerator) emitMarshallable() {
 			g.emit("hdr.Len = %s.SizeBytes()\n", g.r)
 			g.emit("hdr.Cap = %s.SizeBytes()\n\n", g.r)
 
-			g.emit("len, err := task.CopyInBytes(addr, buf)\n")
+			g.emit("_, err := task.CopyInBytes(addr, buf)\n")
 			g.emit("// Since we bypassed the compiler's escape analysis, indicate that %s\n", g.r)
 			g.emit("// must live until after the CopyInBytes.\n")
 			g.emit("runtime.KeepAlive(%s)\n", g.r)
-			g.emit("return len, err\n")
+			g.emit("return err\n")
 		} else {
 			fallback()
 		}

tools/go_marshal/gomarshal/generator_tests.go

@@ -92,7 +92,7 @@ func (g *testGenerator) emitTestNonZeroSize() {
 		g.emit("x := &%s{}\n", g.typeName())
 		g.emit("if x.SizeBytes() == 0 {\n")
 		g.inIndent(func() {
-			g.emit("t.Fatal(\"Marshallable.Size() should not return zero\")\n")
+			g.emit("t.Fatal(\"Marshallable.SizeBytes() should not return zero\")\n")
 		})
 		g.emit("}\n")
 	})

tools/go_marshal/marshal/marshal.go

@@ -91,12 +91,12 @@ type Marshallable interface {
 	// marshalled does not escape. The implementation should avoid creating
 	// extra copies in memory by directly deserializing to the object's
 	// underlying memory.
-	CopyIn(task Task, addr usermem.Addr) (int, error)
+	CopyIn(task Task, addr usermem.Addr) error
 
 	// CopyOut serializes a Marshallable type to a task's memory. This may only
 	// be called from a task goroutine. This is more efficient than calling
 	// MarshalUnsafe on Marshallable.Packed types, as the type being serialized
 	// does not escape. The implementation should avoid creating extra copies in
 	// memory by directly serializing from the object's underlying memory.
-	CopyOut(task Task, addr usermem.Addr) (int, error)
+	CopyOut(task Task, addr usermem.Addr) error
 }