pkg/ipc: don't send program padding to executor

Currently we always send 2MB of data to executor in ipc_simple.go.
Send only what's consumed by the program, and don't send the trailing zeros.
Serialized programs usually take only few KBs.

2 files changed, 6 insertions, 5 deletions

diff --git a/prog/encodingexec.go b/prog/encodingexec.go
index b2b173bbe..e45ba1192 100644
--- a/prog/encodingexec.go
+++ b/prog/encodingexec.go
@@ -57,8 +57,9 @@ func (s ByPhysicalAddr) Less(i, j int) bool {
 }
 
 // SerializeForExec serializes program p for execution by process pid into the provided buffer.
+// Returns number of bytes written to the buffer.
 // If the provided buffer is too small for the program an error is returned.
-func (p *Prog) SerializeForExec(buffer []byte, pid int) error {
+func (p *Prog) SerializeForExec(buffer []byte, pid int) (int, error) {
 	if debug {
 		if err := p.validate(); err != nil {
 			panic(fmt.Errorf("serializing invalid program: %v", err))
@@ -193,9 +194,9 @@ func (p *Prog) SerializeForExec(buffer []byte, pid int) error {
 	}
 	w.write(ExecInstrEOF)
 	if w.eof {
-		return fmt.Errorf("provided buffer is too small")
+		return 0, fmt.Errorf("provided buffer is too small")
 	}
-	return nil
+	return len(buffer) - len(w.buf), nil
 }
 
 func (target *Target) physicalAddr(arg Arg) uint64 {
diff --git a/prog/encodingexec_test.go b/prog/encodingexec_test.go
index 3b37783f2..cff800911 100644
--- a/prog/encodingexec_test.go
+++ b/prog/encodingexec_test.go
@@ -15,7 +15,7 @@ func TestSerializeForExecRandom(t *testing.T) {
 	buf := make([]byte, ExecBufferSize)
 	for i := 0; i < iters; i++ {
 		p := target.Generate(rs, 10, nil)
-		if err := p.SerializeForExec(buf, i%16); err != nil {
+		if _, err := p.SerializeForExec(buf, i%16); err != nil {
 			t.Fatalf("failed to serialize: %v", err)
 		}
 	}
@@ -269,7 +269,7 @@ func TestSerializeForExec(t *testing.T) {
 			if err != nil {
 				t.Fatalf("failed to deserialize prog %v: %v", i, err)
 			}
-			if err := p.SerializeForExec(buf, i%16); err != nil {
+			if _, err := p.SerializeForExec(buf, i%16); err != nil {
 				t.Fatalf("failed to serialize: %v", err)
 			}
 			w := new(bytes.Buffer)