Add support for TCP send buffer auto tuning.

Send buffer size in TCP indicates the amount of bytes available for the sender
to transmit. This change will allow TCP to update the send buffer size when
- TCP enters established state.
- ACK is received.

The auto tuning is disabled when the send buffer size is set with the
SO_SNDBUF option.

PiperOrigin-RevId: 390312274

1 files changed, 11 insertions, 0 deletions

diff --git a/pkg/tcpip/socketops.go b/pkg/tcpip/socketops.go
index 6bce3af04..34ac62444 100644
--- a/pkg/tcpip/socketops.go
+++ b/pkg/tcpip/socketops.go
@@ -57,6 +57,11 @@ type SocketOptionsHandler interface {
 
 	// OnSetReceiveBufferSize is invoked by SO_RCVBUF and SO_RCVBUFFORCE.
 	OnSetReceiveBufferSize(v, oldSz int64) (newSz int64)
+
+	// WakeupWriters is invoked when the send buffer size for an endpoint is
+	// changed. The handler notifies the writers if the send buffer size is
+	// increased with setsockopt(2) for TCP endpoints.
+	WakeupWriters()
 }
 
 // DefaultSocketOptionsHandler is an embeddable type that implements no-op
@@ -98,6 +103,9 @@ func (*DefaultSocketOptionsHandler) OnSetSendBufferSize(v int64) (newSz int64) {
 	return v
 }
 
+// WakeupWriters implements SocketOptionsHandler.WakeupWriters.
+func (*DefaultSocketOptionsHandler) WakeupWriters() {}
+
 // OnSetReceiveBufferSize implements SocketOptionsHandler.OnSetReceiveBufferSize.
 func (*DefaultSocketOptionsHandler) OnSetReceiveBufferSize(v, oldSz int64) (newSz int64) {
 	return v
@@ -626,6 +634,9 @@ func (so *SocketOptions) SetSendBufferSize(sendBufferSize int64, notify bool) {
 		sendBufferSize = so.handler.OnSetSendBufferSize(sendBufferSize)
 	}
 	so.sendBufferSize.Store(sendBufferSize)
+	if notify {
+		so.handler.WakeupWriters()
+	}
 }
 
 // GetReceiveBufferSize gets value for SO_RCVBUF option.