checkpt

udp/conn.go

@@ -8,6 +8,12 @@ import (
 
 const MTU = 9001
 
+// MaxWriteBatch is the largest batch any Conn.WriteBatch implementation is
+// required to accept. Callers SHOULD NOT pass more than this per call; Linux
+// backends preallocate sendmmsg scratch sized to this value, so exceeding it
+// only costs a chunked retry.
+const MaxWriteBatch = 128
+
 type EncReader func(
 	addr netip.AddrPort,
 	payload []byte,
@@ -18,6 +24,12 @@ type Conn interface {
 	LocalAddr() (netip.AddrPort, error)
 	ListenOut(r EncReader) error
 	WriteTo(b []byte, addr netip.AddrPort) error
+	// WriteBatch sends a contiguous batch of packets, each with its own
+	// destination. bufs and addrs must have the same length. Linux uses
+	// sendmmsg(2) for a single syscall; other backends fall back to a
+	// WriteTo loop. Returns on the first error; callers may observe a
+	// partial send if some packets went out before the error.
+	WriteBatch(bufs [][]byte, addrs []netip.AddrPort) error
 	ReloadConfig(c *config.C)
 	SupportsMultipleReaders() bool
 	Close() error
@@ -40,6 +52,9 @@ func (NoopConn) SupportsMultipleReaders() bool {
 func (NoopConn) WriteTo(_ []byte, _ netip.AddrPort) error {
 	return nil
 }
+func (NoopConn) WriteBatch(_ [][]byte, _ []netip.AddrPort) error {
+	return nil
+}
 func (NoopConn) ReloadConfig(_ *config.C) {
 	return
 }

udp/udp_generic.go

@@ -42,6 +42,15 @@ func (u *GenericConn) WriteTo(b []byte, addr netip.AddrPort) error {
 	return err
 }
 
+func (u *GenericConn) WriteBatch(bufs [][]byte, addrs []netip.AddrPort) error {
+	for i, b := range bufs {
+		if _, err := u.UDPConn.WriteToUDPAddrPort(b, addrs[i]); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 func (u *GenericConn) LocalAddr() (netip.AddrPort, error) {
 	a := u.UDPConn.LocalAddr()
 

udp/udp_linux_64.go

@@ -55,3 +55,23 @@ func (u *StdConn) PrepareRawMessages(n int) ([]rawMessage, [][]byte, [][]byte) {
 
 	return msgs, buffers, names
 }
+
+// prepareWriteMessages allocates one Mmsghdr/iovec/sockaddr scratch per slot,
+// wired up so each writeMsgs[i] already points at writeIovs[i] and
+// writeNames[i]. Callers fill in the iovec Base/Len, the sockaddr bytes, and
+// Namelen before each sendmmsg.
+func (u *StdConn) prepareWriteMessages(n int) {
+	u.writeMsgs = make([]rawMessage, n)
+	u.writeIovs = make([]iovec, n)
+	u.writeNames = make([][]byte, n)
+	for i := range u.writeMsgs {
+		u.writeNames[i] = make([]byte, unix.SizeofSockaddrInet6)
+		u.writeMsgs[i].Hdr.Iov = &u.writeIovs[i]
+		u.writeMsgs[i].Hdr.Iovlen = 1
+		u.writeMsgs[i].Hdr.Name = &u.writeNames[i][0]
+	}
+}
+
+func setIovLen(v *iovec, n int) {
+	v.Len = uint64(n)
+}