remove all allocations

net/uring/io_uring_linux.go

@@ -9,11 +9,11 @@
 	"fmt"
 	"net"
 	"os"
-	"runtime"
 	"sync"
 	"time"
 	"unsafe"
 
+	"golang.zx2c4.com/wireguard/device"
 	"inet.af/netaddr"
 )
 
@@ -35,6 +35,7 @@ type UDPConn struct {
 	file  *os.File // must keep file from being GC'd
 	fd    C.int
 	local net.Addr
+	req   req
 }
 
 func NewUDPConn(conn *net.UDPConn) (*UDPConn, error) {
@@ -56,39 +57,53 @@ func NewUDPConn(conn *net.UDPConn) (*UDPConn, error) {
 
 	const queue_depth = 8 // TODO: What value to use here?
 	C.io_uring_queue_init(queue_depth, r, 0)
-	c := &UDPConn{
+	u := &UDPConn{
 		ptr:   r,
 		conn:  conn,
 		file:  file,
 		fd:    C.int(file.Fd()),
 		local: conn.LocalAddr(),
 	}
-	return c, nil
+	if err := u.submitRequest(); err != nil {
+		u.Close() // TODO: will this crash?
+		return nil, err
+	}
+	return u, nil
+}
+
+type req struct {
+	mhdr C.go_msghdr
+	iov  C.go_iovec
+	sa   C.go_sockaddr_in
+	ip   [4]byte // TODO: ipv6
+	port C.uint16_t
+	buf  [device.MaxSegmentSize]byte
+}
+
+func (u *UDPConn) submitRequest() error {
+	// TODO: eventually separate submitting the request and waiting for the response.
+	errno := C.submit_recvmsg_request(u.fd, u.ptr, &u.req.mhdr, &u.req.iov, &u.req.sa, (*C.char)(unsafe.Pointer(&u.req.buf[0])), C.int(len(u.req.buf)))
+	if errno < 0 {
+		return fmt.Errorf("uring.submitRequest failed: %v", errno) // TODO: Improve
+	}
+	return nil
 }
 
 func (u *UDPConn) ReadFromNetaddr(buf []byte) (int, netaddr.IPPort, error) {
 	if u.fd == 0 {
 		return 0, netaddr.IPPort{}, errors.New("invalid uring.UDPConn")
 	}
-	mhdr := new(C.go_msghdr)
-	iov := new(C.go_iovec)
-	sa := new(C.go_sockaddr_in)
-	// TODO: eventually separate submitting the request and waiting for the response.
-	errno := C.submit_recvmsg_request(u.fd, u.ptr, mhdr, iov, sa, (*C.char)(unsafe.Pointer(&buf[0])), C.int(len(buf)))
-	if errno < 0 {
-		return 0, netaddr.IPPort{}, fmt.Errorf("uring.UDPConn recv failed: %v", errno) // TODO: Improve errno
-	}
-
-	a := new([4]byte)
-	var port C.uint16_t
-	n := C.receive_into(u.fd, u.ptr, (*C.char)(unsafe.Pointer(a)), &port)
+	n := C.receive_into(u.fd, u.ptr, (*C.char)(unsafe.Pointer(&u.req.ip)), &u.req.port)
 	if n < 0 {
 		return 0, netaddr.IPPort{}, errors.New("something wrong")
 	}
-	ipp := netaddr.IPPortFrom(netaddr.IPFrom4(*a), uint16(port))
-	runtime.KeepAlive(mhdr)
-	runtime.KeepAlive(iov)
-	runtime.KeepAlive(sa)
+	ipp := netaddr.IPPortFrom(netaddr.IPFrom4(u.req.ip), uint16(u.req.port))
+	copy(buf, u.req.buf[:n])
+	// Queue up a new request.
+	err := u.submitRequest()
+	if err != nil {
+		panic("how should we handle this?")
+	}
 	return int(n), ipp, nil
 }