code review 49920048: net: plan9 changes for default net directory

src/pkg/net/fd_plan9.go

Index: src/pkg/net/fd_plan9.go
===================================================================
--- a/src/pkg/net/fd_plan9.go
+++ b/src/pkg/net/fd_plan9.go
@@ -13,12 +13,23 @@
 
 // Network file descritor.
 type netFD struct {
-	proto, name, dir string
-	ctl, data        *os.File
-	laddr, raddr     Addr
+	// locking/lifetime of sysfd + serialize access to Read and Write methods
+	fdmu fdMutex
+
+	// immutable until Close
+	proto        string
+	n            string
+	dir          string
+	ctl, data    *os.File
+	laddr, raddr Addr
 }
 
+var (
+	netdir string // default network
+)
+
 func sysInit() {
+	netdir = "/net"
 }
 
 func dial(net string, ra Addr, dialer func(time.Time) (Conn, error), deadline time.Time) (Conn, error) {
@@ -27,16 +38,99 @@
 	return dialChannel(net, ra, dialer, deadline)
 }
 
-func newFD(proto, name string, ctl, data *os.File, laddr, raddr Addr) *netFD {
-	return &netFD{proto, name, "/net/" + proto + "/" + name, ctl, data, laddr, raddr}
+func newFD(proto, name string, ctl, data *os.File, laddr, raddr Addr) (*netFD, error) {
+	return &netFD{proto: proto, n: name, dir: netdir + "/" + proto + "/" + name, ctl: ctl, data: data, laddr: laddr, raddr: raddr}, nil
+}
+
+func (fd *netFD) init() error {
+	// stub for future fd.pd.Init(fd)
+	return nil
+}
+
+func (fd *netFD) name() string {
+	var ls, rs string
+	if fd.laddr != nil {
+		ls = fd.laddr.String()
+	}
+	if fd.raddr != nil {
+		rs = fd.raddr.String()
+	}
+	return fd.proto + ":" + ls + "->" + rs
 }
 
 func (fd *netFD) ok() bool { return fd != nil && fd.ctl != nil }
 
+func (fd *netFD) destroy() {
+	if !fd.ok() {
+		return
+	}
+	err := fd.ctl.Close()
+	if fd.data != nil {
+		if err1 := fd.data.Close(); err1 != nil && err == nil {
+			err = err1
+		}
+	}
+	fd.ctl = nil
+	fd.data = nil
+}
+
+// Add a reference to this fd.
+// Returns an error if the fd cannot be used.
+func (fd *netFD) incref() error {
+	if !fd.fdmu.Incref() {
+		return errClosing
+	}
+	return nil
+}
+
+// Remove a reference to this FD and close if we've been asked to do so
+// (and there are no references left).
+func (fd *netFD) decref() {
+	if fd.fdmu.Decref() {
+		fd.destroy()
+	}
+}
+
+// Add a reference to this fd and lock for reading.
+// Returns an error if the fd cannot be used.
+func (fd *netFD) readLock() error {
+	if !fd.fdmu.RWLock(true) {
+		return errClosing
+	}
+	return nil
+}
+
+// Unlock for reading and remove a reference to this FD.
+func (fd *netFD) readUnlock() {
+	if fd.fdmu.RWUnlock(true) {
+		fd.destroy()
+	}
+}
+
+// Add a reference to this fd and lock for writing.
+// Returns an error if the fd cannot be used.
+func (fd *netFD) writeLock() error {
+	if !fd.fdmu.RWLock(false) {
+		return errClosing
+	}
+	return nil
+}
+
+// Unlock for writing and remove a reference to this FD.
+func (fd *netFD) writeUnlock() {
+	if fd.fdmu.RWUnlock(false) {
+		fd.destroy()
+	}
+}
+
 func (fd *netFD) Read(b []byte) (n int, err error) {
 	if !fd.ok() || fd.data == nil {
 		return 0, syscall.EINVAL
 	}
+	if err := fd.readLock(); err != nil {
+		return 0, err
+	}
+	defer fd.readUnlock()
 	n, err = fd.data.Read(b)
 	if fd.proto == "udp" && err == io.EOF {
 		n = 0
@@ -49,6 +143,10 @@
 	if !fd.ok() || fd.data == nil {
 		return 0, syscall.EINVAL
 	}
+	if err := fd.writeLock(); err != nil {
+		return 0, err
+	}
+	defer fd.writeUnlock()
 	return fd.data.Write(b)
 }
 
@@ -67,6 +165,9 @@
 }
 
 func (fd *netFD) Close() error {
+	if !fd.fdmu.IncrefAndClose() {
+		return errClosing
+	}
 	if !fd.ok() {
 		return syscall.EINVAL
 	}