os: Plan 9: add Process.Signal as a way to send notes.

Move the Signal interface from exec_posix.go to exec.go.
Remove some unsused code from file_plan9.go.

R=fshahriar, rsc
CC=golang-dev
https://golang.org/cl/4683044

src/pkg/os/exec.go

@@ -46,6 +46,11 @@ type ProcAttr struct {
 	Sys *syscall.SysProcAttr
 }
 
+// A Signal can represent any operating system signal.
+type Signal interface {
+	String() string
+}
+
 // Getpid returns the process id of the caller.
 func Getpid() int { return syscall.Getpid() }
 

src/pkg/os/exec_plan9.go

@@ -38,6 +38,27 @@ func StartProcess(name string, argv []string, attr *ProcAttr) (p *Process, err E
 	return newProcess(pid, h), nil
 }
 
+// Plan9Note implements the Signal interface on Plan 9.
+type Plan9Note string
+
+func (note Plan9Note) String() string {
+	return string(note)
+}
+
+func (p *Process) Signal(sig Signal) Error {
+	if p.done {
+		return NewError("os: process already finished")
+	}
+
+	f, e := OpenFile("/proc/"+itoa(p.Pid)+"/note", O_WRONLY, 0)
+	if iserror(e) {
+		return NewSyscallError("signal", e)
+	}
+	defer f.Close()
+	_, e = f.Write([]byte(sig.String()))
+	return e
+}
+
 // Kill causes the Process to exit immediately.
 func (p *Process) Kill() Error {
 	f, e := OpenFile("/proc/"+itoa(p.Pid)+"/ctl", O_WRONLY, 0)
@@ -85,6 +106,7 @@ func (p *Process) Wait(options int) (w *Waitmsg, err Error) {
 		}
 
 		if waitmsg.Pid == p.Pid {
+			p.done = true
 			break
 		}
 	}

src/pkg/os/exec_posix.go

@@ -9,11 +9,6 @@ import (
 	"syscall"
 )
 
-// A Signal can represent any operating system signal.
-type Signal interface {
-	String() string
-}
-
 type UnixSignal int32
 
 func (sig UnixSignal) String() string {

src/pkg/os/file_plan9.go

@@ -14,7 +14,6 @@ type File struct {
 	fd      int
 	name    string
 	dirinfo *dirInfo // nil unless directory being read
-	nepipe  int      // number of consecutive EPIPE in Write
 }
 
 // Fd returns the integer Unix file descriptor referencing the open file.
@@ -273,20 +272,6 @@ func Chmod(name string, mode uint32) Error {
 	return nil
 }
 
-// ChownPlan9 changes the uid and gid strings of the named file.
-func ChownPlan9(name, uid, gid string) Error {
-	var d Dir
-	d.Null()
-
-	d.Uid = uid
-	d.Gid = gid
-
-	if e := syscall.Wstat(name, pdir(nil, &d)); iserror(e) {
-		return &PathError{"chown_plan9", name, e}
-	}
-	return nil
-}
-
 // Chtimes changes the access and modification times of the named
 // file, similar to the Unix utime() or utimes() functions.
 //