syscall: Add Foreground and Pgid to SysProcAttr

On Unix, when placing a child in a new process group, allow that group
to become the foreground process group. Also, allow a child process to
join a specific process group.

When setting the foreground process group, Ctty is used as the file
descriptor of the controlling terminal. Ctty has been added to the BSD
and Solaris SysProcAttr structures and the handling of Setctty changed
to match Linux.

Change-Id: I18d169a6c5ab8a6a90708c4ff52eb4aded50bc8c
Reviewed-on: https://go-review.googlesource.com/5130
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 28 insertions, 6 deletions

diff --git a/src/syscall/exec_bsd.go b/src/syscall/exec_bsd.go
index ff78f197f1..4b5774b492 100644
--- a/src/syscall/exec_bsd.go
+++ b/src/syscall/exec_bsd.go
@@ -16,9 +16,12 @@ type SysProcAttr struct {
 	Credential *Credential // Credential.
 	Ptrace     bool        // Enable tracing.
 	Setsid     bool        // Create session.
-	Setpgid    bool        // Set process group ID to new pid (SYSV setpgrp)
-	Setctty    bool        // Set controlling terminal to fd 0
+	Setpgid    bool        // Set process group ID to Pgid, or, if Pgid == 0, to new pid.
+	Setctty    bool        // Set controlling terminal to fd Ctty
 	Noctty     bool        // Detach fd 0 from controlling terminal
+	Ctty       int         // Controlling TTY fd
+	Foreground bool        // Place child's process group in foreground. (Implies Setpgid. Uses Ctty as fd of controlling TTY)
+	Pgid       int         // Child's process group ID if Setpgid.
 }
 
 // Implemented in runtime package.
@@ -101,8 +104,27 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	}
 
 	// Set process group
-	if sys.Setpgid {
-		_, _, err1 = RawSyscall(SYS_SETPGID, 0, 0, 0)
+	if sys.Setpgid || sys.Foreground {
+		// Place child in process group.
+		_, _, err1 = RawSyscall(SYS_SETPGID, 0, uintptr(sys.Pgid), 0)
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	if sys.Foreground {
+		pgrp := sys.Pgid
+		if pgrp == 0 {
+			r1, _, err1 = RawSyscall(SYS_GETPID, 0, 0, 0)
+			if err1 != 0 {
+				goto childerror
+			}
+
+			pgrp = int(r1)
+		}
+
+		// Place process group in foreground.
+		_, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSPGRP), uintptr(unsafe.Pointer(&pgrp)))
 		if err1 != 0 {
 			goto childerror
 		}
@@ -210,9 +232,9 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 		}
 	}
 
-	// Make fd 0 the tty
+	// Set the controlling TTY to Ctty
 	if sys.Setctty {
-		_, _, err1 = RawSyscall(SYS_IOCTL, 0, uintptr(TIOCSCTTY), 0)
+		_, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSCTTY), 0)
 		if err1 != 0 {
 			goto childerror
 		}