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>

src/runtime/syscall2_solaris.go

@@ -15,6 +15,7 @@ import _ "unsafe" // for go:linkname
 //go:cgo_import_dynamic libc_execve execve "libc.so"
 //go:cgo_import_dynamic libc_fcntl fcntl "libc.so"
 //go:cgo_import_dynamic libc_gethostname gethostname "libc.so"
+//go:cgo_import_dynamic libc_getpid getpid "libc.so"
 //go:cgo_import_dynamic libc_ioctl ioctl "libc.so"
 //go:cgo_import_dynamic libc_pipe pipe "libc.so"
 //go:cgo_import_dynamic libc_setgid setgid "libc.so"
@@ -35,6 +36,7 @@ import _ "unsafe" // for go:linkname
 //go:linkname libc_execve libc_execve
 //go:linkname libc_fcntl libc_fcntl
 //go:linkname libc_gethostname libc_gethostname
+//go:linkname libc_getpid libc_getpid
 //go:linkname libc_ioctl libc_ioctl
 //go:linkname libc_pipe libc_pipe
 //go:linkname libc_setgid libc_setgid

src/runtime/syscall_solaris.go

@@ -16,6 +16,7 @@ var (
 	libc_fcntl,
 	libc_forkx,
 	libc_gethostname,
+	libc_getpid,
 	libc_ioctl,
 	libc_pipe,
 	libc_setgid,
@@ -183,6 +184,17 @@ func syscall_gethostname() (name string, err uintptr) {
 	return gostringnocopy(&cname[0]), 0
 }
 
+//go:nosplit
+func syscall_getpid() (pid, err uintptr) {
+	call := libcall{
+		fn:   uintptr(unsafe.Pointer(libc_getpid)),
+		n:    0,
+		args: uintptr(unsafe.Pointer(libc_getpid)), // it's unused but must be non-nil, otherwise crashes
+	}
+	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(&call))
+	return call.r1, call.err
+}
+
 //go:nosplit
 func syscall_ioctl(fd, req, arg uintptr) (err uintptr) {
 	call := libcall{

src/syscall/asm_solaris_amd64.s

@@ -47,6 +47,9 @@ TEXT ·forkx(SB),NOSPLIT,$0
 TEXT ·gethostname(SB),NOSPLIT,$0
 	JMP	runtime·syscall_gethostname(SB)
 
+TEXT ·getpid(SB),NOSPLIT,$0
+	JMP	runtime·syscall_getpid(SB)
+
 TEXT ·ioctl(SB),NOSPLIT,$0
 	JMP	runtime·syscall_ioctl(SB)
 

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
 		}

src/syscall/exec_linux.go

@@ -23,10 +23,12 @@ 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)
+	Setpgid     bool           // Set process group ID to Pgid, or, if Pgid == 0, to new pid.
 	Setctty     bool           // Set controlling terminal to fd Ctty (only meaningful if Setsid is set)
 	Noctty      bool           // Detach fd 0 from controlling terminal
-	Ctty        int            // Controlling TTY fd (Linux only)
+	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.
 	Pdeathsig   Signal         // Signal that the process will get when its parent dies (Linux only)
 	Cloneflags  uintptr        // Flags for clone calls (Linux only)
 	UidMappings []SysProcIDMap // User ID mappings for user namespaces.
@@ -167,8 +169,27 @@ 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
 		}
@@ -277,7 +298,7 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	}
 
 	// Set the controlling TTY to Ctty
-	if sys.Setctty && sys.Ctty >= 0 {
+	if sys.Setctty {
 		_, _, err1 = RawSyscall(SYS_IOCTL, uintptr(sys.Ctty), uintptr(TIOCSCTTY), 0)
 		if err1 != 0 {
 			goto childerror

src/syscall/exec_solaris.go

@@ -12,9 +12,12 @@ type SysProcAttr struct {
 	Chroot     string      // Chroot.
 	Credential *Credential // Credential.
 	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.
@@ -28,6 +31,7 @@ func execve(path uintptr, argv uintptr, envp uintptr) (err Errno)
 func exit(code uintptr)
 func fcntl1(fd uintptr, cmd uintptr, arg uintptr) (val uintptr, err Errno)
 func forkx(flags uintptr) (pid uintptr, err Errno)
+func getpid() (pid uintptr, err Errno)
 func ioctl(fd uintptr, req uintptr, arg uintptr) (err Errno)
 func setgid(gid uintptr) (err Errno)
 func setgroups1(ngid uintptr, gid uintptr) (err Errno)
@@ -97,8 +101,27 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	}
 
 	// Set process group
-	if sys.Setpgid {
-		err1 = setpgid(0, 0)
+	if sys.Setpgid || sys.Foreground {
+		// Place child in process group.
+		err1 = setpgid(0, uintptr(sys.Pgid))
+		if err1 != 0 {
+			goto childerror
+		}
+	}
+
+	if sys.Foreground {
+		pgrp := sys.Pgid
+		if pgrp == 0 {
+			r1, err1 = getpid()
+			if err1 != 0 {
+				goto childerror
+			}
+
+			pgrp = int(r1)
+		}
+
+		// Place process group in foreground.
+		err1 = ioctl(uintptr(sys.Ctty), uintptr(TIOCSPGRP), uintptr(unsafe.Pointer(&pgrp)))
 		if err1 != 0 {
 			goto childerror
 		}
@@ -206,9 +229,9 @@ 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 = ioctl(0, uintptr(TIOCSCTTY), 0)
+		err1 = ioctl(uintptr(sys.Ctty), uintptr(TIOCSCTTY), 0)
 		if err1 != 0 {
 			goto childerror
 		}

src/syscall/exec_unix_test.go

@@ -0,0 +1,217 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build darwin dragonfly freebsd linux netbsd openbsd solaris
+
+package syscall_test
+
+import (
+	"io"
+	"os"
+	"os/exec"
+	"os/signal"
+	"syscall"
+	"testing"
+	"unsafe"
+)
+
+type command struct {
+	pipe io.WriteCloser
+	proc *exec.Cmd
+	test *testing.T
+}
+
+func (c *command) Info() (pid, pgrp int) {
+	pid = c.proc.Process.Pid
+
+	pgrp, err := syscall.Getpgid(pid)
+	if err != nil {
+		c.test.Fatal(err)
+	}
+
+	return
+}
+
+func (c *command) Start() {
+	c.proc.Start()
+}
+
+func (c *command) Stop() {
+	c.pipe.Close()
+	c.proc.Wait()
+}
+
+func create(t *testing.T) *command {
+	proc := exec.Command("cat")
+	stdin, err := proc.StdinPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return &command{stdin, proc, t}
+}
+
+func parent() (pid, pgrp int) {
+	return syscall.Getpid(), syscall.Getpgrp()
+}
+
+func TestZeroSysProcAttr(t *testing.T) {
+	ppid, ppgrp := parent()
+
+	cmd := create(t)
+
+	cmd.Start()
+	defer cmd.Stop()
+
+	cpid, cpgrp := cmd.Info()
+
+	if cpid == ppid {
+		t.Fatalf("Parent and child have the same process ID")
+	}
+
+	if cpgrp != ppgrp {
+		t.Fatalf("Child is not in parent's process group")
+	}
+}
+
+func TestSetpgid(t *testing.T) {
+	ppid, ppgrp := parent()
+
+	cmd := create(t)
+
+	cmd.proc.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
+	cmd.Start()
+	defer cmd.Stop()
+
+	cpid, cpgrp := cmd.Info()
+
+	if cpid == ppid {
+		t.Fatalf("Parent and child have the same process ID")
+	}
+
+	if cpgrp == ppgrp {
+		t.Fatalf("Parent and child are in the same process group")
+	}
+
+	if cpid != cpgrp {
+		t.Fatalf("Child's process group is not the child's process ID")
+	}
+}
+
+func TestPgid(t *testing.T) {
+	ppid, ppgrp := parent()
+
+	cmd1 := create(t)
+
+	cmd1.proc.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
+	cmd1.Start()
+	defer cmd1.Stop()
+
+	cpid1, cpgrp1 := cmd1.Info()
+
+	if cpid1 == ppid {
+		t.Fatalf("Parent and child 1 have the same process ID")
+	}
+
+	if cpgrp1 == ppgrp {
+		t.Fatalf("Parent and child 1 are in the same process group")
+	}
+
+	if cpid1 != cpgrp1 {
+		t.Fatalf("Child 1's process group is not its process ID")
+	}
+
+	cmd2 := create(t)
+
+	cmd2.proc.SysProcAttr = &syscall.SysProcAttr{
+		Setpgid: true,
+		Pgid:    cpgrp1,
+	}
+	cmd2.Start()
+	defer cmd2.Stop()
+
+	cpid2, cpgrp2 := cmd2.Info()
+
+	if cpid2 == ppid {
+		t.Fatalf("Parent and child 2 have the same process ID")
+	}
+
+	if cpgrp2 == ppgrp {
+		t.Fatalf("Parent and child 2 are in the same process group")
+	}
+
+	if cpid2 == cpgrp2 {
+		t.Fatalf("Child 2's process group is its process ID")
+	}
+
+	if cpid1 == cpid2 {
+		t.Fatalf("Child 1 and 2 have the same process ID")
+	}
+
+	if cpgrp1 != cpgrp2 {
+		t.Fatalf("Child 1 and 2 are not in the same process group")
+	}
+}
+
+func TestForeground(t *testing.T) {
+	signal.Ignore(syscall.SIGTTIN, syscall.SIGTTOU)
+
+	tty, err := os.OpenFile("/dev/tty", os.O_RDWR, 0)
+	if err != nil {
+		t.Skipf("Can't test Foreground. Couldn't open /dev/tty: %s",
+			err)
+	}
+
+	fpgrp := 0
+
+	_, _, errno := syscall.Syscall(syscall.SYS_IOCTL,
+		tty.Fd(),
+		syscall.TIOCGPGRP,
+		uintptr(unsafe.Pointer(&fpgrp)))
+
+	if errno != 0 {
+		t.Fatalf("TIOCGPGRP failed with error code: %s", errno)
+	}
+
+	if fpgrp == 0 {
+		t.Fatalf("Foreground process group is zero")
+	}
+
+	ppid, ppgrp := parent()
+
+	cmd := create(t)
+
+	cmd.proc.SysProcAttr = &syscall.SysProcAttr{
+		Ctty:       int(tty.Fd()),
+		Foreground: true,
+	}
+	cmd.Start()
+
+	cpid, cpgrp := cmd.Info()
+
+	if cpid == ppid {
+		t.Fatalf("Parent and child have the same process ID")
+	}
+
+	if cpgrp == ppgrp {
+		t.Fatalf("Parent and child are in the same process group")
+	}
+
+	if cpid != cpgrp {
+		t.Fatalf("Child's process group is not the child's process ID")
+	}
+
+	cmd.Stop()
+
+	_, _, errno = syscall.Syscall(syscall.SYS_IOCTL,
+		tty.Fd(),
+		syscall.TIOCSPGRP,
+		uintptr(unsafe.Pointer(&fpgrp)))
+
+	if errno != 0 {
+		t.Fatalf("TIOCSPGRP failed with error code: %s", errno)
+	}
+
+	signal.Reset()
+}