undo CL 131750044 / 2d6d44ceb80e

Breaks reading from stdin in parent after exec with SysProcAttr{Setpgid: true}.

package main

import (
        "fmt"
        "os"
        "os/exec"
        "syscall"
)

func main() {
        cmd := exec.Command("true")
        cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
        cmd.Run()

        fmt.Printf("Hit enter:")
        os.Stdin.Read(make([]byte, 100))
        fmt.Printf("Bye\n")
}

In go1.3, I type enter at the prompt and the program exits.
With the CL being rolled back, the program wedges at the
prompt.

««« original CL description
syscall: SysProcAttr job control changes

Making the child's process group the foreground process group and
placing the child in a specific process group involves co-ordination
between the parent and child that must be done post-fork but pre-exec.

LGTM=iant
R=golang-codereviews, gobot, iant, mikioh.mikioh
CC=golang-codereviews
https://golang.org/cl/131750044

»»»

LGTM=minux, dneil
R=dneil, minux
CC=golang-codereviews, iant, michael.p.macinnis
https://golang.org/cl/174450043

src/syscall/exec_bsd.go

@@ -19,8 +19,6 @@ type SysProcAttr struct {
 	Setpgid    bool        // Set process group ID to new pid (SYSV setpgrp)
 	Setctty    bool        // Set controlling terminal to fd 0
 	Noctty     bool        // Detach fd 0 from controlling terminal
-	Foreground bool        // Set foreground process group to child's pid. (Implies Setpgid. Stdin should be a TTY)
-	Joinpgrp   int         // If != 0, child's process group ID. (Setpgid must not be set)
 }
 
 // Implemented in runtime package.
@@ -81,22 +79,7 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	if r1 != 0 {
 		// parent; return PID
 		runtime_AfterFork()
-		pid = int(r1)
-
-		if sys.Joinpgrp != 0 {
-			// Place the child in the specified process group.
-			RawSyscall(SYS_SETPGID, r1, uintptr(sys.Joinpgrp), 0)
-		} else if sys.Foreground || sys.Setpgid {
-			// Place the child in a new process group.
-			RawSyscall(SYS_SETPGID, 0, 0, 0)
-
-			if sys.Foreground {
-				// Set new foreground process group.
-				RawSyscall(SYS_IOCTL, uintptr(Stdin), TIOCSPGRP, uintptr(unsafe.Pointer(&pid)))
-			}
-		}
-
-		return pid, 0
+		return int(r1), 0
 	}
 
 	// Fork succeeded, now in child.
@@ -118,30 +101,11 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	}
 
 	// Set process group
-	if sys.Joinpgrp != 0 {
-		// Place the child in the specified process group.
-		_, _, err1 = RawSyscall(SYS_SETPGID, r1, uintptr(sys.Joinpgrp), 0)
-		if err1 != 0 {
-			goto childerror
-		}
-	} else if sys.Foreground || sys.Setpgid {
-		// Place the child in a new process group.
+	if sys.Setpgid {
 		_, _, err1 = RawSyscall(SYS_SETPGID, 0, 0, 0)
 		if err1 != 0 {
 			goto childerror
 		}
-
-		if sys.Foreground {
-			r1, _, _ = RawSyscall(SYS_GETPID, 0, 0, 0)
-
-			pid := int(r1)
-
-			// Set new foreground process group.
-			_, _, err1 = RawSyscall(SYS_IOCTL, uintptr(Stdin), TIOCSPGRP, uintptr(unsafe.Pointer(&pid)))
-			if err1 != 0 {
-				goto childerror
-			}
-		}
 	}
 
 	// Chroot

src/syscall/exec_linux.go

@@ -29,8 +29,6 @@ type SysProcAttr struct {
 	Ctty        int            // Controlling TTY fd (Linux only)
 	Pdeathsig   Signal         // Signal that the process will get when its parent dies (Linux only)
 	Cloneflags  uintptr        // Flags for clone calls (Linux only)
-	Foreground  bool           // Set foreground process group to child's pid. (Implies Setpgid. Stdin should be a TTY)
-	Joinpgrp    int            // If != 0, child's process group ID. (Setpgid must not be set)
 	UidMappings []SysProcIDMap // User ID mappings for user namespaces.
 	GidMappings []SysProcIDMap // Group ID mappings for user namespaces.
 }
@@ -105,19 +103,6 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 			Close(p[1])
 		}
 
-		if sys.Joinpgrp != 0 {
-			// Place the child in the specified process group.
-			RawSyscall(SYS_SETPGID, r1, uintptr(sys.Joinpgrp), 0)
-		} else if sys.Foreground || sys.Setpgid {
-			// Place the child in a new process group.
-			RawSyscall(SYS_SETPGID, 0, 0, 0)
-
-			if sys.Foreground {
-				// Set new foreground process group.
-				RawSyscall(SYS_IOCTL, uintptr(Stdin), TIOCSPGRP, uintptr(unsafe.Pointer(&pid)))
-			}
-		}
-
 		return pid, 0
 	}
 
@@ -179,30 +164,11 @@ func forkAndExecInChild(argv0 *byte, argv, envv []*byte, chroot, dir *byte, attr
 	}
 
 	// Set process group
-	if sys.Joinpgrp != 0 {
-		// Place the child in the specified process group.
-		_, _, err1 = RawSyscall(SYS_SETPGID, r1, uintptr(sys.Joinpgrp), 0)
-		if err1 != 0 {
-			goto childerror
-		}
-	} else if sys.Foreground || sys.Setpgid {
-		// Place the child in a new process group.
+	if sys.Setpgid {
 		_, _, err1 = RawSyscall(SYS_SETPGID, 0, 0, 0)
 		if err1 != 0 {
 			goto childerror
 		}
-
-		if sys.Foreground {
-			r1, _, _ = RawSyscall(SYS_GETPID, 0, 0, 0)
-
-			pid := int(r1)
-
-			// Set new foreground process group.
-			_, _, err1 = RawSyscall(SYS_IOCTL, uintptr(Stdin), TIOCSPGRP, uintptr(unsafe.Pointer(&pid)))
-			if err1 != 0 {
-				goto childerror
-			}
-		}
 	}
 
 	// Chroot