add directory argument to os.ForkExec

R=iant
DELTA=41  (35 added, 0 deleted, 6 changed)
OCL=28892
CL=28895

src/lib/exec/exec.go

@@ -96,7 +96,7 @@ func Run(argv0 string, argv, envv []string, stdin, stdout, stderr int) (p *Cmd,
 	}
 
 	// Run command.
-	p.Pid, err = os.ForkExec(argv0, argv, envv, &fd);
+	p.Pid, err = os.ForkExec(argv0, argv, envv, "", &fd);
 	if err != nil {
 		goto Error;
 	}

src/lib/os/exec.go

@@ -15,7 +15,8 @@ import (
 // file descriptors to be set up in the new process: fd[0] will be Unix file
 // descriptor 0 (standard input), fd[1] descriptor 1, and so on.  A nil entry
 // will cause the child to have no open file descriptor with that index.
-func ForkExec(argv0 string, argv []string, envv []string, fd []*File)
+// If dir is not empty, the child chdirs into the directory before execing the program.
+func ForkExec(argv0 string, argv []string, envv []string, dir string, fd []*File)
 	(pid int, err Error)
 {
 	// Create array of integer (system) fds.
@@ -28,7 +29,7 @@ func ForkExec(argv0 string, argv []string, envv []string, fd []*File)
 		}
 	}
 
-	p, e := syscall.ForkExec(argv0, argv, envv, intfd);
+	p, e := syscall.ForkExec(argv0, argv, envv, dir, intfd);
 	return int(p), ErrnoToError(e);
 }
 

src/lib/os/os_test.go

@@ -6,6 +6,7 @@ package os
 
 import (
 	"fmt";
+	"io";
 	"os";
 	"testing";
 )
@@ -299,3 +300,24 @@ func TestLongSymlink(t *testing.T) {
 		t.Fatalf("after symlink %q != %q", r, s);
 	}
 }
+
+func TestForkExec(t *testing.T) {
+	r, w, err := Pipe();
+	if err != nil {
+		t.Fatalf("Pipe: %v", err);
+	}
+	pid, err := ForkExec("/bin/pwd", []string{"pwd"}, nil, "/", []*File{nil, w, os.Stderr});
+	if err != nil {
+		t.Fatalf("ForkExec: %v", err);
+	}
+	w.Close();
+
+	var b io.ByteBuffer;
+	io.Copy(r, &b);
+	output := string(b.Data());
+	expect := "/\n";
+	if output != expect {
+		t.Errorf("exec /bin/pwd returned %q wanted %q", output, expect);
+	}
+	Wait(pid, 0);
+}

src/lib/syscall/exec.go

@@ -99,7 +99,7 @@ func Wait4(pid int64, wstatus *WaitStatus, options int64, rusage *Rusage)
 // no rescheduling, no malloc calls, and no new stack segments.
 // The calls to RawSyscall are okay because they are assembly
 // functions that do not grow the stack.
-func forkAndExecInChild(argv0 *byte, argv []*byte, envv []*byte, fd []int64, pipe int64)
+func forkAndExecInChild(argv0 *byte, argv []*byte, envv []*byte, dir *byte, fd []int64, pipe int64)
 	(pid int64, err int64)
 {
 	// Declare all variables at top in case any
@@ -132,6 +132,14 @@ func forkAndExecInChild(argv0 *byte, argv []*byte, envv []*byte, fd []int64, pip
 
 	// Fork succeeded, now in child.
 
+	// Chdir
+	if dir != nil {
+		r1, r2, err = RawSyscall(SYS_CHDIR, int64(uintptr(unsafe.Pointer(dir))), 0, 0);
+		if err != 0 {
+			goto childerror;
+		}
+	}
+
 	// Pass 1: look for fd[i] < i and move those up above len(fd)
 	// so that pass 2 won't stomp on an fd it needs later.
 	nextfd = int64(len(fd));
@@ -210,7 +218,7 @@ childerror:
 }
 
 // Combination of fork and exec, careful to be thread safe.
-func ForkExec(argv0 string, argv []string, envv []string, fd []int64)
+func ForkExec(argv0 string, argv []string, envv []string, dir string, fd []int64)
 	(pid int64, err int64)
 {
 	var p [2]int64;
@@ -225,6 +233,10 @@ func ForkExec(argv0 string, argv []string, envv []string, fd []int64)
 	argv0p := StringBytePtr(argv0);
 	argvp := StringArrayPtr(argv);
 	envvp := StringArrayPtr(envv);
+	var dirp *byte;
+	if len(dir) > 0 {
+		dirp = StringBytePtr(dir);
+	}
 
 	// Acquire the fork lock so that no other threads
 	// create new fds that are not yet close-on-exec
@@ -243,7 +255,7 @@ func ForkExec(argv0 string, argv []string, envv []string, fd []int64)
 	}
 
 	// Kick off child.
-	pid, err = forkAndExecInChild(argv0p, argvp, envvp, fd, p[1]);
+	pid, err = forkAndExecInChild(argv0p, argvp, envvp, dirp, fd, p[1]);
 	if err != 0 {
 	error:
 		if p[0] >= 0 {