1 files changed, 111 insertions, 0 deletions
diff --git a/src/syscall/pwd_plan9.go b/src/syscall/pwd_plan9.go
new file mode 100644
index 0000000..28e9956
--- /dev/null
+++ b/src/syscall/pwd_plan9.go
@@ -0,0 +1,111 @@
+// 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.
+
+// The working directory in Plan 9 is effectively per P, so different
+// goroutines and even the same goroutine as it's rescheduled on
+// different Ps can see different working directories.
+//
+// Instead, track a Go process-wide intent of the current working directory,
+// and switch to it at important points.
+
+package syscall
+
+import (
+	"runtime"
+	"sync"
+)
+
+var (
+	wdmu  sync.Mutex // guards following
+	wdSet bool
+	wdStr string
+)
+
+// Ensure current working directory seen by this goroutine matches
+// the most recent Chdir called in any goroutine. It's called internally
+// before executing any syscall which uses a relative pathname. Must
+// be called with the goroutine locked to the OS thread, to prevent
+// rescheduling on a different thread (potentially with a different
+// working directory) before the syscall is executed.
+func Fixwd() {
+	wdmu.Lock()
+	defer wdmu.Unlock()
+	fixwdLocked()
+}
+
+func fixwdLocked() {
+	if !wdSet {
+		return
+	}
+	// always call chdir when getwd returns an error
+	wd, _ := getwd()
+	if wd == wdStr {
+		return
+	}
+	if err := chdir(wdStr); err != nil {
+		return
+	}
+}
+
+// If any of the paths is relative, call Fixwd and return true
+// (locked to OS thread). Otherwise return false.
+func fixwd(paths ...string) bool {
+	for _, path := range paths {
+		if path != "" && path[0] != '/' && path[0] != '#' {
+			runtime.LockOSThread()
+			Fixwd()
+			return true
+		}
+	}
+	return false
+}
+
+// goroutine-specific getwd
+func getwd() (wd string, err error) {
+	fd, err := open(".", O_RDONLY)
+	if err != nil {
+		return "", err
+	}
+	defer Close(fd)
+	return Fd2path(fd)
+}
+
+func Getwd() (wd string, err error) {
+	wdmu.Lock()
+	defer wdmu.Unlock()
+
+	if wdSet {
+		return wdStr, nil
+	}
+	wd, err = getwd()
+	if err != nil {
+		return
+	}
+	wdSet = true
+	wdStr = wd
+	return wd, nil
+}
+
+func Chdir(path string) error {
+	// If Chdir is to a relative path, sync working dir first
+	if fixwd(path) {
+		defer runtime.UnlockOSThread()
+	}
+	wdmu.Lock()
+	defer wdmu.Unlock()
+
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+	if err := chdir(path); err != nil {
+		return err
+	}
+
+	wd, err := getwd()
+	if err != nil {
+		return err
+	}
+	wdSet = true
+	wdStr = wd
+	return nil
+}