code review 12349044: os, syscall: implement Getwd on darwin using getattrlist

src/pkg/syscall/syscall_darwin.go

 // Copyright 2009,2010 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.
 
 // Darwin system calls.
 // This file is compiled as ordinary Go code,
 // but it is also input to mksyscall,
 // which parses the //sys lines and generates system call stubs.
 // Note that sometimes we use a lowercase //sys name and wrap
 // it in our own nicer implementation, either here or in
 // syscall_bsd.go or syscall_unix.go.
 
 package syscall
 
 import (
         errorspkg "errors"
         "unsafe"
 )
+
+const ImplementsGetwd = true
+
+func Getwd() (string, error) {
+        buf := make([]byte, 2048)
+        attrs, err := getAttrList(".", attrList{CommonAttr: attrCmnFullpath}, buf, 0)
+        if err == nil && len(attrs) == 1 && len(attrs[0]) >= 2 {
+                wd := string(attrs[0])
+                // Sanity check that it's an absolute path and ends
+                // in a null byte, which we then strip.
+                if wd[0] == '/' && wd[len(wd)-1] == 0 {
+                        return wd[:len(wd)-1], nil
+                }
+        }
+        // If pkg/os/getwd.go gets ENOTSUP, it will fall back to the
+        // slow algorithm.
+        return "", ENOTSUP
+}
 
 type SockaddrDatalink struct {
         Len    uint8
         Family uint8
         Index  uint16
         Type   uint8
         Nlen   uint8
         Alen   uint8
         Slen   uint8
         Data   [12]int8
@@ skipping 55 matching lines @@
         }
         return origlen - len(buf), count, names
 }
 
 //sys   ptrace(request int, pid int, addr uintptr, data uintptr) (err error)
 func PtraceAttach(pid int) (err error) { return ptrace(PT_ATTACH, pid, 0, 0) }
 func PtraceDetach(pid int) (err error) { return ptrace(PT_DETACH, pid, 0, 0) }
 
 const (
         attrBitMapCount = 5
-        AttrCmnFullpath = 0x08000000
+        attrCmnFullpath = 0x08000000
 )
 
-type AttrList struct {
+type attrList struct {
         bitmapCount uint16
         _           uint16
         CommonAttr  uint32
         VolAttr     uint32
         DirAttr     uint32
         FileAttr    uint32
         Forkattr    uint32
 }
 
-func GetAttrList(path string, attrList AttrList, attrBuf []byte, options uint) (attrs [][]byte, err error) {
+func getAttrList(path string, attrList attrList, attrBuf []byte, options uint) (attrs [][]byte, err error) {
         if len(attrBuf) < 4 {
                 return nil, errorspkg.New("attrBuf too small")
         }
         attrList.bitmapCount = attrBitMapCount
 
         var _p0 *byte
         _p0, err = BytePtrFromString(path)
         if err != nil {
                 return nil, err
         }
@@ skipping 344 matching lines @@
 // Poll_nocancel
 // Msgsnd_nocancel
 // Msgrcv_nocancel
 // Sem_wait_nocancel
 // Aio_suspend_nocancel
 // __sigwait_nocancel
 // __semwait_signal_nocancel
 // __mac_mount
 // __mac_get_mount
 // __mac_getfsstat