pwd_plan9.go

     1  // Copyright 2015 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // The working directory in Plan 9 is effectively per P, so different
     6  // goroutines and even the same goroutine as it's rescheduled on
     7  // different Ps can see different working directories.
     8  //
     9  // Instead, track a Go process-wide intent of the current working directory,
    10  // and switch to it at important points.
    11  
    12  package syscall
    13  
    14  import (
    15  	"runtime"
    16  	"sync"
    17  )
    18  
    19  var (
    20  	wdmu  sync.Mutex // guards following
    21  	wdSet bool
    22  	wdStr string
    23  )
    24  
    25  // Ensure current working directory seen by this goroutine matches
    26  // the most recent [Chdir] called in any goroutine. It's called internally
    27  // before executing any syscall which uses a relative pathname. Must
    28  // be called with the goroutine locked to the OS thread, to prevent
    29  // rescheduling on a different thread (potentially with a different
    30  // working directory) before the syscall is executed.
    31  func Fixwd() {
    32  	wdmu.Lock()
    33  	defer wdmu.Unlock()
    34  	fixwdLocked()
    35  }
    36  
    37  func fixwdLocked() {
    38  	if !wdSet {
    39  		return
    40  	}
    41  	// always call chdir when getwd returns an error
    42  	wd, _ := getwd()
    43  	if wd == wdStr {
    44  		return
    45  	}
    46  	if err := chdir(wdStr); err != nil {
    47  		return
    48  	}
    49  }
    50  
    51  // If any of the paths is relative, call Fixwd and return true
    52  // (locked to OS thread). Otherwise return false.
    53  func fixwd(paths ...string) bool {
    54  	for _, path := range paths {
    55  		if path != "" && path[0] != '/' && path[0] != '#' {
    56  			runtime.LockOSThread()
    57  			Fixwd()
    58  			return true
    59  		}
    60  	}
    61  	return false
    62  }
    63  
    64  // goroutine-specific getwd
    65  func getwd() (wd string, err error) {
    66  	fd, err := open(".", O_RDONLY)
    67  	if err != nil {
    68  		return "", err
    69  	}
    70  	defer Close(fd)
    71  	return Fd2path(fd)
    72  }
    73  
    74  func Getwd() (wd string, err error) {
    75  	wdmu.Lock()
    76  	defer wdmu.Unlock()
    77  
    78  	if wdSet {
    79  		return wdStr, nil
    80  	}
    81  	wd, err = getwd()
    82  	if err != nil {
    83  		return
    84  	}
    85  	wdSet = true
    86  	wdStr = wd
    87  	return wd, nil
    88  }
    89  
    90  func Chdir(path string) error {
    91  	// If Chdir is to a relative path, sync working dir first
    92  	if fixwd(path) {
    93  		defer runtime.UnlockOSThread()
    94  	}
    95  	wdmu.Lock()
    96  	defer wdmu.Unlock()
    97  
    98  	runtime.LockOSThread()
    99  	defer runtime.UnlockOSThread()
   100  	if err := chdir(path); err != nil {
   101  		return err
   102  	}
   103  
   104  	wd, err := getwd()
   105  	if err != nil {
   106  		return err
   107  	}
   108  	wdSet = true
   109  	wdStr = wd
   110  	return nil
   111  }
   112
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