为什么在调用OpenFile时需要设置权限？

问题描述：

I understand what permissions mean for files and dirs stored in filesystem. But why do I need to set permissions when calling os.OpenFile? Does it update file permission on filesystem if opened successfully? If not - what difference does it make to open same file with 0000 or 0777?

https://golang.org/src/os/file.go?s=8454:8520#L272

func OpenFile(name string, flag int, perm FileMode) (*File, error)
...
f, err := os.OpenFile("access.log", os.O_APPEND, 0644)

我了解权限对存储在文件系统中的文件和目录意味着什么。但是为什么我需要设置权限调用os.OpenFile时 strong>？如果打开成功，它会更新文件系统上的文件权限吗？如果不成功-打开带有0000或0777的同一文件有什么区别？ p> https://golang.org/src/os/ file.go？s = 8454：8520＃L272 p>

  func OpenFile（名称字符串，标志int，perm FileMode）（*文件，错误）
。  .. 
f，err：= os.OpenFile（“ access.log”，os.O_APPEND，0644）
  code>  pre> 
  div>

答

As documented (emphasis added):

OpenFile is the generalized open call; most users will use Open or Create instead. It opens the named file with specified flag (O_RDONLY etc.) and perm (before umask), if applicable. If successful, methods on the returned File can be used for I/O. If there is an error, it will be of type *PathError.

So, the perm value is only used when the file is created--when opening an existing file, it is not applicable, so it is ignored.

为什么在调用OpenFile时需要设置权限？

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