[ruby-core:64648] [ruby-trunk - Feature #10181] New method File.openat()

Issue #10181 has been updated by Eric Wong.


 Joel VanderWerf <[e-mail]> wrote:
 > On 08/29/2014 01:21 AM, Eric Wong wrote:
 > >Joel VanderWerf <[e-mail]> wrote:
 > >>On 08/29/2014 12:55 AM, Eric Wong wrote:
 > >>>Joel VanderWerf <[e-mail]> wrote:
 > >>>>On 08/28/2014 02:53 PM, Eric Wong wrote:
 > >>>>>I like this feature.
 > >>>>>
 > >>>>>If matz approves, I assume you also want to add other *at functions?
 > >>>>>e.g. fstatat, renameat, unlinkat, mkdirat, etc.
 > >>>>
 > >>>>Hm, that suggests...
 > >>>>
 > >>>>Dir.at(...).open(...)
 > >>>>Dir.at(...).fstat(...)
 > >>>
 > >>>How would that be implemented?
 > >>
 > >>Couldn't Dir.at(...) return an object that wraps the fd of the dir?
 > >
 > >Yes, but it would need to cache the _same_ object every time it's called
 > >given that arg for a given thread.  Then it might not detect when that
 > >thread might actually want a different FD/object, and the cache can fill
 > >up or expire and we still end up with unpredictable behavior.
 > 
 > What if you always used it like this:
 > 
 > d = Dir.at()
 > d.open()
 > d.fstat()
 > 
 > so it's up to the caller to decide explicitly when to use the same
 > object or not. It reflects the underlying fd-based API, doesn't it?
 
 OK, that would work.  However it ends up creating a new object type
 and overloading of names, making it harder to review code, I think.
 I prefer this:
 
 	d = Dir.open(..)
 	d.openat(...)
 	d.fstatat(..)

----------------------------------------
Feature #10181: New method File.openat()
https://bugs.ruby-lang.org/issues/10181#change-48550

* Author: Technorama Ltd.
* Status: Open
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
----------------------------------------
The purpose of the openat() function is to enable opening files in directories other than the current working directory without exposure to race conditions. Any part of the path of a file could be changed in parallel to a call to open(), resulting in unspecified behavior. By opening a file descriptor for the target directory and using the openat() function it can be guaranteed that the opened file is located relative to the desired directory.

openat() is part of POSIX.1-2008.

Compatibility:
  Linux kernel >= 2.6.16
  FreeBSD >= 7.0
  OpenBSD >= 5.0
  NetBSD >= 6.1.4
  MacOS/X no

Pull request: https://github.com/ruby/ruby/pull/706



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