linux-kernel - Re: [RFC] a corner case of open(2)

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Message-ID: <CALXu0UdvkiMcXm2W0tQUEML2fxVYi2nr5zPu_K32xhk4zs-kLg@mail.gmail.com>
Date:	Tue, 26 Apr 2016 20:05:50 +0200
From:	Cedric Blancher <cedric.blancher@...il.com>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] a corner case of open(2)

Existing UNIX behaviour is better. Also, for open() a directory,
remember that int fd=open(), fchdir(fd) must work.

Ced

On 26 April 2016 at 19:55, Al Viro <viro@...iv.linux.org.uk> wrote:
>         According to POSIX (and behaviour on other Unices) the following
> should succeed: open("/tmp", O_CREAT, 0) does not have O_EXCL and the pathname
> does refer to existing object, so O_CREAT is ignored and the call is
> equivalent to open("/tmp", 0), which succeeds.
>
>         We have it rejected with EISDIR.  The thing is, the standard behaviour
> is actually less messy wrt code, and do_last()/lookup_open()/atomic_open()
> badly needs untangling.
>
>         Another place where we produce a bogus EISDIR is O_CREAT|O_EXCL on
> an existing directory.  POSIX (and other Unices) have EEXIST there.  In some
> cases we produce EEXIST, in some - EISDIR.  Uniform EEXIST is actually easier.
>
>         It is a change of user-visible behaviour, but I would be very
> surprised if anything broke from that change.  And it would help to simplify
> the awful mess we have in there.
>
>         Comments?
> --
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-- 
Cedric Blancher <cedric.blancher@...il.com>
Institute Pasteur