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

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Message-ID: <20160426175538.GO25498@ZenIV.linux.org.uk>
Date:	Tue, 26 Apr 2016 18:55:38 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC] a corner case of open(2)

	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?