From: Al Viro Subject: Re: [RFC] st_nlink after rmdir() and rename() Date: Thu, 3 Mar 2011 19:16:27 +0000 Message-ID: <20110303191626.GM22723@ZenIV.linux.org.uk> References: <20110303032454.GI22723@ZenIV.linux.org.uk> <406B4874-D3D8-4C05-9FA5-8A7A18ABF89C@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Linus Torvalds , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Theodore Tso Return-path: Content-Disposition: inline In-Reply-To: <406B4874-D3D8-4C05-9FA5-8A7A18ABF89C@mit.edu> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Thu, Mar 03, 2011 at 09:34:08AM -0500, Theodore Tso wrote: > > On Mar 2, 2011, at 10:24 PM, Al Viro wrote: > > > We have an interesting problem. Consider the following sequence > > of syscalls: > > mkdir("foo", 0777); > > mkdir("bar", 0777); > > fd1 = open("foo", O_DIRECTORY); > > fd2 = open("bar", O_DIRECTORY); > > rename("foo", "bar"); /* kill old bar */ > > I must be missing something. I didn't think you could rename on > top of a directory and have the directory disappear. Don't you get > an error in that case? What happens if bar contains files? ENOTEMPTY. Checked by ->rename() and yes, ext4 does that. > We don't allow: mkdir("bar", 0777); unlink("bar"); > > Why should this be any different? Because it worked since 4.2BSD and got into POSIX. Replacing rename() works; the only restrictions are * you can't replace directory with non-directory * you can't replace non-directory with directory * directory being replaced shall be empty * you can't replace a mountpoint or filesystem root If the target is not busy, it is required to work. Whether it returns -EBUSY for busy target is implementation-dependent and we allow that for most of the filesystems.