Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758024AbYBQC66 (ORCPT ); Sat, 16 Feb 2008 21:58:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754981AbYBQC5t (ORCPT ); Sat, 16 Feb 2008 21:57:49 -0500 Received: from filer.fsl.cs.sunysb.edu ([130.245.126.2]:36246 "EHLO filer.fsl.cs.sunysb.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754202AbYBQC5p (ORCPT ); Sat, 16 Feb 2008 21:57:45 -0500 From: Erez Zadok To: akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, viro@ftp.linux.org.uk, hch@infradead.org, Erez Zadok Subject: [PATCH 03/17] Unionfs: document behavior when the lower topology changes Date: Sat, 16 Feb 2008 21:57:12 -0500 Message-Id: <1203217048256-git-send-email-ezk@cs.sunysb.edu> X-Mailer: git-send-email 1.5.2.2 X-MailKey: Erez_Zadok In-Reply-To: <12032170461107-git-send-email-ezk@cs.sunysb.edu> References: <12032170461107-git-send-email-ezk@cs.sunysb.edu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1876 Lines: 35 Signed-off-by: Erez Zadok --- Documentation/filesystems/unionfs/concepts.txt | 13 +++++++++++++ 1 files changed, 13 insertions(+), 0 deletions(-) diff --git a/Documentation/filesystems/unionfs/concepts.txt b/Documentation/filesystems/unionfs/concepts.txt index bed69bd..8d9a1c5 100644 --- a/Documentation/filesystems/unionfs/concepts.txt +++ b/Documentation/filesystems/unionfs/concepts.txt @@ -210,4 +210,17 @@ there's a lot of concurrent activity on both the upper and lower objects, for the same file(s). Lastly, this delayed time attribute detection is similar to how NFS clients operate (e.g., acregmin). +Finally, there is no way currently in Linux to prevent lower directories +from being moved around (i.e., topology changes); there's no way to prevent +modifications to directory sub-trees of whole file systems which are mounted +read-write. It is therefore possible for in-flight operations in unionfs to +take place, while a lower directory is being moved around. Therefore, if +you try to, say, create a new file in a directory through unionfs, while the +directory is being moved around directly, then the new file may get created +in the new location where that directory was moved to. This is a somewhat +similar behaviour in NFS: an NFS client could be creating a new file while +th NFS server is moving th directory around; the file will get successfully +created in the new location. (The one exception in unionfs is that if the +branch is marked read-only by unionfs, then a copyup will take place.) + For more information, see . -- 1.5.2.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/