From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Biggers Subject: Re: [PATCH] ext4: inherit encryption xattr before other xattrs Date: Mon, 27 Feb 2017 13:36:37 -0800 Message-ID: <20170227213637.GA123733@gmail.com> References: <20170217233321.108637-1-ebiggers3@gmail.com> <2F4F7FA9-37C2-4FF1-9365-EF38D57FE7CA@dilger.ca> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ext4 Developers List , linux-fscrypt@vger.kernel.org, Theodore Ts'o , Jaegeuk Kim , Eric Biggers To: Andreas Dilger Return-path: Received: from mail-pg0-f66.google.com ([74.125.83.66]:35463 "EHLO mail-pg0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751617AbdB0WIs (ORCPT ); Mon, 27 Feb 2017 17:08:48 -0500 Received: by mail-pg0-f66.google.com with SMTP id 1so2278257pgz.2 for ; Mon, 27 Feb 2017 14:08:41 -0800 (PST) Content-Disposition: inline In-Reply-To: <2F4F7FA9-37C2-4FF1-9365-EF38D57FE7CA@dilger.ca> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, Feb 27, 2017 at 01:28:28PM -0700, Andreas Dilger wrote: > On Feb 17, 2017, at 4:33 PM, Eric Biggers wrote: > > > > From: Eric Biggers > > > > When using both encryption and SELinux (or another feature that requires > > an xattr per file) on a filesystem with 256-byte inodes, each file's > > xattrs usually spill into an external xattr block. Currently, the > > xattrs are inherited in the order ACL, security, then encryption. > > Therefore, if spillage occurs, the encryption xattr will always end up > > in the external block. This is not ideal because the encryption xattrs > > contain a nonce, so they will always be unique and will prevent the > > external xattr blocks from being deduplicated. > > > > To improve the situation, change the inheritance order to encryption, > > ACL, then security. This gives the encryption xattr a better chance to > > be stored in-inode, allowing the other xattr(s) to be deduplicated. > > > > Note that it may be better for userspace to format the filesystem with > > 512-byte inodes in this case. However, it's not the default. > > > > Signed-off-by: Eric Biggers > > Reviewed-by: Andreas Dilger > > Note that we've been using 512-byte xattrs for Lustre metadata servers > for ages. We may want to consider enabling this by default when the > filesystem features are set (e.g. crypto, inline data, etc). > > Having a general mechanism to bias xattrs to in-inode or external xattr > storage would be nice also, but I don't know any way to do this beyond > just having a list of xattr names and then prioritizing the ones that > go into the in-inode space. > I think it's a good idea to have mke2fs default to 512-byte inodes if '-O inline_data' is specified. But with '-O encrypt' it may be more debatable because there is no guarantee as to how many files userspace will actually choose to encrypt. It could be almost the whole filesystem, or just a few files, or even nothing at all. Regardless, I think adjusting the xattr inheritance order (as this patch does) has advantages but no real disadvantages, so it might as well be done too. Eric