From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: size limit of extended attributes Date: Tue, 5 May 2015 17:43:48 +0200 Message-ID: <20150505154348.GA16223@quack.suse.cz> References: <20150501154351.GC15810@dastard> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Dave Chinner , Trond Myklebust , Linux FS-devel Mailing List To: =?iso-8859-1?Q?Bj=F6rn?= JACKE Return-path: Received: from cantor2.suse.de ([195.135.220.15]:33978 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2993445AbbEEPnv (ORCPT ); Tue, 5 May 2015 11:43:51 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue 05-05-15 15:38:11, Bj=F6rn JACKE wrote: > On 2015-05-02 at 01:43 +1000 Dave Chinner sent off: > > On Thu, Apr 30, 2015 at 03:57:37PM +0200, Bj=F6rn JACKE wrote: > > > Can we get rid of the 64k size limit for EAs? The API on AIX is t= he same as on > > > Linux. But there is a huge size limit - which would help us alre= ady a lot. > >=20 > > No - the maximum xattr size of 64k is encoded into the on-disk > > format of many filesystems and that's not a simple thing to change. >=20 > I know ext4 even has a much lower limit. But some filesystems don't h= ave a > limit, and there the kernel 64k limit strikes in. The EA size limit o= f some > file systems could also be increased. As there is a real use case for= that I > guess filesystems would like to be able to support larger EA sizes. Yeah, so XFS could support more than 64K in principle if I look corre= ct. Supporting it for ext4 would mean ondisk format change - doable but requires some non-trivial effort. Regarding the API, the issue with larger xattr size is that currently w= e copy whole xattr into kernel memory and process it in one go. Currently that's OK but if you want xattrs that have megabytes, it may become an effective way to DOS a system. So to support that we'd need to change a= t least the API from VFS into filesystems so that xattrs could be process= ed in smaller chunks. Again doable but quite some work. All in all I don't think this is going to happen unless someone interes= ted in this invests significant amount of time to make this happen. Honza --=20 Jan Kara SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel= " in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html