Return-Path: linux-nfs-owner@vger.kernel.org Received: from fieldses.org ([174.143.236.118]:60780 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752212AbaGBVmF (ORCPT ); Wed, 2 Jul 2014 17:42:05 -0400 Date: Wed, 2 Jul 2014 17:42:04 -0400 From: "J. Bruce Fields" To: Kinglong Mee Cc: Avi Kivity , linux-nfs@vger.kernel.org Subject: Re: [PATCH] nfs: fix nfs4d readlink truncated packet Message-ID: <20140702214204.GF11510@fieldses.org> References: <1403792592-1517-1-git-send-email-avi@cloudius-systems.com> <53B2999C.6090401@cloudius-systems.com> <53B3C56F.20406@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <53B3C56F.20406@gmail.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Wed, Jul 02, 2014 at 04:40:15PM +0800, Kinglong Mee wrote: > > On 7/1/2014 19:21, Avi Kivity wrote: > > On 06/26/2014 05:23 PM, Avi Kivity wrote: > >> XDR requires 4-byte alignment; nfs4d READLINK reply writes out the padding, > >> but truncates the packet to the padding-less size. > >> > >> Fix by taking the padding into consideration when truncating the packet. > >> > > > > Ping. I should have mentioned that without this, readlink() returns an I/O error on the client. Thanks, queueing up for 3.16. > Yes, I got > [root@localhost ~]# ll /mnt/ > ls: cannot read symbolic link /mnt/test: Input/output error > total 4 > -rw-r--r--. 1 root root 0 Jun 14 01:21 123456 > lrwxrwxrwx. 1 root root 6 Jul 2 03:33 test > drwxr-xr-x. 1 root root 0 Jul 2 23:50 tmp > drwxr-xr-x. 1 root root 60 Jul 2 23:44 tree > [root@localhost ~]# > > It's introduced by commit 476a7b1f4b2c (nfsd4: don't treat readlink like a zero-copy operation). ... > >> + xdr_truncate_encode(xdr, length_offset + 4 + ALIGN(maxcount, 4)); > > NFSD uses (XDR_QUADLEN(maxcount) << 2)) usually. Eh, I didn't know about ALIGN()--I think I prefer it. > Anyway, it's a nice fix. > > Reviewed-by: Kinglong Mee Thanks! I've also added your symptoms and the problematic commit to the changelog. --b.