From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752240AbaLXPNB (ORCPT ); Wed, 24 Dec 2014 10:13:01 -0500 Received: from mail.eperm.de ([89.247.134.16]:51031 "EHLO mail.eperm.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751990AbaLXPM7 convert rfc822-to-8bit (ORCPT ); Wed, 24 Dec 2014 10:12:59 -0500 X-AuthUser: sm@eperm.de From: Stephan Mueller To: leroy christophe Cc: Herbert Xu , linux-crypto , "'LKML'" Subject: Re: algif_hash: splice of data > 2**16 Date: Wed, 24 Dec 2014 16:12:53 +0100 Message-ID: <1444883.Oc8SnflNUU@tachyon.chronox.de> User-Agent: KMail/4.14.3 (Linux/3.17.7-300.fc21.x86_64; KDE/4.14.3; x86_64; ; ) In-Reply-To: <549AC946.2000909@c-s.fr> References: <8707521.TbV00HIEUx@tauon> <11733044.fQnf94a6to@tachyon.chronox.de> <549AC946.2000909@c-s.fr> MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset="iso-8859-1" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am Mittwoch, 24. Dezember 2014, 15:10:14 schrieb leroy christophe: Hi leroy, > Le 24/12/2014 10:03, Stephan Mueller a écrit : > > Am Dienstag, 23. Dezember 2014, 18:16:01 schrieb leroy christophe: > > > > Hi leroy, > > > >> Le 20/12/2014 07:37, Stephan Mueller a écrit : > >>> Am Donnerstag, 18. Dezember 2014, 13:22:20 schrieb leroy christophe: > >>> > >>> Hi Christophe, > >>> > >>>> Le 18/12/2014 13:15, Stephan Mueller a écrit : > >>>>> Hi Herbert, > >>>>> > >>>>> While testing the vmsplice/splice interface of algif_hash I was made > >>>>> aware of the problem that data blobs larger than 16 pages do not seem > >>>>> to > >>>>> be hashed properly. > >>>>> > >>>>> For testing, a file is mmap()ed and handed to vmsplice / splice. If > >>>>> the > >>>>> file is smaller than 2**16, the interface returns the proper hash. > >>>>> However, when the file is larger, only the first 2**16 bytes seem to > >>>>> be > >>>>> used. > >>>>> > >>>>> When adding printk's to hash_sendpage, I see that this function is > >>>>> invoked exactly 16 times where the first 15 invocations have the > >>>>> MSG_MORE flag set and the last invocation does not have MSG_MORE. > >>>> > >>>> Hi Stephan, > >>>> > >>>> I have already noticed the same issue and proposed a patch, but I never > >>>> got any feedback and it has never been merged, allthought I pinged it a > >>>> few times. > >>>> > >>>> See https://lkml.org/lkml/2014/4/18/276 > >>> > >>> After testing, this patch does not work for me. The operation still > >>> stops > >>> after 16 pages. > >> > >> Yes, it looks like the function I fixed is exclusively used by > >> sendfile() system call. > >> So there is probably the same kind of fix to be done in another function. > > > > I do not believe that is the case. IMHO the blocking issue is found in the > > following code: > > > > splice_from_pipe_feed walks the pipe->nrbufs. And vmsplice_to_pipe defines > > the maximum number of nrbufs as PIPE_DEF_BUFFERS -- which is 16. As > > subsequent functions allocate memory based on PIPE_DEF_BUFFERS, there is > > no trivial way to increase the number of pages to be processed. > > > > Thus I see that the vmsplice/splice combo can at most operate on a chunk > > of 16 pages. Thus, you have to segment your input buffer into chunks of > > that size and invoke the vmsplice/splice syscalls for each segment. > > Yes your are probably right. There splice needs to be called with > SPLICE_F_MORE flag, hope that works. That is not the only one. Vmsplice works on a pipe. A pipe is backed by 16 pages max. Thus, you have to call vmsplice once per 16 pages. The current code I am testing which seems to work is the following: while (inlen) { size_t datalen = (inlen > MAXLEN) ? MAXLEN : inlen; iov.iov_len = datalen; ret = _kcapi_common_vmsplice_data(handle, &iov, 1, datalen, 1); if (0 > ret) return ret; processed += ret; iov.iov_base = (void*)(uintptr_t)(in + processed); inlen -= ret; } return _kcapi_common_read_data(handle, out, outlen); -- Ciao Stephan