From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.6 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 02039C43461 for ; Fri, 4 Sep 2020 14:03:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C974420684 for ; Fri, 4 Sep 2020 14:03:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=fieldses.org header.i=@fieldses.org header.b="OmBh0pe+" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730624AbgIDODd (ORCPT ); Fri, 4 Sep 2020 10:03:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56170 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730577AbgIDOD0 (ORCPT ); Fri, 4 Sep 2020 10:03:26 -0400 Received: from fieldses.org (fieldses.org [IPv6:2600:3c00:e000:2f7::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B8229C061244 for ; Fri, 4 Sep 2020 07:03:25 -0700 (PDT) Received: by fieldses.org (Postfix, from userid 2815) id AD724BD6; Fri, 4 Sep 2020 10:03:24 -0400 (EDT) DKIM-Filter: OpenDKIM Filter v2.11.0 fieldses.org AD724BD6 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fieldses.org; s=default; t=1599228204; bh=JGuLMailkMi3fuQyKJdz5LqWHpzKZU7ykXCcJh9nTac=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=OmBh0pe++JZl+3e8zqwJrGiSY2spH4aD1DlE+bQm51YORYJzQTrXcEE4p4lEw/fLE e9WBLVoAQrY7d1REeRsDTRqsXgJ7Gra+DMn4MCRqz3HcBQfW7VHJELwPmmSPoUXT3e /Ccg66/eVeVISd31bTrZsAbZcm3Dd5MY4nHjpnqc= Date: Fri, 4 Sep 2020 10:03:24 -0400 From: Bruce Fields To: Chuck Lever Cc: Anna Schumaker , Bruce Fields , Linux NFS Mailing List Subject: Re: [PATCH v4 2/5] NFSD: Add READ_PLUS data support Message-ID: <20200904140324.GC26706@fieldses.org> References: <20200817165310.354092-1-Anna.Schumaker@Netapp.com> <20200817165310.354092-3-Anna.Schumaker@Netapp.com> <20200828212521.GA33226@pick.fieldses.org> <20200828215627.GB33226@pick.fieldses.org> <20200901164938.GC12082@fieldses.org> <20200901191854.GD12082@fieldses.org> <20200904135259.GB26706@fieldses.org> <00931C34-6C86-46A2-A3B3-9727DA5E739E@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <00931C34-6C86-46A2-A3B3-9727DA5E739E@oracle.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Fri, Sep 04, 2020 at 09:56:19AM -0400, Chuck Lever wrote: > > > > On Sep 4, 2020, at 9:52 AM, J. Bruce Fields wrote: > > > > On Tue, Sep 01, 2020 at 03:18:54PM -0400, J. Bruce Fields wrote: > >> On Tue, Sep 01, 2020 at 01:40:16PM -0400, Anna Schumaker wrote: > >>> On Tue, Sep 1, 2020 at 12:49 PM J. Bruce Fields wrote: > >>>> > >>>> On Mon, Aug 31, 2020 at 02:16:26PM -0400, Anna Schumaker wrote: > >>>>> On Fri, Aug 28, 2020 at 5:56 PM J. Bruce Fields wrote: > >>>>>> We really don't want to bother encoding small holes. I doubt > >>>>>> filesystems want to bother with them either. Do they give us any > >>>>>> guarantees as to the minimum size of a hole? > >>>>> > >>>>> The minimum size seems to be PAGE_SIZE from everything I've seen. > >>>> > >>>> OK, can we make that assumption explicit? It'd simplify stuff like > >>>> this. > >>> > >>> I'm okay with that, but it's technically up to the underlying filesystem. > >> > >> Maybe we should ask on linux-fsdevel. > >> > >> Maybe minimum hole length isn't the right question: suppose at time 1 a > >> file has a single hole at bytes 100-200, then it's modified so at time 2 > >> it has a hole at bytes 50-150. If you lseek(fd, 0, SEEK_HOLE) at time > >> 1, you'll get 100. Then if you lseek(fd, 100, SEEK_DATA) at time 2, > >> you'll get 150. So you'll encode a 50-byte hole in the READ_PLUS reply > >> even though the file never had a hole smaller than 100 bytes. > >> > >> Minimum hole alignment might be the right idea. > >> > >> If we can't get that: maybe just teach encode_read to stop when it > >> *either* returns maxcount worth of file data (and holes) *or* maxcount > >> of encoded xdr data, just to prevent a weird filesystem from triggering > >> a bug. > > > > Alternatively, if it's easier, we could enforce a minimum alignment by > > rounding up the result of SEEK_HOLE to the nearest multiple of (say) 512 > > bytes, and rounding down the result of SEEK_DATA. > > Perhaps it goes without saying, but is there an effort to > ensure that the set of holes is represented in exactly the > same way when accessing a file via READ_PLUS and > SEEK_DATA/HOLE ? So you're thinking of something like a pynfs test that creates a file with holes and then tries reading through it with READ_PLUS and SEEK and comparing the results? There are lots of legitimate reasons that test might "fail"--servers aren't required to support holes at all, and have a lot of lattitude about how to report them. But it might be a good idea to test anyway. --b.