From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:39802) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RLKJc-0008V3-UV for qemu-devel@nongnu.org; Tue, 01 Nov 2011 15:48:10 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RLKJb-0005by-Mg for qemu-devel@nongnu.org; Tue, 01 Nov 2011 15:48:08 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:41964) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RLKJb-0005bq-BF for qemu-devel@nongnu.org; Tue, 01 Nov 2011 15:48:07 -0400 Received: from /spool/local by e34.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 1 Nov 2011 13:48:04 -0600 Received: from d03av01.boulder.ibm.com (d03av01.boulder.ibm.com [9.17.195.167]) by d03relay03.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id pA1JjchS043682 for ; Tue, 1 Nov 2011 13:45:40 -0600 Received: from d03av01.boulder.ibm.com (loopback [127.0.0.1]) by d03av01.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id pA1JjaRm016319 for ; Tue, 1 Nov 2011 13:45:36 -0600 Message-ID: <4EB04C5F.3040108@us.ibm.com> Date: Tue, 01 Nov 2011 14:45:35 -0500 From: Anthony Liguori MIME-Version: 1.0 References: <1317292461-12291-1-git-send-email-berrange@redhat.com> <87sjnfqu0y.fsf@skywalker.in.ibm.com> <20110929152216.GU30524@redhat.com> <20111007092755.GE31228@redhat.com> <874nzldp72.fsf@skywalker.in.ibm.com> <20111020151319.GA12001@redhat.com> <4EB03A2C.8050302@us.ibm.com> <20111101184847.GM22168@redhat.com> In-Reply-To: <20111101184847.GM22168@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] Raise 9pfs mount_tag limit from 32 to 255 bytes List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: Harsh Bora , "Aneesh Kumar K.V" , qemu-devel@nongnu.org On 11/01/2011 01:48 PM, Daniel P. Berrange wrote: > On Tue, Nov 01, 2011 at 01:27:56PM -0500, Anthony Liguori wrote: >> On 10/20/2011 10:13 AM, Daniel P. Berrange wrote: >>> On Fri, Oct 07, 2011 at 04:49:13PM +0530, Aneesh Kumar K.V wrote: >>>> On Fri, 7 Oct 2011 10:27:56 +0100, "Daniel P. Berrange" wrote: >>>>> On Thu, Sep 29, 2011 at 04:22:16PM +0100, Daniel P. Berrange wrote: >>>>> I've done some tests with ever larger mount tags, and managed to increase >>>>> the MAX_TAG_LEN value to 1023 before I started getting guest failures. >>>>> >>>>> So if the config space is really 1023 bytes in size, it doesn't seem too >>>>> unrealistic to allow 255 bytes of it for the mount_tag, or at the very >>>>> least increase it from 32 to 128 ? >>>>> >>>> >>>> Last time we discussed this Anthony wanted to keep the config space >>>> usage minimal, hence we agreed on the size 32 bytes. >>> >>> Ping ? Anyone .... >>> >>> Does anyone have any clear information about the per-device config >>> space we have available ? As above I'd really like us to raise >>> the mount_tag length even just a little bit higher for QEMU 1.0, >>> if we have the PCI config space available to play with. >> >> Yes, PCI PIO space is very small. I think 128 is even pushing it. > > Odd, because I managed to pass through a 1023 byte path without > appearing to have any trouble. Is the space per-device, or global > to all devices. If the latter, I could understand the desire to > keep it smaller. It's global so it ends up being a problem when you have many devices. > >> Why not add a feature that exchanges the tag through another >> mechanism such that there doesn't need to be a limit? It could be >> as simple as adding an fsstat .L operation or something like that. > > That would require kernel side updates too I presume, so if that > kind of change is the only option, I think I'll just have to change > my app's code to cope with the current smaller limits for now. Right. Regards, Anthony Liguori > > Regards, > Daniel