From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:51528) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RLJ4C-0004Ye-UI for qemu-devel@nongnu.org; Tue, 01 Nov 2011 14:28:09 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RLJ4B-0007oh-UP for qemu-devel@nongnu.org; Tue, 01 Nov 2011 14:28:08 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:43029) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RLJ4B-0007ob-Qv for qemu-devel@nongnu.org; Tue, 01 Nov 2011 14:28:07 -0400 Received: from /spool/local by e9.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 1 Nov 2011 14:28:05 -0400 Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by d01relay06.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id pA1IS17E1941532 for ; Tue, 1 Nov 2011 14:28:01 -0400 Received: from d01av02.pok.ibm.com (loopback [127.0.0.1]) by d01av02.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id pA1IS1sJ025323 for ; Tue, 1 Nov 2011 16:28:01 -0200 Message-ID: <4EB03A2C.8050302@us.ibm.com> Date: Tue, 01 Nov 2011 13:27:56 -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> In-Reply-To: <20111020151319.GA12001@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 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: >>>> On Thu, Sep 29, 2011 at 08:23:49PM +0530, Aneesh Kumar K.V wrote: >>>>> On Thu, 29 Sep 2011 11:34:21 +0100, "Daniel P. Berrange" wrote: >>>>>> From: "Daniel P. Berrange" >>>>>> >>>>>> The Linux guest kernel does not appear to have a problem handling >>>>>> a mount_tag larger than 32 bytes. Increase the limit to 255 bytes, >>>>>> though perhaps it can be made larger still, or not limited at all ? >>>>>> >>>>>> Tested with a 3.0.4 kernel and a mount_tag 255 bytes in length. >>>>>> >>>>>> * hw/9pfs/virtio-9p.h: Change MAX_TAG_LEN to 255 >>>>> >>>>> >>>>> mount_tag is passed via pci config space, do we want to have 255 bytes >>>>> out of that for device identification. >>>> >>>> How big is the config space available for each 9pfs device and what >>>> other info does it need to keep there ? >>> >>> Does anyone have an clear answer for this ? >>> >>> 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. 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. Regards, Anthony Liguori > > Regards, > Daniel