From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:59149) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RC8Sg-0004Bt-8R for qemu-devel@nongnu.org; Fri, 07 Oct 2011 07:19:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RC8Sf-0006E3-50 for qemu-devel@nongnu.org; Fri, 07 Oct 2011 07:19:30 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:52674) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RC8Se-0006Dy-T0 for qemu-devel@nongnu.org; Fri, 07 Oct 2011 07:19:29 -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 ; Fri, 7 Oct 2011 05:19:27 -0600 Received: from d03av04.boulder.ibm.com (d03av04.boulder.ibm.com [9.17.195.170]) by d03relay01.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p97BJOQP206946 for ; Fri, 7 Oct 2011 05:19:24 -0600 Received: from d03av04.boulder.ibm.com (loopback [127.0.0.1]) by d03av04.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p97BJMII013559 for ; Fri, 7 Oct 2011 05:19:23 -0600 From: "Aneesh Kumar K.V" In-Reply-To: <20111007092755.GE31228@redhat.com> References: <1317292461-12291-1-git-send-email-berrange@redhat.com> <87sjnfqu0y.fsf@skywalker.in.ibm.com> <20110929152216.GU30524@redhat.com> <20111007092755.GE31228@redhat.com> Date: Fri, 07 Oct 2011 16:49:13 +0530 Message-ID: <874nzldp72.fsf@skywalker.in.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii 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" , Anthony Liguori Cc: Harsh Bora , qemu-devel@nongnu.org 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. Anthony, Any comments ? -aneesh