From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: [PATCH RFC 0/4] tools: Upstream blktap "2.5" as an external repo Date: Thu, 26 Mar 2015 17:05:36 +0000 Message-ID: <55143C60.2000907@eu.citrix.com> References: <1427373970-25399-1-git-send-email-george.dunlap@eu.citrix.com> <20150326154736.GC4790@humongous.uk.xensource.com> <55142F09.4020401@eu.citrix.com> <9F2C4E7DFB7839489C89757A66C5AD62A4BE57@AMSPEX01CL03.citrite.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <9F2C4E7DFB7839489C89757A66C5AD62A4BE57@AMSPEX01CL03.citrite.net> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Felipe Franciosi , George Dunlap , Jonathan Ludlam Cc: Dave Scott , Wei Liu , Ian Campbell , Wen Congyang , "xen-devel@lists.xen.org" , Ian Jackson , Yang Hongyang List-Id: xen-devel@lists.xenproject.org On 03/26/2015 04:25 PM, Felipe Franciosi wrote: >> Another thing I'd like to explore (since this took all of about an afternoon to get >> working) is what it would take to switch to using >> blktap3 instead. As I understand from my conversations with the XenServer >> team, they use a kernel module in XenServer when mounting an image in dom0 >> for scalability reasons; but there's no reason XenProject need to do the same >> thing. > > Today, to access virtual disks in dom0 we use the blktap2 kernel module that Jonathan Ludlam mentioned. This provides a block device (in /dev/xen/blktap-2/tapdev). In the (somewhat distant) past, we actually had blkfront in dom0. OK -- so the XenServer blktap2 kernel module is definitely being maintained. That's good to know. > What is also needed to get blktap3 working is a gntdev supporting grant copy. I believe this is the order they are applied in 3.10: > https://github.com/xenserver/linux-3.x.pg/blob/master/master/0001-xen-install-xen-gntdev.h-and-xen-gntalloc.h.patch > https://github.com/xenserver/linux-3.x.pg/blob/master/master/xen-gntdev-grant-copy.patch > https://github.com/xenserver/linux-3.x.pg/blob/master/master/0002-xen-gntdev-mark-userspace-PTEs-as-special-on-x86-PV-.patch > https://github.com/xenserver/linux-3.x.pg/blob/master/master/0003-xen-gntdev-provide-a-set-of-pages-for-the-VMA.patch > > The _main_ difference between tapdisk2 and 3 is that tapdisk3 can connect directly to blkfront. It does all I/O via grant copies which has some implications in the way memory is handled in dom0. Right, I didn't realize blktap3 also required kernel changes. Are those reasonably upstream-able, and is there any plan by the XenServer team to upstream them? -George