From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [OSSTEST PATCH 4/9] mg-schema-test-database: Borrow shares properly Date: Thu, 17 Dec 2015 18:08:05 +0000 Message-ID: <1450375685.1617.85.camel@citrix.com> References: <1450371968-27997-1-git-send-email-ian.jackson@eu.citrix.com> <1450371968-27997-4-git-send-email-ian.jackson@eu.citrix.com> <1450373180.4053.143.camel@citrix.com> <22130.62535.141240.627734@mariner.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta4.messagelabs.com ([85.158.143.247]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1a9cyJ-0004iC-0P for xen-devel@lists.xenproject.org; Thu, 17 Dec 2015 18:08:11 +0000 In-Reply-To: <22130.62535.141240.627734@mariner.uk.xensource.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Jackson Cc: xen-devel@lists.xenproject.org List-Id: xen-devel@lists.xenproject.org On Thu, 2015-12-17 at 17:43 +0000, Ian Jackson wrote: > Ian Campbell writes ("Re: [OSSTEST PATCH 4/9] mg-schema-test > -database: Borrow shares properly"): > > On Thu, 2015-12-17 at 17:06 +0000, Ian Jackson wrote: > > > # As we copy, we note everything we're not borrowing as > > > - # belonging to the parent db. > > > + # belonging to the parent db. We borrow shares of a > shared > > > + # resource. If we borrow only some rather than all of > the > > > + # shares, neither DB will be able to unshare it. > > > > This is what actually happens, rather than this comment explaining > a thing > > we are avoiding, right? > > Yes. > > > I ask because although the text (and the use of "properly" in the subject) > > seems pretty clear it's the former I was surprised to find this code was > > borrowing partial shares and therefore setting up such a situation. Given > > the caveat below would it not be better to just never allow this? > > I have added this to the commit message: > > Previously, the test database would be generated in a broken state: > resources share-host/foo/{1,2,...} exist but the resource host/foo/0 > is allocated to magic/xdbref rather than to magic/shared. This causes > various resource allocation machinery to crash. (Even if the host is > entirely un-borrowed.) > > I guess it might be possible for mg-schema-test-database to check that > either none or all of the shares of a host are being borrowed, but I > don't think it's worth it. The osstest git hash in the sharetype will > in practice mostly prevent undesirable sharing of the same resource > between test and real db instances. > > > I suppose that given the list of tasks to borrow came from the user > > this might be considered a "keep both pieces" situation. > > Yes. This partial sharing can only affect you if you have allocated > individual shares to the task you say you want to borrow from. Grand, with the extra commit log bit from above: Acked-by: Ian Campbell