From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: Issues regarding "mem_access: Add helper API to setup ring and enable mem_access" Date: Mon, 30 Jun 2014 14:10:53 +0100 Message-ID: <53B161DD.1010809@citrix.com> References: <1403882455.3169.72.camel@kazak.uk.xensource.com> <21425.23379.795171.801716@mariner.uk.xensource.com> <1404132276.14488.41.camel@kazak.uk.xensource.com> <53B1611D.2080502@citrix.com> <1404133751.14488.56.camel@kazak.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1404133751.14488.56.camel@kazak.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 Campbell Cc: Tamas Lengyel , "xen-devel@lists.xen.org" , Ian Jackson , Aravindh Puthiyaparambil List-Id: xen-devel@lists.xenproject.org On 30/06/14 14:09, Ian Campbell wrote: > On Mon, 2014-06-30 at 14:07 +0100, Andrew Cooper wrote: >> On 30/06/14 13:44, Ian Campbell wrote: >>> On Mon, 2014-06-30 at 13:42 +0100, Ian Jackson wrote: >>>> Tamas Lengyel writes ("Re: [Xen-devel] Issues regarding "mem_access: Add helper API to setup ring and enable mem_access""): >>>>> > Now with this function being reintroduced, it becomes more complicated >>>>> > to determine which version of the mem_access API does Xen actually >>>>> > provide. A #define indicating mem_access API version would nicely >>>>> > overcome this issue, or naming xc_mem_event_enable something else. >>>>> >>>>> Doesn't configure support checking for functions with a given prototype? >>>>> >>>>> It does but in a very hacky way, essentially trying to compile code where the >>>>> function is being called with different prototypes. We can work around it but a >>>>> clean solution would be preferred at some point. >>>> I agree with your criticism, TBH. Aravindh/Ian, can we rename this >>>> function ? >>> I have no objection to some other name. >>> >>>>> This is now a rather opaque behavior of libxc. As it is not merged >>>>> into master I guess I will just submit a patch for it.. >>>> Yes. I think this would be the right approach to addressing both of >>>> these problems. (Please send two patches, one for each.) >>>> >>>> Thanks, >>>> Ian. >> There is a bug in Xen. domctl pause and unpause hypercalls are not >> properly refcounted. Patch on its way. > I had convinced myself by reading that they were, but Tamas' > experimental evidence obviously counters that ;-) > > Ian. > The "d->is_paused_by_controller" is a boolean, not an atomic count. The second pause doesn't add an extra pause ref to the domain, and the first unpause resumes the domain. ~Andrew