From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tamas K Lengyel Subject: Re: [PATCH V5 08/12] xen/vm_event: Check for VM_EVENT_FLAG_DUMMY only in Debug builds Date: Sat, 14 Feb 2015 00:02:35 +0100 Message-ID: References: <1423845203-18941-1-git-send-email-tamas.lengyel@zentific.com> <1423845203-18941-9-git-send-email-tamas.lengyel@zentific.com> <54DE5B2F.60108@citrix.com> <54DE8208.30906@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <54DE8208.30906@citrix.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: Andrew Cooper Cc: "Tian, Kevin" , "wei.liu2@citrix.com" , Ian Campbell , Stefano Stabellini , Tim Deegan , Steven Maresca , "xen-devel@lists.xen.org" , Jan Beulich , "Dong, Eddie" , Andres Lagar-Cavilla , Jun Nakajima , "rshriram@cs.ubc.ca" , Keir Fraser , Daniel De Graaf , "yanghy@cn.fujitsu.com" , Ian Jackson List-Id: xen-devel@lists.xenproject.org On Sat, Feb 14, 2015 at 12:00 AM, Andrew Cooper wrote: > On 13/02/2015 22:53, Tamas K Lengyel wrote: >> On Fri, Feb 13, 2015 at 11:48 PM, Tamas K Lengyel >> wrote: >>> On Fri, Feb 13, 2015 at 9:14 PM, Andrew Cooper >>> wrote: >>>> On 13/02/15 16:33, Tamas K Lengyel wrote: >>>>> The flag is only used for debugging purposes, thus it should be only checked >>>>> for in debug builds of Xen. >>>>> >>>>> Signed-off-by: Tamas K Lengyel >>>> What is the purpose of the dummy flag? I would have thought it would be >>>> more dangerous to accidentally process a dummy response in a non-debug Xen. >>>> >>>> ~Andrew >>> I honestly have no idea what was the real use-case for it. It is a way >>> to signal to Xen to just remove the reponse from the ring without >>> doing anything else with it so I figured it might be handy when >>> debugging a toolstack. >>> >>> Tamas >> As for processing it on a non-debug Xen: I think it's safe as the >> response would just be handled according to the other flags that are >> set in the response, like unpausing the vCPU that triggered the event. >> IMHO its a wasteful check on production systems. > > If it is not useful then discard it completely (seeing as the entire > system is being overhauled). I can't see any purpose in having a method > of telling Xen to ignore a request placed on the ring. If the toolstack > wishes Xen not to do anything then it should not have put a request on > the ring in the first place. > > ~Andrew Ack. Tamas