From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46280) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dIee8-00058w-Ow for qemu-devel@nongnu.org; Wed, 07 Jun 2017 13:21:30 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dIee4-0002Tl-Kr for qemu-devel@nongnu.org; Wed, 07 Jun 2017 13:21:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48254) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dIee4-0002TS-Bz for qemu-devel@nongnu.org; Wed, 07 Jun 2017 13:21:24 -0400 Date: Wed, 7 Jun 2017 18:21:19 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20170607172119.GM2099@work-vm> References: <20170606165510.33057-1-pasic@linux.vnet.ibm.com> <20170606165510.33057-3-pasic@linux.vnet.ibm.com> <20170607110758.GC2099@work-vm> <20170607120138.GD2384@work-vm> <1fb16203-3857-d0aa-498e-4acca6a28a41@linux.vnet.ibm.com> <20170607171021.GK2099@work-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [RFC PATCH 2/3] vmstate: error hint for failed equal checks part 2 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Halil Pasic Cc: Christian Borntraeger , "Jason J . Herne" , Juan Quintela , qemu-devel@nongnu.org * Halil Pasic (pasic@linux.vnet.ibm.com) wrote: > > > On 06/07/2017 07:10 PM, Dr. David Alan Gilbert wrote: > > * Halil Pasic (pasic@linux.vnet.ibm.com) wrote: > >> > >> > >> On 06/07/2017 02:01 PM, Dr. David Alan Gilbert wrote: > >>> * Halil Pasic (pasic@linux.vnet.ibm.com) wrote: > >>>> > >>>> > >>>> On 06/07/2017 01:07 PM, Dr. David Alan Gilbert wrote: > >>>>> * Halil Pasic (pasic@linux.vnet.ibm.com) wrote: > >>>>>> Verbose error reporting for the _EQUAL family. Modify the standard _EQUAL > >>>>>> so the hint states the assertion probably failed due to a bug. Introduce > >>>>>> _EQUAL_HINT for specifying a context specific hint. > >>>>>> > >>>>>> Signed-off-by: Halil Pasic > >>>>> > >>>>> I'd prefer not to print 'Bug!?' by default - they already get the > >>>>> message telling them something didn't match and the migration fails. > >>>>> There are none-bug ways of this happening, e.g. a user starting a VM on > >>>>> the source and destination with different configs. > >>>> > >>>> I admit, my objective with 'Bug!?' was to provoke. My train of thought is > >>>> to encourage the programmer to think about and document the circumstances > >>>> under which such an assertion is supposed to fail (and against which it > >>>> is supposed to guard). > >>>> > >>>> I do not know how skillful are our users but a 4 != 5 then maybe a name > >>>> of a vmstate field is probably quite scary and not very revealing. I doubt > >>>> a non qemu developer can use it for something else that reporting a bug. > >>>> > >>>> Consequently if there are non-bug ways one can use the hint and state them. > >>>> Your example with the misconfigured target, by the way, is IMHO also be due > >>>> to a bug of the management software IMHO. > >>>> > >>>> To sum it up: IMHO the message provided by a failing _EQUAL is to ugly > >>>> and Qemuspeak to be presented to an user-user in non-bug cases. Agree? > >>>> Disagree? > >>> > >>> Disagree. > >>> > >>> I don't mind giving field names etc; they make it easy for us as > >>> developers to track down what's happening, but also sometimes they help > >>> endusers work around a prolem or see where the problem is; of course > >>> that varies depending on the field name, but some of our names are > >>> reasonable (e.g. there's a VMSTATE_INT32_EQUAL on 'queue_size' in > >>> vmmouse.c). They're also pretty good if two end users hit the same > >>> problem they can see the same error message in a bug report. > >>> > >>> We often have customer-facing support people look at logs before they > >>> get as far as us developers; if we have bugs that are > >>> 'if it's a failing BLAH device complaining about the BAR field' > >>> then this fixes it, then that helps them find workarounds/fixes quickly > >>> even if they don't understand what the BAR field is. > >>> > >> > >> You seem to forget, that I'm not proposing omitting this information, > >> but extending it with something civilized so one can distinguish between > >> an assert failed should have never happened situation an a as good as > >> reasonable error handling for an expected error scenario. IMHO the current > >> EQUAL looks more like the former (assert) and less like the later (error > >> reporting for an expected error scenario). Agree? Dissagree? > > > > Yes, the current EQUAL is very terse; but we can't actually tell from > > the use which case it is; it'll all work nicely when people actually add > > the correct hint text in useful locations. > > > > You are right. > > Since Juan also requested the adding an extra param to the original > macros variant I will go with that. > > I shied away form it in the first place because I did not want to > bother the users of the macros without clarifying with the migration > gurus how the new interface should look like. If you just make the existing callers pass NULL then that's fine. Dave > Thanks a lot! > > Regards, > Halil > > >> Having a field name is great! That's beyond discussion. > >> > >> I see, my 'sum it up' above was a bit unfortunate: it sounds like I'm > >> against the inclusion of technical info and not against a lack of non > >> technical info. Sorry for that! > > > > No, that's fine. > > > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK