From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59602) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dIZfE-0008Rm-Ba for qemu-devel@nongnu.org; Wed, 07 Jun 2017 08:02:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dIZf4-0002d2-J9 for qemu-devel@nongnu.org; Wed, 07 Jun 2017 08:02:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:59822) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dIZf4-0002cd-B6 for qemu-devel@nongnu.org; Wed, 07 Jun 2017 08:02:06 -0400 Date: Wed, 7 Jun 2017 13:01:39 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20170607120138.GD2384@work-vm> References: <20170606165510.33057-1-pasic@linux.vnet.ibm.com> <20170606165510.33057-3-pasic@linux.vnet.ibm.com> <20170607110758.GC2099@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 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. > > > > > (I also worry we have a lot f macros for each size; > > EQUAL, EQUAL_V, EQUAL_V_HINT but I don't know of a better answer for > > that) > > > > If we are going to drop the default hint ('Bug?!' or whatever) then > I think we could just add an extra NULL hint to each existing _EQUAL > usage, re-purpose EQUAL, and forget about introducing new _HINT macros. > > What to you think? Yes, that would be a lot simpler; and there aren't that many VMSTATE*EQUAL* macros in use. Dave > Regards, > Halil > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK