From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 47262C388F3 for ; Tue, 1 Oct 2019 09:22:09 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1C5D721924 for ; Tue, 1 Oct 2019 09:22:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1C5D721924 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:39554 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iFEMC-0002cZ-A8 for qemu-devel@archiver.kernel.org; Tue, 01 Oct 2019 05:22:08 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34315) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iFEKQ-0000VO-9Q for qemu-devel@nongnu.org; Tue, 01 Oct 2019 05:20:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iFEKP-0006JS-0s for qemu-devel@nongnu.org; Tue, 01 Oct 2019 05:20:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60884) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iFEKJ-0006CO-6D; Tue, 01 Oct 2019 05:20:11 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 3FBC081F07; Tue, 1 Oct 2019 09:20:09 +0000 (UTC) Received: from linux.fritz.box (ovpn-117-215.ams2.redhat.com [10.36.117.215]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4AD343DE2; Tue, 1 Oct 2019 09:19:46 +0000 (UTC) Date: Tue, 1 Oct 2019 11:19:44 +0200 From: Kevin Wolf To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH v3 04/25] error: auto propagated local_err Message-ID: <20191001091944.GB4688@linux.fritz.box> References: <20190924200902.4703-1-vsementsov@virtuozzo.com> <20190924200902.4703-5-vsementsov@virtuozzo.com> <20190930151215.GB12777@linux.fritz.box> <20190930160039.GC12777@linux.fritz.box> <495102b2-5d1a-f659-4387-5733ae34b3e2@virtuozzo.com> <20190930163909.GD12777@linux.fritz.box> <8d55df7a-abe6-bebc-a6bd-a1a2db4b8946@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8d55df7a-abe6-bebc-a6bd-a1a2db4b8946@virtuozzo.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Tue, 01 Oct 2019 09:20:09 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Fam Zheng , Peter Maydell , Paul Burton , Jeff Cody , Jason Wang , Mark Cave-Ayland , "qemu-devel@nongnu.org" , Michael Roth , Gerd Hoffmann , Subbaraya Sundeep , "qemu-block@nongnu.org" , Juan Quintela , Aleksandar Rikalo , "Michael S. Tsirkin" , Markus Armbruster , Halil Pasic , Christian Borntraeger , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , David Gibson , Eric Farman , Eduardo Habkost , Greg Kurz , Yuval Shaia , "Dr. David Alan Gilbert" , Alex Williamson , "qemu-arm@nongnu.org" , David Hildenbrand , John Snow , Richard Henderson , "integration@gluster.org" , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Cornelia Huck , "qemu-s390x@nongnu.org" , Max Reitz , "qemu-ppc@nongnu.org" , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 01.10.2019 um 10:39 hat Vladimir Sementsov-Ogievskiy geschrieben: > 30.09.2019 19:39, Kevin Wolf wrote: > > Am 30.09.2019 um 18:26 hat Vladimir Sementsov-Ogievskiy geschrieben: > >> 30.09.2019 19:00, Kevin Wolf wrote: > >>> Am 30.09.2019 um 17:19 hat Vladimir Sementsov-Ogievskiy geschrieben: > >>>> 30.09.2019 18:12, Kevin Wolf wrote: > >>>>> Am 24.09.2019 um 22:08 hat Vladimir Sementsov-Ogievskiy geschrieben: > >>>>>> Here is introduced ERRP_FUNCTION_BEGIN macro, to be used at start of > >>>>>> functions with errp parameter. > >>>>> > >>>>> A bit of bike shedding, but FOO_BEGIN suggests to me that a FOO_END will > >>>>> follow. Can we find a different name, especially now that we won't use > >>>>> this macro in every function that uses an errp, so even the "errp > >>>>> function" part isn't really correct any more? > >>>>> > >>>>> How about ERRP_AUTO_PROPAGATE? > >>>> > >>>> I have an idea that with this macro we can (optionally) get the whole call stack > >>>> of the error and print it to log, so it's good to give it more generic name, not > >>>> limited to propagation.. > >>> > >>> Hm, what's the context for this feature? > >>> > >>> The obvious one where you want to have a stack trace is &error_abort, > >>> but that one crashes, so you get it automatically. If it's just a normal > >>> error (like a QAPI option contains an invalid value and some function > >>> down the call chain checks it), why would anyone want to know what the > >>> call chain in the QEMU code was? > >>> > >> > >> When I have bug from testers, call stack would be a lot more descriptive, than just > >> an error message. > >> > >> We may add trace point which will print this information, so with disabled trace point > >> - no extra output. > > > > But wouldn't it make much more sense then to optionally add this > > functionality to any trace point? I really don't see how this is related > > specifically to user-visible error messages. > > Interesting idea > > > > > However, even if we decide that we want to have this in Error objects, > > wouldn't it make much more sense to use the real C stack trace and save > > it from the innermost error_set() using backtrace() or compiler > > built-ins rather than relying on an error_propagate() chain? > > > Hmm, I thought about this.. And in concatenation with the fact that > we'll have macro not everywhere, backtrace may be better.. > > On the other hand, backtrace will not show coroutine entries.. Hm, good point. I wonder if we can easily get a stack trace not starting at the current point, but from a jmp_buf. Then we could just switch to the coroutine caller whenever we reach coroutine_trampoline(). But glibc doesn't seem to support this case easily, so that might mean rewriting all of the stack unwinding inside QEMU... Maybe not then. > OK, anyway, if we will track some additional information in > trace-events or in macros or in error_* API functions, it's not bad to > track some additional information in macro named ERRP_AUTO_PROPAGATE. Yes, I think tracking the information where we use ERRP_AUTO_PROPAGATE anyway is okay. I just wouldn't add the macro everywhere just for the sake of the additional information. Kevin