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Thu, 19 Sep 2019 13:03:18 +0000 (UTC) Date: Thu, 19 Sep 2019 15:03:17 +0200 From: Kevin Wolf To: Vladimir Sementsov-Ogievskiy Message-ID: <20190919130317.GG10163@localhost.localdomain> References: <20190918130244.24257-1-vsementsov@virtuozzo.com> <20190919091720.GB10163@localhost.localdomain> <1ee95d94-d3f9-2f56-a0bb-61d31e3ceeb7@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1ee95d94-d3f9-2f56-a0bb-61d31e3ceeb7@virtuozzo.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Thu, 19 Sep 2019 13:03:39 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [RFC] error: auto propagated local_err 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@euphon.net" , "peter.maydell@linaro.org" , "mst@redhat.com" , "codyprime@gmail.com" , "mark.cave-ayland@ilande.co.uk" , "qemu-devel@nongnu.org" , "armbru@redhat.com" , "kraxel@redhat.com" , "mreitz@redhat.com" , "qemu-block@nongnu.org" , "quintela@redhat.com" , "david@redhat.com" , "mdroth@linux.vnet.ibm.com" , "pasic@linux.ibm.com" , "borntraeger@de.ibm.com" , "marcandre.lureau@redhat.com" , "rth@twiddle.net" , "farman@linux.ibm.com" , "groug@kaod.org" , "dgilbert@redhat.com" , "alex.williamson@redhat.com" , "qemu-arm@nongnu.org" , "stefanha@redhat.com" , "jsnow@redhat.com" , "david@gibson.dropbear.id.au" , "berrange@redhat.com" , "cohuck@redhat.com" , "qemu-s390x@nongnu.org" , "sundeep.lkml@gmail.com" , "qemu-ppc@nongnu.org" , "pbonzini@redhat.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 19.09.2019 um 14:00 hat Vladimir Sementsov-Ogievskiy geschrieben: > 19.09.2019 12:17, Kevin Wolf wrote: > > Am 18.09.2019 um 19:10 hat Eric Blake geschrieben: > >> On 9/18/19 8:02 AM, Vladimir Sementsov-Ogievskiy wrote: > >>> + */ > >>> +#define MAKE_ERRP_SAFE(errp) \ > >>> +g_auto(ErrorPropagationStruct) (__auto_errp_prop) = {.errp = (errp)}; \ > >>> +if ((errp) == NULL || *(errp) == error_abort || *(errp) == error_fatal) { \ > >>> + (errp) = &__auto_errp_prop.local_err; \ > >>> +} > >> > >> Not written to take a trailing semicolon in the caller. > >> > >> You could even set __auto_errp_prop unconditionally rather than trying > >> to reuse incoming errp (the difference being that error_propagate() gets > >> called more frequently). > > > > I think this difference is actually a problem. > > > > When debugging things, I hate error_propagate(). It means that the Error > > (specifically its fields src/func/line) points to the outermost > > error_propagate() rather than the place where the error really happened. > > It also makes error_abort completely useless because at the point where > > the process gets aborted, the interesting information is already lost. > > > > So I'd really like to restrict the use of error_propagate() to places > > where it's absolutely necessary. Unless, of course, you can fix these > > practical problems that error_propagate() causes for debugging. > > > > In fact, in the context of Greg's series, I think we really only need to > > support hints for error_fatal, which are cases that users are supposed > > to see. We should exclude error_abort in MAKE_ERRP_SAFE() because these > > are things that are never supposed to happen. A good stack trace is more > > important there than adding a hint to the message. > > > > Interesting, that to handle error_append_hint problem, we don't need to > create local_err in case of errp==NULL either.. > > So, possibly, we need the following steps: > > 1. implement MAKE_ERRP_SAFE_FOR_HINT (which only leave "*(errp) == error_fatal" in the if condition > 2. rebase Greg's series on it, to fix hints for fatal errors > 3. implement MAKE_ERRP_SAFE_FOR_DEREFERENCE (which only leave "(errp) == NULL" in the if condition > 4. convert all (almost all) local_err usage to use MAKE_ERRP_SAFE_FOR_DEREFERENCE, which will > fix problem with error_abort (and also drop a lot of calls of error_propagate) > 5. merely convert "void func(.., errp)" to "int func(.., errp)" and drop MAKE_ERRP_SAFE_FOR_DEREFERENCE() > magic, together with dereferencing. Long macro names, but as the parameter will always only be "errp", it fits easily on a line, so this is fine. I think I like this plan. Kevin