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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 A0558C433E7 for ; Tue, 21 Jul 2020 14:59:35 +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 6B9EA20578 for ; Tue, 21 Jul 2020 14:59:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="TW7y8XRV" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6B9EA20578 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]:35996 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jxtjy-0002Ax-KE for qemu-devel@archiver.kernel.org; Tue, 21 Jul 2020 10:59:34 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:45190) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jxtj7-0001i9-46 for qemu-devel@nongnu.org; Tue, 21 Jul 2020 10:58:41 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:57216 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jxtj5-0000eH-Gw for qemu-devel@nongnu.org; Tue, 21 Jul 2020 10:58:40 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1595343518; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=/urrWh8kmsRnAtvlzIN0fYA06DD+Z0xlQ3Rf671P/Ck=; b=TW7y8XRVrz5/PUaR8A4P6JDAVsukZfiQ6pSbT2V/7+zIdch0An3cLp97V+Q++E/ETETksx We3aqyAT9COLaqNK5ccDjOVBUX4UR0J3jn2wGp/1dOkny4aTEEtCfYO4Cqq+79diAQ6KvY p/WtMSmeu0FCNfgorNpZTWA7AtkVL7Y= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-440-eaZuK8DbNCi_Y66xHHBYCA-1; Tue, 21 Jul 2020 10:58:36 -0400 X-MC-Unique: eaZuK8DbNCi_Y66xHHBYCA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 033FE107ACCA; Tue, 21 Jul 2020 14:58:36 +0000 (UTC) Received: from work-vm (ovpn-114-151.ams2.redhat.com [10.36.114.151]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 32B5E1001901; Tue, 21 Jul 2020 14:58:35 +0000 (UTC) Date: Tue, 21 Jul 2020 15:58:32 +0100 From: "Dr. David Alan Gilbert" To: Peter Maydell Subject: Re: error reporting from pre_load etc callbacks Message-ID: <20200721145832.GC2800@work-vm> References: MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.14.5 (2020-06-23) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.120; envelope-from=dgilbert@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/21 10:58:38 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action 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: QEMU Developers , Juan Quintela Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Peter Maydell (peter.maydell@linaro.org) wrote: > (This was pointed out to me off-list.) > > What is the intended API of the pre_load() etc callbacks? > docs/devel/migration.rst doesn't say, and there's no doc comment > in include/migration/vmstate.h. Most actual device implementations > of the hooks seem to return 0 on success and -1 on failure. > But the callers of the hooks like vmstate_load_state() seem to > assume they return negative-errnos: a non-zero return value > is just propagated up to the caller, and can end up for > instance treated as negative-errno in process_incoming_migration_co(): > error_report("load of migration failed: %s", strerror(-ret)); > which results in nonsensical error messages to the user like: > qemu-system-aarch64: load of migration failed: Operation not permitted In theory (pre|post)_(load|save) have the same interface; in practice they're all rather inconsistent. Returning 0 on success, -errno on failure is my preference. > More generally, it would be nice if a pre_load/post_load/etc > hook could report an error more precisely than just yes/no > or even than just an errno: in the case of arm CPU loading > we could in theory report more detail like which register the > kernel didn't handle... On the load side, just error_report as tightly as you can; what you should see on stderr is basically a backtrace: 'failed to do something in ...' 'load of migration failed of ...' Dave > thanks > -- PMM > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK