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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 798B0CE7B03 for ; Thu, 28 Sep 2023 06:50:21 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qlkpo-0001JB-Oi; Thu, 28 Sep 2023 02:49:16 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qlkpl-0001Im-Dz for qemu-devel@nongnu.org; Thu, 28 Sep 2023 02:49:13 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qlkpj-0008Vt-6k for qemu-devel@nongnu.org; Thu, 28 Sep 2023 02:49:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1695883748; 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=Rr+d6uzkCDlT0VD6DyKF1xaqGXeZCIpoy98t36Y5ZIE=; b=MUlXVERBCskkQUFlieAIxS6upGzecD11KFw7ecJv65R2CZNxd+35Ljctd46SrEZCICIZ0q fhS0hUQK5wcwY1qelU6dWPdmcoqWf6K1DAHKaJW/U7xAXoRlxRBe0wce6QcUf7aWKEPT4q mRSP/IiyBbhCTimJnfJDsaz/VPvWlrU= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-466-Ce1aei6OPxi6_sgIzholrQ-1; Thu, 28 Sep 2023 02:49:04 -0400 X-MC-Unique: Ce1aei6OPxi6_sgIzholrQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 3B1C3101A550; Thu, 28 Sep 2023 06:49:04 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.25]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D7883C15BB8; Thu, 28 Sep 2023 06:49:03 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id C902D21E6900; Thu, 28 Sep 2023 08:49:02 +0200 (CEST) From: Markus Armbruster To: "Zhijian Li (Fujitsu)" Cc: "qemu-devel@nongnu.org" , "quintela@redhat.com" , "peterx@redhat.com" , "leobras@redhat.com" Subject: Re: [PATCH 39/52] migration/rdma: Convert qemu_rdma_write_one() to Error References: <20230918144206.560120-1-armbru@redhat.com> <20230918144206.560120-40-armbru@redhat.com> <9e117d0c-cf2b-dd01-7fef-55d1c41d254c@fujitsu.com> <87ttrhgu9e.fsf@pond.sub.org> <87zg17dejj.fsf@pond.sub.org> Date: Thu, 28 Sep 2023 08:49:02 +0200 In-Reply-To: <87zg17dejj.fsf@pond.sub.org> (Markus Armbruster's message of "Wed, 27 Sep 2023 13:46:40 +0200") Message-ID: <87ttre3i8x.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, 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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Let me try to map solutions. Markus Armbruster writes: > migration/rdma.c uses errno directly or via perror() after the following > functions: > > * poll() > > POSIX specifies errno is set on error. Good. Nothing wrong, nothing to do. > * rdma_get_cm_event(), rdma_connect(), rdma_get_cm_event() > > Manual page promises "if an error occurs, errno will be set". Good. Nothing wrong, nothing to do. > * ibv_open_device() > > Manual page does not mention errno. Using it seems ill-advised. > > qemu_rdma_broken_ipv6_kernel() recovers from EPERM by trying the next > device. Wrong if ibv_open_device() doesn't actually set errno. > > What is to be done here? 1. Investigate whether ibv_open_device() sets errno. I can't spare time for that. 2. Add a comment pointing out the problem, in the hope somebody investigates later. 3. Do nothing. > * ibv_reg_mr() > > Manual page does not mention errno. Using it seems ill-advised. > > qemu_rdma_reg_whole_ram_blocks() and qemu_rdma_register_and_get_keys() > recover from errno = ENOTSUP by retrying with modified @access > argument. Wrong if ibv_reg_mr() doesn't actually set errno. > > What is to be done here? Likewise. > * ibv_get_cq_event() > > Manual page does not mention errno. Using it seems ill-advised. > > qemu_rdma_block_for_wrid() calls perror(). Removed in PATCH 48. Good > enough. 1. Add a comment pointing out the problem, remove it in PATCH 48. 2. Nothing wrong after the series, nothing to do. > * ibv_post_send() > > Manual page has the function return "the value of errno on failure". > Sounds like it sets errno to the value it returns. However, the > rdma-core repository defines it as > > static inline int ibv_post_send(struct ibv_qp *qp, struct ibv_send_wr *wr, > struct ibv_send_wr **bad_wr) > { > return qp->context->ops.post_send(qp, wr, bad_wr); > } > > and at least one of the methods fails without setting errno: > > static int mana_post_send(struct ibv_qp *ibqp, struct ibv_send_wr *wr, > struct ibv_send_wr **bad) > { > /* This version of driver supports RAW QP only. > * Posting WR is done directly in the application. > */ > return EOPNOTSUPP; > } > > qemu_rdma_write_one() calls perror(). PATCH 39 (this one) replaces it > by error_setg(), not error_setg_errno(). Seems prudent, but should be > called out in the commit message. 1. Add a comment pointing out the problem, remove it in PATCH 39. 2. Pass @ret, not @errno to error_setg_errno(). 3. Nothing wrong after the series, nothing to do. Since 2. is easy, let's do it. > * ibv_advise_mr() > > Manual page has the function return "the value of errno on failure". > Sounds like it sets errno to the value it returns, but my findings for > ibv_post_send() make me doubt it. > > qemu_rdma_advise_prefetch_mr() traces strerror(errno). Could be > misleading. Drop that part? 1. Change sterror(errno) to strerror(ret) 2. Drop strerror(errno) 3. Do nothing. Since 1. is easy, let's do it. > * ibv_dereg_mr() > > Manual page has the function return "the value of errno on failure". > Sounds like it sets errno to the value it returns, but my findings for > ibv_post_send() make me doubt it. > > qemu_rdma_unregister_waiting() calls perror(). Removed in PATCH 51. > Good enough. 1. Add a comment pointing out the problem, remove it in PATCH 51. 2. Nothing wrong after the series, nothing to do. > * qemu_get_cm_event_timeout() > > Can fail without setting errno. > > qemu_rdma_connect() calls perror(). Removed in PATCH 45. Good > enough. > > Thoughts? Considering all of the above... I'd like to stick a patch documenting problematic errno use early in the series, and fix all the easy ones later in the series, leaving just the two difficult ones in qemu_rdma_broken_ipv6_kernel() and qemu_rdma_reg_whole_ram_blocks(). Makes sense? > [...] > > [*] https://github.com/linux-rdma/rdma-core.git > commit 55fa316b4b18f258d8ac1ceb4aa5a7a35b094dcf