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=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 12C3DC433DB for ; Mon, 22 Mar 2021 11:04:08 +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 C37C461879 for ; Mon, 22 Mar 2021 11:04:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C37C461879 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]:45860 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lOILt-0003lu-Hz for qemu-devel@archiver.kernel.org; Mon, 22 Mar 2021 07:04:06 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42944) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lOIJ4-0001Hc-Qp for qemu-devel@nongnu.org; Mon, 22 Mar 2021 07:01:10 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:59710) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lOIJ2-0008I2-14 for qemu-devel@nongnu.org; Mon, 22 Mar 2021 07:01:10 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1616410867; 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=2neSUoOKQlzRUDRQfXu8oad3mw9Yn0JoIdvnWS2K/SE=; b=Jy4UFszWWh9n2CHpHZHzJ9mFi2i+O9eYiXFg9t5Hhx3exRvzRmv4BESnI1axPICKFjnpq9 zBWMoZGX8iLT9YRdRlAaZxT202fFQFy4o9qntd0Fqz9rlf88WAE4zAqMyrc/Q53Ck+rCpW WU1CaJKHczOrcjhAfejg970WFuoZ/SI= 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-204-2XDGNYuKPUezIiVnOPCfdw-1; Mon, 22 Mar 2021 07:01:04 -0400 X-MC-Unique: 2XDGNYuKPUezIiVnOPCfdw-1 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 mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7BD1A593A0; Mon, 22 Mar 2021 11:01:03 +0000 (UTC) Received: from localhost (ovpn-114-89.ams2.redhat.com [10.36.114.89]) by smtp.corp.redhat.com (Postfix) with ESMTP id 830D32B3C0; Mon, 22 Mar 2021 11:00:53 +0000 (UTC) Date: Mon, 22 Mar 2021 11:00:52 +0000 From: Stefan Hajnoczi To: Jiachen Zhang Subject: Re: [External] Re: [RFC PATCH 0/9] Support for Virtio-fs daemon crash reconnection Message-ID: References: <20201215162119.27360-1-zhangjiachen.jaycee@bytedance.com> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=stefanha@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="LHuo8nVlDM+kCL5G" Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=stefanha@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_LOW=-0.7, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, 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: "Daniel P. Berrange" , slp@redhat.com, "Michael S . Tsirkin" , QEMU , "Dr . David Alan Gilbert" , virtio-fs@redhat.com, Xie Yongji , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --LHuo8nVlDM+kCL5G Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Wed, Mar 17, 2021 at 08:32:31PM +0800, Jiachen Zhang wrote: > On Wed, Mar 17, 2021 at 6:05 PM Stefan Hajnoczi wrote: > > On Fri, Dec 18, 2020 at 05:39:34PM +0800, Jiachen Zhang wrote: > I agreed with you that a virtiofsd must be launched by a software like > systemd. So we are planning to define more generic persist/restore > interfaces (callbacks). Then anyone can implement their own persist/restore > callbacks to store states to proper places. And I think in the next > version we will implement default callbacks for the interfaces. Instead of > vhost-user messages, systemd's sd_notify(3) will be the default method for > storing fds, and several tmpfs files can be the default place to store the > shm regions. Okay, great! I was thinking about how to make the crash recovery mechanism reusable as a C library or Rust crate. The mechanism is a combination of: 1. sd_listen_fds(3) for restoring the fds on restart. 2. sd_notify(3) for storing the fds. 3. memfd or tmpfs for storing state (could be mmapped). I'm not sure if there is enough common behavior to create a reusable API or if this is quite application-specific. 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