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 8B8A4C54E71 for ; Tue, 19 Mar 2024 19:53:30 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rmfWP-0000EO-GQ; Tue, 19 Mar 2024 15:53:17 -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 1rmfWN-0000E8-Qd for qemu-devel@nongnu.org; Tue, 19 Mar 2024 15:53:15 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rmfWL-0002Wv-Ug for qemu-devel@nongnu.org; Tue, 19 Mar 2024 15:53:15 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1710877992; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ipNVNVh0PVDjyOfi/LUI7HBCeDThBHx/w871huSWljM=; b=FSp0GEmGutVV9IT6Rox2AGureLw6EyKpQyQRMsU396K/8U6df3UlTHR24V6bnzPgCY7/x2 6TWkob3zZdD1YqRiCgkDGSq/fytVyQrHIO3HtBabetLZzFkF8SlmkjvLi4exFcHPLIELlN qELu7tHo7EEByBrN7o4fKm3UcMCmV7k= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-167-neNn-DIEN369eViSdVJevQ-1; Tue, 19 Mar 2024 15:53:10 -0400 X-MC-Unique: neNn-DIEN369eViSdVJevQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 3901A3C0D7C1; Tue, 19 Mar 2024 19:53:10 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.88]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 70C4F40C6DB5; Tue, 19 Mar 2024 19:53:09 +0000 (UTC) Date: Tue, 19 Mar 2024 19:52:47 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Xu Cc: Fabiano Rosas , qemu-devel@nongnu.org, Eric Blake , Markus Armbruster Subject: Re: [RFC PATCH v3 3/3] migration: Add fd to FileMigrationArgs Message-ID: References: <20240315032040.7974-1-farosas@suse.de> <20240315032040.7974-4-farosas@suse.de> <87y1aj74t6.fsf@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.2 Received-SPF: pass client-ip=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.422, 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Mar 19, 2024 at 03:25:18PM -0400, Peter Xu wrote: > On Tue, Mar 19, 2024 at 04:25:32PM +0000, Daniel P. Berrangé wrote: > > On Fri, Mar 15, 2024 at 04:54:27PM -0400, Peter Xu wrote: > > > On Fri, Mar 15, 2024 at 03:01:09PM -0300, Fabiano Rosas wrote: > > > > Peter Xu writes: > > > > > > > > > [I queued patch 1-2 into -stable, leaving this patch for further > > > > > discussions] > > > > > > > > > > On Fri, Mar 15, 2024 at 08:55:42AM +0000, Daniel P. Berrangé wrote: > > > > >> The 'file:' protocol eventually calls into qemu_open, and this > > > > >> transparently allows for FD passing using /dev/fdset/NNN syntax > > > > >> to pass in FDs. > > > > > > > > > > If it always use /dev/fdsets for files, does it mean that the newly added > > > > > SOCKET_ADDRESS_TYPE_FD support on mapped-ram will never be used (so we can > > > > > drop them)? > > > > > > > > We already have SOCKET_ADDRESS_TYPE_FD + file since 8.2 when the > > > > MigrationAddress was added. So this: > > > > > > > > 'channels': [ { 'channel-type': 'main', > > > > 'addr': { 'transport': 'socket', > > > > 'type': 'fd', > > > > 'str': 'fdname' } } ] > > > > > > > > works without multifd and without mapped-ram if the fd is a file or > > > > socket. > > > > > > > > So yes, you're correct, but given we already have this^ it would be > > > > perhaps more confusing for users to allow it, but not allow the very > > > > same JSON when multifd=true, mapped-ram=true. > > > > > > I don't think the fd: protocol (no matter the old "fd:", or the new JSON > > > format) is trivial to use. If libvirt didn't use it I won't be surprised to > > > see nobody using it. I want us to avoid working on things that nobody is > > > using, or has a better replacement. > > > > > > So even if Libvirt supports both, I'm wondering whether /dev/fdset/ works > > > for all the cases that libvirt needs. I am aware that the old getfd has > > > the monitor limitation so that if the QMP disconnected and reconnect, the > > > fd can be gone. However I'm not sure whether that's the only reason to > > > have add-fd, and also not sure whether it means add-fd is always preferred, > > > so that maybe we can consider obsolete getfd? > > > > Historically libvirt primariily uses the 'fd:' protocol, with a > > socket FD. It never gives QEMU a plain file FD, since it has > > always added its "iohelper" as a MITM, in order to add O_DIRECT > > on top. > > > > The 'getfd' command is something that is needed when talking to > > QEMU for any API that involves a "SocketAddress" QAPI type, > > which is applicable for migration. > > > > With the introduction of 'MigrationAddress', the 'socket' protocol > > is backed by 'SocketAddress' and thus supports FD passing for > > sockets (or potentally pipes too), in combination with 'getfd'. > > > > With the 'file' protocol in 'MigrationAddress', since it gets > > backed by qemu_open(), then /dev/fdset/NN and 'add-fd' provide > > passing for plain files. > > I see. I assume it means we still have multiple users of getfd so it's > still in use where add-fd is not yet avaiable. > > But then, SOCKET_ADDRESS_TYPE_FD is then not used for libvirt in the whole > mapped-ram effort, neither do we need any support on file migrations over > "fd", e.g. fd_start_incoming_migration() for files. So we can drop these > parts, am I right? Correct, libvirt hasn't got any impl for 'mapped-ram' yet, at least not something merged. Since this is new functionality, libvirt could go straight for the 'file' protocol / address type. At some point I think we can stop using 'fd' for traditional migration too and pass the socket address to QEMU and let QEMU open the socket. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|