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 F119FC25B75 for ; Wed, 8 May 2024 08:54:14 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1s4d3r-0001Ih-2Z; Wed, 08 May 2024 04:54:03 -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 1s4d3n-00018Z-5h for qemu-devel@nongnu.org; Wed, 08 May 2024 04:54:00 -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 1s4d3i-0007wc-W5 for qemu-devel@nongnu.org; Wed, 08 May 2024 04:53:58 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1715158433; 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:in-reply-to:in-reply-to: references:references; bh=Z+SXa6ZH+M0Iix3vdbwNB6xSc6JQWCRkIX4/cPiCdBk=; b=GvgIhaaX4wcMcBtIWo0QEe9y8oytCsCRu/R7kklYUWzM/j1v7IXrSEHW7jLrtpyAV6+uj7 ksX9NHQCMNZoQru2vdOA/RRTNBN5MFLXJqpTiPw/pM/Hykpzp+7dO5QjtxGRO04XdjH70v hzibo+vvdtvZ7gWryPLBKibklx59Gdo= 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-63-IZANiXtCNS2bkNQnfVnidw-1; Wed, 08 May 2024 04:53:52 -0400 X-MC-Unique: IZANiXtCNS2bkNQnfVnidw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (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 B94DF29AB410; Wed, 8 May 2024 08:53:51 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.29]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 9E0C03C25; Wed, 8 May 2024 08:53:50 +0000 (UTC) Date: Wed, 8 May 2024 09:53:48 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Fabiano Rosas Cc: qemu-devel@nongnu.org, armbru@redhat.com, Peter Xu , Claudio Fontana , Jim Fehlig Subject: Re: [PATCH 8/9] migration: Add support for fdset with multifd + file Message-ID: References: <20240426142042.14573-1-farosas@suse.de> <20240426142042.14573-9-farosas@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20240426142042.14573-9-farosas@suse.de> User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.1 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: -26 X-Spam_score: -2.7 X-Spam_bar: -- X-Spam_report: (-2.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.581, 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 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 Fri, Apr 26, 2024 at 11:20:41AM -0300, Fabiano Rosas wrote: > Allow multifd to use an fdset when migrating to a file. This is useful > for the scenario where the management layer wants to have control over > the migration file. > > By receiving the file descriptors directly, QEMU can delegate some > high level operating system operations to the management layer (such > as mandatory access control). The management layer might also want to > add its own headers before the migration stream. > > Enable the "file:/dev/fdset/#" syntax for the multifd migration with > mapped-ram. The requirements for the fdset mechanism are: > > On the migration source side: > > - the fdset must contain two fds that are not duplicates between > themselves; > - if direct-io is to be used, exactly one of the fds must have the > O_DIRECT flag set; > - the file must be opened with WRONLY both times. > > On the migration destination side: > > - the fdset must contain one fd; > - the file must be opened with RDONLY. > > Signed-off-by: Fabiano Rosas > --- > docs/devel/migration/main.rst | 18 ++++++++++++++ > docs/devel/migration/mapped-ram.rst | 6 ++++- > migration/file.c | 38 ++++++++++++++++++++++++++++- > 3 files changed, 60 insertions(+), 2 deletions(-) > > diff --git a/docs/devel/migration/main.rst b/docs/devel/migration/main.rst > index 54385a23e5..50f6096470 100644 > --- a/docs/devel/migration/main.rst > +++ b/docs/devel/migration/main.rst > @@ -47,6 +47,24 @@ over any transport. > QEMU interference. Note that QEMU does not flush cached file > data/metadata at the end of migration. > > + The file migration also supports using a file that has already been > + opened. A set of file descriptors is passed to QEMU via an "fdset" > + (see add-fd QMP command documentation). This method allows a > + management application to have control over the migration file > + opening operation. There are, however, strict requirements to this > + interface: > + > + On the migration source side: > + - if the multifd capability is to be used, the fdset must contain > + two file descriptors that are not duplicates between themselves; > + - if the direct-io capability is to be used, exactly one of the > + file descriptors must have the O_DIRECT flag set; > + - the file must be opened with WRONLY. > + > + On the migration destination side: > + - the fdset must contain one file descriptor; > + - the file must be opened with RDONLY. > + > In addition, support is included for migration using RDMA, which > transports the page data using ``RDMA``, where the hardware takes care of > transporting the pages, and the load on the CPU is much lower. While the > diff --git a/docs/devel/migration/mapped-ram.rst b/docs/devel/migration/mapped-ram.rst > index fa4cefd9fc..e6505511f0 100644 > --- a/docs/devel/migration/mapped-ram.rst > +++ b/docs/devel/migration/mapped-ram.rst > @@ -16,7 +16,7 @@ location in the file, rather than constantly being added to a > sequential stream. Having the pages at fixed offsets also allows the > usage of O_DIRECT for save/restore of the migration stream as the > pages are ensured to be written respecting O_DIRECT alignment > -restrictions (direct-io support not yet implemented). > +restrictions. > > Usage > ----- > @@ -35,6 +35,10 @@ Use a ``file:`` URL for migration: > Mapped-ram migration is best done non-live, i.e. by stopping the VM on > the source side before migrating. > > +For best performance enable the ``direct-io`` capability as well: > + > + ``migrate_set_capability direct-io on`` > + > Use-cases > --------- > > diff --git a/migration/file.c b/migration/file.c > index b9265b14dd..3bc8bc7463 100644 > --- a/migration/file.c > +++ b/migration/file.c > @@ -17,6 +17,7 @@ > #include "io/channel-file.h" > #include "io/channel-socket.h" > #include "io/channel-util.h" > +#include "monitor/monitor.h" > #include "options.h" > #include "trace.h" > > @@ -54,10 +55,18 @@ static void file_remove_fdset(void) > } > } > > +/* > + * With multifd, due to the behavior of the dup() system call, we need > + * the fdset to have two non-duplicate fds so we can enable direct IO > + * in the secondary channels without affecting the main channel. > + */ > static bool file_parse_fdset(const char *filename, int64_t *fdset_id, > Error **errp) > { > + FdsetInfoList *fds_info; > + FdsetFdInfoList *fd_info; > const char *fdset_id_str; > + int nfds = 0; > > *fdset_id = -1; > > @@ -71,6 +80,32 @@ static bool file_parse_fdset(const char *filename, int64_t *fdset_id, > return false; > } > > + if (!migrate_multifd() || !migrate_direct_io()) { > + return true; > + } > + > + for (fds_info = qmp_query_fdsets(NULL); fds_info; > + fds_info = fds_info->next) { > + > + if (*fdset_id != fds_info->value->fdset_id) { > + continue; > + } > + > + for (fd_info = fds_info->value->fds; fd_info; fd_info = fd_info->next) { > + if (nfds++ > 2) { > + break; > + } > + } > + } > + > + if (nfds != 2) { > + error_setg(errp, "Outgoing migration needs two fds in the fdset, " > + "got %d", nfds); > + qmp_remove_fd(*fdset_id, false, -1, NULL); > + *fdset_id = -1; > + return false; > + } > + > return true; > } Related to my thoughts in an earlier patch, where I say that use of fdsets ought to be transparent to QEMU code, I'm not a fan of having this logic in migration code. IIUC, the migration code will call qio_channel_file_new_path twice, once with O_DIRECT and once without. This should trigger two calls into monitor_fdset_dup_fd_add with different flags. If we're matching flags in that monitor_fdset_dup_fd_add(), then if only 1 FD was provided, are we not able to report an error there ? > > @@ -209,10 +244,11 @@ void file_start_incoming_migration(FileMigrationArgs *file_args, Error **errp) > g_autofree char *filename = g_strdup(file_args->filename); > QIOChannelFile *fioc = NULL; > uint64_t offset = file_args->offset; > + int flags = O_RDONLY; > > trace_migration_file_incoming(filename); > > - fioc = qio_channel_file_new_path(filename, O_RDONLY, 0, errp); > + fioc = qio_channel_file_new_path(filename, flags, 0, errp); > if (!fioc) { > return; > } > -- > 2.35.3 > 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 :|