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 39ECCC25B5F for ; Wed, 8 May 2024 08:03:11 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1s4cGQ-0008EV-A1; Wed, 08 May 2024 04:02:58 -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 1s4cG2-00086N-LS for qemu-devel@nongnu.org; Wed, 08 May 2024 04:02:41 -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 1s4cFy-0008PA-M0 for qemu-devel@nongnu.org; Wed, 08 May 2024 04:02:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1715155348; 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=9gxNroo/yIgDKQMkEv39lBtbUS5mR6uvbvpXdf7xFjQ=; b=VeKkwqC4UQ1ngqCIIvxhsvHZDgbkqfzc8KlZrf65ooGC4nxRilRbZhyio3GP4quuV5dkUV aFFEUZOrn1U1w3IX736dPd2dRQ8+jIFWRvE6PcQO3mlZdVreVPkDlLx0scK2nK9xRhqlel eiD08iSChADWjBk+TE70CtPY9NC5JII= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-384-OH5ABRdrN9C-L0QAVFKUMg-1; Wed, 08 May 2024 04:02:21 -0400 X-MC-Unique: OH5ABRdrN9C-L0QAVFKUMg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (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 BE7C0101A525; Wed, 8 May 2024 08:02:19 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.29]) by smtp.corp.redhat.com (Postfix) with ESMTPS id ECEC310000AD; Wed, 8 May 2024 08:02:18 +0000 (UTC) Date: Wed, 8 May 2024 09:02:16 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Peter Xu Cc: Fabiano Rosas , qemu-devel@nongnu.org, armbru@redhat.com, Claudio Fontana , Jim Fehlig Subject: Re: [PATCH 2/9] migration: Fix file migration with fdset Message-ID: References: <20240426142042.14573-1-farosas@suse.de> <20240426142042.14573-3-farosas@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.3 Received-SPF: pass client-ip=170.10.133.124; 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, May 03, 2024 at 12:23:51PM -0400, Peter Xu wrote: > On Fri, Apr 26, 2024 at 11:20:35AM -0300, Fabiano Rosas wrote: > > When the migration using the "file:" URI was implemented, I don't > > think any of us noticed that if you pass in a file name with the > > format "/dev/fdset/N", this allows a file descriptor to be passed in > > to QEMU and that behaves just like the "fd:" URI. So the "file:" > > support has been added without regard for the fdset part and we got > > some things wrong. > > > > The first issue is that we should not truncate the migration file if > > we're allowing an fd + offset. We need to leave the file contents > > untouched. > > I'm wondering whether we can use fallocate() instead on the ranges so that > we always don't open() with O_TRUNC. Before that.. could you remind me > why do we need to truncate in the first place? I definitely missed > something else here too. You're mixing distinct concepts here. fallocate makes a file region non-sparse, while O_TRUNC removes all existing allocation, making it sparse if we write at non-contiguous offsets. I don't think we would want to call fallocate, since we /want/ a sparse file so that we don't needlessly store large regions of all-zeros as RAM maps. 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 :|