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 D8B3DC5478C for ; Wed, 28 Feb 2024 12:11:44 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rfIkY-0003Kc-UF; Wed, 28 Feb 2024 07:09:28 -0500 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 1rfIk6-00039F-0D for qemu-devel@nongnu.org; Wed, 28 Feb 2024 07:09:00 -0500 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 1rfIjy-0004rC-8n for qemu-devel@nongnu.org; Wed, 28 Feb 2024 07:08:57 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1709122128; 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=CrLHz7Mdxdz0Y8CUgYDc4Z7fJj/1afhw+Y5Zqw5kDoU=; b=btUV7LeJMJ3PGQTl5s6vpgX37XYRfS1vGXjk8ILTlWXmXWe02e5tfB/LJpz5/mlI8/2bUm G6iwuvD40VVZs/4jlOEQDSoiqHQc+UPVwiM65AO3cRyNFLNX8yH119XXEAH9aOVOVt1JoF wRNsevz0bTBCEmBwWDq1tRrv0hg3DlM= 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-371-smFtZx2SN2m8aA8Jcl0I7A-1; Wed, 28 Feb 2024 07:08:46 -0500 X-MC-Unique: smFtZx2SN2m8aA8Jcl0I7A-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (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 8610385A58C; Wed, 28 Feb 2024 12:08:45 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.37]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2510F8173; Wed, 28 Feb 2024 12:08:39 +0000 (UTC) Date: Wed, 28 Feb 2024 12:08:37 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Stefano Garzarella Cc: qemu-devel@nongnu.org, Paolo Bonzini , qemu-block@nongnu.org, Thomas Huth , "Michael S. Tsirkin" , Jason Wang , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Markus Armbruster , Eric Blake , Coiby Xu , slp@redhat.com, Eduardo Habkost , Hanna Reitz , Igor Mammedov , Raphael Norwitz , Kevin Wolf , David Hildenbrand , stefanha@redhat.com, gmaglione@redhat.com Subject: Re: [PATCH 9/9] hostmem-file: support POSIX shm_open() Message-ID: References: <20240228114759.44758-1-sgarzare@redhat.com> <20240228114759.44758-10-sgarzare@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20240228114759.44758-10-sgarzare@redhat.com> User-Agent: Mutt/2.2.12 (2023-09-09) X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.5 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: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, DKIM_INVALID=0.1, DKIM_SIGNED=0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=no 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 Wed, Feb 28, 2024 at 12:47:59PM +0100, Stefano Garzarella wrote: > Add a new `shm` bool option for `-object memory-backend-file`. > > When this option is set to true, the POSIX shm_open(3) is used instead > of open(2). > > So a file will not be created in the filesystem, but a "POSIX shared > memory object" will be instantiated. In Linux this turns into a file > in /dev/shm, but in other OSes this may not happen (for example in > macOS or FreeBSD nothing is shown in any filesystem). > > This new feature is useful when we need to share guest memory with > another process (e.g. vhost-user backend), but we don't have > memfd_create() or any special filesystems (e.g. /dev/shm) available > as in macOS. > > Signed-off-by: Stefano Garzarella > --- > I am not sure this is the best way to support shm_open() in QEMU. > > Other solutions I had in mind were: > > - create a new memory-backend-shm > > - extend memory-backend-memfd to use shm_open() on systems where memfd is > not available (problem: shm_open wants a name to assign to the object, but > we can do a workaround by using a random name and do the unlink right away) IMHO, create a new memory-backend-shm, don't overload memory-backend-memfd, as this lets users choose between shm & memfd, even on Linux. 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 :|