From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Subject: Re: [Qemu-devel] [RFC] qemu: Add virtio pmem device Date: Mon, 9 Apr 2018 08:42:35 +0200 Message-ID: <36218ea8-5fa8-e670-104d-616da790a333@redhat.com> References: <20180405104834.10457-1-pagupta@redhat.com> <20180405104834.10457-4-pagupta@redhat.com> <416823501.16310251.1522930166070.JavaMail.zimbra@redhat.com> <20180409032601.GA1648@stefanha-x1.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180409032601.GA1648-lxVrvc10SDRcolVlb+j0YCZi+YwRKgec@public.gmane.org> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-nvdimm-bounces-hn68Rpc1hR1g9hUCZPvPmw@public.gmane.org Sender: "Linux-nvdimm" To: Stefan Hajnoczi , Pankaj Gupta Cc: kwolf-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, jack-AlSwsSmVLrQ@public.gmane.org, xiaoguangrong eric , kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, riel-ebMLmSuQjDVBDgjK7y7TUQ@public.gmane.org, linux-nvdimm-y27Ovi1pjclAfugRpC6u6w@public.gmane.org, mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, ross zwisler , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org, hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, imammedo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, stefanha-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, niteshnarayanlal-PkbjNfxxIARBDgjK7y7TUQ@public.gmane.org, marcel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, pbonzini-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, nilal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org List-Id: linux-nvdimm@lists.01.org On 09.04.2018 05:26, Stefan Hajnoczi wrote: > On Thu, Apr 05, 2018 at 08:09:26AM -0400, Pankaj Gupta wrote: >>> Will this raw file already have the "disk information header" (no idea >>> how that stuff is called) encoded? Are there any plans/possible ways to >>> >>> a) automatically create the headers? (if that's even possible) >> >> Its raw. Right now we are just supporting raw format. >> >> As this is direct mapping of memory into guest address space, I don't >> think we can have an abstraction of headers for block specific features. >> Or may be we can get opinion of others(Qemu block people) it is at all possible? > > memdev and the block layer are completely separate. The block layer > isn't designed for memory-mapped access. > Not questioning if this is the right thing to do now. I was wondering if we could expose any block device in the future as virtio-pmem. And I think with quite some work it could be possible. As you said, we will need some buffering. Maybe userfaultfd and friends (WP) could allow to implement that. > I think it makes sense to use memdev here. If the user wants a block > device, they should use an emulated block device, not virtio-pmem, > because buffering is necessary anyway when an image file format is used. > > Stefan > -- Thanks, David / dhildenb