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From: David Hildenbrand <david-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: Stefan Hajnoczi
	<stefanha-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Pankaj Gupta <pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: kwolf-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org,
	jack-AlSwsSmVLrQ@public.gmane.org,
	xiaoguangrong eric
	<xiaoguangrong.eric-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	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
	<ross.zwisler-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
	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
Subject: Re: [Qemu-devel] [RFC] qemu: Add virtio pmem device
Date: Mon, 9 Apr 2018 08:42:35 +0200	[thread overview]
Message-ID: <36218ea8-5fa8-e670-104d-616da790a333@redhat.com> (raw)
In-Reply-To: <20180409032601.GA1648-lxVrvc10SDRcolVlb+j0YCZi+YwRKgec@public.gmane.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

      parent reply	other threads:[~2018-04-09  6:42 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-05 10:48 [RFC 0/2] kvm "fake DAX" device flushing Pankaj Gupta
     [not found] ` <20180405104834.10457-1-pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2018-04-05 10:48   ` [RFC 1/2] kvm: add virtio pmem driver Pankaj Gupta
2018-04-05 10:48   ` [RFC 2/2] pmem: device flush over VIRTIO Pankaj Gupta
2018-04-05 10:48   ` [RFC] qemu: Add virtio pmem device Pankaj Gupta
     [not found]     ` <20180405104834.10457-4-pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2018-04-05 11:26       ` David Hildenbrand
     [not found]         ` <ad08ca09-71ee-08d5-3479-8b3d06380a03-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2018-04-05 12:09           ` [Qemu-devel] " Pankaj Gupta
     [not found]             ` <416823501.16310251.1522930166070.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2018-04-05 12:19               ` David Hildenbrand
2018-04-09  3:26             ` Stefan Hajnoczi
     [not found]               ` <20180409032601.GA1648-lxVrvc10SDRcolVlb+j0YCZi+YwRKgec@public.gmane.org>
2018-04-09  6:42                 ` David Hildenbrand [this message]

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