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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <9357a268-3801-367e-0aaa-a01163ea0cbc@redhat.com>
Date: Fri, 24 Nov 2017 14:20:22 +0100
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Subject: Re: [Qemu-devel] KVM "fake DAX" flushing interface - discussion
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To: Pankaj Gupta <pagupta@redhat.com>, Christoph Hellwig <hch@infradead.org>
Cc: Dan Williams <dan.j.williams@intel.com>, Rik van Riel <riel@redhat.com>, Xiao Guangrong <xiaoguangrong.eric@gmail.com>, Kevin Wolf <kwolf@redhat.com>, Haozhong Zhang <haozhong.zhang@intel.com>, Jan Kara <jack@suse.cz>, kvm-devel <kvm@vger.kernel.org>, "linux-nvdimm@lists.01.org" <linux-nvdimm@ml01.01.org>, Ross Zwisler <ross.zwisler@intel.com>, Qemu Developers <qemu-devel@nongnu.org>, Stefan Hajnoczi <stefanha@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, ross zwisler <ross.zwisler@linux.intel.com>, Nitesh Narayan Lal <nilal@redhat.com>

On 24/11/2017 14:02, Pankaj Gupta wrote:
> 
>>>    - Suggestion by Paolo & Stefan(previously) to use virtio-blk makes sense
>>>    if just
>>>      want a flush vehicle to send guest commands to host and get reply
>>>      after asynchronous
>>>      execution. There was previous discussion [1] with Rik & Dan on this.
>>>
>>>     [1] https://lists.gnu.org/archive/html/qemu-devel/2017-07/msg08373.html
>>
>> ... in fact, the virtio-blk device _could_ actually accept regular I/O
>> too.  That would make it easier to boot from pmem.  Is there anything
>> similar in regular hardware?
> 
> there is existing block device associated(hard bind) with the pmem range.
> Also, comment by Christoph [1], about removing block device with DAX support.
> Still I am not clear about this. Am I missing anything here?

The I/O part of the blk device would only be used by the firmware.  In
Linux, the different device id would bind the device to a different
driver that would only be used for flushing.

But maybe this idea makes no sense. :)

Paolo