On 15/09/2016 17:23, Alex Bligh wrote:
> Paolo,
>
>> On 15 Sep 2016, at 15:07, Paolo Bonzini wrote:
>>
>> I don't think QEMU forbids multiple clients to the single server, and
>> guarantees consistency as long as there is no overlap between writes and
>> reads. These are
On 09/15/2016 11:27 AM, Wouter Verhelst wrote:
> On Thu, Sep 15, 2016 at 05:08:21PM +0100, Alex Bligh wrote:
>> Wouter,
>>
>>> The server can always refuse to allow multiple connections.
>>
>> Sure, but it would be neater to warn the client of that at negotiation
>> stage (it would only be one
Wouter,
> On 15 Sep 2016, at 17:27, Wouter Verhelst wrote:
>
> On Thu, Sep 15, 2016 at 05:08:21PM +0100, Alex Bligh wrote:
>> Wouter,
>>
>>> The server can always refuse to allow multiple connections.
>>
>> Sure, but it would be neater to warn the client of that at negotiation
On Thu, Sep 15, 2016 at 05:08:21PM +0100, Alex Bligh wrote:
> Wouter,
>
> > The server can always refuse to allow multiple connections.
>
> Sure, but it would be neater to warn the client of that at negotiation
> stage (it would only be one flag, e.g. 'multiple connections
> unsafe').
I
On 09/15/2016 09:17 AM, Wouter Verhelst wrote:
On Thu, Sep 15, 2016 at 01:44:29PM +0100, Alex Bligh wrote:
On 15 Sep 2016, at 13:41, Christoph Hellwig wrote:
On Thu, Sep 15, 2016 at 01:39:11PM +0100, Alex Bligh wrote:
That's probably right in the case of file-based back
On Thu, Sep 15, 2016 at 01:44:29PM +0100, Alex Bligh wrote:
>
> > On 15 Sep 2016, at 13:41, Christoph Hellwig wrote:
> >
> > On Thu, Sep 15, 2016 at 01:39:11PM +0100, Alex Bligh wrote:
> >> That's probably right in the case of file-based back ends that
> >> are running on a
> On 15 Sep 2016, at 13:41, Christoph Hellwig wrote:
>
> On Thu, Sep 15, 2016 at 01:39:11PM +0100, Alex Bligh wrote:
>> That's probably right in the case of file-based back ends that
>> are running on a Linux OS. But gonbdserver for instance supports
>> (e.g.) Ceph based
On Thu, Sep 15, 2016 at 01:39:11PM +0100, Alex Bligh wrote:
> That's probably right in the case of file-based back ends that
> are running on a Linux OS. But gonbdserver for instance supports
> (e.g.) Ceph based backends, where each connection might be talking
> to a completely separate ceph node,
> On 15 Sep 2016, at 13:36, Christoph Hellwig wrote:
>
> On Thu, Sep 15, 2016 at 01:33:20PM +0100, Alex Bligh wrote:
>> At an implementation level that is going to be a little difficult
>> for some NBD servers, e.g. ones that fork() a different process per
>> connection.
> On 15 Sep 2016, at 13:23, Christoph Hellwig wrote:
>
> On Thu, Sep 15, 2016 at 02:21:20PM +0200, Wouter Verhelst wrote:
>> Right. So do I understand you correctly that blk-mq currently doesn't
>> look at multiple queues, and just assumes that if a FLUSH is sent over
>> any
> On 15 Sep 2016, at 13:18, Christoph Hellwig wrote:
>
> Yes, please do that. A "barrier" implies draining of the queue.
Done
--
Alex Bligh
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On Thu, Sep 15, 2016 at 05:20:08AM -0700, Christoph Hellwig wrote:
> On Thu, Sep 15, 2016 at 02:01:59PM +0200, Wouter Verhelst wrote:
> > Yes. There was some discussion on that part, and we decided that setting
> > the flag doesn't hurt, but the spec also clarifies that using it on READ
> > does
On Thu, Sep 15, 2016 at 04:38:07AM -0700, Christoph Hellwig wrote:
> On Thu, Sep 15, 2016 at 12:49:35PM +0200, Wouter Verhelst wrote:
> > A while back, we spent quite some time defining the semantics of the
> > various commands in the face of the NBD_CMD_FLUSH and NBD_CMD_FLAG_FUA
> > write
On Thu, Sep 15, 2016 at 01:55:14PM +0200, Wouter Verhelst wrote:
> Maybe I'm not using the correct terminology here. The point is that
> after a FLUSH, the server asserts that all write commands *for which a
> reply has already been sent to the client* will also have reached
> permanent storage.
On Thu, Sep 15, 2016 at 04:52:17AM -0700, Christoph Hellwig wrote:
> On Thu, Sep 15, 2016 at 12:46:07PM +0100, Alex Bligh wrote:
> > Essentially NBD does supports FLUSH/FUA like this:
> >
> > https://www.kernel.org/doc/Documentation/block/writeback_cache_control.txt
> >
> > IE supports the same
On Thu, Sep 15, 2016 at 12:43:35PM +0100, Alex Bligh wrote:
> Sure, it's at:
>
> https://github.com/yoe/nbd/blob/master/doc/proto.md#ordering-of-messages-and-writes
>
> and that link takes you to the specific section.
>
> The treatment of FLUSH and FUA is meant to mirror exactly the
> linux
> On 15 Sep 2016, at 12:40, Christoph Hellwig wrote:
>
> On Thu, Sep 15, 2016 at 01:29:36PM +0200, Wouter Verhelst wrote:
>> Yes, and that is why I was asking about this. If the write barriers
>> are expected to be shared across connections, we have a problem. If,
>>
Christoph,
> On 15 Sep 2016, at 12:38, Christoph Hellwig wrote:
>
> On Thu, Sep 15, 2016 at 12:49:35PM +0200, Wouter Verhelst wrote:
>> A while back, we spent quite some time defining the semantics of the
>> various commands in the face of the NBD_CMD_FLUSH and
On Thu, Sep 15, 2016 at 01:29:36PM +0200, Wouter Verhelst wrote:
> Yes, and that is why I was asking about this. If the write barriers
> are expected to be shared across connections, we have a problem. If,
> however, they are not, then it doesn't matter that the commands may be
> processed out of
On Thu, Sep 15, 2016 at 12:09:28PM +0100, Alex Bligh wrote:
> A more general point is that with multiple queues requests
> may be processed in a different order even by those servers that
> currently process the requests in strict order, or in something
> similar to strict order. The server is
On Thu, Sep 15, 2016 at 12:09:28PM +0100, Alex Bligh wrote:
> Wouter, Josef, (& Eric)
>
> > On 15 Sep 2016, at 11:49, Wouter Verhelst wrote:
> >
> > Hi,
> >
> > On Fri, Sep 09, 2016 at 10:02:03PM +0200, Wouter Verhelst wrote:
> >> I see some practical problems with this:
> >
Hi,
On Fri, Sep 09, 2016 at 10:02:03PM +0200, Wouter Verhelst wrote:
> I see some practical problems with this:
[...]
One more that I didn't think about earlier:
A while back, we spent quite some time defining the semantics of the
various commands in the face of the NBD_CMD_FLUSH and
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