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Re: [Qemu-devel] [Nbd] [PATCH] Improve documentation of FUA and FLUSH

From: Wouter Verhelst
Subject: Re: [Qemu-devel] [Nbd] [PATCH] Improve documentation of FUA and FLUSH
Date: Fri, 1 Apr 2016 12:10:19 +0200
User-agent: Mutt/1.5.24 (2015-08-30)

On Fri, Apr 01, 2016 at 10:28:03AM +0100, Alex Bligh wrote:
> On 1 Apr 2016, at 09:35, Wouter Verhelst <address@hidden> wrote:
> >> +* All write commands (that includes both `NBD_CMD_WRITE` and
> >> +  `NBD_CMD_TRIM`) that the server completes (i.e. replies to)
> >> +  prior to processing to a `NBD_CMD_FLUSH` MUST be written to non-volatile
> >> +  storage prior to replying to that `NBD_CMD_FLUSH`. The server SHOULD 
> >> ensure
> >> +  that all write command received prior to processing the `NBD_CMD_FLUSH`
> >> +  (whether they are replied to or not) are written to non-volatile
> >> +  storage prior to processing an `NBD_CMD_FLUSH`; note this is a
> >> +  stronger condition than the previous 'MUST' condition. This
> > 
> > This seems to make little sense. Are you saying that suddenly now
> > sending a reply for FLUSH with outstanding writes is wrong? If not, the
> > above should be clarified.
> The MUST sentence does not cover that situation as it only refers
> to completed writes.
> The SHOULD sentence says that's a 'SHOULD NOT' situation in respect
> of writes that have PROCESSED (i.e actioned) whether or not they
> have been replied to. Of course the client has no way of knowing
> whether they have been PROCESSED without a reply.
> Personally I think the SHOULD clause is pretty pointless and is
> unnecessary, but that's where the conversation got to n years
> ago I believe.

I'm still not sure what it's supposed to mean, though. Clearly, you
should at the very least reword it, if not...

> Happy to delete the last sentence if that's wrong.

... remove it instead.

< ron> I mean, the main *practical* problem with C++, is there's like a dozen
       people in the world who think they really understand all of its rules,
       and pretty much all of them are just lying to themselves too.
 -- #debian-devel, OFTC, 2016-02-12

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