Re: [Nbd] [PATCH][V3] nbd: add multi-connection support

On Thu, Sep 29, 2016 at 10:03:50AM -0400, Josef Bacik wrote:

So think of it like normal disks with multiple channels.  We don't send flushes 
down all the hwq's to make sure they are clear, we leave that decision up to the 
application (usually a FS of course).

Well, when I asked earlier, Christoph said[1] that blk-mq assumes that
when a FLUSH is sent over one channel, and the reply comes in, that all
commands which have been received, regardless of which channel they were
received over, have reched disk.

[1] Message-ID: [ref]

It is impossible for nbd to make such a guarantee, due to head-of-line
blocking on TCP.

[...]

perhaps we could add a flag later that says send all the flushes down
all the connections for the paranoid, it should be relatively
straightforward to do.  Thanks,

That's not an unreasonable approach, I guess.

-- 
< 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