Re: [PATCH 2/2] nbd/server: Use drained block ops to quiesce the server

[Eric Blake <eblake@redhat.com>]

On Tue, Jun 01, 2021 at 06:31:29PM +0200, Sergio Lopez wrote:
> > Hm, how do you get more than one coroutine per client yielding in
> > nbd_read_eof() at the same time? I thought the model is that you always
> > have one coroutine reading the next request (which is
> > client->recv_coroutine) and all the others are just processing the
> > request they had read earlier. Multiple coroutines reading from the
> > same socket would sound like a bad idea.
> 
> You're right, there's only a single coroutine yielding on
> nbd_read_eof(). I've added the list while at a moment I was trying to
> keep track of every coroutine, and I kept it without thinking if it
> was really needed.
> 
> I'll drop it, entering just client->recv_coroutine is it isn't NULL.

Sounds like I'll wait for the v2 before applying.  But the overall
logic changes made sense to me.

> > The patch looks correct to me, though I'm not sure if yield_co_list is
> > an unnecessary complication (and if it isn't, whether that's safe).
> > 
> > I would be happy enough to apply it anyway if you can explain the
> > yield_co_list thing, but I'll give Eric some time to have a look, too.

Thanks for catching my attention on this!

-- 
Eric Blake, Principal Software Engineer
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