Re: [Qemu-block] [PATCH 0/2] nbd server: drop old-style negotiation

[Eric Blake]

On 10/3/18 12:59 PM, Vladimir Sementsov-Ogievskiy wrote:
> 03.10.2018 20:32, Eric Blake wrote:
> On 10/3/18 12:02 PM, Vladimir Sementsov-Ogievskiy wrote:
> It's unexpected behavior that without -x option qemu-nbd do old-style
> negotiation. Let's use "" as a default name instead (as it is already
> done if tls is used) and therefore, drop old-style negotiation from
> Qemu NBD server.

Hmm, your email quoting style changed from prior emails that used to 
prepend '>' when quoting, making it harder to tell where the text you 
are quoting ends,...

> Oddly enough, I wrote a similar patch in parallel, and am only now just seeing 
> your mail. Yours is a bit stronger than mine (I added 'qemu-nbd -O' to allow 
> explicit fallback to oldstyle, while you ripped it out altogether).  The client 
> can negotiate either style, so we don't need an option on the client side; 
> rather, this is all about what the server should do by default.
>
> https://lists.gnu.org/archive/html/qemu-devel/2018-10/msg00568.html
>
> Does anyone have a preference between the two? Here's the last time it was 
> discussed:
>
> https://lists.gnu.org/archive/html/qemu-devel/2018-08/msg03252.html

and your reply begins.

> Hm, I think everyone who like new-style should answer that he don't care 
> (except stricter way is a bit better: don't have options and code which we 
> don't need).
> But if there is someone who has client which support only old-style negotiation his 
> unhappiness (in case of strict way) will outweigh all our "bits":)
>
> I'm from the first group). But let's chose your patch

My argument in favor of your patch over mine: nbdkit is a GREAT testbed 
for forcing all sorts of integration testing scenarios, including 
oldstyle servers.  Also, it includes a plugin for translating between 
new and oldstyle at will.  That is, if we ever legitimately encounter a 
client that can only talk oldstyle, but qemu only talks newstyle, we 
just tell the user to connect:

old client => nbdkit -o nbd => newstyle qemu

and then qemu doesn't have to worry about oldstyle because nbdkit does 
instead.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org