Re: [Qemu-devel] [PATCH] nbd: Flip qemu-nbd to prefer newstyle; add -O for old behavior

[Eric Blake]

On 10/3/18 12:19 PM, Eric Blake wrote:
> Oldstyle NBD negotiation cannot perform any of the extensions that
> we have recently been relying on.  While you can always pass -x ""
> to get newstyle negotiation, these days, it is better to just default
> to newstyle (with an empty export name) and fall back to oldstyle
> only on an explicit request.
>
> For comparison:
>
> nbdkit 1.3 switched its default to newstyle (Jan 2018):
> https://github.com/libguestfs/nbdkit/commit/b2a8aecc
> https://github.com/libguestfs/nbdkit/commit/8158e773
>
> nbd 3.10 dropped oldstyle long ago (Mar 2015):
> https://github.com/NetworkBlockDevice/nbd/commit/36940193

Oh, I should also add:

qemu as client can manage either style since 2.6.0, commit 69b49502d8

> +++ b/qemu-nbd.c
> @@ -86,6 +86,7 @@ static void usage(const char *name)
>   "  -v, --verbose             display extra debugging information\n"
>   "  -x, --export-name=NAME    expose export by name\n"
>   "  -D, --description=TEXT    with -x, also export a human-readable 
> description\n"
> +"  -O, --oldstyle            force oldstyle negotiation\n"

and maybe I should touch up the -x and -D wording, to at least mention 
that -x defaults to "" without -O.

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