vfs_fruit: Time Machine/FULLSYNC: add mDNS/DNS-SD advertisement

[Ralph Böhme]

On Wed, Jul 19, 2017 at 09:37:33PM -0400, Kevin Anderson via samba-technical wrote:
> > The service definition for Time Machine is nontrivial.
> > _adisk._tcp requires two TXT records:
> > sys=waMa=0,adVF=0x100
> > dk0=adVN=Time Machine,adVF=0x82,adVU=00000000-0000-0000-0000-000000000000
> >
> > adVN is the Time Machine share name, adVF sets up volume flags (macOS Server
> > uses 0xa2 instead, Netatalk also uses the 0xa prefix instead of 0x8, though
> > it’s unknown what the 0x2 flag does:
> > http://netatalk.sourceforge.net/wiki/index.php/Bonjour_record_adisk_adVF_values). adVU
> > is a UUID, which isn’t strictly necessary, but I think helps keep track of
> > backup disks.
> 
> Just for clarification when I started down this path, I based the work
> off of the Apple published "spec" that can be found at
> https://developer.apple.com/library/content/releasenotes/NetworkingInternetWeb/Time_Machine_SMB_Spec/index.html.
> In the spec it doesn't mention the adVU value at all so I think it
> should be left out IMO. It also states that a value of 0x2 is for SMB
> protocol support for that volume.

I don't quite remember the details, but iirc we just added adVU support to
Netatalk to behave exactly like a OS X (back then) server. If it does work without a adVU or
a fake one that might be ok, but lacking clear documentation and spec I guess
the safest approach is still to behave exactly like a macOS server.

Cheerio!
-slow