bug#19702: 25.0.50; Tramp with ssh not working with openssh 6.7 while worked with 6.6

[Filipp Gunbin <fgunbin@fastmail.fm>]

On 02/02/2015 16:16 +0100, Michael Albinus wrote:

> Filipp Gunbin <fgunbin@fastmail.fm> writes:
>>
>> Thanks, but it didn't work:
>>
>> 17:02:55.588956 tramp-send-command (6) # exec ssh -l root -o
>> ControlMaster=auto -o
>> ControlPath=/var/folders/yb/0cdss5q52d1848_2th2kp_740000gn/T/tramp.54213PO4.%C
>> -o ControlPersist=no -e none <myhost>
>
> Is the ControlPath still too long? What happens, if you call the command
> directly in the shell?
>
> # ssh -l root -o ControlMaster=auto -o
> ControlPath=/var/folders/yb/0cdss5q52d1848_2th2kp_740000gn/T/tramp.54213PO4.%C
> -o ControlPersist=no -e none <myhost>
>
> And what happens if you call
>
> # ssh -l root -o ControlMaster=auto -o ControlPath=tramp.54213PO4.%C
> -o ControlPersist=no -e none <myhost>

$ ssh -l root -o ControlMaster=auto -o ControlPath='/var/folders/yb/0cdss5q52d1848_2th2kp_740000gn/T/tramp.54213PO4.%C' -o ControlPersist=no -e none <myhost>
ControlPath too long

$ ssh -l root -o ControlMaster=auto -o ControlPath='tramp.54213PO4.%C' -o ControlPersist=no -e none <myhost>
root@<myhost>'s password: 
... <asks for password>
Welcome to Ubuntu 12.04.4 LTS (GNU/Linux 3.11.0-15-generic x86_64)
...

>> Aren't values produced by %C supposed to be unique?  Then probably the
>> temporary file isn't needed.
>
> No, they are unique for the triple (user, host, port) only. This triple
> could be used also outside Emacs for an ssh connection.

But how does openssh prevent collisions between separate running
instances of itself, then?

Filipp