kern/138244: dd attempts bitwise transfer onto ZFS pool

[Weldon S Godfrey 3]

> example ls(1) the target you won't be able to use it for dd(1).
>
>> however, the result was understood correctly, it zeroed out the dir, it
>> appeared in FreeBSD as if it was blank.  I tried to do a rollback but that
>> caused the system to panic.  Which turned out to be great, the system came
>> back fine (not zeroed out) and not rolled back (as it was before the dd
>> comand was executed).
>>
>> sorry, this may not be an issue at all.  we are happy that zfs didn't kill
>> the data on this accident.
>
> You must misinterpret something, because it is not possible to write to
> a directory...
>
The engineer pulled the command from the history, so it is correct.
  When he freaked out from executing that, I went to the console he was on, 
did an 'ls' and 'pwd' of the directory that he did it to, it was empty. 
So at least, however, old(dec 2008) version of head, dd did something bad.