kern/138244: dd attempts bitwise transfer onto ZFS pool

[Pawel Jakub Dawidek]

On Fri, Sep 11, 2009 at 09:57:45AM -0400, Weldon S Godfrey 3 wrote:
> 
> Sorry, I lost the reply to this
> 
> the command was:
> 
> dd if=/dev/zero of=/export/store1-1 bs=64k count=10000
> the 'of' was an accident,  it was meant to be to a file and not the 
> mountpoint
> here is the df
> tank/store1-1     2882037632 1161418880 1720618752    40% 
> /export/store1-1

Hmm, bascially you cannot write to directories directly:

	tank/foobar on /foo/bar (zfs, local)
	# dd if=/dev/zero of=/foo/bar bs=64k count=10000
	dd: /foo/bar: Is a directory

> sorry, I didn't execute this and I misunderstood what happened.   I 
> thought the 'of' was to tank/store1-1 so this may not be 
> such an issue.
> 
> I personally never tested to see if you use the mountpoint 
> instead of the /dev special file (or zfs volume in this case) with the 'of 
> argument in dd, would dd treat the mountpoint as if it was the /dev 
> special file.

dd(1) simply use open(2) to open the 'of' target. If you can't for
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...

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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