Re: kern/138244: dd attempts bitwise transfer onto ZFS pool

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On Fri, Sep 11, 2009 at 09:57:45AM -0400, Weldon S Godfrey 3 wrote:
>=20
> Sorry, I lost the reply to this
>=20
> the command was:
>=20
> dd if=3D/dev/zero of=3D/export/store1-1 bs=3D64k count=3D10000
> the 'of' was an accident,  it was meant to be to a file and not the=20
> mountpoint
> here is the df
> tank/store1-1     2882037632 1161418880 1720618752    40%=20
> /export/store1-1

Hmm, bascially you cannot write to directories directly:

	tank/foobar on /foo/bar (zfs, local)
	# dd if=3D/dev/zero of=3D/foo/bar bs=3D64k count=3D10000
	dd: /foo/bar: Is a directory

> sorry, I didn't execute this and I misunderstood what happened.   I=20
> thought the 'of' was to tank/store1-1 so this may not be=20
> such an issue.
>=20
> I personally never tested to see if you use the mountpoint=20
> instead of the /dev special file (or zfs volume in this case) with the 'o=
f=20
> argument in dd, would dd treat the mountpoint as if it was the /dev=20
> 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=
=20
> appeared in FreeBSD as if it was blank.  I tried to do a rollback but tha=
t=20
> caused the system to panic.  Which turned out to be great, the system cam=
e=20
> back fine (not zeroed out) and not rolled back (as it was before the dd=
=20
> comand was executed).
>=20
> sorry, this may not be an issue at all.  we are happy that zfs didn't kil=
l=20
> the data on this accident.

You must misinterpret something, because it is not possible to write to
a directory...

--=20
Pawel Jakub Dawidek                       http://www.wheel.pl
[e-mail]                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!

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