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References: <alpine.BSF.2.00.1110071352210.2450@wonkity.com>
	<4360.1318021854@critter.freebsd.dk>
Date: Fri, 7 Oct 2011 17:22:54 -0400
Message-ID: <CACqU3MVgVUxe+Mtaf9wq6oz5=PZAq=Sx-ihyQh1GyjD3PXmjhQ@mail.gmail.com>
From: Arnaud Lacombe <lacombar@gmail.com>
To: Poul-Henning Kamp <phk@phk.freebsd.dk>
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Cc: Warren Block <wblock@wonkity.com>, Glen Barber <gjb@freebsd.org>,
	freebsd-current@freebsd.org, Garrett Cooper <yanegomi@gmail.com>,
	Benjamin Kaduk <kaduk@mit.edu>
Subject: Re: aliasing (or renaming) kern.geom.debugflags
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Hi,

On Fri, Oct 7, 2011 at 5:10 PM, Poul-Henning Kamp <phk@phk.freebsd.dk> wrot=
e:
> In message <alpine.BSF.2.00.1110071352210.2450@wonkity.com>, Warren Block=
 write
> s:
>
>># mount /dev/da0p2 /mnt
>># dd if=3D/tmp/FreeBSD-9.0-BETA3-amd64-memstick.img of=3D/dev/da0 bs=3D64=
k
>>dd: /dev/da0: Operation not permitted
>># sysctl kern.geom.debugflags=3D16
>>kern.geom.debugflags: 0 -> 16
>># dd if=3D/tmp/FreeBSD-9.0-BETA3-amd64-memstick.img of=3D/dev/da0 bs=3D64=
k
>>10463+1 records in
>>10463+1 records out
>>685731840 bytes transferred in 52.915362 secs (12959031 bytes/sec)
>>
>>Followed by removing the memory stick without unmounting it to avoid
>>overwriting part of the image. =A0No obvious problems, but no, it's not
>>polite. =A0(I'm thinking "automounter" here.)
>
> And you are sure the stick now contains what you expect ?
>
> If the dirty filesystem had blocks to write, it might have done so...
>
> debugflags are called debugflags for a reason: =A0You should never
> need them, unless you are debugging a problem.
>
How about disabling debugflags=3D16's action unless for DIAGNOSTICS kernel =
?

If you expose a setting, you cannot rely on a user not to use it even
if you told him not to. As long as this is exposed and usable, it will
be used, even more when it was documented.

 - Arnaud