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Date:      Fri, 7 Oct 2011 17:22:54 -0400
From:      Arnaud Lacombe <lacombar@gmail.com>
To:        Poul-Henning Kamp <phk@phk.freebsd.dk>
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
Message-ID:  <CACqU3MVgVUxe%2BMtaf9wq6oz5=PZAq=Sx-ihyQh1GyjD3PXmjhQ@mail.gmail.com>
In-Reply-To: <4360.1318021854@critter.freebsd.dk>
References:  <alpine.BSF.2.00.1110071352210.2450@wonkity.com> <4360.1318021854@critter.freebsd.dk>

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Hi,

On Fri, Oct 7, 2011 at 5:10 PM, Poul-Henning Kamp <phk@phk.freebsd.dk> wrote:
> In message <alpine.BSF.2.00.1110071352210.2450@wonkity.com>, Warren Block write
> s:
>
>># mount /dev/da0p2 /mnt
>># dd if=/tmp/FreeBSD-9.0-BETA3-amd64-memstick.img of=/dev/da0 bs=64k
>>dd: /dev/da0: Operation not permitted
>># sysctl kern.geom.debugflags=16
>>kern.geom.debugflags: 0 -> 16
>># dd if=/tmp/FreeBSD-9.0-BETA3-amd64-memstick.img of=/dev/da0 bs=64k
>>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.  No obvious problems, but no, it's not
>>polite.  (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:  You should never
> need them, unless you are debugging a problem.
>
How about disabling debugflags=16'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


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