Opening raw disk while mounted in 5.x?

[David Andersen]

To answer my own question - this appears to be done in the geom 
subsystem now.  It can be avoided by enabling the magic foot-shooting 
debug flag:

   sysctl -w kern.geom.debugflags=16

if you're inclined to shoot yourself in the foot.

   -Dave

On May 25, 2005, at 1:10 PM, David Andersen wrote:

> Hoping someone knows the quick answer to this - in 4.x, it was 
> possible to open /dev/ad0 while a filesystem one one of its slices was 
> mounted.  This no longer appears possible under 5.x.  Could someone 
> point me to the spot in the code where I'd need to disable a 
> permissions check (or a sysctl, or anything) to permit this behavior 
> again?
>
> (The context:  mounting slice 2 of a disk and using it to store a 
> compressed filesystem image.  Then opening the primary disk device to 
> directly write the filesystem image onto slice 1.  The kernel seems to 
> muck with the write calls if we try to do the write onto slice 1 
> instead of the raw disk).  This is using the very cool 
> imagezip/imageunzip utilities from the Utah Emulab project.
>
> Thanks!
>
>   -Dave
>