[dm-devel] Question about dm target size

Heinz Mauelshagen heinzm at redhat.com
Wed Nov 12 11:15:16 UTC 2014

On 11/12/2014 01:37 AM, Josef Bacik wrote:
> Hello,
> I'm creating a dm target to better test power fail situations and I'm 
> having trouble figuring out how to make the dm device appear as a 
> different size.  So for example you do the normal dm table
> offset size power-fail /dev/whatever args
> I want to use the entire size of /dev/whatever, but I want my dm 
> device to show up as size/2.  So right now I'm doing this in my ->ctr 
> function
> ti->len /= 2;

Passing in "ti->len = 'size of your dev in sectors' / 2" is what you want.


> Is that acceptable, or will this have some side-effect that's going to 
> bite me in the ass?  I can't see any other target that does something 
> similar and there appears to be no helper function.  This seems to 
> work as far as blockdev --getsz is concerned, but I'm worried I need 
> to do more.  Thanks,
> Josef
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