[dm-devel] puzzled by the usage of dm_get_device(.....)

[Thomas S. Iversen]

Hi There

I am developing a device-mapper plugin as part of an assignment. Reading 
through dm-crypt, dm-snapshot and various other i see this construct

static int <name>_ctr(struct dm_target *ti, unsigned int argc, char ** 
argv)
{

.....

	if(dm_get_device(ti, ..., ..., ti->len, ..) {
		// ERROR
	}
	ti->private = ....
	return 0;
}

My question now is, why do ppl pass ti->len onto dm_get_device. ti->len 
is not set by the plugins and could be very wrong (is in my case 
anyhow)? And what part of the code actually sets the value of ti->len 
before the ctr routine is called.

My module bails out at sectors over 14MB, but thats because ti->len is 
around 28000 when dm_get_device is called. But thats just play wrong, my 
   partition is much bigger than that.

Could someone enlighten me, please :-)

Regards Thomas, Denmark.