Re: [PATCH 01/15] dm: support ioctls on mapped devices

[Alasdair G Kergon]

On Wed, Jun 21, 2006 at 08:52:06PM -0700, Andrew Morton wrote:
> I don't understand that.  We're taking an ioctl against a dm device and
> we're passing it through to an underlying device?  Or something else?
 
Indeed.  The motivation behind this came from multipath: people want to
issue certain types of ioctls directly against a dm multipath device and
have them pass through one of the paths to the underlying device.
(Otherwise they'd need a knowledge of dm internals to poke around the tree
of dm devices and probe path statuses to determine the correct path(s) to
use - effectively implementing 'multipath' ioctls themselves from userspace
with unavoidable races.)

Alasdair
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