Re: [PATCH] Support HDIO_GETGEO on device-mapper volumes

From: Alasdair G Kergon
Date: Fri Feb 10 2006 - 10:11:15 EST

On Fri, Feb 10, 2006 at 02:53:48PM +0000, Alasdair G Kergon wrote:
> I disagree - either dm should work out the *correct* geometry to
> return for those mappings where a geometry is known and it's sensible
> to return one (e.g. linear mapping to the start of certain scsi
> devices), or else it should leave it to userspace to decide how to
> handle the situation. (And there's nothing currently stopping
> userspace seeing that a dm device is constructed out of a scsi device
> and choosing to use the geometry of that underlying device.)

s/scsi/hd/ in those examples for slightly more sense

What would the 'geometry' of a dm 'error' target mean?
Or of a snapshot?

In any patch, consider that we've already identified a need
(e.g. for multipath) to add a framework to device-mapper to pass
certain ioctls along to the underlying devices. I'd prefer
to see that approach here: for tables with a single entry, pass
the ioctl into the target. Linear and multipath would then pass
it along to the underlying device; other targets would return zeros.

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