RFC: Pass TRIM through GELI

[Steven Hartland]

On 08/03/2015 22:35, Matthew D. Fuller wrote:
> On Sun, Mar 08, 2015 at 01:28:57PM +0000 I heard the voice of
> Steven Hartland, and lo! it spake thus:
>> I don't see where your checking if the underlying device supports DELETE?
>  From my understanding (which is hardly authoritative, to be sure, so
> I'm open to correction), I don't have to.  GELI itself doesn't
> originate any BIO_DELETE's, so they're only coming from stuff on top
> of us.  We just pass those through to what's underneath us and it does
> all the answering.  If that doesn't support it, it would return an "I
> don't do that" response, which the filesystem (or whatever) on top of
> us handles[0] its way.  So for _DELETE, as for _FLUSH and _GETATTR,
> GELI is just transparent.
>
> Am I mistaken?
>
Underlying BIO_DELETE support is optional, typically only supported by 
SSD's via TRIM or UNMAP, so unless you check to see if the device 
supports it you'll be translating delete so a noop, actually you'll be 
forcing an extra layer to process the delete when it will never be able 
to to.

Given GEIL is all about security translating the delete to a noop 
results in a pretty serious security issue I would say as it will leave 
data which he user intended to be removed present on the device.

     Regards
     Steve