linux-kernel - Re: [PATCH] xen-blkfront: remove type check from blkfront_setup

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Date:	Mon, 13 Jan 2014 21:11:33 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	Olaf Hering <olaf@...fle.de>
CC:	konrad.wilk@...cle.com, xen-devel@...ts.xen.org,
	linux-kernel@...r.kernel.org, david.vrabel@...rix.com
Subject: Re: [PATCH] xen-blkfront: remove type check from blkfront_setup_discard

On 01/13/2014 06:07 PM, Olaf Hering wrote:
> On Mon, Jan 13, Boris Ostrovsky wrote:
>
>> On 01/13/2014 04:30 AM, Olaf Hering wrote:
>>>> Similarly, if xenbug_gather("discard-secure") fails, I think the code will
>>>> assume that secure discard has not been requested. I don't know what
>>>> security implications this will have but it sounds bad to me.
>>> There are no security implications, if the backend does not advertise it
>>> then its not present.
>> Right. But my questions was what if the backend does advertise it and wants
>> the frontent to use it but xenbus_gather() in the frontend fails. Do we want
>> to silently continue without discard-secure? Is this safe?
> The frontend can not know that the backend advertised discard-secure
> because the frontend just failed to read the property which indicates
> discard-secure should be enabled.

And is it OK for the frontend not to know about this?

I don't understand what the use model for this feature is. Is it just 
that the backend advertises its capability and it's up to the frontend 
to use it or not -or- is it that the user/admin created the storage with 
expectations that it will be used in "secure" manner.

I think if it's the former then losing information about storage 
features is OK but if it's the latter then I am not so sure.

Or perhaps it's neither of these two and I am completely missing the 
point of this feature.

-boris

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