Re: [Xen-devel] blkif discard attributes

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-07-07 at 14:40 -0400, Konrad Rzeszutek Wilk wrote:
> On Thu, Jul 03, 2014 at 11:24:30AM +0100, Jan Beulich wrote:
> > >>> On 03.07.14 at 12:17, <david.vrabel@xxxxxxxxxx> wrote:
> > > On 03/07/14 11:08, Jan Beulich wrote:
> > >>>>> On 03.07.14 at 11:43, <david.vrabel@xxxxxxxxxx> wrote:
> > >>> On 03/07/14 08:59, Jan Beulich wrote:
> > >>>> discard_zeroes_data also be communicated from backend to frontend?
> > >>>
> > >>> Perhaps. But how would you handle a guest that used to have
> > >>> discard_zeroes_data but is restored with different storage that no
> > >>> longer has this property?
> > >> 
> > >> Don't these attributes gets re-evaluated after restore anyway?
> > > 
> > > I don't see how that helps.  What if a discard request was submitted
> > > before the suspend, expecting the discard to zero and on restore the
> > > requests is queued for the new backend which then might not zero.
> > 
> > Hmm, good point. So it's then indeed better to not communicate this.
> > Albeit similar issues arise with the existing attributes we communicate:
> > What if the new backend doesn't satisfy the assumptions on the old
> > one? Possibly the request may get failed, but possibly it may also get
> > executed wrongly. Neither of which is very desirable.
> 
> That is OK with discard operations. It is OK if they fail intermediately.

Are there not security implications to failing a discard? Or do the
interfaces not make that promise to the higher layers?

Ian.


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