Re: luks2 + integrity + discard

[Piergiorgio Sartor <piergiorgio.sartor@nexgo.de>]

On Mon, Jul 20, 2026 at 10:28:27PM +0200, Milan Broz wrote:
> On 7/20/26 2:16 PM, Piergiorgio Sartor wrote:
> > Hello,
> > 
> > I'm quite puzzled about the, apparently,
> > missing support of discard (or trim) in
> > case of encryption with integrity.
> > 
> >  From what I understand, which might be
> > very wrong, both the encryption layer
> > and dm-integrity should support discard.
> > 
> > Reading the documentation does not really,
> > at least for me, clarify what is the
> > reason why it should not be possible to
> > have encryption + integrity + discard.
> > 
> > On the other hand, in case of integrity
> > under the raid, with lvm and luks2 on
> > top, it seems possible to have discard.
> > 
> > Can someone provide some clarification
> > on this?
> 
> Discard (TRIM) is supported for dm-integrity
> standalone mode. It is also supported for dm-crypt
> standalone.
> 
> It is not supported for stacked dm-crypt over dm-integrity
> (In authenticated encryption mode where dm-integrity only provides
> interleaved metadata sectors for dm-crypt.)

Thanks for the answer.

I was curious about the technical reason
for this.
Why the stacked mode should not made
possible the discard.
Is this because they're "interleaved"?
Could explain or point out to some
explanation of what is intended with
"interleaved"?

> (And it never will be implemented for this case.)

Well, is this because is too complex or
for some other reasons?
I mean, SSD are more and more common,
giving up discard seems a bit of a problem.

Thanks again,

bye,

-- 

piergiorgio