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SubjectRe: [PATCH v7 1/2] crypto: AF_ALG: add AEAD support
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Am Montag, 5. Januar 2015, 21:51:06 schrieb Herbert Xu:

Hi Herbert,

> On Mon, Jan 05, 2015 at 11:46:50AM +0100, Stephan Mueller wrote:
> > The need for that check lies in aead_recvmsg:
> > /*
> >
> > * first chunk of input is AD -- one scatterlist entry is one
> > page,
> > * and we process only one scatterlist, the maximum size of AD is
> > * one page
> > */
> >
> > sg_init_table(&assoc, 1);
> > sg_set_page(&assoc, sg_page(sg), ctx->aead_assoclen, sg->offset);
> > aead_request_set_assoc(&ctx->aead_req, &assoc,
> > ctx->aead_assoclen);
> >
> > There you see that I only create an sg table with one entry for the AD. If
> > we would allow an arbitrary AD size, I would see the need of a for loop
> > in addition to the one directly beneath this AD scatterlist setting: one
> > for identifying how many sg entries I need to allocate and one for the
> > actual assignment.
> >
> > As I felt that one page should be sufficient for the AD, I wanted to avoid
> > the extra overhead for another for loop.
>
> Please remove the limit as otherwise we would never be able to
> add support for this in a future kernel as appliations won't be
> able to rely on it.
>
> There is no such limit in the kernel interface and we shouldn't
> be adding one here.

One question: are you aware of an existing mechanism to split one scatterlist
into two at a given offset?

>
> Cheers,


--
Ciao
Stephan


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