linux-kernel - Re: [PATCH 1/9] crypto: add zbufsize() interface

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Message-ID: <20211207052029.GA12141@gondor.apana.org.au>
Date:   Tue, 7 Dec 2021 16:20:29 +1100
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Geliang Tang <geliangtang@...il.com>,
        Arnd Bergmann <arnd@...db.de>, Haren Myneni <haren@...ibm.com>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Zhou Wang <wangzhou1@...ilicon.com>,
        linux-crypto <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/9] crypto: add zbufsize() interface

On Fri, Dec 03, 2021 at 12:49:26PM -0800, Dmitry Torokhov wrote:
>
> I must be getting lost in terminology, and it feels to me that what is
> discussed here is most likely of no interest to a lot of potential
> users, especially ones that do compression/decompression. In majority of
> cases they want to simply compress or decompress data, and they just
> want to do it quickly and with minimal amount of memory consumed. They
> do not particularly care if the task is being offloaded or executed on
> the main CPU, either on separate thread or on the same thread, so the
> discussion about scomp/acomp/etc is of no interest to them. From their
> perspective they'd be totally fine with a wrapper that would do:
> 
> int decompress(...) {
> 	prepare_request()
> 	send_request()
> 	wait_for_request()
> }
> 
> and from their perspective this would be a synchronous API they are
> happy with.

You can certainly do that as a Crypto API user.  And we do have
some users who do exactly this (for example, testmgr does that
when testing async algorithms).  However, this can't be a part of
the API itself since many of our users execute in atomic contexts.

> So from POV of such users what is actually missing is streaming mode of
> compressing/decompressing where core would allow supplying additonal
> data on demand and allow consuming output as it is being produced, and I
> do not see anything like that in either scomp or acomp.

That is indeed a very crucial part of the compression API that is
missing.  And I would love someone to donate some time to addressing
this.

Thanks,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt