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

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Date:   Mon, 6 Dec 2021 22:24:47 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
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 Tue, Dec 07, 2021 at 04:20:29PM +1100, Herbert Xu wrote:
> 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.

That is what I am confused about: why can't it be a part of API? Users
that are running in atomic contexts would not be able to use it, but we
have a lot of precedents for it. See for example spi_sync() vs
spi_async(). Callers have a choice as to which one to use, based on
their needs.

Thanks.

-- 
Dmitry