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Date: Tue, 30 Apr 2024 12:28:00 +0900
From: Sergey Senozhatsky <senozhatsky@chromium.org>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	"David S. Miller" <davem@davemloft.net>,
	linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC] crypto: passing configuration parameters to comp algos
Message-ID: <20240430032800.GF14947@google.com>
References: <20240430030447.GE14947@google.com>
 <20240430031847.GB10165@sol.localdomain>
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On (24/04/29 20:18), Eric Biggers wrote:
> On Tue, Apr 30, 2024 at 12:04:47PM +0900, Sergey Senozhatsky wrote:
> > Hi,
> > 
> > 	We'd like to be able to pass algorithm-specific parameters to
> > comp backends. As of this moment, crypto usees hard-coded default
> > values and does not permit any run-time algorithm configuration,
> > which in some cases simply disables the most interesting functionality.
> > E.g. zstd can be configured to use a pre-trained (in the user-space)
> > compression dictionary, which significantly changes algorithms
> > characteristics. Another, obvious and trivial example, is algorithms
> > compression level.
> > 
> > The problem is that we need to pass params to cra_init() function,
> > because for some algorithms that's the only place where configuration
> > can take place (e.g. zstd). Changing cra_init() to accept additional
> > `struct crypto_comp_params` looks to be a little intrusive so before
> > I write any patches I'd like to hear your thoughts.
> > 
> 
> Have you considered just using the zstd library (<linux/zstd.h>) directly?

Yes, sort of.

> Which kernel subsystem are you working on that uses compression?

Forgot to mention - this is for zram primarily (and potentially for zswap).
Both of which take advantage of crypto API and can be configured to use
various compression algorithms (per-device).

So, on the zram side, in theory, I can stop using crypto API and start
calling lzo/zstd/lz4/etc. compression/decompression functions directly
(in fact we used to do that many many years ago, before we switched to
cypto API).