linux-kernel - Re: [PATCH v2 1/8] crypto: support (de)compression API that doesn't require tfm object

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Date:	Thu, 20 Aug 2015 16:52:17 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan@...nel.org>,
	Nitin Gupta <ngupta@...are.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Stephan Mueller <smueller@...onox.de>
Subject: Re: [PATCH v2 1/8] crypto: support (de)compression API that doesn't
 require tfm object

On Thu, Aug 20, 2015 at 02:47:28PM +0800, Herbert Xu wrote:
> On Thu, Aug 20, 2015 at 03:34:57PM +0900, Joonsoo Kim wrote:
> > Until now, tfm object embeds (de)compression context in it and
> > (de)compression in crypto API requires tfm object to use
> > this context. But, there are some algorithms that doesn't need
> > such context to operate. Therefore, this patch introduce new crypto
> > compression API that call (de)compression function via crypto_alg,
> > instead of tfm object. crypto_alg is required to get appropriate
> > (de)compression function pointer. This can reduce overhead of
> > maintaining multiple tfm if (de)compression doesn't require
> > any context to operate.
> > 
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> This isn't going to fly I'm afraid.  The main purpose of a tfm
> is not to allocate memory but to track the crypto_alg object
> which could be a hardware device.
> 
> So you're not going to get away with not allocating it.

Hmm... I guess there is no problem. crypto_alg object fetched by
crypto_get_comp() introduced in this patch could be hardware device
algorithm which is same one that we can eventually fetch from tfm object.
So, this approach would correctly track the crypto_alg regardless
it is a hardware one or not. If there is some dependency between
algorithm and tfm, it can't support _noctx API. Am I missing
something?

> 
> What you can do for these contextless algorithms (and by definition
> every compression algorithm is conxteless) is to allocate a system-
> wide tfm that is used by everybody, or at least by every one within
> your subsystem.

Yes, I thought this way before, but, current way is much simpler so
I try it first. If it is not acceptable, I will implement this
approach.

Thanks.

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