Date:	Wed, 14 Jan 2009 16:01:34 +0100 (CET)
From:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
cc:	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: compress - Add pcomp interface

	Hi Herbert,

On Wed, 14 Jan 2009, Herbert Xu wrote:
> On Tue, Jan 13, 2009 at 04:59:40PM +0100, Geert Uytterhoeven wrote:
> > The current "comp" crypto interface supports one-shot (de)compression only,
> > i.e. the whole data buffer to be (de)compressed must be passed at once, and
> > the whole (de)compressed data buffer will be received at once.
> > In several use-cases (e.g. compressed file systems that store files in big
> > compressed blocks), this workflow is not suitable.
> > Furthermore, the "comp" type doesn't provide for the configuration of
> > (de)compression parameters, and always allocates workspace memory for both
> > compression and decompression, which may waste memory.
> 
> Thanks for the patch-set!
> 
> > diff --git a/crypto/pcompress.c b/crypto/pcompress.c
> > new file mode 100644
> > index 0000000..b9e3724
> > --- /dev/null
> > +++ b/crypto/pcompress.c
> > @@ -0,0 +1,94 @@
> > +/*
> > + * Cryptographic API.
> > + *
> > + * Partial compression operations.
> > + *
> > + * Copyright 2008 Sony Corporation
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License as published by
> > + * the Free Software Foundation; version 2 of the License.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU General Public License
> > + * along with this program; if not, write to the Free Software Foundation,
> > + * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA
> > + */
> > +
> > +#define pr_fmt(fmt)	"%s: " fmt, __func__
> 
> This appears to be unused?

It's used by the pr_*() macros in <linux/kernel.h>.

Since commit d091c2f58ba32029495a933b721e8e02fbd12caa ("Add 'pr_fmt()' format
modifier to pr_xyz macros."), this is the new way to have a common prefix in
all printed output.

> > +static int crypto_pcomp_init_tfm(struct crypto_tfm *tfm,
> > +				 const struct crypto_type *frontend)
> > +{
> > +	if (frontend->type != CRYPTO_ALG_TYPE_PCOMPRESS)
> > +		return -EINVAL;
> 
> This is my fault.  The check is redundant so you can remove it.
> I'll kill it in shash too.

Ok, removed.

> > +struct pcomp_alg {
> > +	int (*setup)(struct crypto_tfm *tfm, const void *params);
> 
> Actually I was thinking of separate alloc functions for compress
> and decompress so that

For compatibility with crypto_comp, we also need an alloc function for both
compress and decompress, so that makes 3 alloc functions.

That would also solve the issue where there's hardware support for e.g.
decompression, but not for compression.

> 1) We know what the user wants to do without every algorithm
> reinventing their own signalling for it;

I guess you want to use the flags to indicate compress/decompress/both?
Unfortunately I'm still struggling to fully understand the type/mask handling,
so I would appreciate it if you could give me a hint how to handle that.

> 2) The parameters can be separated.

OK.

> Also, this is something that we'll potentially export to user-space,
> so we need to ensure that it is invariant to word length.
> 
> So something like this would be good
> 
> 	int (*setup_comp)(struct crypto_pcomp *tfm, const void *params,
> 			  unsigned int length);
> 	int (*setup_decomp)(struct crypto_pcomp *tfm, const void *params,
> 			    unsigned int length);

I assume "length" is the size of the passed params, so the algorithms can
return -EINVAL if they're passed the wrong size?

> The actual parameters should be formatted using the netlink helpers
> (nla_*).  So each parameter that you want to set should show up as
> a netlink attribute.  If a paramter is absent then you'd just use
> the default, etc.

I'll look into the netlink formatting...

> > +	int (*compress_init)(struct crypto_tfm *tfm);
> 
> That should be struct crypto_pcomp.

OK, I updated all pcomp_alg operations to take crypto_pcomp pointers instead of
crypto_tfm pointers.

> > +static inline struct crypto_pcomp *crypto_alloc_pcomp(const char *alg_name,
> > +						      u32 type, u32 mask)
> > +{
> > +	type &= ~CRYPTO_ALG_TYPE_MASK;
> > +	type |= CRYPTO_ALG_TYPE_PCOMPRESS;
> > +	mask |= CRYPTO_ALG_TYPE_MASK;
> > +
> > +	return __crypto_pcomp_cast(crypto_alloc_base(alg_name, type, mask));
> > +}
> 
> That's the old way to allocate tfm's which won't work since pcomp
> is using the new type API.  You should do it the way that shash
> does it.

I tried to do this, but stumbled across a dependency problem: as
crypto_alloc_tfm() needs a pointer to crypto_pcomp_type(), crypto_alloc_pcomp()
can no longer be static inline, and must be moved to crypto/pcompress.c.

However, pcompress can be a module, while testmgr (which uses
crypto_alloc_pcomp()) seems to be always builtin.

Ah, CRYPTO_MANAGER2 has to select CRYPTO_PCOMP. OK.

Thanks for your review!

With kind regards,

Geert Uytterhoeven
Software Architect

Sony Techsoft Centre Europe
The Corporate Village · Da Vincilaan 7-D1 · B-1935 Zaventem · Belgium

Phone:    +32 (0)2 700 8453
Fax:      +32 (0)2 700 8622
E-mail:   Geert.Uytterhoeven@...ycom.com
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