Re: [PATCH 2.6.1 -- take two] Add CRC32C chksums to crypto and lib routines

From: Clay Haapala (chaapala_at_cisco.com)
Date: 02/03/04

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    To: Matt Mackall <mpm@selenic.com>
Date:	Tue, 03 Feb 2004 13:13:48 -0600

    On Tue, 3 Feb 2004, Matt Mackall uttered the following:

    > On Tue, Feb 03, 2004 at 11:50:06AM -0600, Clay Haapala wrote:
    >
    >> + * 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; either version 2 of
    >> + the License, or (at your option) * any later version.
    > ...
    >> +MODULE_LICENSE("GPL and additional rights");
    >
    > "additional rights?"
    >
    Take it up with Matt_Domsch@dell.com -- it's his code that I
    cribbed, so that's the license line I used.

    >> +#if __GNUC__ >= 3 /* 2.x has "attribute", but only 3.0 has "pure
    >> +*/ #define attribute(x) __attribute__(x) #else #define
    >> +attribute(x) #endif
    >
    > This sort of thing ought to be added to linux/compiler.h if it's not
    > there already.
    >
    +/*
    + * Haven't generated a big-endian table yet, but the bit-wise version
    + * should at least work.
    + */
    >
    > Big-endian in this context means, of course, the order of the bits in
    > the byte rather than bytes in a word, and as this CRC polynomial was
    > chosen especially for its robustness on noise bursts in little-endian
    > transmission (aka standard serial and network *bit* transmission
    > ordering), I think we should intentionally omit BE support and make
    > note of it.
    >
    Yes, it is about transmission bit-order. Is the crc32 BE code also
    not necessary? Does it deal with how various networking hardware
    and architecture combos present this data?

    >> +static inline void crypto_chksum_final(struct crypto_tfm *tfm, u32 *out)
    >> +{
    >> + BUG_ON(crypto_tfm_alg_type(tfm) != CRYPTO_ALG_TYPE_CHKSUM);
    >
    > A lot of these BUG_ONs seem to be overkill. You're not going to get
    > here by someone accidentally misusing the interface. You can only get
    > here by some very willful abuse of the interface or by extremely
    > unlikely fandango on core, neither of which is worth trying to defend
    > against.

    That would be a worth changing in a clean-up pass over all of
    crypto, then. 

    -- 
Clay Haapala (chaapala@cisco.com) Cisco Systems SRBU +1 763-398-1056
   6450 Wedgwood Rd, Suite 130 Maple Grove MN 55311 PGP: C89240AD
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