Re: [RFC PATCH] Btrfs: add sha256 checksum option

[Austin S Hemmelgarn <ahferroin7@gmail.com>]

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On 2014-11-29 16:21, John Williams wrote:
> On Sat, Nov 29, 2014 at 1:07 PM, Alex Elsayed <eternaleye@gmail.com> wrote:
>> I'd suggest looking more closely at the crypto api section of menuconfig -
>> it already has crc32c, among others. Just because it's called the "crypto
>> api" doesn't mean it only has cryptographically-strong algorithms.
>
> I have looked. What 128- or 256-bit hash functions in "crypto api" are
> you referring to that are as fast as Spooky2 or CityHash?

Just because it's a filesystem doesn't always mean that speed is the 
most important thing.  Personally, I can think of multiple cases where 
using a cryptographically strong hash would be preferable, for example:
  * On an fs used solely for backup purposes
  * On a fs used for /boot
  * On an fs spread across a very large near-line disk array and mounted
    by a system with a powerful CPU
  * Almost any other case where data integrity is more important than
    speed

The biggest reason to use the in-kernel Crypto API though, is that it 
gives a huge amount of flexibility, and provides pretty much transparent 
substitution of CPU optimized versions of the exported hash functions 
(for example, you don't have to know whether or not your processor 
supports Intel's CRC32 ISA extensions).


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