Re: [MirageOS-devel] Mirage on Xen/ARM status

[Dave Scott <Dave.Scott@xxxxxxxxxx>]

Hi,

On 19 Jun 2014, at 14:36, Richard Mortier <Richard.Mortier@xxxxxxxxxxxxxxxx> 
wrote:

> 
> On 19 Jun 2014, at 12:24, Thomas Leonard <talex5@xxxxxxxxx> wrote:
> 
>> Perhaps the ones complement stuff should be moved out of
>> mirage-platform anyway? It seems to be specific to networking, rather
>> than to any particular platform. I see there's also a third version in
>> the ns3 directory, which always returns zero.
> 
> yes; ones complement checksums are used in several IP protocols. i don't know 
> that they're used elsewhere (storage, etc). i guess efficient implementations 
> are likely to be platform specific, though perhaps one would expect the 
> compiler to dtrt rather than hand tweaking.

IIRC the reason the checksum code didn’t get moved out of the platform tree 
when the network stack itself was moved out was because we don’t have the right 
build/link magic to include C code from other libraries.

I’m not sure if ones complement checksums are used in storage. However I 
believe the CRC polynomial used by iSCSI (and btrfs?) is now implemented in 
Intel CPUs. Perhaps one day our OCaml CRC library will have optimised asm code 
for several platforms (generated via some staged compilation from some OCaml 
source I’m sure)

Cheers,
Dave


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