[rrd-developers] [PATCH] generalisation of rrd_open API

[Daniel.Pocock at barclayscapital.com]

> I think the best would be if you started writing 
> documentation for the functions you are implementing / 
> planning as well as some general notes on the design ideas.
> 
> To become realy useful, the abstraction may have to be pushed 
> even further ... keep in minde that as we go to a new cross 
> platform data format, the on disk structures will change, I 
> would like for that new abstraction to work with this.
>

My goal is to provide an alternative to directly invoking the C library
filesystem functions (open, read, write) without  needing to understand
the data format.

There are only a couple of areas where the file format does become an
issue for such a low level API:

- specifying the file size, so that mmap can be done behind the scenes

- how to generalise madvise (my striping implementation potentially
needs to extrapolate madvise to all the headers)

- whether to treat different parts of the file in different ways (e.g.
no striping for headers so that they can be mmaped, striping the RRAs
behind the scenes)

- how to (not) align the RRAs - this could actually be specified
independently, although it is convenient to bundle this logic with the
filesystem

Rather than hammering out an API spec and then finding that it has to be
changed, I would like to get my stripe implementation running this week,
test it a little, and use feedback from that to guide decisions on the
API.

Regards,

Daniel

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