Hi Mark,
On Feb 16, 2010, at 11:21 AM, Mark Miller wrote:
> On Tue, 2010-02-16 at 06:40 -0600, Quincey Koziol wrote:
>
>>
>> Yes, the split, multi & family file drivers create an interesting
>> batch of problems. I'm not certain exactly how to solve the problems
>> that arise when dealing with an HDF5 "file" that maps onto multiple
>> system files. If you've got any suggestions for solving some of the
>> problems exhibited by the use cases you outline above, that would be
>> great. :-)
>
>
> Well, I haven't read the VFL docs in detail but I did see something in
> there regarding a USER_BLOCK. I wonder if the split vfd could somehow
> use that to help solve the fundamental problem here; that is ensuring
> that HDF5 library proper 'knows' that a given set of files represent a
> 'split' file. I was thinking that if the filenaming convention is stored
> in this USER_BLOCK then an attempt to open the 'meta' part could be made
> to 'automagically' work correctly; that is identify that its a 'split'
> file AND setup the correct extensions for the set_fapl call to succeed
> in opening it. Such an approach may NOT work if HDF5 library is asked to
> open some other part of the split stream in which the USER_BLOCK does
> not exist. But, its a step in the right direction.
I think you mean the super block here, not the user block. With that
in mind, yes, it is possible to "probe" for the correct VFD to use for the file
and then re-open the file with the information from the super block. I think
we even have an existing issue in our tracker for this, so it's mostly a matter
of priorities and funding at this point (which could be routed around with a
well-written patch, also).
Quincey
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