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Subject: Re: [hwloc-devel] userdata import/export
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2012-08-27 11:26:20


Looks good.

My only comment is that it seems a little odd to pass the "reserved" context through. Is that some internal XML state? Can that be hidden somewhere else, on the topo or the obj?

But that's a minor quibble.

On Aug 26, 2012, at 5:52 AM, Brice Goglin wrote:

> (breaking the thread since we're far from valarrays now).
>
> I've played with this idea and came with the attached interface change.
> Aside from low-level backend changes, everything was very easy to implement.
>
> Let's take an example. I modified lstopo to add some userdata to the
> root object and define the following export callback:
>
> static void export(void *reserved, hwloc_topology_t topo, hwloc_obj_t obj)
> {
> /* we export random stuff instead of the actual userdata content */
> hwloc_export_obj_userdata(reserved, topo, obj, NULL, "coincoin", 8); /* no name */
> hwloc_export_obj_userdata(reserved, topo, obj, "MyName", "foobar", 6);
> hwloc_export_obj_userdata(reserved, topo, obj, "MyValue", "foobarbarbar", 10); /* truncated to 10 chars */
> }
>
>
> This callback is only called for the root object since others have
> userdata=NULL. It exports three lines to XML:
>
> <userdata length="8">coincoin</userdata>
> <userdata name="MyName" length="6">foobar</userdata>
> <userdata name="MyValue" length="10">foobarbarb</userdata>
>
>
> The idea behind multiple userdata lines per object is that it helps the
> application structure its userdata without having to create a single
> contigous buffer.
>
> When you import this with an import() callback, you get three
> invocations of the callback:
>
> ##### name (null) value coincoin length 8
> ##### name MyName value foobar length 6
> ##### name MyValue value foobarbarb length 10
>
>
> The optional "name" attribute lets the application recognize things (but
> they always looked in-order in my testing).
>
> My user that wants valarrays would likely export:
> * the number of elements in his arrays as a first line
> * the content of his latency array as a second line
> * the content of his bandwidth array as a third line
>
> We set import() and export() callbacks with two different function
> because it makes the doc much more clear and the requirements are
> different (import() must be set before load(), export() must use
> export_userdata()).
>
> I am satisfied with all this, I don't have any concern with the
> genericity of the interface anymore.
>
>
> Now, I still think we should offer some optional basic encoding
> capability since many users have no clue about XDR or base64. For
> instance, add export_userdata_encoded() on the side of
> export_userdata(). On the import side, we could let the application
> decode with a dedicated hwloc function. But I think I would rather mark
> the XML line as "encoded" so that hwloc transparently decodes before
> passing the data to the import() callback.
>
> Brice
>
> <userdata.patch>_______________________________________________
> hwloc-devel mailing list
> hwloc-devel_at_[hidden]
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-- 
Jeff Squyres
jsquyres_at_[hidden]
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