[onert] Change metadata pointer type to ExternalData

[ragmani]

This commit changes metadata pointer type to ExternalData.

ONE-DCO-1.0-Signed-off-by: ragmani ragmani0216@gmail.com

[zetwhite]

Thanks for trying 😄

I think we can use ExternalData for now and change it to use ir::Data (include CachedData) later when we need it.
I put my detailed opinion here - #12408 (comment).

[ragmani]

I have a question regardless to this PR.
Is model going to have metadata as only external data(i.g. ir::MMapedData) in the future?

Originally posted by @ragmani in #12408 (comment)

[ragmani]

Let me clarify the word first, to make sure that we have the same understanding.

• ir::CachedData : holds copy of original data
• ir::ExternalData : points original data, we have to make sure that the original data is not lost.

Originally posted by @zetwhite in #12408 (comment)

[ragmani]

Is model going to have metadata as only external data(i.g. ir::MMapedData) in the future?

@ragmani
For now, only TrainingInfo is passed through Model's Metadata.
Since TrainingInfo is extracted when loaded time, we could use ExternalData.
If Metadata is used(extracted) at another time, I'm not sure that the original buffer (mmaped data) is not damaged.

So, About your question, For now, Yes only external data is used in metadata.
About the future, I'm not 100% sure.

Originally posted by @zetwhite in #12408 (comment)

[ragmani]

• ir::ExternalData : points original data, we have to make sure that the original data is not lost.

@zetwhite
Can we make sure if original data(external data) is not lost?

[ragmani]

As talked offline with @zetwhite,

1. We confirmed that mmaped original data(external data) is not lost unless we call munmap(). So metadata cannot be danging pointer in the current code.
2. @zetwhite is going to resolve the issue of having metadata information twice in memory.(i.g. TrainingInfo and mmaped metadata for TrainingInfo)

For those reasons, I close this PR. Sorry for interrupting you due to my misunderstanding.

[zetwhite]

For those reasons, I close this PR. Sorry for interrupting you due to my misunderstanding.

No problem at all.
I appreciate your interest and by this chance, I could rethink about overall direction:)