fuchsia.mem.Data & Buffer's deprecation

[Adam Perry]

I'm looking at the docs for fuchsia.mem.Data and I noticed that Buffer has been deprecated in favor of using a property on the VMO itself. Should this guidance also apply to Data since one of its variants is a Buffer? Should existing clients of Data migrate to a new "maybe-inline" type with only a VMO for the large variant?

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Adam Perry

[James Robinson]

Hi Adam,

I think fuchsia.mem/Data is fine (although it's tricky to use correctly) and we should introduce a VMO entry to the union to replace the Buffer member. Doing this will be a bit difficult as there are many users of fuchsia.mem/Data in the system but could be done in the following way:

- Add a VMO entry to the union, but do not set it anywhere

- Teach all of the codepaths and libraries that consume fuchsia.mem/Data how to consume data from a VMO

- Wait at least one Fuchsia milestone

- Teach codepaths and libraries that produce fuchsia.mem/Data instances to write to the VMO instead of the Buffer

- Wait at least one Fuchsia milestone

- Remove the fuchsia.mem/Buffer entry from the union.

Note that this is only possible because Data is a flexible union. There are also some clones of this type that are structs or non flexible unions that use Buffer - those should migrate to use a flexible type (such as fuchsia.mem/Data) or one that knows about VMOs.

- James

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[Adam Perry]

That makes sense to me! Is fxb/85452 the right place to track this?

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Adam Perry

[James Robinson]

Yup!

https://groups.google.com/a/fuchsia.dev/g/api-council/c/UJBAYTYpamU/m/goPElqsnBQAJ is a longer email about fuchsia.mem/Buffer deprecation. Perhaps I should have cross-posted that - the api-council list is open the world, but difficult to follow as a non API council member since there's no way to subscribe currently as far as I know.

- James