Simple IO run

[geekyang95]

Need a simple demo to check afs_store Local IO path. My plan:

1. run it as a unittest. use gtest/gmock to do, will add a submodule.
2. only check IO / volume meta data, without network part.
3. mock metadata initialize, only a few metadata is needed for testing purpose
4. write a memstore to store testing data. It's core part is a map<size_t offset, void *data>. It will be very fast for testing purpose than write to a file.

[cocalele]

I think it's more simple to use a file rather than to construct a memstore, because S5FlashStore communicate to system only via a file descirptor(S5FlashStore::dev_fd). Create memstore may need a lot coding work.

[geekyang95]

That's not a problem, only a little code changes need to make by using gmock to mock read/write operations. Maybe I should write a simple demo for discussing, at first.

[geekyang95]

And, it would be a good idea to seperate OS operations from S5FlashStore, because we may need to support spdk in the future, or like the test purpose. If we can make dev_handle_t more powerful (not just a file descripter), it would be much easier to do things like that. That's a more CPP way to solve problem :)

[geekyang95]

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