Re: [PATCH v2 05/13] reftable: utility functions

> In order to be as thorough as possible, we thus also need to replace
> these function pointers for libgit2's dependencies. As registration of
> the allocator happens at runtime, we need to also be able to replace
> function pointers of dependencies at runtime. E.g. for OpenSSL, it
> provides an API `CRYPTO_set_mem_functions(malloc, realloc, free)` which
> we call on global initialization of the libgit2 library.
>
> So, to answer your questions:
>
>     - The allocator is global and cannot be changed after initialization
>       of libgit2.
>
>     - It is pluggable, users can set up their own allocators by filling
>       a structure with function pointers for `free`, `malloc`, `realloc`
>       etc.
>
>     - Due to the pluggable nature, we need to be able to set up those
>       pointers at runtime. We can provide a set of static wrappers
>       though which then call into the pluggable functions, so defines
>       would probably work for us, too.
>
> I hope that answers all of your questions.