Re: [PATCH v2 3/4] odb: prepare `struct odb_transaction` to become generic

[Justin Tobler <jltobler@gmail.com>]

On 26/02/03 04:54PM, Toon Claes wrote:
> Justin Tobler <jltobler@gmail.com> writes:
> > -static void prepare_loose_object_transaction(struct odb_transaction *transaction)
> > +static void prepare_loose_object_transaction(struct odb_transaction *base)
> >  {
> > +	struct odb_transaction_files *transaction = (struct odb_transaction_files *)base;
> 
> So you're assuming `struct odb_transaction` is the first field in
> `struct odb_transaction_files`?

Yes, `struct odb_transaction_files` contains a reference to `struct
odb_transaction` as its first member which is the "base" transaction
type. This way we can easily cast to the containing "concrete" type.

> I think it would be safer to do this instead:
> 
> +	struct odb_transaction_files *transaction =
> +		container_of(base, struct odb_transaction_files, base);
> 
> (this also can be applied in a few other places in this patch)

So long as `struct odb_transaction` remains the first member of `struct
odb_transaction_files`, using `container_of()` is functionally the same
thing as casting. This is also how we do things for `odb_read_stream`
and `odb_loose_read_stream` so I don't think it is too big of a deal
either way.

I've made the change locally, but will hold off from sending another
version unless folks feel strongly about this change or there is other
feedback.

Thanks,
-Justin