Re: [PATCH 1/7] files_transaction_prepare(): don't leak flags to packed transaction

>> That much I can understand.  But it is not explained why (1) we do
>> not pass old_oid anymore and (2) we do give HAVE_NEW.  
>> 
>> Presumably the justification for (1) is something like "because we
>> are not passing HAVE_OLD, we shouldn't have been passing old_oid at
>> all---it was a harmless bug because lack of HAVE_OLD made the callee
>> ignore old_oid"
>
> It's debatable whether the old code should even be called a bug. The
> callee is documented to ignore `old_oid` if `HAVE_OLD` is not set. But
> it was certainly misleading to pass unneeded information to the function.
>
>>                     (2) is "we need to pass HAVE_NEW, and we have
>> been always passing HAVE_NEW because update->flags at this point is
>> guaranteed to have it" or something like that?
>
> Correct. `REF_DELETING` is set by `lock_ref_for_update()` only if
> `update->flags & REF_HAVE_NEW` was set, and this code is only called if
> `REF_DELETING` is set.