On 02/12/2015 06:32 PM, Junio C Hamano wrote:
> On Thu, Feb 12, 2015 at 3:12 AM, Michael Haggerty <mhag...@alum.mit.edu>
> wrote:
>> Instead, verify the reference's old value if and only if old_sha1 is
>> non-NULL.
>>
>> ...
>> @@ -3664,9 +3664,6 @@ int ref_transaction_update(struct ref_transaction
>> *transaction,
>> if (transaction->state != REF_TRANSACTION_OPEN)
>> die("BUG: update called for transaction that is not open");
>>
>> - if (have_old && !old_sha1)
>> - die("BUG: have_old is true but old_sha1 is NULL");
>> -
>
> In the old world, old_sha1 here used to be one of
> (1) NULL, (2) null_sha1[], or (3) a real object name.
> What is the rule in the new world?
The new world is explained in the docstring in refs.h, which was updated
in this same commit:
If old_sha1 is non-NULL, then it the value
that the reference should have had before the update, or null_sha1
if it must not have existed beforehand.
The docstring is further revised later in the patch series to
old_sha1 is the value that the reference must have
before the update, or null_sha1 if it must not have existed
beforehand. The old value is checked after the lock is taken to
prevent races. If the old value doesn't agree with old_sha1, the
whole transaction fails. If old_sha1 is NULL, then the previous
value is not checked.
The new rule is extended to ref_transaction_delete() in the subsequent
commit. I like the new semantics because it removes redundancy in the
interpretation of parameters.
Is that explanation adequate?
Michael
--
Michael Haggerty
mhag...@alum.mit.edu
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