On Tue, Dec 23, 2008 at 2:51 PM, C. Michael Pilato <cmpilato_at_collab.net> wrote:
> David Glasser wrote:
>> Oh, huh. So, um, which FS is implementing the FS API correctly then?
>> This sort of difference should not be externally observable...
>
> Sometime after FSFS was added, this additional restriction on the API was
> added to the docstring:
>
> * The caller must send all delta windows including the terminating
> * NULL window to @a *contents_p before making further changes to the
> * transaction.
>
> And, really, this restriction only makes any sense at all for FSFS, because
> BDB doesn't care if you start sending some windows, then go off and do other
> stuff, and then come back later to finish up the textdelta.
>
> So FSFS enforces this requirement, though I suspect not explicitly. (If you
> try to violate it, you get the generic error, "Cannot write to the prototype
> revision file of transaction 'f00' because a previous representation is
> currently being written by this process".) BDB doesn't even try, and really
> has no way to do so.
>
> So, in answer to your question, both FS APIs behave correctly if said APIs
> are used as demanded by the docstring and no problems occur. If a problem
> occurs such that the window-sending doesn't complete successfully, *and* the
> FS API driver decides not to care and commit the transaction anyway, I
> noticed that BDB would register text-mod changes on the file that was being
> edited even though those changes never "took". Now, having just typed that,
> I've looked into the FSFS code, and it records the change at the same time
> that BDB did -- when editing was started, not when it was finalized. But I
> don't know enough about FSFS to say if that leads to the same busted place
> that BDB does, though, and I can't easily construct a test case that obeys
> the API's documented rules *and* still triggers the problem.
I see.
Perhaps add a comment to the test saying essentially "We are testing
that undefined calls to the FS API don't introduce more damage to the
repository than they have to"?
--dave
--
glasser_at_davidglasser.net | langtonlabs.org | flickr.com/photos/glasser/
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Received on 2008-12-24 01:23:49 CET