Re: [PATCH 1/9] xfs: don't set XFS_TRANS_HAS_INTENT_DONE when there's no ATTRD log item

[Christoph Hellwig <hch@lst.de>]

On Mon, Dec 04, 2023 at 10:43:48AM -0800, Darrick J. Wong wrote:
> Dave and Allison and I at some point realized that the defer ops
> machinery works even if ->create_intent and ->create_done return NULL.
> You'd lose the ability to restart the operation after a crash, but if
> the upper layers can tolerate a half-finished operation
> (e.g.  ATTR_INCOMPLETE) then that should be ok.
> 
> Obviously you wouldn't touch any such *existing* code except as part of
> adapting it to be capable of using log items, and that's exactly what
> Allison did.  She refactor the old xattr code to track the state of the
> operation explicitly, then moved all that into the ->finish_item
> implementation.  Now, if the setattr operation does not set the LOGGED
> flag (the default), the behavior should be exactly the same as before.
> If they do set LOGGED (either because the debug knob is set; or because
> the caller is parent pointers) then ->create_{intent,done} actually
> create log intent and done items.
> 
> It should never create an intent item and not the done item or the other
> way 'round, obviously.  Either both functions return NULL, or they both
> return non-NULL.

It would be really good to document this, the name LARP and why it is
considered a debug feature somewhere in the tree.  No need to hold
up this series for that of course.