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

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Dec 04, 2023 at 08:44:45PM +0100, Christoph Hellwig wrote:
> 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.

Yeah, that'll become a third cleanup series to add a comment and elide
tthe create_done thing. :)

--D