On Fri, Mar 20, 2020 at 10:23:43AM -0400, Josef Bacik wrote:

I'm not sure what you're looking at specifically wrt error handling, but I
can explain __endio_write_update_ordered.

Btrfs has ordered extents to keep track of an extent that currently has IO
being done on it.  Generally that IO takes multiple bio's, so we keep track
of the outstanding size of the IO being done, and each bio completes and
thus removes its size from the pending size.  If any one of those bios has
an error we need to make sure we discard the whole ordered extent, as part
of it won't be valid. Just a cursory look at the current code I assume
that's what's confusing you, we call this when we have an error in the
O_DIRECT code.  This is just so we get the proper cleanup for the ordered
extent.  People will wait on the ordered extent to be completed, so if we've
started an ordered extent and aren't able to complete the range we need to
do __endio_write_update_ordered() so that the ordered extent is finished and
we wakeup any waiters.

Does this help?  If I need to I can context switch into whatever you're
looking at, but I'm going to avoid looking and hope I can just shout useful
information in your direction ;).  Thanks,

Yes, this helps a lot.  This is about the patches from Goldwyn to
convert btrfs to use the iomap direct I/O code.  And in that series
he currently calls __endio_write_update_ordered from the ->iomap_end
method, which for direct I/O is called after all bios are submitted
to complete ordered extents for a range after an I/O error, that
is one that no I/O has been submitted to, and the accounting for that
is a little complicated..