On 7/10/20 7:10 AM, Christoph Hellwig wrote:

On Fri, Jul 10, 2020 at 12:35:43AM +0530, Kanchan Joshi wrote:

quoted

Append required special treatment (conversion for sector to bytes) for io_uring.
And we were planning a user-space wrapper to abstract that.

But good part (as it seems now) was: append result went along with cflags at
virtually no additional cost. And uring code changes became super clean/minimal
with further revisions.
While indirect-offset requires doing allocation/mgmt in application,
io-uring submission
and in completion path (which seems trickier), and those CQE flags
still get written
user-space and serve no purpose for append-write.

I have to say that storing the results in the CQE generally make
so much more sense.  I wonder if we need a per-fd "large CGE" flag
that adds two extra u64s to the CQE, and some ops just require this
version.

I have been pondering the same thing, we could make certain ops consume
two CQEs if it makes sense. It's a bit ugly on the app side with two
different CQEs for a request, though. We can't just treat it as a large
CQE, as they might not be sequential if we happen to wrap. But maybe
it's not too bad.

-- 
Jens Axboe