On 9/9/21 3:19 PM, Jens Axboe wrote:

quoted

That "req->result" is once again the *original* length, and the above
code once again mis-handles the case of "oh, the iov got truncated
because of some IO limit".

So I've pulled this, but I think it is

 (a) ugly nasty

 (b) incomplete and misses a case

and needs more thought. At the VERY least it needs that
iov_iter_reexpand() in io_resubmit_prep() too, I think.

I'd like the comments expanded too. In particular that

                /* some cases will consume bytes even on error returns */

That comment is from me, and it goes back a few years. IIRC, it was the
iomap or xfs code that I hit this with, but honestly I don't remember
all the details at this point. I can try and play with it and see if it
still reproduces.

OK, one that I immediately found is just doing O_DIRECT to a block
device or file on XFS. As pages are mapped and added, the iov_iter is
advanced. If we then go and submit and get -EAGAIN, for example, then we
return with what we mapped already consumed.

-- 
Jens Axboe