Re: [GIT PULL] iov_iter retry fixes

[Al Viro <viro@zeniv.linux.org.uk>]

On Fri, Sep 17, 2021 at 08:44:32AM -0600, Jens Axboe wrote:
> Hi Linus,
> 
> This adds a helper to save/restore iov_iter state, and modifies io_uring
> to use it. After that is done, we can kill the iter->truncated addition
> that we added for this release. The io_uring change is being overly
> cautious with the save/restore/advance, but better safe than sorry and
> we can always improve that and reduce the overhead if it proves to be of
> concern. The only case to be worried about in this regard is huge IO,
> where iteration can take a while to iterate segments.
> 
> I spent some time writing test cases, and expanded the coverage quite a
> bit from the last posting of this. liburing carries this regression test
> case now:
> 
> https://git.kernel.dk/cgit/liburing/tree/test/file-verify.c
> 
> which exercises all of this. It now also supports provided buffers, and
> explicitly tests for end-of-file/device truncation as well.
> 
> On top of that, Pavel sanitized the IOPOLL retry path to follow the
> exact same pattern as normal IO.

I can live with that; I do have problems with io-uring and its interactions
with iov_iter, but those are mostly independent from the stuff you are
doing here.

Still digging through your FSM from hell... ;-/