Re: copy on write for splice() from file to pipe?

Jens Axboe
2023-02-10T22:16:53Z

On 2/10/23 3:08?PM, Linus Torvalds wrote:
> On Fri, Feb 10, 2023 at 1:51 PM Jens Axboe <axboe@kernel.dk> wrote:
>>
>> Speaking of splice/io_uring, Ming posted this today:
>>
>> https://lore.kernel.org/io-uring/20230210153212.733006-1-ming.lei@redhat.com/
>
> Ugh. Some of that is really ugly. Both 'ignore_sig' and
> 'ack_page_consuming' just look wrong. Pure random special cases.
>
> And that 'ignore_sig' is particularly ugly, since the only thing that
> sets it also sets SPLICE_F_NONBLOCK.
>
> And the *only* thing that actually then checks that field is
> 'splice_from_pipe_next()', where there are exactly two
> signal_pending() checks that it adds to, and
>
> (a) the first one is to protect from endless loops
>
> (b) the second one is irrelevant when SPLICE_F_NONBLOCK is set
>
> So honestly, just NAK on that series.
>
> I think that instead of 'ignore_sig' (which shouldn't exist), that
> first 'signal_pending()' check in splice_from_pipe_next() should just
> be changed into a 'fatal_signal_pending()'.
>
> But that 'ack_page_consuming' thing looks even more disgusting, and
> since I'm not sure why it even exists, I don't know what it's doing
> wrong.
>
> Let's agree not to make splice() worse, while people are talking about
> how bad it already is, ok?

I was in no way advocating for this series, but it seems relevant as we
are discussing splice :-). I have pointed Ming at this discussion too.

--
Jens Axboe