linux-kernel - Re: [PATCHSET 0/2] Fix splice from random/urandom

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Date:   Fri, 20 May 2022 02:48:54 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Theodore Ts'o <tytso@....edu>, Christoph Hellwig <hch@....de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHSET 0/2] Fix splice from random/urandom

Hi Jens,

On Thu, May 19, 2022 at 06:02:55PM -0600, Jens Axboe wrote:
> On 5/19/22 6:00 PM, Jason A. Donenfeld wrote:
> > Hi Jens,
> > 
> > On Fri, May 20, 2022 at 1:57 AM Jens Axboe <axboe@...nel.dk> wrote:
> >>
> >> On 5/19/22 5:27 PM, Jason A. Donenfeld wrote:
> >>> Hi Jens,
> >>>
> >>> On Fri, May 20, 2022 at 1:25 AM Jens Axboe <axboe@...nel.dk> wrote:
> >>>> I'll leave that to you :-)
> >>>
> >>> Alright, I'll have a look. Which one do I want here? This series adds
> >>> splice_read/splice_write. The new thing would be sendpage? Or
> >>> copy_file_range? Or something else?
> >>
> >> For copying kernel memory? It's really the same thing, you just
> >> initialize the iter as an ITER_KVEC instead. The nice thing about the
> >> iov_iter iterator that it then hides that for you, call the same copy
> >> in/out helpers for it.
> > 
> > Err, maybe we're talking about different things? I was thinking about
> > the plumbing to make splice/sendfile work on non-pipes.
> 
> Ah I see. sendfile() just uses splice() internally, so that'll work
> (again) with my changes. splice(), by definition, either moves to and
> from a pipe. Hence one of the fds must be a pipe. Does that answer the
> question?

sendfile() returns -EINVAL even with your patches. Only splicing to pipes
seems to work.

Jason