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

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Message-ID: <13899409-e81b-8689-3380-249de46c0b6f@kernel.dk>
Date:   Thu, 19 May 2022 18:02:55 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
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

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?

> get_random_bytes() itself doesn't need to become iovec'd, as that has
> no IO callers.

I was a little puzzled, but didn't look deeper and see if it would make
sense to do so.

-- 
Jens Axboe