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

From: Jens Axboe <axboe@kernel.dk>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Theodore Ts'o <tytso@mit.edu>, Christoph Hellwig <hch@lst.de>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCHSET 0/2] Fix splice from random/urandom
Date: Thu, 19 May 2022 19:05:57 -0600	[thread overview]
Message-ID: <8f890747-c37f-2fd4-2428-4a9ffc865cac@kernel.dk> (raw)
In-Reply-To: <YoboEokc00YACuha@zx2c4.com>

On 5/19/22 7:00 PM, Jason A. Donenfeld wrote:
> Hi Jens,
> 
> On Thu, May 19, 2022 at 06:56:12PM -0600, Jens Axboe wrote:
>> On 5/19/22 6:48 PM, Jason A. Donenfeld wrote:
>>> sendfile() returns -EINVAL even with your patches. Only splicing to pipes
>>> seems to work.
>>
>> Huh, that really should work. Are you trying to sendfile() to random? If
>> so, you need that last write_iter patch too, and add the splice_write as
>> I mentioned.
>  
> No, I've only tried the read side so far. I made a little program:
> 
> #include <sys/sendfile.h>
> #include <stdio.h>
> 
> int main(int argc, char *argv[])
> {
>         ssize_t s = sendfile(1, 0, NULL, 0xffff);
>         fprintf(stderr, "ret: %zd\n", s);
>         return 0;
> }
> 
> Then I ran `./a.out < /dev/urandom > /dev/null`. Fails. OTOH, if I
> replace /dev/urandom with an ordinary file, it succeeds.

Yeah I reproduced the same, doing it the other way works fine. Curious
enough to see what it is, looking into it.

-- 
Jens Axboe