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

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Date:   Fri, 20 May 2022 03:00:02 +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 06:56:12PM -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.

Jason