Re: [RFC] extending splice for copy offloading

From: Miklos Szeredi
Date: Mon Sep 30 2013 - 12:31:35 EST

Here's an example "cp" app using direct splice (and without fallback to
non-splice, which is obviously required unless the kernel is known to support
direct splice).

Untested, but trivial enough...

The important part is, I think, that the app must not assume that the kernel can
complete the request in one go.


#define _GNU_SOURCE

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <limits.h>
#include <sys/stat.h>
#include <err.h>

#define SPLICE_F_DIRECT (0x10) /* neither splice fd is a pipe */

int main(int argc, char *argv[])
struct stat stbuf;
int in_fd;
int out_fd;
int res;
off_t off;

if (argc != 3)
errx(1, "usage: %s from to", argv[0]);

in_fd = open(argv[1], O_RDONLY);
if (in_fd == -1)
err(1, "opening %s", argv[1]);

res = fstat(in_fd, &stbuf);
if (res == -1)
err(1, "fstat");

out_fd = open(argv[2], O_CREAT | O_WRONLY | O_TRUNC, stbuf.st_mode);
if (out_fd == -1)
err(1, "opening %s", argv[2]);

do {
off_t in_off = off, out_off = off;
ssize_t rres;

rres = splice(in_fd, &in_off, out_fd, &out_off, SSIZE_MAX,
if (rres == -1)
err(1, "splice");
if (rres == 0)

off += rres;
} while (off < stbuf.st_size);

res = close(in_fd);
if (res == -1)
err(1, "close");

res = fsync(out_fd);
if (res == -1)
err(1, "fsync");

res = close(out_fd);
if (res == -1)
err(1, "close");

return 0;
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