On 09/30/2013 06:31 PM, Miklos Szeredi wrote:
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.
Thanks,
Miklos
----
#define _GNU_SOURCE
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <limits.h>
#include <sys/stat.h>
#include <err.h>
#ifndef SPLICE_F_DIRECT
#define SPLICE_F_DIRECT (0x10) /* neither splice fd is a pipe */
#endif
int main(int argc, char *argv[])
{
struct stat stbuf;
int in_fd;
int out_fd;
int res;
off_t off;
off_t off = 0;
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,
SPLICE_F_DIRECT);
if (rres == -1)
err(1, "splice");
if (rres == 0)
break;
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;
}
It would be nice if there would be way if the file system would get a
hint that the target file is supposed to be copy of another file. That
way distributed file systems could also create the target-file with the
correct meta-information (same storage targets as in-file has).
Well, if we cannot agree on that, file system with a custom protocol at
least can detect from 0 to SSIZE_MAX and then reset metadata. I'm not
sure if this would work for pNFS, though.
Bernd
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