I'm trying to test the sendfile()
system call under Linux 2.6.32 to zero-copy data between two regular files.
As far as I understand, it should work: ever since 2.6.22, sendfile()
has been implemented using splice()
, and both the input file and the output file can be either regular files or sockets.
The following is the content of sendfile_test.c
:
#include <sys/sendfile.h>
#include <fcntl.h>
#include <stdio.h>
int main(int argc, char **argv) {
int result;
int in_file;
int out_file;
in_file = open(argv[1], O_RDONLY);
out_file = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, 0644);
result = sendfile(out_file, in_file, NULL, 1);
if (result == -1)
perror("sendfile");
close(in_file);
close(out_file);
return 0;
}
And when I'm running the following commands:
$ gcc sendfile_test.c
$ ./a.out infile outfile
The output is
sendfile: Invalid argument
And when running
$ strace ./a.out infile outfile
The output contains
open("infile", O_RDONLY) = 3
open("outfile", O_WRONLY|O_CREAT|O_TRUNC, 0644) = 4
sendfile(4, 3, NULL, 1) = -1 EINVAL (Invalid argument)
What am I doing wrong?