Invalid argument when calling linux splice()

Question

Hi

I wanted to try out the splice syscall. I have this function - it should copy content of one file to another:

static void test_splice( int in, int out ) {

        int i = 0, rcvd = 0;
        int filedes[2];
        off_t off = 0;

        if ( pipe( filedes ) < 0 ) {
                perror( "Kicha pipe" );
                exit( EXIT_FAILURE );
        }

        for ( i = 0; i < NUMLOOPS; ++i ) {

                if ( ( rcvd = splice( in, NULL, filedes[1], NULL, BUFSIZE, SPLICE_F_MORE | SPLICE_F_MOVE ) ) < 0 ) {
                        perror( "splice" );
                        exit( EXIT_FAILURE );
                }

                if ( splice( filedes[0], NULL, out, NULL, rcvd, SPLICE_F_MORE | SPLICE_F_MOVE ) < 0 ) {
                        perror( "splice" );
                        exit( EXIT_FAILURE );
                }
        }
}

The second call to splice in first iteration returns EINVAL ( invalid argument from perror ) everytime - what could be the reason?

Answer 1

I have no idea whether this is the best way of doing this, but this works for me:

http://vectrex.org.uk/mark/splicecopy.cpp

It creates one thread to read and another for writing. This may be unnecessary. The writing thread only appears to require one splice() call, but the reader does approximately every 64k on my system.

The above was tested on Fedora 13 x86_64 and appears to be able to copy larg(ish) files.