c - 调用 linux splice() 时参数无效

Question

我想尝试 splice 系统调用。我有这个功能 - 它应该将一个文件的内容复制到另一个文件:

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 );
                }
        }
}

在第一次迭代中对 splice 的第二次调用每次都会返回 EINVAL(来自 perror 的无效参数)——可能是什么原因？

Answer 1

来自 splice(2) :

ERRORS
       ...    
       EINVAL Target  filesystem  doesn't  support  splicing;  target  file is
              opened in append mode; neither of the file descriptors refers to
              a pipe; or offset given for nonseekable device.
       ...    

OP 的评论表明他以追加模式打开文件。