Dear Hans Petter Selasky I understood your points. Thank you for your kind explanation I found that the buffer size is 65535 like below source code. The 65535 is not the power of two. So it can still be a problem. ... #define RX_BUFFER_SIZE 65535 ... rxbuf = vmalloc(RX_BUFFER_SIZE); ... dvb_ringbuffer_init(&ca->slot_info[slot].rx_buffer, rxbuf, RX_BUFFER_SIZE); } ... 2022년 9월 12일 (월) 오후 9:36, Hans Petter Selasky <hps@xxxxxxxxxxx>님이 작성: > > Hi Mauro and YongSu, > > Answering my own question: The reason nobody has triggered this yet, is > because the buffer size used is power of two. Because unsigned modulus > is used, the result becomes correct. See below. But if non-power of two > ring-buffer is used, then the result becomes incorrect. There is no > block for non-power of two sized buffers. See: > > https://github.com/search?q=dvb_set_pesfilter&type=code > > cat << EOF > testX.c > #include <stdio.h> > > int > main() > { > int consumed_old; > int consumed_fix; > size_t idx = 3; > ssize_t pread = 15; > ssize_t size = 256; > > consumed_old = (idx - pread) % size; > > consumed_fix = (idx - pread); > if (consumed_fix < 0) > consumed_fix += size; > > printf("old=%d new=%d size=%zd\n", consumed_old, consumed_fix, size); > > size = 254; > > consumed_old = (idx - pread) % size; > > consumed_fix = (idx - pread); > if (consumed_fix < 0) > consumed_fix += size; > > printf("old=%d new=%d size=%zd\n", consumed_old, consumed_fix, size); > > return (0); > } > EOF > > cc testX.c && ./a.out > old=244 new=244 size=256 > old=244 new=242 size=254 > > So either push the suggested fix, or block non-power of two buffer sizes! > > Best regards, > --HPS
