Aio_read() for tty device signals after 4 chars input.

Question

Hi,
I tried to use aio_read() on a tty device with a signal notification. However, I noticed that
signal is delivered after 4 charcters input, not delivered until then. Here's the sample code,
which is also available from http://www.octopath.jp/~yab/aiotest.c It runs without problems
on linux(CentOS-4.4), FreeBSD-6.2-PRERELEASE.
Does anybody tell me what I need to do?
Thanks in advance.
#include <stdio.h>
#include <aio.h>
#include <signal.h>
#include <errno.h>
#include <sys/time.h>
#include <termios.h>
aiocb_t aiocb_r;
unsigned char buf_r[128];
int flag = 0;
int offset = 0;
struct timeval tp;
void
sigio_handler(int signo)
    flag++;
void
init_aiocbs()
    struct sigaction sigact;
    aiocb_r.aio_fildes = 0;
    aiocb_r.aio_buf = buf_r;
    aiocb_r.aio_nbytes = 1;
    aiocb_r.aio_offset = 0;
    aiocb_r.aio_reqprio = 0;
    aiocb_r.aio_sigevent.sigev_notify = SIGEV_SIGNAL;
    aiocb_r.aio_sigevent.sigev_signo = SIGIO;
    aiocb_r.aio_sigevent.sigev_value.sival_ptr = &aiocb_r;
    sigact.sa_flags = SA_SIGINFO;
    sigact.sa_handler = (void (*)(int)) sigio_handler;
    sigemptyset(&(sigact.sa_mask));
    sigaction(SIGIO, &sigact, NULL);
int
main(int argc, char *argv[])
    int rv;
    int lpcnt = 0;
    struct termios saved_term;
    struct termios term;
    init_aiocbs();
    tcgetattr(0, &saved_term);
    term = saved_term;
    term.c_lflag &= ~(ECHO | ICANON);
    tcsetattr(0, TCSAFLUSH, &term);
    offset = 0;
    aiocb_r.aio_offset = offset;
    rv = aio_read(&aiocb_r);
    for(;;) {
     rv = aio_error(&aiocb_r);
     if (rv == 0) {
         rv = aio_return(&aiocb_r);
         if (rv != 0) {
          offset += rv;
          aiocb_r.aio_offset = offset;
          fprintf(stderr,"buf_r=%c(0x%x), signal handler is called %d times\n", buf\_r[0], buf_r[0], flag);
         else {
          fprintf(stderr, "EOF\n");
          break;
         rv = aio_read(&aiocb_r);
     else if (rv != EINPROGRESS) {
         if (rv == EAGAIN) {
          rv = aio_return(&aiocb_r);
          offset += rv;
          aiocb_r.aio_offset = offset;
          rv = aio_read(&aiocb_r);
         else {
          // ERROR
          rv = aio_return(&aiocb_r);
          fprintf(stderr,"R:rv = %d, errno=%d, flag=%d, buf_r=%c(%x)\n", rv, errno,\ flag, buf_r[0], buf_r[0]);
     rv = sleep(1);
     fprintf(stderr, "sleep % 3d\n", ++lpcnt);
    fprintf(stderr, "----Finished\n");
}

Answer 1

Hello.
Sounds like a wrong value in your termios structure.
Depending on the value of c_lflag there are two modes:
Canonical:
Backspace is processed, read() will receive the input when Enter is pressed.
Non-Canonical:
read() will return whenever N characters are received. (You always receive blocks of N characters.)
In Solaris the default value for N is 4 (unlike Linux where it is 1).
To solve your problem I would try to insert the following line that changes N to 1:
term.c_cc[MIN]=1;
I hope this helps you.
Martin