Bug 20251

If I turn off ICANON via tcsetattr(), and then do several reads(), EOT
characters sometimes are turned into NUL's and sometimes remain EOT's.

Build the following program, and run it.  It expects input, will print
"EOF" for every EOT character, and will print the hex code for any other
character, including NUL as "00".  Then type control-D over and over again
real fast.  You'll see "00" sometimes and "EOF" sometimes.

I notice that, in n_tty.c, EOF_CHAR(tty) is mutated into __DISABLED_CHAR,
and I suspect it's something to do with that.  I'm guessing there's
supposed to be a place where that's undone and it's not working right with
ICANON turned off.  That's all I've been able to deduce.

Here's the source:

#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <stdio.h>
#include <termios.h>

static int  fd       = 0;
static int  waiting  = 0;
static int  sleepily = 0;

main()
{
   for (;;) {
      int             eof_ch       = '\004'; /* EOT, a.k.a. ^D */
      char            c;
      int             got;
      struct termios  termios_rec;
      struct termios  otermios_rec;

      tcgetattr(fd, &termios_rec);
      memcpy(&otermios_rec, &termios_rec, sizeof(struct termios));

      eof_ch = termios_rec.c_cc[VEOF];

      termios_rec.c_lflag     &= ~ICANON;
      termios_rec.c_cc[VMIN]  =  waiting;
      termios_rec.c_cc[VTIME] =  0;
      tcsetattr(fd, TCSANOW, &termios_rec);

      do {
         got = read(fd, &c, 1);
         if (got == -1 && errno != EAGAIN && errno != EINTR) {
            printf("read() go boom; errno = %d\n", errno);
            exit(1);
         }
      } while (waiting && got <= 0);

      tcsetattr(fd, TCSANOW, &otermios_rec);

      if (got <= 0) {
         if (sleepily) {
            printf("!avail\n");
         }
      } else if (c == eof_ch) {
         printf("EOF\n");
      } else {
         printf("%02x\n", c);
      }

      if (sleepily) {
         sleep(1);
      }
   }
}