sizeof PIPE_BUF

Hi!

How big is actally PIPE_BUF?  Seems that on 2.6 kernels it is 64K
and on 2.4 is 4K.  Or I make a mistake?  The program bellow show
this.  The result is the same with glibc, or dietlibc.

=============
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>

int ndelay_on(int fd) {
  return fcntl(fd,F_SETFL,fcntl(fd,F_GETFL,0) | O_NONBLOCK);
}

void wr_number(unsigned long u) {
  char buf[64], *p, *e;
  e = p = buf + sizeof(buf);
  *--p = '\n';
  do { *--p = '0' + u%10; u /= 10; } while (u);
  write(1, "#define MAX_PIPE_length ", 24);  
  write(1, p, e-p);
}

int main() {
  int r, pi[2];
  pid_t pid;

  if (pipe(pi)) return 21;
  if (ndelay_on(pi[1])) return 22;
  
  pid = fork();
  if (pid==-1) return 23;

  if (pid==0) {
    char buf[1024];
    unsigned long total=0;

    close(pi[0]);
    while (1) {
      r = write(pi[1], buf, sizeof(buf));
      if (r <= 0) break;
      total += r;
    }
    wr_number(total);
  } else {
    close(pi[1]);
    waitpid(pid, 0, 0);
  }

  _exit(0);
  return 0;
}