zcyes.c

#define _GNU_SOURCE         /* See feature_test_macros(7) */
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <assert.h>

int main(int argc, char ** argv) {
   const int bs = 4096;
   unsigned char buf[bs];
   for (int i = 0; i < bs; i+=2) {
       buf[i] = 'y';
       buf[i+1] = '\n';
   }

   int p[2];
   assert(pipe(p) == 0);
   int r = fcntl(p[1], F_SETPIPE_SZ, bs);
   fprintf(stderr, "bs %d r %d\n", bs, r);
   assert(r >= bs);

   assert(write(p[1], buf, bs) == bs);

   while (1) {
       int z = tee(p[0], STDOUT_FILENO, bs, 0);
       if (z != bs) {
           fprintf(stderr, "z %d bs %d\n", z, bs);
       }
       assert(z == bs);
   }

   return 0;
}