Is it possible to have read not block, but write block for pipes?
You surely can remove O_NONBLOCK flag before each write with fcntl and put it back after write completes. However, it seems better to keep the socket non-blocking all the time and to put write into a loop until it finishes. In order not to overload the CPU, put a select which will block the process until the socket is ready for write.
So, the writing code will look like:
int blockingWriteOnNonBlockingFd(int fd, char *buf, int size) { fd_set wset, w; int n, r; FD_ZERO(&wset); FD_SET(fd, &wset); n = 0; while (n < size) { w = wset; select(fd+1, NULL, &w, NULL, NULL); r = write(fd, buf+n, size-n); if (r <= 0) { if (r<0 && (errno == EWOULDBLOCK || errno == EAGAIN)) r = 0; else { /* broken connection */ break; } } n += r; } return(n);}