-rw-r--r-- 1406 librandombytes-20230905/kernel/devurandom_wrapper.c raw
// version 20230126
// public domain
// djb

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <poll.h>
#include "devurandom_wrapper.h"

static void wait_for_random(void)
{
  int random_fd;
  struct pollfd p;

  if (access("/var/run/urandom-ready",F_OK) == 0)
    return;

  for (;;) {
    errno = 0;
    random_fd = open("/dev/random",O_RDONLY);
    if (random_fd >= 0) break;
    if (errno == ENOENT) return;
    sleep(1);
  }

  for (;;) {
    p.fd = random_fd;
    p.events = POLLIN;
    p.revents = 0;
    errno = 0;
    if (poll(&p,1,0) == 1) break;
    if (errno != EINTR) sleep(1); // e.g., ENOMEM
  }

  close(random_fd);
}

static int urandom_fd = -1;

int devurandom_wrapper_ready(void)
{
  wait_for_random();

  for (;;) {
    errno = 0;
    urandom_fd = open("/dev/urandom",O_RDONLY);
    if (urandom_fd >= 0) break;
    if (errno == ENOENT) return 0;
    sleep(1);
  }

  fcntl(urandom_fd,F_SETFD,1);
  // O_CLOEXEC is better but limits portability and is not necessary here:
  // librandombytes runs *_ready only in static constructors

  return 1;
}

void devurandom_wrapper(void *x,long long xbytes)
{
  while (xbytes > 0) {
    int todo = 1048576;
    if (xbytes < 1048576) todo = xbytes;

    todo = read(urandom_fd,x,todo);
    if (todo < 1) {
      sleep(1);
      continue;
    }

    x += todo;
    xbytes -= todo;
  }
}