Function execShortLivedProcessAndExit

src/execwrappers.cpp:355–385

Special short-lived processes from executables like /lib/libc.so.6 and man setuid/setgid executables cannot be loaded with LD_PRELOAD. Since they're short-lived, we execute them while holding a lock delaying checkpointing.

// Since they're short-lived, we execute them while holding a lock
// delaying checkpointing.
static void
execShortLivedProcessAndExit(const char *path, const char *argv[])
{
  unsetenv("LD_PRELOAD"); // /lib/ld.so won't let us preload if exec'ing lib
  const unsigned int bufSize = 100000;
  char *buf = (char *)JALLOC_HELPER_MALLOC(bufSize);
  memset(buf, 0, bufSize);
  FILE *output;
  if (argv[0] == NULL) {
    output = _real_popen(path, "r");
  } else {
    string command = path;
    for (int i = 1; argv[i] != NULL; i++) {
      command = command + " " + argv[i];
    }
    output = _real_popen(command.c_str(), "r");
  }
  int numRead = fread(buf, 1, bufSize - 1, output);
  numRead++, numRead--; // suppress unused-var warning
  buf[bufSize - 1] = '\0'; // NULL terminate in case the last char is not null

  pclose(output); // /lib/libXXX process is now done; can checkpoint now

  // We  are now the new /lib/libXXX process, and it's safe for DMTCP to ckpt
  // us.
  printf("%s", buf); // print buf, which is what /lib/libXXX would print
  JALLOC_HELPER_FREE(buf);

  // Avoid running exit handlers of the parent process by calling _exit.
  _exit(0);
}

// FIXME:  Unify this code with code prior to execvp in dmtcp_launch.cpp
// Can use argument to dmtcpPrepareForExec() or getenv("DMTCP_...")