You hit the nail right on the head... I had the second, but Dumper \@a instead of Dumper $a[0], and my test code was assuming I was returning a list. Hate it when that happens ;-)

OK, so now at least I have it returning something sensible, which is always good. In which case, the question is why does this:

AV *
readdir_inode(dirname)
     char*    dirname
INIT:
  struct dirent *ent;
  DIR* dir;
  SV* record[2];
  AV *entry, *ret_val;
CODE:
  RETVAL = newAV();
  dir = opendir(dirname);
  if (!dir)
    perror("Cannot open dir");
  while ((ent=readdir(dir))) {
    printf("%ld %x\n", ent->d_ino, ent->d_name);
    record[0] = newSVpv(ent->d_name, 0);
    record[1] = newSViv((IV)ent->d_ino);
    entry = av_make(2, record);
    av_push(RETVAL, newRV_inc((SV*) entry));
  }
  closedir(dir);
/*RETVAL=*ret_val;*/
/*RETVAL=newRV_inc((SV*) ret_val);*/
OUTPUT:
    RETVAL
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Return an extra level of arrays?

The calling code:

my @ents = readdir_inode(".");
print Dumper @ents;
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The output:

$VAR1 = [
          [
            '.',
            67586
          ],
          [
            '..',
            255604
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...