> Uncached_readdir is not really a problem. The real problem is > filesystems that generate "infinite directories" by producing looping > combinations of cookies. > > IOW: I've seen servers that generate cookies in a sequence of a form > vaguely resembling > > 1 2 3 4 5 6 7 8 9 10 11 12 3... > > (with possibly a thousand or so entries between the first and second > copy of '3') > > The kernel won't loop forever with something like that (because > eventually filldir() will declare it is out of buffer space), but > userland has a halting problem: it needs to detect that every > sys_getdents() call it is making is generating another copy of the > sequence associated with '4 5 6 7 8 9 10 11 12 3'... Huh? This is not only an easy problem, it's a well-known problem. http://en.wikipedia.org/wiki/Cycle_detection Here's Brent's algorithm: n = 0; saved_cookie = <invalid> For each cookie { if (n && cookie == saved_cookie) die("Loop detected!"); if (++n is a power of 2) saved_cookie = cookie; } You can tweak the performance with other exponentially-growing functions, saving k > 1 old cookies for comparison, etc., but the above will work very well. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
