On Sun, 23 May 2004, Jim Carter wrote: > > > So you are saying we only set a flag when the tests above indicate a map > > is out of date. But how do we know when user space expects to see an > > up-to-date map other than a changed map entry? So to use a TTL will give > > us the oppertunity to check for an outdated map entry. Again only for > > ghosted maps. > > The issue I'm worrying about is, suppose all cache hits until now, that had > timed out and were rechecked from the map, turned out to be correct. But > suppose there is a map row which we haven't seen yet, either because we > just never read it, or because the map was enumerated some time ago but has > been added to since then? If the user reads the whole directory you have > to ignore the cache and re-read the NIS map every time (unless you rely on > the NIS order number, not generalizable) (OK to just stat a file map). > But then, if you can't distinguish "read whole directory" from "hunt for > one file in directory", you end up re-reading the entire map when you don't > want to.
I'm concerned about that issue as well. I'm still not sure how to deal with that. One thing to be aware of is that the kernel module and the daemon don't really know much about each other. So the cache is, for the purpose of this issue, either not available or is available much to late to be able to change the directory listing. Essentially, the directories are created in the filesystem by the daemon after reading the map and at some later time the kernel uses that alone to list the directory contents. I think that, for this, modifiying the kernel module is an absolute last resort as the place for handling this context information is the daemon. > > Forgive my meager kernel knowledge, but even if opendir is the same for > both uses, isn't there a separate object method implementing readdir, > versus looking up a file by name? Readdir should bypass the cache, reading > the NIS or LDAP map directly, while lookup should and does use the cache. The kernel never sees the cache. The filesystem itself must be kept up to date. Creating or removing directories during a readdir operation will end in tears without a doubt. But the real worry is the frequency with which this happens (as I mentioned above). If we could just come up with a workable heuristic for map refresh we would be OK. Ian _______________________________________________ autofs mailing list [EMAIL PROTECTED] http://linux.kernel.org/mailman/listinfo/autofs
