Case-insensitive ext4

Posted Mar 27, 2019 20:17 UTC (Wed) by mathstuf (subscriber, #69389)
In reply to: Case-insensitive ext4 by rweikusat2
Parent article: Case-insensitive ext4

Ideally this would be some kind of LRU cache which would have some flag to say "this is a one-off open, don't cache" to avoid the inotify (or whatever) mechanism. Plus, I'm sure folks would love having the C library run a thread in the background to listen for its notifications taking locks on this cache whenever something happens. Yeah, I don't see any race conditions, unpredicitable latency issues, or TOCTOU/cache coherency issues here at all.

Sorry for the snark, it's not in response to your comment in particular, but my mind coming up with all the Pandora's boxes this is threatening to open.

Case-insensitive ext4

Posted Mar 27, 2019 21:11 UTC (Wed) by rweikusat2 (subscriber, #117920) [Link] (1 responses)

There's no point in special-casing "one-off opens" unless this demonstrably solves a problem. As then kernel open has to scan the directory, anyway, you'll end up with the exact same kind of TOCTOU races. This is a problem which can't really be solved. As to your other objections: These is a generic list of programming errors, some of them attributable to the idea with "a background thread".

It's possible to implement case-insensitive open in user space without doing a second linear search through a directory for every open.

Case-insensitive ext4

Posted Mar 27, 2019 21:19 UTC (Wed) by Cyberax (✭ supporter ✭, #52523) [Link]

As I understand, the kernel will keep track of canonicalized names in file cache, so it won't have to do a search.

There's also the problem of making sure that no duplicate files exist.