[Adding linux-fsdevel here as well.] On Tuesday 17 August 2010 10:09:50 Andreas Gruenbacher wrote: > > > Q: What prevents the system from going out of memory when a listener > > > decides to stop reading events or simply can't keep up? There doesn't > > > seem to be a limit on the queue depth. Listeners currently need > > > CAP_SYS_ADMIN, but somehow limiting the queue depth and throttling when > > > things start to go bad still sounds like a reasonable thing to do, > > > right? > > > > It's an interesting question and obviously one that I've thought about. > > You remember when we talked previously I said the hardest part left was > > allowing non-root users to use the interface. It gets especially > > difficult when thinking about perm-events. I was specifically told not > > to timeout or drop those. But when dealing with non-root users using > > perm events? As for pure notification we can do something like inotify > > does quite easily. > > > > I'm not certain exactly what the best semantics are for non trusted > > users, so I didn't push any patches that way. Suggestions welcome :) > > The system will happily go OOM for trusted users and non-perm events if the > listener doesn't keep up, so some throttling, dropping, or both needs to > happen for non-perm events. This is the critical case. Doing what inotify > does (queue an overflow event and drop further events) seems to make sense > here. > > The situation with perm-events is less severe because the number of > outstanding perm events is bounded by the number of running processes. > This may be enough of a limit. > > I don't think we need to worry about perm-events for untrusted users. We > can start supporting some kinds of non-perm-events for untrusted users > later; this won't change the existing interface. Another case where fanotify fails to generate useful events is when a listener runs out of file descriptors; events will simply end up with fd == -EMFILE in that case. I don't think this behavior is useful; instead, reading from the fanotify file descriptor (he one returned by fanotify_init()) should fail to give the listener a chance to react. Andreas -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
