Hi Eric, Very interesting work. On Mon, 1 Jun 2009, Eric W. Biederman wrote: > The file_hotplug_lock has a very unique implementation necessitated by > the need to have no performance impact on existing code. Classic locking > primitives and reference counting cause pipeline stalls, except for rcu > which provides no ability to preventing reading a data structure while > it is being updated. Well, the simple solution to that is to add another level of indirection: old: fdtable -> file new: fdtable -> persistent_file -> file Then it is possible to replace persistent_file->file with a revoked one under RCU. This has the added advantage that it supports arbitrary file replacements, not just ones which return EIO. Another advantage is that dereferencing can normally be done "under the hood" in fget()/fget_light(). Only code which wants to permanently store a file pointer (like the SCM_RIGHTS thing) would need to be aware of the extra complexity. Would that work, do you think? Thanks, Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
