Hi, as far as I know individual filesystems are not aware an inotify watch has been set on a inode managed by that filesystem. For local only filesystems like ext2/3/4 etcetera this is no problem. But with network filesystems like nfs and cifs (and also fuse types) this is not ideal, since changes made by others (since the backend is shared with others) are never watched. I'm working on a filesystem change watcher notifyfs, and puzzling already for a long time howto enable the watching of fs events on these filesystems. I've some idea's: a. notifyfs is working on the local (A) and the remote host (B), and is doing it's thing without using the filesystem. When a client contacts notifyfs to set a watch on a nfs (or cifs) share, notifyfs detects it a nfs share. It finds out the remote host by analyzing the mount, and gets the details like remote address and directory. With nfs that's easy, since the mount is like remotehost:/directory, with cifs this is a bit more difficult, but doable. After getting the details, it can forward the watch to the remote host (B), on which also notifyfs is running, and listning to a tcp port. This notifyfs process on his turn watches the desired fs object using the abilities on that host, and sends anything back to the local host (A). I've experimented with this, and got it working when using sshfs. This is very easy to setup, and simple to understand, but some drawbacks: 1. while the filesystems are using credentails or tickets to get access to a remote resource, this is a bit difficult for notifyfs. Notifyfs bypasses that. Maybe this leads to permissions/abuse I cannot see directly. 2. the filesystem still does not know that something has changed (on B). It should be made aware as fast as possible to make the changes effective on localhost A. Maybe notifyfs should just trigger that by doing a lookup on an entry when it has been removed on the remote host for example. b. notifyfs forwards the watch to nfs (and cifs) using netlink. Since nfs and cifs are in kernelspace, and notifyfs is in userspace, netlink is the way to go to communicate.This is possible, and I've thought this is the best way to go for a long time, but complicated when compared to the last method: c. make filesystems like nfs and cifs aware a inotify watch has been set. Untill now the filesystems self are totally not notified a watch has been set (and of course also changed/removed). This is by design. For local filesystems it's not required, it will not get any extra, but nfs and cifs and fuse fs's can use this info to set a watch on the backend using the methods/api specific to the filesystem. For example cifs will send a SMB2_CHANGE_NOTIFY to the server, and waiting for results. What do you think, is the latest option possible?? Stef Bon -- 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
