Our use case is an NFS+pNFS+9P user mode server. We need to keep our caches (dentry+inode) current with the underlying kernel. To do this we need inotify to feed filesystem events to our upcall infrastructure. We place a watch on each directory we have cached and any events that morph that directory would cause invalidates and/or updates to those entries. The current fsnotify subsystem does most of what we want but implicit in the dnotify/inotify/fanotify interfaces is the assumption that the watcher is an "innocent bystander" whose sole/main function is to draw/remove icons on a window when someone else adds/removes things from a directory. Part of our use case is that the ganesha.nfsd server is co-resident with a CIFS server which is also exporting the same filesystem(s) and service management tools that modify the filesystem structure (snapshots and volume adds...). The current inotify interface will send up all events but if both servers are equally busy we get two bad results: 1. each server gets twice the traffic it really needs (theirs and ours). 2. there is no simple way to tell their events from ours in each event. This patch set adds a new watch/mark flag (FS_IGNORE_ME) to fsnotify. Setting this flag causes the watching process's pid to be stored in the mark for the inode. The flag is tested at event time and if set and if the pid of the event generating process matches the stored pid, the event is ignored, saving the overhead of allocating an event, pushing it up to user space only to be rejected. Being in fsnotify makes it available to any notification scheme built on fsnotify. The IN_IGNORE_ME flag bit is added to inotify. When set, none of the other event flags will generate an event if the calling process generated the event. Given the current way that inotify_add_watch() validates the flags argument, discovering whether the kernel supports the flag requires an extra test (set the watch and generate an event...). The FAN_IGNORE_ME flag bit does the same for fanotify. fanotify in current kernels will return an EINVAL error if this bit is set, making discovery easier. One performance side effect is that this flag eliminates the need and overhead for a test of my_pid == e.pid in the event processing loop. We chose inotify rather than the current fanotify because we need the extra events that fanotify cannot (currently) support. dnotify was not touched because it is both obsolete and its api makes this extension difficult. Please review and comment. If it is acceptable, please ACK and merge. Thanks Jim Lieb, NFS Ganesha project -- 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
