On Tue, Mar 30, 2021 at 3:12 PM Christian Brauner <christian.brauner@xxxxxxxxxx> wrote: > > On Sun, Mar 28, 2021 at 06:56:24PM +0300, Amir Goldstein wrote: > > Add a high level hook fsnotify_path_create() which is called from > > syscall context where mount context is available, so that FAN_CREATE > > event can be added to a mount mark mask. > > > > This high level hook is called in addition to fsnotify_create(), > > fsnotify_mkdir() and fsnotify_link() hooks in vfs helpers where the mount > > context is not available. > > > > In the context where fsnotify_path_create() will be called, a dentry flag > > flag is set on the new dentry the suppress the FS_CREATE event in the vfs > > level hooks. > > Ok, just to make sure this scheme would also work for overlay-style > filesystems like ecryptfs where you possible generate two notify events: > - in the ecryptfs layer > - in the lower fs layer > at least when you set a regular inode watch. > > If you set a mount watch you ideally would generate two events in both > layers too, right? But afaict that wouldn't work. > > Say, someone creates a new link in ecryptfs the DENTRY_PATH_CREATE > flag will be set on the new ecryptfs dentry and so no notify event will > be generated for the ecryptfs layer again. Then ecryptfs calls > vfs_link() to create a new dentry in the lower layer. The new dentry in > the lower layer won't have DCACHE_PATH_CREATE set. Ok, that makes sense. > > But since vfs_link() doesn't have access to the mnt context itself you > can't generate a notify event for the mount associated with the lower > fs. This would cause people who a FAN_MARK_MOUNT watch on that lower fs > mount to not get notified about creation events going through the > ecryptfs layer. Is that right? Seems like this could be a problem. > Not sure I follow what the problem might be. FAN_MARK_MOUNT subscribes to get only events that were generated via that vfsmount - that has been that way forever. A listener may subscribe to (say) FAN_CREATE on a certain mount AND also also on a specific parent directory. If the listener is watching the entire ecryptfs mount and the specific lower directory where said vfs_link() happens, both events will be reported. One from fsnotify_create_path() and the lower from fsnotify_create(). If one listener is watching the ecryptfs mount and another listener is watching the specific ecryptfs directory, both listeners will get a single event each. They will both get the event that is emitted from fsnotify_path_create(). Besides I am not sure about ecryptfs, but overlayfs uses private mount clone for accessing lower layer, so by definition users cannot watch the underlying overlayfs operations using a mount mark. Also, overlayfs suppresses fsnotify events on underlying files intentionally with FMODE_NONOTIFY. Hope that answers your question. Thanks, Amir.
