On Tue, Mar 30, 2021 at 3:53 PM Christian Brauner <christian.brauner@xxxxxxxxxx> wrote: > > On Tue, Mar 30, 2021 at 03:33:23PM +0300, Amir Goldstein wrote: > > 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 > > I know. That's why I was using ecryptfs as an example which doesn't do > that (And I think it should be switched tbh.). It simply uses > kern_path() and then stashes that path. > > My example probably would be something like: > > mount -t ext4 /dev/sdb /A > > 1. FAN_MARK_MOUNT(/A) > > mount --bind /A /B > > 2. FAN_MARK_MOUNT(/B) > > mount -t ecryptfs /B /C > > 3. FAN_MARK_MOUNT(/C) > > let's say I now do > > touch /C/bla > > I may be way off here but intuitively it seems both 1. and 2. should get > a creation event but not 3., right? > Why not 3? You explicitly set a mark on /C requesting to be notified when objects are created via /C. > But with your proposal would both 1. and 2. still get a creation event? > They would not get an event, because fsnotify() looks for CREATE event subscribers on inode->i_fsnotify_marks and inode->i_sb_s_fsnotify_marks and does not find any. The vfs_create() -> fsnotify_create() hook passes data_type inode to fsnotify() so there is no fsnotify_data_path() to extract mnt event subscribers from. The same fate would be to files created by overlayfs, nfsd and cachefiles. Only the create event on /C/bla from the syscall context would call fsnoity_path_create() and result with path data in fsnotify(), so the mnt event subscriber would be found. > > users cannot watch the underlying overlayfs operations using > > a mount mark. Also, overlayfs suppresses fsnotify events on > > underlying files intentionally with FMODE_NONOTIFY. > > Probably ecryptfs should too? > <shrug> :) FMODE_NONOTIFY is there not because there was a requirement not to send events, but because the path of the internal file is "fake", so it has a weird looking path. After all there are many other events that would be sent (not on open files). At least I think that's the reason... Thanks, Amir.
