[LFS/MM TOPIC] Enabling file and directory change notification for network and cluster file systems

ronnie sahlberg ronniesahlberg at gmail.com
Tue Jan 21 08:30:46 UTC 2020

On Tue, Jan 21, 2020 at 5:48 PM Amir Goldstein <amir73il at gmail.com> wrote:
> On Tue, Jan 21, 2020 at 5:55 AM Steve French <smfrench at gmail.com> wrote:
> >
> > Currently the inotify interface in the kernel can only be used for
> > local file systems (unlike the previous change notify API used years
> > ago, and the change notify interface in Windows and other OS which is
> > primarily of interest for network file systems).
> >
> > I wanted to discuss the VFS changes needed to allow inotify requests
> > to be passed into file systems so network and cluster file systems (as
> > an example in the SMB3 case this simply means sending a
> > SMB3_CHANGE_NOTIFY request to the server, whether Samba or Cloud
> > (Azure) or Mac or Windows or Network Appliance - all support the API
> > on the server side, the problem is that the network or cluster fs
> > client isn't told about the request to wait on the inotify event).
> > Although user space tools can use file system specific ioctls to wait
> > on events, it is obviously preferable to allow network and cluster
> > file systems to wait on events using the calls which current Linux
> > GUIs use.
> >
> > This would allow gnome file manager GUI for example to be
> > automatically updated when a file is added to an open directory window
> > from another remote client.
> >
> > It would also fix the embarrassing problem noted in the inotify man page:
> >
> > "Inotify  reports  only events that a user-space program triggers
> > through the filesystem
> >        API.  As a result, it does not catch remote events that occur
> > on  network  filesystems."
> >
> > but that is precisely the types of notifications that are most useful
> > ... users often are aware of updates to local directories from the
> > same system, but ... automatic notifications that allow GUIs to be
> > updated on changes from **other** clients is of more value (and this
> > is exactly what the equivalent API allows on other OS).
> >
> > The changes to the Linux VFS are small.
> >
> >
> Miklos has already posted an RFC patch:
> https://lore.kernel.org/linux-fsdevel/20190507085707.GD30899@veci.piliscsaba.redhat.com/
> Did you try it?
> You also did not answer Miklos' question:
> does the smb protocol support whole filesystem (or subtree) notifications?
> (or just per-directory notifications)?

SMB can do both. There is a flag that specifies if you want to just
get notified about the directory itself
or whether  you want notifications from the whole subtree.

> Thanks,
> Amir.

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