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

From: Amir Goldstein <amir73il@gmail.com>
To: Steve French <smfrench@gmail.com>
Cc: linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	CIFS <linux-cifs@vger.kernel.org>,
	samba-technical <samba-technical@lists.samba.org>,
	Jan Kara <jack@suse.cz>, Miklos Szeredi <miklos@szeredi.hu>
Subject: Re: [LFS/MM TOPIC] Enabling file and directory change notification for network and cluster file systems
Date: Tue, 21 Jan 2020 09:47:42 +0200	[thread overview]
Message-ID: <CAOQ4uxipauh1UXHSFt=WsiaDexqecjm4eDkVfnQXN8eYofdg2A@mail.gmail.com> (raw)
In-Reply-To: <CAH2r5mvUmZca8TRVsyZvrB_Loeeo4Kd8T7rHw5s6iaN=yC+O_Q@mail.gmail.com>

On Tue, Jan 21, 2020 at 5:55 AM Steve French <smfrench@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)?

Thanks,
Amir.