linux-kernel - Re: [LSF/MM/BPF TOPIC] Enabling change notification for network and cluster fs

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Date:   Fri, 25 Feb 2022 09:27:55 -0600
From:   Steve French <smfrench@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Vivek Goyal <vgoyal@...hat.com>, lsf-pc@...ts.linux-foundation.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ioannis Angelakopoulos <jaggel@...edu>,
        CIFS <linux-cifs@...r.kernel.org>,
        samba-technical <samba-technical@...ts.samba.org>
Subject: Re: [LSF/MM/BPF TOPIC] Enabling change notification for network and
 cluster fs

On Fri, Feb 25, 2022 at 7:49 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Fri, Feb 25, 2022 at 08:23:20AM -0500, Vivek Goyal wrote:
> > What about local events. I am assuming you want to supress local events
> > and only deliver remote events. Because having both local and remote
> > events delivered at the same time will be just confusing at best.
>
> This paragraph confuses me.  If I'm writing, for example, a file manager
> and I want it to update its display automatically when another task alters
> the contents of a directory, I don't care whether the modification was
> done locally or remotely.
>
> If I understand the SMB protocol correctly, it allows the client to take
> out a lease on a directory and not send its modifications back to the
> server until the client chooses to (or the server breaks the lease).
> So you wouldn't get any remote notifications because the client hasn't
> told the server.

Directory leases would be broken by file create so the more important
question is what happens when client 1 has a change notification on writes
to files in a directory then client 2 opens a file in the same directory and is
granted a file lease and starts writing to the file (which means the
writes could get cached).   This is probably a minor point because when
writes get flushed from client 2, client 1 (and any others with notifications
requested) will get notified of the event (changes to files in a directory
that they are watching).

Local applications watching a file on a network or cluster mount in Linux
(just as is the case with Windows, Macs etc.) should be able to be notified of
local (cached) writes to a remote file or remote writes to the file from another
client.  I don't think the change is large, and there was an earlier version of
a patch circulated for this

-- 
Thanks,

Steve