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

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Message-ID: <CAOQ4uxi+VJG56TPvcpOqoVAGgbb8gZQJEfvhXyGyB5VboRE2wA@mail.gmail.com>
Date:   Sat, 26 Feb 2022 12:22:26 +0200
From:   Amir Goldstein <amir73il@...il.com>
To:     Steve French <smfrench@...il.com>
Cc:     Vivek Goyal <vgoyal@...hat.com>, CIFS <linux-cifs@...r.kernel.org>,
        samba-technical <samba-technical@...ts.samba.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Ioannis Angelakopoulos <jaggel@...edu>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        lsf-pc <lsf-pc@...ts.linux-foundation.org>
Subject: Re: [Lsf-pc] [LSF/MM/BPF TOPIC] Enabling change notification for
 network and cluster fs

On Fri, Feb 25, 2022 at 8:11 PM Steve French <smfrench@...il.com> wrote:
>
> > IOW, in general disable all local events and let filesystems decide which
> local events to generate? And locally cached write is one such example?
>
> The fs doesn't see cached writes so probably best to still use the common
> existing code for notification on local writes
>

I guess SMB protocol does not allow client B to request a NOTIFY on change
when client A has a directory lease, because requesting NOTIFY requires
getting a read file handle on the dir?

Effectively, smb client needs to open the remote directory for read in order
to prove that the client has read access to the directory, which is the
prerequisite for getting directory change notifications.

The local check for permissions is not enough for remote notifications:
        /* you can only watch an inode if you have read permissions on it */
        error = path_permission(path, MAY_READ);

Thanks,
Amir.