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From:   Steve French <smfrench@gmail.com>
Date:   Thu, 24 Feb 2022 16:55:42 -0600
Message-ID: <CAH2r5mt6Sh7qorfCHWnZzc6LUDd-s_NzGB=sa-UDM2-ivzpmAQ@mail.gmail.com>
Subject: Re: [LSF/MM/BPF TOPIC] Enabling change notification for network and
 cluster fs
To:     Vivek Goyal <vgoyal@redhat.com>
Cc:     lsf-pc@lists.linux-foundation.org,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Ioannis Angelakopoulos <jaggel@bu.edu>
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>  With this proposal, you are trying to move away from cifs specific ioctl?

Yes - since there are some applications that already use inotify
(although presumably less common than the similar API on Macs and
Windows), just fixing inotify to call into the fs to register events
is a good first step.  See inotify(7) - Linux manual page e.g.

For the case of SMB3.1.1 the wire protocol should be fine for this
(although perhaps could be a few flags added to inotify to better
match what servers support) See
https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-smb2/598f395a-e7a2-4cc8-afb3-ccb30dd2df7c

But there may be other APIs other than inotify that could be mapped to
what is already supported on the wire (with minor changes to the vfs)

On Thu, Feb 24, 2022 at 3:52 PM Vivek Goyal <vgoyal@redhat.com> wrote:
>
> On Wed, Feb 23, 2022 at 11:16:33PM -0600, Steve French wrote:
> > Currently only local events can be waited on with the current notify
> > kernel API since the requests to wait on these events is not passed to
> > the filesystem.   Especially for network and cluster filesystems it is
> > important that they be told that applications want to be notified of
> > these file or directory change events.
> >
> > A few years ago, discussions began on the changes needed to enable
> > support for this.   Would be timely to finish those discussions, as
> > waiting on file and directory change events to network mounts is very
> > common for other OS, and would be valuable for Linux to fix.
> >
>
> This sounds like which might have some overlap with what we are trying
> to do.
>
> Currently inotify/fanotify only work for local filesystems. We were
> thinking is it possible to extend it for remote filesystems as well. My
> interest primarily was to make notifications work on virtiofs. So I
> asked Ioannis (an intern with us) to try to prototype it and see what are
> the challenges and roadblocks.
>
> He posted one version of patches just as proof of concept and only tried
> to make remote inotify work. One primary feedback from Amir was that
> this is too specific to inotify and if you are extending fsnotify, then
> it should have some support for fanotify as well. There is bunch of
> other feedback too. So Ioannis is trying to rework his patches now.
>
> https://lore.kernel.org/linux-fsdevel/20211025204634.2517-1-iangelak@redhat.com/
>
> Anyway, you had pointed to following commit.
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/fs/cifs/ioctl.c?id=d26c2ddd33569667e3eeb577c4c1d966ca9192e2
>
> So looks like application calls this cifs specific ioctl and blocks and
> unblocks when notifications comes, IIUC.
>
> I don't know about SMB and what kind of other notifications does it
> support. With this proposal, you are trying to move away from cifs
> specific ioctl? What will user use to either block or poll for the
> said notification.
>
> Sorry, I might be just completely off the mark. Just trying to find out
> if there is any overlap in what you are looking for and what we are
> trying to do.
>
> Thanks
> Vivek
>
> > --
> > Thanks,
> >
> > Steve
> >
>


-- 
Thanks,

Steve