Re: [Ksummit-discuss] [TECH TOPIC] Linux kernel SMB server (CIFSD)

[Jan Kara <jack@suse.cz>]

On Wed 24-07-19 06:55:53, Jeff Layton wrote:
> On Wed, 2019-07-24 at 13:50 +0300, Amir Goldstein wrote:
> > On Wed, Jul 24, 2019 at 11:03 AM Sergey Senozhatsky
> > <sergey.senozhatsky.work@gmail.com> wrote:
> > > On (07/24/19 14:52), Sergey Senozhatsky wrote:
> > > > On (05/30/19 01:59), Theodore Ts'o wrote:
> > > > > From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> > > [..]
> > > > To extend the topic with some discussion points:
> > > > 
> > > > - We are facing a rather familiar problem. Basically, SMB2 CHANGE_NOTIFY
> > > >   [1] is something what fsnotify normally does, except that we can't use
> > > >   it in cifsd kernel module. I see that NFS guys had [2] same issues some
> > > >   time ago.
> > > > 
> > > >   So the question is - how to do fs notify style monitoring in a kernel
> > > >   module (nfsd, cifsd)? Any chance the kernel can start exporting fsnotify
> > > >   symbols?
> > 
> > I don't see a problem with exporting those symbols.
> > As a matter of fact, I have a plan to use them also from overlayfs.
> > At the time that Jeff posted his patches, there was no active fsnotify
> > maintainer.
> > Jeff, did you abandon this effort for nfsd?
> > 
> 
> (cc'ing Trond)
> 
> Trond has been driving those patches more recently. He posted a revised
> set of them recently, and they still use fsnotify to detect unlink
> activity:
> 
> https://www.spinics.net/lists/linux-nfs/msg73692.html

The fsnotify export bits look sane to me except perhaps
fsnotify_put_group() and fsnotify_wait_marks_destroyed(). Their usage in
"[PATCH 05/16] nfsd: add a new struct file caching facility to nfsd" looks
buggy AFAICT. One is supposed to destroy a group with
fsnotify_destroy_group() instead of just dropping the group reference (that
does just the final cleanup but expects fsnotify_destroy_group() has been
already called).

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR