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From: Al Viro <viro@zeniv.linux.org.uk>
To: Amir Goldstein <amir73il@gmail.com>
Cc: ksummit-discuss@lists.linuxfoundation.org
Subject: Re: [Ksummit-discuss] [TECH TOPIC] Linux kernel SMB server (CIFSD)
Date: Wed, 24 Jul 2019 17:42:56 +0100
Message-ID: <20190724164256.GE1131@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CAOQ4uxhdJDnTiANsC4Cv42A5ooeYaTphtGvZgP9Wvp+LCCh1NA@mail.gmail.com>

On Wed, Jul 24, 2019 at 01:50:57PM +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?
> 
> >
> > I even looked at LSM hooks, because they do what we need - invoke
> > creat, open, truncate, chmod, chown, unlink, callbacks. But, first,
> > I do realize that LSM was not meant to be used as some sort of fsnotify
> > replacement, and, second, LSM symbols are not exported anyway :)
> >
> 
> fsnotify could actually be called from LSM hooks, see:
> https://github.com/amir73il/linux/commits/fsnotify_dirent_perm
> 
> It may or may not be clear to you, but what you get extra from fsnotify
> compared to using bare LSM hooks is:
> - Minimal performance overhead for a non-marked object
> - Ability to subscribe/unsubscribe to certain events dynamically
> - Manage multiple subscriber instances (groups), like one per SMB session
> - Queuing infrastructure for async events if you need it

.... and then there's the sad fact that LSM hooks have no well-defined
semantics and their coverage is... suboptimal, to put it very mildly.

      parent reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-30  5:59 Theodore Ts'o
2019-07-24  5:52 ` Sergey Senozhatsky
2019-07-24  8:03   ` Sergey Senozhatsky
2019-07-24 10:50     ` Amir Goldstein
2019-07-24 10:55       ` Jeff Layton
2019-07-25  5:00         ` Sergey Senozhatsky
2019-07-30 17:01           ` Jan Kara
2019-07-31  3:09             ` Sergey Senozhatsky
2019-07-30 16:55         ` Jan Kara
2019-07-24 11:28       ` Sergey Senozhatsky
2019-07-24 16:42       ` Al Viro [this message]

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