mount options and dnotify

mount options and dnotify

[Steve French]

Since two of the linux specific fcntls
	F_NOTIFY
and
	F_SETLEASE

could have performance implications if allowed over the network, yet in
at least the case of directory change notification can be quite
important (e.g. for KDE and GNOME to auto refresh their file manager
GUIs as new files appear) - is there a precedent for a filesystem
specific mount option to disable (or enable) directory change (and/or
file change) notification?

I was thinking of adding parsing for "notify=no" (or perhaps better to
call it dnotify=no) or "lease=no" on the cifs specific mount options to
allow control over whether these notification events only work locally
(or work for both local and remote changes) in case there are servers
out which contribute to "dnotify storms" (lots of directory change
notifications in a short period).

And on a loosely related subject, I noticed that kernel.org has gz
snapshots of the mount utility and man page (e.g.in
http://www.kernel.org/pub/linux/utils/util-linux/) but I did not see the
name of a maintainer of the mount(8) man page in the page.  I wanted to
send them suggested additional text pointing to the mount.cifs(8) man
page for cifs mounts (similar to what they do for a few others including
smbfs).

Re: mount options and dnotify

[Jamie Lokier]

Steve French wrote:
> I was thinking of adding parsing for "notify=no" (or perhaps better to
> call it dnotify=no) or "lease=no" on the cifs specific mount options to
> allow control over whether these notification events only work locally
> (or work for both local and remote changes) in case there are servers
> out which contribute to "dnotify storms" (lots of directory change
> notifications in a short period).

What is the point in adding those options now?  Last time I looked
(kernel 2.6.5) notifications and leases only apply to local operations
- there is no interaction with the server.

If notifications and leases are eventually extended to communicate
with the server, then you probably want an option to restrict them to
local operations only, rather than disable altogether -- as your text
says.  In which case, "dnotify=local" and "lease=local" makes sense, no?

-- Jamie

Re: mount options and dnotify

[Steve French]

On Wed, 2004-04-28 at 14:33, Jamie Lokier wrote:
> What is the point in adding those options now?  Last time I looked
> (kernel 2.6.5) notifications and leases only apply to local operations
> - there is no interaction with the server.

Changes were made recently to fs/fcntl.c about line 360 to make it an
optional file_operation (nfs apparently needed to hook one of the other
fcntls now that they have directio) but this helps cifs vfs solve
problems like the bugzilla bug someone opened about new files not
showing up automitically in some GUI filemanager.  The required function
dnotify parent was already exported so the fcntl file op was the only
other thing that was needed.

> If notifications and leases are eventually extended to communicate
> with the server,

The cifs code for this is not complete (it is #ifdeffed out in 2.6.6)
but it should be reasonably easy since Samba and Windows servers support
the function already.