samba - Jan 2023 - oplocks, kernel oplocks, kernel share modes, .. - how it all works?

Howdy!

On 1/20/23 14:50, Michael Tokarev via samba wrote:
>> Client side caching (oplocks/leases): somewhat limitted support by 
>> enabled "kernel oplocks". Kernel oplocks don't work with
SMB2 Leases,
>> so you're restricted to SMB1 oplocks. Cf man smb.conf "kernel
oplocks".
> 
> And SMB1 oplocks does not work when SMB2+ protocol is negotiated/used, 
> right?
No, they work just fine even with SMB2 and newer. Leases just offer a 
richer set of caching operations and are thus more efficient for certain 
workloads. Enabling "kernel oplocks" makes it worse as they don't
work
with shared/read oplocks, only for exclusive/read+write ones.
> But the lease which is granted to windows on that file.. stays. And it 
> is even
> funnier - I open this file in a text viewer (read-only), win asks shared 
> lease
> for it, next I modify the file on linux, close it on windows and re-open 
> it on
> windows. And it shows me the old cached contents of this file, while in the
> directory listing which windows displayed already even before second open,
> this file has zero size.
As said, change notify is something else entirely then caching via 
oplocks or leases. Change notify is a pure notification system while 
oplocks requires blocking oplock contenders from accessing a file until 
the client holding the oplock downgrades his oplock or times out.
> It is either that samba does not try to break this lease even if it 
> detects the
> file change (ie, change notify isn't hooked into the file lease code), 
Enable "kernel oplocks", then it should work.
> And it deserves a separate wiki page too, at least :)
That would be awesome! Contributions welcome! :)

-slow

-- 
Ralph Boehme, Samba Team                 https://samba.org/
SerNet Samba Team Lead      https://sernet.de/en/team-samba

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20.01.2023 17:06, Ralph Boehme wrote:
> Howdy

>> And SMB1 oplocks does not work when SMB2+ protocol is negotiated/used,
right?
> 
> No, they work just fine even with SMB2 and newer. Leases just offer a
richer set of caching operations and are thus more efficient for certain
> workloads. Enabling "kernel oplocks" makes it worse as they
don't work with shared/read oplocks, only for exclusive/read+write ones.
Aha. That makes sense. Somehow it looked like anything SMB1 is bad and must
be avoided at all costs :)
>> But the lease which is granted to windows on that file.. stays. And it
is even
>> funnier - I open this file in a text viewer (read-only), win asks
shared lease
>> for it, next I modify the file on linux, close it on windows and
re-open it on
>> windows. And it shows me the old cached contents of this file, while in
the
>> directory listing which windows displayed already even before second
open,
>> this file has zero size.
> 
> As said, change notify is something else entirely then caching via oplocks
or leases. Change notify is a pure notification system while oplocks
> requires blocking oplock contenders from accessing a file until the client
holding the oplock downgrades his oplock or times out.
> 
>> It is either that samba does not try to break this lease even if it
detects the
>> file change (ie, change notify isn't hooked into the file lease
code),
> 
> Enable "kernel oplocks", then it should work.
It's been enabled for this share for a few days already.
But it looks like it is not sufficient to just reload-config
for this change to actually take effect, - I just restarted
smbd and voila, it all finally seems to be working fine,
including all the right oplock breaks when rsyncing many
files which are open on the client.

As you might imagine, it's been several days I'm trying to collect
some info about this (doing it in background but still) - and to me
it *looks* like it should work, - sure thing, I enabled kernel oplocks
for a reason! - but it doesn't. This is why I wrote the email which
started this thread, - because I wanted to understand where things
actually *are* in samba these days, before concluding something's
not working.

(and received reply from Rowland telling whole world is wrong
and use samba incorrectly :) ).

Samba is excellent software. It has quit some unknowns, but the
design seems to be exactly right!

Thank you very much for all this info. It definitely should become
a more wider knowledge! :) (I'm working on this)

/mjt

20.01.2023 17:06, Ralph Boehme via samba wrote:
..
>> And it deserves a separate wiki page too, at least :)
> 
> That would be awesome! Contributions welcome! :)
I tried to create a new page, here:

 
https://wiki.samba.org/index.php?title=Editing_files_locally_on_server:_interoperability

but I can't, because I don't have permission to create new page on
the samba wiki.

Can someone please grant me such permission?

Thanks,

/mjt