[Samba] oplocks, kernel oplocks, kernel share modes, .. - how it all works?

[Jeremy Allison]

On Wed, Jan 25, 2023 at 12:33:57AM +0300, Michael Tokarev wrote:
>>@Michael: move the kernel oplocks setting to the global section, then things may start to work as expected.
>
>With kernel oplocks = yes in [global] but without mentioning
>smb2 leases, this thing behaves in a way similar to when setting
>smb2 leases to no (also globally, as it is a global parameter), --
>I see the original NONE/BATCH/LEVEL_II oplocks in there as in the
>old good times.
>
>So looks like Ralph is correct here. Effectively, kernel oplocks
>turn smb2 leases off, and work on the global level, not on a share
>level.

Easiest fix is to just change the docs here :-).

>It looks like this needs some more experiments on my side though,
>I'm not sure if it actually works and the cache is being invalidated
>properly.  Also from my own description of whole thing, it looks
>like there's no way to do anything when the file is actually locked.

Locking and share modes have bugger-all to do with leases and oplocks.

Please separate the two in your mind, things will make
much more sense when you do :-).

>Why inotify can't be used instead of F_SETLEASE here?

Because the local unix process *must* be blocked from
doing *anything* to the file until the SMB client has
flushed all changes back to the file.

inotify just notifies, it doesn't stop any local
client doing anything.