[Samba] file leases and replacing files

[Jeremy Allison]

On Fri, Dec 30, 2022 at 09:30:04AM +0300, Michael Tokarev wrote:
>
>I thought about it some more now, and think the best would
>be to "notify" all consumers about the changed files (eg,
>to send "oplock break requests" to all involved parties,
>speaking in the old terms).
>
>When we initially implemented this, we had oplocks=no for
>this share. This made it noticeable slower obviously, but
>there were no issues like this (and windows weren't that
>sophisticated in this area, ditto for samba).
>
>Maybe turning off share modes will help here as well.
>Though if possible, I'd love to find a way to allow
>share modes, since the update is rare, and 99.9% of
>we can allow caching for sure.
>
>Can one tell smbd to send an oplock break request
>somehow?

The easiest way to do that is simply to open
each file you want to break the oplock on
via an smb share.

e.g. On a share [foo], directory bar/
to break all leases on files under bar,
do a loopback cifsfs mount (over SMB3)
from the server using: mount.cifs
to share //localhost/foo to mountpoint
/mnt and simply do a:

find /mnt/bar -type f -exec cp {} /dev/null ;

That will open for read all files under [foo]/bar
and cause any read/write/handle leases to get
broken.

Might need some tweaking to get the desired
semantics but I'm sure you get the idea.