[Samba] oplocks, kernel oplocks, kernel share modes, .. - how it all works?
slow at samba.org
Fri Jan 20 11:49:34 UTC 2023
I don't have that much time to explain this in glory detail, but here
are a few pointers.
There are three different apsects:
- locking in the Windows sharemode flavor
- file change notify
- client side caching via oplocks/leases
File change notify is fully supported and will detect local changes via
inotify on Linux. Iirc there are some caveats like recursive change
notify but that doesn't seem to be a production problem as Windows
clients typically don't make use of this feature.
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".
Locking (sharemodes): we used to leverage Linux support for mandatory
flock() locks (LOCK_MAND) to "store" and let the kernel enforce access
restrictions for local access, but unfortunately the kernel support got
removed because it was buggy:
We still have VFS hooks for this but iirc the only filesystem that
supports this via the VFS interface is GPFS.
Hope this helps somewhat.
Ralph Boehme, Samba Team https://samba.org/
SerNet Samba Team Lead https://sernet.de/en/team-samba
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