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

Jeremy Allison jra at samba.org
Tue Jan 24 21:43:55 UTC 2023

On Tue, Jan 24, 2023 at 01:39:34PM -0800, Jeremy Allison via samba wrote:
>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 :-).

Actually, separate the three :-).

Locking: Byte-ranges that control access to *parts* of a file.
	 Mandatory on Windows, advisory on Linux. Samba maps
	 Mandatory Windows byte-range locks to advisory locks
	 on Linux so it works smbd -> smbd, but not if local
	 processes ignore the locks (they are advisory on Linux).

Share modes: Controls on how a file may be opened simultaneously.
	 Windows-only, no analogue in Linux at all.

Leases and Oplocks: Windows only (although NFSv4 has leases also).
	 Controls client side caching of file data. No analogue
	 in local processes on Linux.

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