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Date:   Mon, 23 Aug 2021 18:15:40 -0400
To:     Jeff Layton <jlayton@kernel.org>
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Subject: Re: Removing Mandatory Locks
Message-ID: <20210823221540.GB10881@fieldses.org>
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From:   bfields@fieldses.org (J. Bruce Fields)
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On Sat, Aug 21, 2021 at 08:45:54AM -0400, Jeff Layton wrote:
> On Fri, 2021-08-20 at 17:29 -0400, Jeff Layton wrote:
> > No, Windows has deny-mode locking at open time, but the kernel's
> > mandatory locks are enforced during read/write (which is why they are
> > such a pain). Samba will not miss these at all.
> > 
> > If we want something to provide windows-like semantics, we'd probably
> > want to start with something like Pavel Shilovsky's O_DENY_* patches.
> > 
> > -- Jeff
> > 
> 
> Doh! It completely slipped my mind about byte-range locks on windows...
> 
> Those are mandatory and they do block read and write activity to the
> ranges locked. They have weird semantics vs. POSIX locks (they stack
> instead of splitting/merging, etc.).
> 
> Samba emulates these with (advisory) POSIX locks in most cases. Using
> mandatory locks is probably possible, but I think it would add more
> potential for deadlock and security issues.

Right, so Windows byte-range locks are different from Windows open deny
modes.

But even if somebody wanted to implement them, I doubt they'd start with
the mandatory locking code you're removing here, so I think they're
irrelevant to this discussion.

--b.