Re: fcntl: F_SETLEASE/F_RDLCK question
From: Michael Kerrisk (mtk-lkml_at_gmx.net)
Date: 05/31/05
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Date: Tue, 31 May 2005 17:41:51 +0200 (MEST) To: "J. Bruce Fields" <bfields@fieldses.org>
Bruce,
> On Tue, May 31, 2005 at 04:53:50PM +0200, Michael Kerrisk wrote:
> > I applied this against 2.6.12-rc4, and it fixes the problem
> > (and I've also teasted various other facets of file leases
> > and this change causes no obvious breakage elsewhere).
> >
> > Are you going to push this fix into 2.6.12?
>
> Are you sure this is actually a problem?
>
> I still have the following questions I had before:
>
> > I'm a little confused as to why anyone would have the expectation
> > that read leases would not conflict with write opens by the same
> > process, given that break_lease() has never functioned that way, so
> > later write opens by the same process have always broken any read
> > lease.
> >
> > Are there applications that actually depend on the old behaviour? Is
> > there any documentation that blesses it? All I can find is the fcntl
> > man page, and as far as I can tell an implementation that makes read
> > leases conflict with all write opens (by the same process or not) is
> > consistent with that man page.
I believe it is still a problem: primarily because it broke
old behavior for no apparent reason (Stephen Rothwell, who was
one of the original implementers seems to agree, since he
suggested that one line patch). I suspect the change was
unintentional.
By the way, I wrote the text in the fcntl() man page
by looking at the code and experimenting. There was no
existing documentation of F_SETLEASE. I'm questioning
the change based on my understanding of how things should
work (I didn't happen to write up this point because it
seemed self-evident *to me*); however, I know rather
little of the workings of SAMBA.
Cheers,
Michael
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