linux-kernel - Re: Support for applications which need NFS or CIFS "share

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Message-ID: <524f69650812021221g7e5163e6y5b5bafa3b157092e@mail.gmail.com>
Date:	Tue, 2 Dec 2008 14:21:35 -0600
From:	"Steve French" <smfrench@...il.com>
To:	"Jamie Lokier" <jamie@...reable.org>
Cc:	"Andreas Dilger" <adilger@....com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-cifs-client@...ts.samba.org" 
	<linux-cifs-client@...ts.samba.org>
Subject: Re: Support for applications which need NFS or CIFS "share_deny" flags on open

On Tue, Dec 2, 2008 at 2:20 PM, Steve French <smfrench@...il.com> wrote:
> On Tue, Dec 2, 2008 at 2:06 PM, Jamie Lokier <jamie@...reable.org> wrote:
>> Andreas Dilger wrote:
>>
>>> I can't see any reason for O_DENYREAD or O_DENYWRITE that can't be met
>>> with existing file locking to maintain coherency if that is really needed.
>
> I don't see how O_DENYREAD or more importantly, O_DENYWRITE can help.

A typo in my earlier post ... I meant ... I don't think (just) posix locking
(without also using O_DENYREAD) can be sufficient.

> If client A (Linux/Wine) does an open O_DENYWRITE, and we don't send
> the O_DENYWRITE on open, Samba (or Windows or NetApp or random NAS
> appliance etc.)
> will allow the open even if another Windows client is writing to the
> file.   The Linux/Wine
> subsystem could try to do a posix byte range lock from byte 0 to end
> of file and that
> would get mapped by the cifs client to a mandatory lock, but it
> doesn't help the case
> where another Windows client already has the file open for write, and you expect
> the open from your client to fail in that case.
>
>> Is there any reason why Wine cannot take an advisory lock _every_ time
>> it opens a file?  That would give Windows apps the behaviour they
>> expect, including across the network, without DOSing unix apps.
>>
>>> As for O_DENYDELETE - wouldn't that be irrelevant if the WINE code keeps
>>> an open file reference?  The data would still be accessible until WINE
>>> exits, and it wouldn't be a DOS.
>>
>> Windows apps do expect a file can't disappear while it's open.  This
>> is one way to detect if an app is running, and this particular
>> behaviour goes back to the oldest versions of Windows.
>>
>> Inside a single WINE instance or on a single host, your suggestion
>> works, but what about Windows apps on different hosts over a network share?
>>
>> The bit I find interesting is that other CIFS clients are said to
>> implement these flags.  If that means real unixes, maybe they've
>> worked out a sensible way to handle them?
>
> I thought that MacOS uses these flags (not just Windows, and of course
> older clients too OS/2, DOS etc.).
>
>
> --
> Thanks,
>
> Steve
>



-- 
Thanks,

Steve
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