Re: Support for applications which need NFS or CIFS "share_deny" flags on open

From: Steve French
Date: Tue Dec 02 2008 - 15:21:49 EST

On Tue, Dec 2, 2008 at 2:20 PM, Steve French <smfrench@xxxxxxxxx> wrote:
> On Tue, Dec 2, 2008 at 2:06 PM, Jamie Lokier <jamie@xxxxxxxxxxxxx> 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


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