Date: Mon, 04 Oct 2004 08:26:14 +0200 From: Uwe Doering <gemini@geminix.org> To: Takanori Watanabe <takawata@init-main.com> Cc: freebsd-current@FreeBSD.org Subject: Re: Your CVS fix 1.109 to union_vnops.c Message-ID: <4160ED06.6070603@geminix.org> In-Reply-To: <200410040606.i9466UVm012207@sana.init-main.com> References: <200410040606.i9466UVm012207@sana.init-main.com>
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Takanori Watanabe wrote:
> In message <20041004053106.GQ88303@vertex.kz>, Boris Popov wrote:
>
>>On Sun, Oct 03, 2004 at 11:06:42PM +0200, Uwe Doering wrote:
>>
>>>>That isn't the issue. The issue is that an application might open
>>>>the vnode in the unionfs mount, and another application might
>>>>modify the same file in the underlying file system. If the kernel
>>>>doesn't understand that it is really the same file, then cache
>>>>incoherencies will occur. I'm actually not sure to what extent
>>>>this is a problem already; John Heidemann's Phd thesis had a way
>>>>of dealing with it, but FreeBSD doesn't do things that way AFAIK.
>>>
>>>Okay, but that's a different matter. What I was addressing at the start
>>>of this discussion is an ambiguity issue with meta data, that is,
>>>information that ends up in stat(2) and friends.
>>
>> Exactly, one never knows what parts of metadata used by applications.
>>I can confirm that ino are ought to be unique inside filesystem, otherwise
>>some programs will fail in a very obscure ways.
>
> Ok, the issue Uwe says is when underlying filesystem and
> wrapping filesystem are diffent and if there are two files
> with same identifier exists.
> And the issue I want to fix is when underlying filesystem and
> wrapping filesystem are same so getcwd routine failed to distinguish
> the mount point.
>
> So it can be solved by translating fsid if the fsid of a file is same as
> that of mountpoint. True?
Correct. In this case the inode number is guaranteed to be unique.
This might be okay as a local patch, but it is IMHO not a fix suited for
FreeBSD in general.
Uwe
--
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