Your CVS fix 1.109 to union_vnops.c

Uwe Doering gemini at
Sun Oct 3 23:26:20 PDT 2004

Takanori Watanabe wrote:
> In message <20041004053106.GQ88303 at>, 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 Doering         |  EscapeBox - Managed On-Demand UNIX Servers
gemini at  |

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