[OpenAFS] Mount points for .backup volumes

[Jeffrey Hutzelman]

On Mon, 30 Jul 2001 Warren.Yenson@morganstanley.com wrote:

> On Mon, 30 Jul 2001, Nickolai Zeldovich wrote:
> 
> > > On the windows client, a colleague was also faced with a directory listing
> > > along the lines of
> > >
> > >     \.backup\.backup\.backup\.backup\.backup\.backup\.backup\.backup\...
> >
> > This certainly seems like a bug in the windows client -- the unix
> > cache manager refuses to evaluate a backup volume mountpoint in
> > a backup volume, returning ELOOP.
> 
> Actually, ELOOP is returned when the number of symbolic links followed is
> greater than the system defined limit, meaning the client was in fact
> traversing the mount points recursively.

Not in this case.  AFS mount points are not symbolic links, and they are
not evaluated as symlinks.  There is no arbitrary limit to the number of
mount points that may be followed in looking up a path.  As it turns out,
kolya is correct -- the AFS cache manager contains a special case such
that when evaluating a directory lookup on a mount point, the lookup fails
with ELOOP if the mount point both refers to a backup volume and is
contained in one.

Take a look at
http://www.openafs.org/frameset/cgi-bin/cvsweb.cgi/openafs/src/afs/VNOPS/afs_vnop_lookup.c%3frev%3d1.12%26content-type%3dtext/x-cvsweb-markup
where the following appears in EvalMountPoint():

    /* Don't cross mountpoint from a BK to a BK volume */
    if ((avc->states & CBackup) && (tvp->states & VBackup)) {
        afs_PutVolume(tvp, WRITE_LOCK);
        return ELOOP;
    }


> > (FWIW, in the athena.mit.edu cell, backup user volumes are mounted
> > as ~/OldFiles by default, and it seems to work fairly well..)
> 
> And on ~/.OldFiles in Morgan Stanley.
> 
>               - Warren
> 
> Warren Yenson          	          mailto: warren.yenson@morganstanley.com
> Morgan Stanley                    Tel: +1 (212) 762 2334
> 750 7th Ave, New York NY 10019    Fax: +1 (212) 762 1009
> 
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