unionfs problem

[Moritz Schulte]

Hi,

  I have a problem with unionfs, maybe somebody can give me advice; it
is about symbolic links.

  An example:

  I use unionfs on /lib and in /lib there is libfnord.so, which is a
symbolic link to libfnord.so.42; now /lib/libfnord.so is looked up via
file_name_lookup_under.

  Since the requested file libfnord.so is a link, ext2fs returns a
retry name of /lib/libfnord.so.42.  glibc then triggers a `lookup
during a lookup'; the unionfs root node (lib) is locked during the
lookup of that retry name, which leads to a dead lock.

  How can this problem be prevented?

  One idea I had in mind is: unionfs would do O_NOFOLLOW lookups, read
the name a symbolic links point to and check wether that path is
beneath one of the underlying filesystems.  If it is (like
`/lib/libfnord.so.42') , then we make a name out of it, which is
relative to the underlying file system (i.e.: cutting out that `/lib/'
part).  But this ugly and doesn't have to work in all cases.

Any ideas?

Thanks,
                moritz
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moritz@duesseldorf.ccc.de - http://duesseldorf.ccc.de/~moritz/
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