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List:       linux-kernel
Subject:    Re: Subtle NFS/VFS/GLIBC interaction bug
From:       Trond Myklebust <trond.myklebust () fys ! uio ! no>
Date:       2001-03-12 14:45:27
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>>>>> " " == Leon Bottou <leonb@research.att.com> writes:

     > Note the strange numbers in the d_off fields.  These are in
     > fact cookies used internally by nfs.  Under nfs2, these are 32
     > bit unsigned number, sign extended to 64 bits.

     > The last cookie has not been properly sign extended.  The
     > glibc-2.2.2 source code for readdir uses __NR_getdents64 and
     > converts the result into 32 bit dirents.  But it sees that the
     > last d_ino cannot fit in an off_t and it simply bails out.

     > There is already a problem in the making since nfs3 cookies are
     > 64 bits long.  But things should work with nfs2.

This is why I wish glibc would drop the whole idea of relying on
seekdir/telldir existing. The LFS does in fact not specify any
equivalent seekdir64/telldir64, and most implementations of *NIX don't
support them.
Currently, the VFS only allows us to support the minimum
implementation which is required to support the 32-bit interface.

     > I can fix the problem using the following hack:

I've got a more complete one. See the 'IRIX' patch on

  http://www.fys.uio.no/~trondmy/src/2.4.2/linux-2.4.2-dir.dif

That patch also sign-extends 32-bit cookies at the NFS level, so that
we can
  a) convert cookies back so that the server accepts them
  b) match sign-extended 32-bit cookies in the page cache

     > That is acceptable as long as filldir_t does not handle 64bits
     > offsets anyway.

     > But it won't last.

Yes and no. All NFSv3 implementations are supposed to support 32-bit
client implementations. All you lose here is the ability to handle
multi-Gigabyte directories.

Cheers,
  Trond
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