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The Kernel-Space NFS Server next up previous
Next: File Handle in Kernel-Space Up: Interoperability Previous: File Handle

The Kernel-Space NFS Server

The Connectathon testsuites revealed several flaws in the NFS server implementation in the Linux kernel 2.2.9. The test result from Solaris clients showed that the Solaris NFS client assumes:

  • Files are unstructured streams of uninterpreted bytes.

  • If 2 file handles from the same server are identical, they represent the same file on the server.

  • If 2 file handles from the same server are different, they must represent the different files on the server.

  • All the hard links should be represented by the same file handle

  • When a client renames a file within the same file system, the file handle should be unchanged.

However, two fields in the file handle in the Linux NFS server, fb_dentry and fb_dirino, make Solaris's assumption untrue.

fb_dentry is for dentry, which is the internal part for the Linux file system. It determined by pathname. That implies several things:

  • When a pathname is deleted and then created, their dentries will be the same although they are different files.

  • The hard links have different dentries.

  • Rename will lead to different dentries.

Those make dentry very unsuitable for file handle. Even worse, dentry is a memory pointer. That means the file handle from the Linux NFS server is not persistent. When the server is rebooted, the file handlers which clients have may become stale and for the same file the Linux NFS server may return a different file handle.


next up previous
Next: File Handle in Kernel-Space Up: Interoperability Previous: File Handle
H.J. Lu
1999-08-15

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