HP UX Common Internet File System (CIFS) Client/Server Software manual

B.5 Competitor’s Claims for NFS Non-Locking Protection

Competitors claim to protect their CIFS clients from NFS clients that are not participating in the advisory locking protocol. Their claim is based upon their mechanism of comparing every NFS read and write operation with locking records in the Kernel Lock Manager (or similar lock manager). The KLM will record every outstanding lock that is held by a CIFS or NFS client. If a non -locking NFS client attempts a write to a file, the write location will be compared against lock records in the KLM. If that file is already locked, the operation will fail. This mechanism works well for that case. Howev er, the figure below illustrates how data integrity is at risk even with their protection mechanism:

1.If NFS clients B and/or C have a file cached (like in vi), a CIFS client or locking NFS client can lock the file. Since the KLM has no record of A or B access, it grants the lock. Now client A and/or B have “stale” data.

2.If one non-locking NFS client has access to a file, then two or more non-locking NFS clients have access to a file.

a.Client B can overwrite C causing data corruption

b.Client C can overwrite B causing data corruption.

An HP bid for a customer deal should not be won based upon this file locking issue. This file locking functionality does not provide any real protection from data corruption.

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