HP CIFS File Locking Interoperation

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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.