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Are exclusive locks implemented in the ONTAP file system using the fcntl or the LockFileEx ?

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Applies to

ONTAP 9

Answer

  • No,ONTAP file system does not provide exclusive locking at the file system level using fcntl or LockFileEx.
  • For NFSv3 access, file locking is managed by Network Lock Manager (NLM). 
    • NLM provides advisory locks only.
    • Advisory locks require client applications to check and honor locks.
    • Clients may access locked files or regions if the application does not check the lock.
  • For NFSv4.x, mandatory locking is supported via the Share Reservation Lock mechanism. 
    • Share Reservation Lock is enforced at the protocol level.
    • When a file is locked with Share Reservation Lock, access from other clients is blocked according to the lock type.
    • Details on mandatory locking for NFSv4 are available in How is Mandatory Locking supported for NFSv4 on ONTAP 9.
  • fcntl on UNIX/Linux uses POSIX advisory byte-range (record) locking. 
    • On NFSv4.x, the kernel maps fcntl locks to NFSv4 LOCK operations.
    • NFSv4 Share Reservation Lock is different from fcntl locks; it is part of the OPEN operation and controls file open modes (share_access and share_deny).
    • POSIX does not expose share deny semantics via fcntl.
    • Most UNIX/Linux NFSv4 clients use share_deny-none by default.
  • For Windows clients, LockFileEx is used for advisory locking over CIFS/SMB. 

Lock enforcement depends on application and protocol behavior.

  • NFSv3 does not support mandatory locking.
  • NFSv4.x supports mandatory locking via Share Reservation Lock, but POSIX APIs (fcntl) do not provide a way to request share deny semantics

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