HP CIFS File Locking Interoperation

(mixed-mode access) does not remove the element of risk from data corruption

because the locking interoperability is not comprehensive system-wide

Byte Range locking is implemented for both Windows and UNIX/NFS access with UNIX

advisory byte range locking via the fcntl function. Since UNIX/NFS byte range locking is

advisory, a UNIX process must be properly coded to participate in the locking protocol. The

CIFS/9000 smbd process actually calls the UNIX fcntl function to implement Windows byte

range locking. When both processes correctly interact, byte range locking is fully effective in

a mixed Windows-UNIX/NFS access environment. Byte range locking should remain

enabled.

Opportunistic (Oplocks) locking should be disabled for any share that has mixed Windows

and UNIX/NFS client access. A UNIX process has no concept of an oplock, therefore cannot

send an oplock break when a Windows client has cached a copy of a file. A UNIX process

could open and write to a disk file that has been modified in the Windows client cache, which

results in an unacceptable risk of data corruption. Oplocks should be disabled in a mixed

Windows-UNIX/NFS access environment.

Mandatory, Byte Range, and Opportunistic locking are all enabled by default. Disable

oplocks for Windows-UNIX share file access explicitly on a per -share basis by editing the

smb.conf file:

[share_name]

share modes = yes <default config – shown for example only>

locking = yes <default config – shown for example only>

oplocks = no

veto oplocks can be used to specify particular files on a share that will encounter mixed

Windows and UNIX access, and prevent the CIFS/9000 server from granting oplock requests

upon those files. By enabling veto oplocks for mixed-mode shared access, Windows clients

can continue to utilize oplocks for Windows-only shared access and gain the performance

benefit of file caching.

[share_name]

share modes = yes <default config – shown for example only>

locking = yes <default config – shown for example only>

oplocks = yes

veto oplock files = /filename.ext/

See Appendix B.5