Interaction of DIO, CIO, regular opens, and mapped files for NFS

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The following behaviors exist between the different access modes that can occur with DIO and CIO.

When existing DIO opens are in effect:
  • A regular open causes DIO to be turned off until there are no longer regular opens. When a close reduces the regular opens to 0, DIO is re-enabled if there are still DIO opens outstanding.
  • Mapping a file with shmat() or mmap() will deactivate DIO on the file until the number of mappings drops to 0. Then if there are still DIO opens, DIO will be re-enabled.
  • Attempts to open the file for CIO will fail with the EINVAL error.
When there are regular opens (no CIO or DIO) in effect:
  • DIO open attempts succeed, but DIO is not activated until the count of regular opens drops to 0.
  • Opens for CIO will fail with the EINVAL error.
When CIO opens are in effect:
  • Regular, DIO, and attempts to map the file will all fail with the EINVAL error.
When CIO|CIOR opens are in effect:
  • Regular, DIO, and attempts to map the file will all fail with the EINVAL error except Read-only and CIO|CIOR opens.
Note: When there is a transition to DIO or CIO, client-cached modifications will first write back to the NFS server prior to deleting all cached information.