HP Integrity NonStop J-Series - Manual (Page 55)

Securing Disk Files
Safeguard User’s Guide — 422089-020
3 - 21
The TRUST Attribute
The TRUST Attribute
The TRUST attribute enables the operating system to optimize I/O performance and
applies only to object files. It is available only in H-series RVUs and can be set only by
the super ID.
On systems running H-series RVUs, these two types of user I/O buffer access should
not be performed:
•
Reading from a nowaited I/O buffer that has an ongoing read operation
•
Writing to an I/O buffer that has any type of ongoing operation
These actions are detected and prevented by the operating system. The prevention
mechanism detects the access, suspends the process until the I/O operation has
completed, and then resumes the process. This suspend/resume behavior can
significantly affect process performance.
The TRUST attribute informs the operating system that the process can be “trusted”
not to access I/O buffers in the preceding manner. The system will bypass the
checking behavior, thus improving performance.
The TRUST attribute has three settings:
•
TRUST OFF specifies that the program is not to be trusted. The initial value of the
TRUST attribute is OFF.
•
TRUST ME specifies that the program can be trusted not to access I/O buffers
private to the process before I/O completion.
•
TRUST SHARED specifies that the program can be trusted not to access buffers
private to the process, or shared with another process that also has TRUST
SHARED set, before I/O completion.
To set the TRUST attribute of the program file progfile used in the previous example:
=ALTER DISKFILE progfile, TRUST SHARED