SCF Reference Manual for G-Series RVUs (G06.24+)

Introduction to SCF
SCF Reference Manual for G-Series RVUs—520413-004
3-4
How SCF Works
Because some commands can have detrimental effects if improperly used, special
qualification is required to use them. These commands are called sensitive
commands. When used in conjunction with the security features of the operating
system, SCF provides effective access control for sensitive commands. Commands
that request information or status but do not affect operation are called nonsensitive
commands. Nonsensitive commands are available to all users. See page 5-15 for lists
of sensitive and nonsensitive commands.
How SCF Works
For commands that relate only to SCF (rather than a subsystem), SCF takes
appropriate action without involving the subsystem product modules or SCP. For
commands that relate to a subsystem or its objects, SCF performs syntax checking
and validates the object specification. Then SCF forwards the command to the
subsystem product module for the specified object. From there, the subsystem
product module validates the command again and translates it into a formatted
message for SCP, which then communicates with the appropriate subsystem to
perform the specified task.
SCF accepts commands from a workstation, a disk file, or an application process. It
sends display output to a workstation, a file, a process, or a printer.
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If you start SCF interactively, the TACL RUN command specifies the input source
and output destination.
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If you start SCF by using a process creation system procedure, the startup
message specifies the input source and output destination. Subsequent SCF
commands can change the input source and output destination.
Section 4, Using SCF, describes how to run SCF. SCF performs most commands in
the following sequence:
1. When SCF receives a command, it interprets the command and performs the
necessary steps to execute it. Some commands can be handled by SCF with no
interaction with SCP (for example, VOLUME and OUT).
2. If the command involves control or configuration of an object or a request for
information about an object, SCF produces a subsystem programmatic interface
(SPI) message that describes the object and the operation to be performed on it.
This message is then sent to a subsystem I/O process or a subsystem manager
process through SCP. A single command might require several SPI messages
before the operation can be completed. The exact number of steps required to
execute a command varies from subsystem to subsystem and from command to
command.
3. When the subsystem I/O process or subsystem manager process has processed
the message, it returns a completion message to SCF through SCP. If the
message indicates a successful completion, SCF displays its prompt and waits for
the next command. If the completion message indicates an exception condition,
SCF displays an appropriate message and then displays its prompt.