Introduction to Networking for NonStop S-Series Servers

Application Programming With Communications
Products
Introduction to Networking for HP NonStop S-Series Servers—520670-005
3-15
File-System Procedures
When you use files on other NonStop servers in an Expand network, the filename
includes the name of the system on which the file resides. Thus, when you refer to a
line attached to some other system, you give the name of the system as well as the
name of the line. For instance, a multipoint line of automated teller machines (ATMs)
controlled by a NonStop S-series server in New York could have the name
\NY.$MTATM. An ATM on that line could have the name \NY.$MTATM.#R86.
File-System Procedures
Your programs manipulate files by calling file-system procedures, which provide a
uniform method for accessing to files. Interprocess communication is accomplished by
procedures with names like READ, WRITE, and WRITEREAD. When the requested
action is complete, the file system completes the call, informing the application of the
success or failure of the request and delivering requested data.
Nowait Operation
Whether control returns to the application immediately or only after the requested
action is complete depends on whether the application has requested nowait
operation. Nowait operation is common for communications applications; it allows the
application to issue a series of requests without waiting for each to complete before
issuing the next, allowing the application to have multiple requests outstanding. If the
application uses nowait operation, control returns to the application before the
requested action is complete; status and data are returned in response to a special
completion call.
Types of File-System Requests
File-system requests to communications subsystems fall into two categories. Some
requests pertain to the connection between the application and the subsystem; for
example, a request might allocate resources—such as control blocks or a
communications line—to the application or report configuration or status information
that the subsystem maintains. Other requests pertain to the connection between the
application and the line or remote device; such requests result in protocol actions such
as transfer of data or control information on the line. Some requests are for both kinds
of functions.
Products vary somewhat in the range of file-system requests they support and in their
treatment of specific requests. The following subsections describe the most common
file-system calls and give general definitions. Requests pertaining to the connection
between the application and the subsystem are listed as logical connection, request
management, or general information requests; those pertaining to the connection
between the application and the line or device are listed as data transfer, line, or
subsystem-control requests.