The file system layer provides the main interface between the application programming interfaces (APIs) and the transport layers. The first component of the file system layer is the z/OS® UNIX logical file system (LFS). The LFS provides the API layer with a common interface to access files and sockets. In a POSIX-compliant environment, applications can access both files and sockets in a similar fashion. For example, both files and sockets are represented by a 32-bit integer referred to as a descriptor. Common functions can be used to access both file and socket resources.
The layer beneath the LFS is the physical file system (PFS). The PFS layer is where the distinction between files, sockets, and other resources is made. Based on the resource type, the LFS passes the incoming function requests to the appropriate PFS, which handles requests related to resources in the z/OS UNIX file system. For more information about these physical file systems, see z/OS UNIX System Services Planning.
From a TCP/IP perspective, the AF_INET and the AF_INET6 PFS are of main interest. TCP/IP is enabled for IPv6 by defining an AF_INET6 PFS. Defining the file systems is the responsibility of the installation's z/OS UNIX programmer. The definitions are found in the BPXPRMxx member of SYS1.PARMLIB.
For information about defining AF_INET and AF_INET6 physical file systems, and about customizing BPXPRMxx for INET and CINET systems, see z/OS UNIX System Services Planning.
Under this configuration, it is also possible for TCP/IP application servers using the z/OS UNIX socket APIs to field incoming client requests from all AF_INET transport providers without knowing the particular transport provider.