File systems
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.
- Integrated sockets PFS
- The integrated sockets PFS can support the AF_INET PFS alone or AF_INET and AF_INET6 PFS together, but not AF_INET6 PFS alone.
- Common INET PFS
- This configuration is commonly referred to as the C_INET PFS configuration.
It enables multiple AF_INET and AF_INET6 transport providers to be
configured and active concurrently. Applications using the z/OS UNIX APIs do not know that multiple transport providers exist.
For example, multiple TCP/IP Services components of z/OS Communications Server can be configured
at the same time. The C_INET PFS is responsible for selecting the
PFS over which to flow the request, based on the IP routing information
from each of the AF_INET providers.
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.