POSIX-layer data structures

There are three data structures that relate to the POSIX-layer support routines. As far as the base layer is concerned, you can use any data structures you want; it's the POSIX layer that requires you to conform to a certain content and layout. The benefits delivered by the POSIX layer are well worth this tiny constraint. As we'll see later, you can add your own content to the structures as well.

The three data structures are illustrated in the following diagram, showing some clients using a resource manager that happens to manifest two devices:

The data structures (defined in <sys/iofunc.h>) are:

iofunc_ocb_t

Open Control Block structure: used to track client access to a particular service offered by a resource manager. This information is typically on a per-open basis.

iofunc_attr_t

Attributes structure: contains information on a per-resource basis

iofunc_mount_t

Mount structure: contains information on a per-mountpoint basis

When we talked about the I/O and connect tables, you saw the OCB and attributes structures—in the I/O tables, the OCB structure was the last parameter passed. The attributes structure was passed as the handle in the connect table functions (third argument). The mount structure is usually a global structure and is bound to the attributes structure by hand (in the initialization code that you supply for your resource manager).