Overview¶

Central to these interfaces is a simple `result' structure reflecting an `item' plus its value (in a union with standard C language types as members). All `result' structures are automatically allocated and provided by the library.

By specifying an array of `items', these structures can be organized as a `stack', potentially yielding many results with a single function call. Thus, a `stack' can be viewed as a variable length record whose content and order is determined solely by the user.

As part of each interface there are two unique enumerators. The `noop' and `extra' items exist to hold user values. They are never set by the library, but the `extra' result will be zeroed with each library interaction.

The named_interface header file will be an essential document during user program development. There you will find available items, their return type (the `result' struct member name) and the source for such values. Additional enumerators and structures are also documented there.

Usage¶

The following would be a typical sequence of calls to these interfaces.

1. procps_new()
2. procps_get(), procps_select() or procps_reap()
3. procps_unref()

The get function is used to retrieve a `result' structure for a single `item'. Alternatively, a GET macro is available when only the return value is of interest.

The select function can retrieve multiple `result' structures in a single `stack'.

For unpredictable variable outcomes, the diskstats, slabinfo and stat interfaces export a reap function. It is used to retrieve multiple `stacks' each containing multiple `result' structures. Optionally, a user may choose to sort those results.

To exploit any `stack', and access individual `result' structures, a relative_enum is required as shown in the VAL macro defined in the header file. Such values could be hard coded as: 0 through numitems-1. However, this need is typically satisfied by creating your own enumerators corresponding to the order of the `items' array.

Caveats¶

The new, ref, unref, get and select functions are available in all five interfaces.

For the new and unref functions, the address of an info struct pointer must be supplied. With new it must have been initialized to NULL. With unref it will be reset to NULL if the reference count reaches zero.

In the case of the diskstats interface, a name parameter on the get and select functions identifies a disk or partition name

For the stat interface, a what parameter on the reap function identifies whether data for just CPUs or both CPUs and NUMA nodes is to be gathered.

When using the sort function, the parameters stacks and numstacked would normally be those returned in the `reaped' structure.

Functions Returning an `int'¶

An error will be indicated by a negative number that is always the inverse of some well known errno.h value.

Success is indicated by a zero return value. However, the ref and unref functions return the current info structure reference count.

Functions Returning an `address'¶

An error will be indicated by a NULL return pointer with the reason found in the formal errno value.

Success is indicated by a pointer to the named structure.