Supported KPIs

Q:  How do I tell whether a kernel function is part of a supported KPI?

A: How do I tell whether a kernel function is part of a supported KPI?

There are two basic criteria:

• Does the function appear in the Kernel framework headers?

• Is the function exported by one of the supported KPI symbol sets?

Checking the first criterion is easy: use your favorite text search tool to see if the function is declared in the Kernel framework headers.

There are two ways to check the second criterion.

• If you have already built a KEXT, you can use the kextlibs tool to determine the KPI symbol sets that it requires. See the man page for more details.

• If you haven't yet built a KEXT, you can use the FindKPI.py script to determine the KPI symbol set, if any, for a given symbol. Listing 1 shows an example of this.

Listing 1  Using FindKPI.py

$ ./FindKPI.py vnode_create lck_mtx_lock
vnode_create com.apple.kpi.bsd
lck_mtx_lock com.apple.kpi.libkern
$ # You can also supply C++ class names.
$ ./FindKPI.py OSDictionary IOMemoryDescriptor
OSDictionary com.apple.kpi.libkern
IOMemoryDescriptor com.apple.kpi.iokit

Of course, there are exceptions to every rule. For example:

• The header <sys/appleapiopts.h> defines a set of compile-time variables that are used to indicate the stability of a particular interface. Some of these—specifically __APPLE_API_EVOLVING, __APPLE_API_UNSTABLE, __APPLE_API_PRIVATE and __APPLE_API_OBSOLETE—are used to guard KPIs that are not 100% stable. You should try to avoid such KPIs where possible.

  To check whether you depend on such KPIs, define the compile-time variable __APPLE_API_STRICT_CONFORMANCE.

• Technical Q&A QA1574, 'Kernel's MAC framework' documents a bug that might mislead you into thinking that the kernel's MAC framework is a supported KPI.

• The com.apple.kpi.unsupported KPI is a compatibility measure intended for use by a limited number of Apple KEXTs. Your KEXT should not depend on this unsupported functionality.

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