One of the most common problems faced when programming in the kernel
is use of “standard” functions—things like printf or bcopy. Many
commonly used standard C library functions are implemented in the
kernel. In order to use them, however, you need to include the
appropriate prototypes, which may be different from the user space
prototypes for those functions, and which generally have different
names when included from kernel code.
In general, any non–I/O Kit header that you can safely include in the
kernel is located in xnu/bsd/sys or xnu/osfmk/mach, although there
are a few specialized headers in other places like libkern and libsa.
Normal headers (those in /usr/include) cannot be used in the kernel
(or rather, cannot be used 'properly').
If the standard C function you are trying to use is not in one of the
following files, chances are the function is not supported for use
within the kernel, and you need to implement your code in another way:
<sys/systm.h> (printf can be used with this)
<sys/buf.h> (buffer cache functions like bread)
<sys/dirent.h> (directory entries)
<sys/errno.h> (Error numbers)
<sys.kernel.h> (kernel special variables)
<sys/lock.h> (spinlocks)
<sys/malloc.h> (malloc)
<sys/queue.h> (queues)
<sys/rand.h> (random generation numbers)
<sys/systm.h> (bzero, bcopy.. etc)
<sys/system.h> (timeout, untimeout)
<sys/time.h> (time functions)
<sys/types.h> <mach/mach_types.h> (standard type declarations)
<sys/ucred.h> (user credentials)
<sys/utsname.h> (os and system information)
For developing kernel extensions, surely it is better to be guided by
the header files that are in Kernel.framework in the SDK which are
also the ones that should be used - at least they are the ones that
XCode uses when it creates a new kext project.
"I know that fewer people are won over by the written word than by the spoken word and that every great movement on this earth owes its growth to great speakers and not to great writers."
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