C equivalent of IOMemoryDescriptor class

I'm writing some C code using IOKit, and need to use IOMemoryDescriptor methods. Unfortunately, I can only compile pure C sources, and that is a C++ class. So, I'm asking if there is some C interface that lets me perform the same operations.

Specifically, I want a function that does pretty much this, but that can be compiled as C:

#include <IOKit/IOMemoryDescriptor.h>
extern "C" void CopyOut(mach_vm_address_t src, void *dst, size_t size)
{
    IOMemoryDescriptor *memDesc;
    memDesc = IOMemoryDescriptor::withAddressRange(src, size, kIODirectionOut, current_task());
    // Error checking removed for brevity
    memDesc->prepare();
    memDesc->readBytes(0, dst, size);
    memDesc->complete();
    memDesc->release();
}

Solution

Being based on BSD, xnu has inherited some of BSD's kernel APIs, including the copyin and copyout functions. They are declared in libkern.h, and they do pretty much what you're using an IOMemoryDescriptor for, but nothing else.

You do mention you're using IOKit - if you need anything beyond this out of IOKit's functionality, you'll pretty much have to go with a C++ compiler, or use C to call mangled names directly.

If you're new to using a weird compiler for building kexts, I'll just warn you that kernel code for x86_64 must not use the red zone of the stack, as that can't exist due to interrupt handling. If your compiler assumes a red zone is present, you'll get bizarre crashes. Clang and gcc have corresponding flags for disabling the red zone. (-mno-red-zone, if I remember correctly, automatically activated via the kernel mode flag) Even if you're using a non-official compiler, linking against an object file built with clang's C++ compiler at the last stage should work fine for wrapping any other C++ APIs.