Please madvise re: buffer alignment

[dstuebe]

Trying to call madvise on a MappedByteBuffer via JNR-FFI.

According to the man page, both the pointer address and the size need to be page aligned but I am not sure how to do that using FFI? I can call long address = MemoryIO.getInstance().getDirectBufferAddress(buffer); but unsure how to use it in my interface to madvise how do I pass a long as a void pointer?

I can validate that my method fails if I hard code a negative size, but I am having a hard time parsing what FFI is doing to get the buffer address and whether it is already aligned the way I would do it in c?

[dstuebe]

It just works!

public interface NativeC {
    int madvise(@size_t long address, @size_t long size, int advice);
    int getpagesize();
}
...
long address = MemoryIO.getInstance().getDirectBufferAddress(buffer);
long alignedAddress = alignedAddress(address);
long alignedSize = alignedSize(alignedAddress, buffer.capacity());
int val = nativeC.madvise(alignedAddress, alignedSize, advice.value);

Will comment and close - thank you for this!