#include <k/mem.h>
#include <k/core.h>
#include <k/def.h>
#include <k/type.h>
/* heapa.c - kmheapa() "heap alloc"
 * ~ lexi hale <lexi@hale.su>
 * kmheapa() allocates a pointer on the heap à la libc malloc()
 * see also: kmheapf() "heap free"
 */

/* arch specific headers */
#ifdef KFenv_posix
#	include <posix/posix.h>
#endif

#include <error_table.h>

/* we define all our platform functions here, whether or not
 * they're for the correct platform - only the ones that are
 * called by the preprocessed form of the code will actually
 * be linked, linker errors are our friend here! */

kmcond kmheapa(void** where, sz len) {
	/* allocate an object on the heap and return
	 * a pointer, or NULL if the allocation failed. */
	union {
		void* raw;
		ubyte* byte;
		kmbox* header;
	} region;
	/* we need to allocate space for the
	 * header and for the actual object */
	sz region_size = sizeof(kmbox) + len;

#	ifdef KFenv_posix
		/* posix  APIs  - we've  got  it  easy. currently  for
		 * nonlinear  heap  allocation   kmheapa  simply  uses
		 * m(un)map  and lets  the kernel  worry about  it. it
		 * may  ultimately  be  worth replacing  this  with  a
		 * more sophisticated  implementation, most  likely an
		 * existing allocator  like jemalloc, though  i'm wary
		 * of including outside code  - it creates a licensing
		 * mess and  i'd prefer libk  to be AGPLv3  across the
		 * board.  possibility:  include  hooks  for  multiple
		 * allocators, allowing  the user to select  & link in
		 * her preferred allocator at compile time? */

		/* because munmap needs to be informed of the size of
		 * the region we are going to unmap, we need to store
		 * that information in the region that we are mapping.
		 * the user will receive an adjusted pointer that can
		 * be adjusted to point a field of type size_t that
		 * contains the size of the allocated space.*/

		k_platform_syscall_arg args[] = {
			null, region_size, 
			posix_prot_read | posix_prot_write,
			posix_flag_anonymous | posix_map_shared,
			-1, 0
		};

		/* impl note: while per manpage fd is "ignored"
		 * for MAP_ANONYMOUS, "some implementations" require
		 * a value of -1 */

		struct k_platform_syscall_answer r = k_platform_syscall
			(k_platform_syscall_mmap, Kmsz(args), args);

		if (r.error == 0) region.byte = (ubyte*)r.ret; else {
			switch (r.error) {
				case k_platform_error_EAGAIN: return kmcond_bad_lock;
				case k_platform_error_EINVAL: return kmcond_bad_size;
				case k_platform_error_EMFILE: return kmcond_too_many;
				case k_platform_error_ENOMEM: return kmcond_no_room;
				default: return kmcond_fail_assert;
			}
		}
#	else
 	   Knoimpl(kmheapa,KVos);
#		error missing implementation
#	endif
	
	void* const object = (region.byte + sizeof (kmbox));

	region.header -> kind = kmkind_heap;
	region.header -> size = len;

	*where = object;
	return kmcond_ok;
}