hos/mm.c

// mm.c
// 09/01/03 Josh Holtrop

// 0x368000 is first available byte (this is right after the kernel @ 1mb and the initrd @ 2mb, 1440kb.


pageblock *first_pageblock = (pageblock *) 0;
dword	mm_totalmem = 0x100000;				//assume 1mb

void	mm_init()
{
	dword	*memmap_entries = (dword *) 0x9040A;
	memmap_entry	*maps = (memmap_entry *) 0x92000;
	dword a;
	for (a=0;a<(*memmap_entries);a++)
	{
		if (maps[a].attributes == 1)		// (1) mem free to OS
		{
			mm_totalmem += maps[a].limit.lowdword;
			if  ((maps[a].base.lowdword + maps[a].limit.lowdword) > (FREERAM_START+8192))	//goes past where we start freeram
			{
				if (maps[a].base.lowdword < FREERAM_START)
				{
					maps[a].limit.lowdword = maps[a].limit.lowdword - (FREERAM_START - maps[a].base.lowdword);
					maps[a].base.lowdword = FREERAM_START;	//block at least 4kb, starts >= FREERAM_START
				}
				if (first_pageblock == 0)	//no pageblock page set up yet, so set it up here
				{
					first_pageblock = (pageblock *) maps[a].base.lowdword        ;
					maps[a].base.lowdword += 4096;
					maps[a].limit.lowdword -= 4096;
					mm_init_pageblockpage(first_pageblock);
					first_pageblock->base = maps[a].base.lowdword;
					first_pageblock->length = maps[a].limit.lowdword / 4096;
					first_pageblock->flags = MM_PB_AVAIL;
				}
				else				//first_pageblock already set up, add on segment
				{
					pageblock *pb = first_pageblock;
					for (;;)
					{
						if (pb->flags == MM_PB_NP)
							break;
						else
							pb++;
					}
					pb->base = maps[a].base.lowdword;
					pb->length = maps[a].limit.lowdword / 4096;
					pb->flags = MM_PB_AVAIL;
				}
			}
		}
	}
	if (first_pageblock == 0)
	{
		printf("ERROR! NO INITIAL PAGE BLOCK COULD BE CREATED.");
		asm("cli");
		asm("hlt");
	}
}




void	mm_init_pageblockpage(pageblock *pbp)
{
	pageblock *pb = pbp;
	int a;
	for (a=0; a<512; a++)
	{
		pb->base = 0;
		pb->length = 0;
		pb->flags = MM_PB_NP;
		if (a<511)
			pb->link = (dword)pb + sizeof(pageblock);
		else
			pb->link = 0;
		pb++;
	}
}


void   *mm_palloc(dword numpages)
{
	pageblock *pb = first_pageblock;
	dword freeentries = mm_freeentries();
	if (freeentries < 2)
	{
		if(mm_new_pageblock_page() == 0)
			return 0;
	}
	pageblock *newentry = mm_nextpageblockentry();
	for (;;)
	{
		if ((pb->flags == MM_PB_AVAIL) && (pb->length >= numpages))
			break;
		if (pb->link == 0)
			return 0;
		pb = (pageblock *)pb->link;
	}
	if (pb->length == numpages)		//dont need a new entry, just mark this one as used :)
	{
		pb->flags = MM_PB_USED;
		return pb;
	}
	else					//subtract out allocated number of pages from length
	{
		newentry->base = pb->base;
		newentry->length = numpages;
		newentry->flags = MM_PB_USED;
		pb->base += (numpages * 4096);
		pb->length -= numpages;
		return (void *)newentry->base;
	}
}


dword	mm_freeentries()
{
	pageblock *pb = first_pageblock;
	dword counter = 0;
	for (;;)
	{
		if (pb->flags == MM_PB_NP)
			counter++;
		if (pb->link == 0)
			return counter;
		pb = (pageblock *) pb->link;
	}
}


pageblock *mm_new_pageblock_page()
{
	pageblock *pb = first_pageblock;
	for (;;)
	{
		if ((pb->flags == MM_PB_AVAIL) && (pb->length > 1))
		{
			pageblock *retval = (pageblock *)pb->base;
			pb->base += 4096;
			pb->length--;
			mm_init_pageblockpage(retval);			//zeros out, links new pageblock page
			mm_lastpageblockentry()->link = (dword)retval;	//set up link to new pageblock page
			return retval;
		}
		pb = (pageblock *) pb->link;
		if (pb == 0)
			return 0;
	}
}


int	mm_pfree(void *ptr)
{
	pageblock *pb = first_pageblock;
	dword tofree = (dword) ptr;
	for (;;)
	{
		if ((pb->base == tofree) && (pb->flags == MM_PB_USED))
		{
			pb->flags = MM_PB_AVAIL;		//found block, mark available / coalesce it
			pageblock *pbc = first_pageblock;
			for (;;)
			{
			    	if (pbc->flags == MM_PB_AVAIL)
			    	{
			    		if ((pbc->base + (pbc->length * 4096)) == pb->base)	//pbc ends where pb starts
					{
						pbc->length += pb->length;	//extend pbc's length by pb's length
						pb->flags = MM_PB_NP;		//mark pb as an unused entry
						return 0;
					}
					if ((pb->base + (pb->length * 4096)) == pbc->base)	//pb ends where pb starts
					{
						pb->length += pbc->length;
						pbc->flags = MM_PB_NP;
						return 0;
					}
				 }
				if (pbc->link == 0)			//no entry found to consolidate...
					return 0;
				pbc = (pageblock *) pbc->link;		//next entry to test
			}
		}
		if (pb->link == 0)
			return 1;
		pb = (pageblock *) pb->link;
	}
}


pageblock *mm_lastpageblockentry()
{
	pageblock *pb = first_pageblock;
	for (;;)
	{
		if (pb->link == 0)
			return pb;
		pb = (pageblock *)pb->link;
	}
}


pageblock *mm_nextpageblockentry()
{
	pageblock *pb = first_pageblock;
	for (;;)
	{
		if (pb->flags == MM_PB_NP)
			return pb;
		if (pb->link == 0)
			return 0;
		pb = (pageblock *)pb->link;
	}
}


dword mm_freemem()
{
	dword amount = 0;
	pageblock *pb = first_pageblock;
	for (;;)
	{
		if (pb->flags == MM_PB_AVAIL)
			amount += (pb->length)*4096;
		if (pb->link == 0)
			return amount;
		pb = (pageblock *) pb->link;
	}
}