void *MMU::palloc(size_t numberOfPages)
{
size_t contiguousFoundPages = 0;
size_t retpde = 0, retpte = 0;
void *retval = nullptr;
for (size_t pde = 0; pde < 1024 && contiguousFoundPages != numberOfPages; ++pde) {
PageTable table = getOrCreateTable(pde);
// look through page table
for (size_t pte = 0; pte < 1024; ++pte) {
PageEntry entry = table.entryAtIndex(pte);
if (!entry.getFlag(kPresentBit)) { // found a page that isn't present (is available)
if (contiguousFoundPages == 0) { // this is the first available page, set our return pointer to it
retpde = pde;
retpte = pte;
}
++contiguousFoundPages;
if (contiguousFoundPages == numberOfPages) { // done
retval = (void *) ((retpde << 22) | (retpte << 12));
break;
}
} else if (contiguousFoundPages) { // current page is used, reset our contiguous page count
retval = nullptr;
contiguousFoundPages = 0;
}
}
}
if (retval) { // if we succeeded in finding space
allocatePages(retval, numberOfPages);
}
return retval;
}
int MMU::pfree(void *startOfMemoryRange, size_t numberOfPages)
{
uint32_t virtualAddress = (uint32_t) startOfMemoryRange;
if (!numberOfPages) return -1;
while (numberOfPages--) {
uint32_t pdeIndex = virtualAddress >> 22;
uint32_t pteIndex = virtualAddress >> 12 & 0x03FF;
PageTable table = PageTableForDirectoryIndex(pdeIndex);
PageEntry pte = table.entryAtIndex(pteIndex);
_pageFrameAllocator.free(pte.address());
table.setEntry(pteIndex, PageEntry(0));
virtualAddress += 0x1000;
}
_flush();
return 0;
}
