aedrix-kernel/kernel/frames.c

/*
    Copyright (C) 2012, Aaron Lindsay <aaron@aclindsay.com>

    This file is part of Aedrix.

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License along
    with this program; if not, write to the Free Software Foundation, Inc.,
    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include <list.h>
#include <frames.h>
#include <print.h>
#include <types.h>

struct dlist_node free_frames_list;

void frames_init() {
	init_list(&free_frames_list);
}

/*
 * Adds a page frame struct to the list of free page frames. Presupposes
 * free_frames_list is a properly initialized list.
 */
static void insert_page_frame(struct frame *p) {
	if (list_empty(&free_frames_list) || p->address < container(free_frames_list.next, struct frame, list)->address) {
		insert_after(&free_frames_list, &p->list);
	} else if (p->address > container(free_frames_list.prev, struct frame, list)->address) {
		insert_before(&free_frames_list, &p->list);
	} else {
		struct frame *it;
		for_each_list(it, &free_frames_list, struct frame, list) {
			if (p->address < it->address) {
				insert_before(&it->list, &p->list);
				return;
			}
		}
		print("Error: failed to insert page frame\n");
	}
}

/*
 * Called to add a segment of memory to the frame allocation pool.
 */
static void add_physical_memory(void *start, void *end) {
	unsigned int num_pages, usable_pages;
	struct frame *p;
	void *page;

	//If region starts at 0x0, make it start at next page to not screw up null pointer detection, etc.
	if (start == 0)
		start = (char *)start + MM_PAGE_SIZE;

	//make sure both start and end address are aligned to the size of a page
	if ((arch_uint_ptr)start % MM_PAGE_SIZE != 0)
		start = (char*)start + (MM_PAGE_SIZE - ((arch_uint_ptr)start % MM_PAGE_SIZE));
	if (((arch_uint_ptr)end + 1) % MM_PAGE_SIZE != 0)
		end = (char*)end - ((arch_uint_ptr)end + 1) % MM_PAGE_SIZE;

	if ((char *)end + 1 - (char *)start < MM_PAGE_SIZE<<1) {
		print("Error: Supplied memory area(%x,%x) is smaller than the page size (%d)\n", (arch_uint_ptr)start, (arch_uint_ptr)end, MM_PAGE_SIZE);
		return;
	}

	//reserve enough pages at the front of this chunk of memory to hold the
	//page structs, then build the structs and add them to the list

	//TODO we're potentially losing memory here because we're calculating
	//the number of page structs we need even for those pages that will contain only page structs
	num_pages = ((char *)end + 1 - (char *)start) / MM_PAGE_SIZE;
	usable_pages = num_pages - num_pages * sizeof(struct frame) / MM_PAGE_SIZE;
	if (num_pages * sizeof(struct frame) % MM_PAGE_SIZE)
		usable_pages--;

	p = (struct frame *)start;
	for (page = ((char *)start) + (num_pages - usable_pages)*MM_PAGE_SIZE; page < end; page = (void *)(((char *)page) + MM_PAGE_SIZE)) {
		p->address = page;
		insert_page_frame(p);
		p++;
	}
}

/*
 * Attempt to get 2^power contiguous page frames. Returns the frame struct of
 * the first frame on success or a null pointer on failure.
 */
struct frame* get_free_frames(unsigned int power) {
	unsigned int num_pages = 1<<power;
	struct frame *it;

	if (list_empty(&free_frames_list)) {
		print("Error: Out of memory\n");
		return (struct frame*)0;
	}

	if (!num_pages) {
		print("Error: mm_get_free_pages must be called with power from 0 to 31, inclusive (power=%d)\n", power);
		return (struct frame*)0;
	}

	for_each_list(it, &free_frames_list, struct frame, list) {
		unsigned int curr_pages = 1;
		struct frame *it2;
		for (it2 = container(it->list.next, struct frame, list);
					it2->list.next != &free_frames_list && curr_pages < num_pages;
					it2 = container(it2->list.next, struct frame, list)) {
			if ((char*)it2->address != (char*)container(it2->list.prev, struct frame, list)->address + MM_PAGE_SIZE) {
				it = it2; //fast-forward 'it' to start of next contiguous section of pages
				break;
			} else {
				curr_pages++;
			}
		}
		if (curr_pages == num_pages) {
			remove_splice(&it->list, it2->list.prev);
			return it;
		}
	}
	return (struct frame*)0;
}

/*
 * Return pages allocated to the pool of unused pages.
 */
int put_free_frames(struct frame *f) {
	struct frame *it;
	for_each_list(it, &free_frames_list, struct frame, list) {
		if (f->address < it->address) {
			insert_splice_before(&it->list, &f->list, f->list.prev);
			return 0;
		}
	}
	return 1;
}