Subversion Repositories HelenOS

/*

 * Copyright (c) 2008 Jakub Jermar

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 * - Redistributions of source code must retain the above copyright

 *   notice, this list of conditions and the following disclaimer.

 * - Redistributions in binary form must reproduce the above copyright

 *   notice, this list of conditions and the following disclaimer in the

 *   documentation and/or other materials provided with the distribution.

 * - The name of the author may not be used to endorse or promote products

 *   derived from this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

/** @addtogroup fs

 * @{

 */ 

/**

 * @file	fat_idx.c

 * @brief	Layer for translating FAT entities to VFS node indices.

 */

#include "fat.h"

#include "../../vfs/vfs.h"

#include <errno.h>

#include <string.h>

#include <libadt/hash_table.h>

#include <libadt/list.h>

#include <assert.h>

#include <futex.h>

/** Each instance of this type describes one interval of freed VFS indices. */

typedef struct {

	link_t		link;

	fs_index_t	first;

	fs_index_t	last;

} freed_t;

/**

 * Each instance of this type describes state of all VFS indices that

 * are currently unused.

 */

typedef struct {

	link_t		link;

	dev_handle_t	dev_handle;

	/** Next unassigned index. */

	fs_index_t	next;

	/** Number of remaining unassigned indices. */

	uint64_t	remaining;

	/** Sorted list of intervals of freed indices. */

	link_t		freed_head;

} unused_t;

static LIST_INITIALIZE(unused_head);

/** Allocate a VFS index which is not currently in use. */

static bool fat_idx_alloc(dev_handle_t dev_handle, fs_index_t *index)

{

	link_t *l;

	unused_t *u;

	assert(index);

	for (l = unused_head.next; l != &unused_head; l = l->next) {

		u = list_get_instance(l, unused_t, link);

		if (u->dev_handle == dev_handle) 

			goto hit;

	}

	/* dev_handle not found */

	return false;	

hit:

	if (list_empty(&u->freed_head)) {

		if (u->remaining) { 

			/*

			 * There are no freed indices, allocate one directly

			 * from the counter.

			 */

			*index = u->next++;

			--u->remaining;

			return true;

		}

	} else {

		/* There are some freed indices which we can reuse. */

		freed_t *f = list_get_instance(u->freed_head.next, freed_t,

		    link);

		*index = f->first;

		if (f->first++ == f->last) {

			/* Destroy the interval. */

			list_remove(&f->link);

			free(f);

		}

		return true;

	}

	/*

	 * We ran out of indices, which is extremely unlikely with FAT16, but

	 * theoretically still possible (e.g. too many open unlinked nodes or

	 * too many zero-sized nodes).

	 */

	return false;

}

/** If possible, merge two intervals of freed indices. */

static void try_merge_intervals(link_t *l, link_t *r, link_t *cur)

{

	freed_t *fl = list_get_instance(l, freed_t, link);

	freed_t *fr = list_get_instance(r, freed_t, link);

	if (fl->last + 1 == fr->first) {

		if (cur == l) {

			fl->last = fr->last;

			list_remove(r);

			free(r);

		} else {

			fr->first = fl->first;

			list_remove(l);

			free(l);

		}

	}

}

/** Free a VFS index, which is no longer in use. */

static void fat_idx_free(dev_handle_t dev_handle, fs_index_t index)

{

	link_t *l;

	unused_t *u;

	for (l = unused_head.next; l != &unused_head; l = l->next) {

		u = list_get_instance(l, unused_t, link);

		if (u->dev_handle == dev_handle)

			goto hit;

	}

	/* should not happen */

	assert(0);

hit:

	if (u->next == index + 1) {

		/* The index can be returned directly to the counter. */

		u->next--;

		u->remaining++;

		return;

	} else {

		/*

		 * The index must be returned either to an existing freed

		 * interval or a new interval must be created.

		 */

		link_t *lnk;

		freed_t *n;

		for (lnk = u->freed_head.next; lnk != &u->freed_head;

		    lnk = lnk->next) {

			freed_t *f = list_get_instance(lnk, freed_t, link);

			if (f->first == index + 1) {

				f->first--;

				if (lnk->prev != &u->freed_head)

					try_merge_intervals(lnk->prev, lnk,

					    lnk);

				return;

			}

			if (f->last == index - 1) {

				f->last++;

				if (lnk->next != &u->freed_head)

					try_merge_intervals(lnk, lnk->next,

					    lnk);

				return;

			}

			if (index > f->first) {

				n = malloc(sizeof(freed_t));

				/* TODO: sleep until allocation succeeds */

				assert(n);

				link_initialize(&n->link);

				n->first = index;

				n->last = index;

				list_insert_before(&n->link, lnk);

				return;

			}

		}

		/* The index will form the last interval. */

		n = malloc(sizeof(freed_t));

		/* TODO: sleep until allocation succeeds */

		assert(n);

		link_initialize(&n->link);

		n->first = index;

		n->last = index;

		list_append(&n->link, &u->freed_head);

	}

}

fat_idx_t *fat_idx_map(dev_handle_t dev_handle, fat_cluster_t pfc, unsigned pdi)

{

	return NULL;	/* TODO */

}