/*
   * This file is part of UBIFS.
   *
   * Copyright (C) 2006-2008 Nokia Corporation.
   *
   * This program is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 as published by
   * the Free Software Foundation.
   *
   * 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 St, Fifth Floor, Boston, MA 02110-1301 USA
   *
   * Authors: Adrian Hunter
   *          Artem Bityutskiy (Битюцкий Артём)
   */
  
  /*
   * This file implements the budgeting sub-system which is responsible for UBIFS
   * space management.
   *
   * Factors such as compression, wasted space at the ends of LEBs, space in other
   * journal heads, the effect of updates on the index, and so on, make it
   * impossible to accurately predict the amount of space needed. Consequently
   * approximations are used.
   */
  
  #include "ubifs.h"
  #include <linux/writeback.h>

  #include <linux/math64.h>

  
  /*
   * When pessimistic budget calculations say that there is no enough space,
   * UBIFS starts writing back dirty inodes and pages, doing garbage collection,

   * or committing. The below constant defines maximum number of times UBIFS

   * repeats the operations.
   */

  #define MAX_MKSPC_RETRIES 3

  
  /*
   * The below constant defines amount of dirty pages which should be written
   * back at when trying to shrink the liability.
   */
  #define NR_TO_WRITE 16
  
  /**

   * shrink_liability - write-back some dirty pages/inodes.
   * @c: UBIFS file-system description object
   * @nr_to_write: how many dirty pages to write-back
   *
   * This function shrinks UBIFS liability by means of writing back some amount

   * of dirty inodes and their pages.

   *
   * Note, this function synchronizes even VFS inodes which are locked
   * (@i_mutex) by the caller of the budgeting function, because write-back does
   * not touch @i_mutex.
   */

  static void shrink_liability(struct ubifs_info *c, int nr_to_write)

  {

  	down_read(&c->vfs_sb->s_umount);

  	writeback_inodes_sb(c->vfs_sb, WB_REASON_FS_FREE_SPACE);

  	up_read(&c->vfs_sb->s_umount);

  }

  /**
   * run_gc - run garbage collector.
   * @c: UBIFS file-system description object
   *
   * This function runs garbage collector to make some more free space. Returns
   * zero if a free LEB has been produced, %-EAGAIN if commit is required, and a
   * negative error code in case of failure.
   */
  static int run_gc(struct ubifs_info *c)
  {
  	int err, lnum;
  
  	/* Make some free space by garbage-collecting dirty space */
  	down_read(&c->commit_sem);
  	lnum = ubifs_garbage_collect(c, 1);
  	up_read(&c->commit_sem);
  	if (lnum < 0)
  		return lnum;
  
  	/* GC freed one LEB, return it to lprops */
  	dbg_budg("GC freed LEB %d", lnum);
  	err = ubifs_return_leb(c, lnum);
  	if (err)
  		return err;
  	return 0;
  }
  
  /**

   * get_liability - calculate current liability.
   * @c: UBIFS file-system description object
   *
   * This function calculates and returns current UBIFS liability, i.e. the
   * amount of bytes UBIFS has "promised" to write to the media.
   */
  static long long get_liability(struct ubifs_info *c)
  {
  	long long liab;
  
  	spin_lock(&c->space_lock);

  	liab = c->bi.idx_growth + c->bi.data_growth + c->bi.dd_growth;

  	spin_unlock(&c->space_lock);
  	return liab;
  }
  
  /**

   * make_free_space - make more free space on the file-system.
   * @c: UBIFS file-system description object

   *
   * This function is called when an operation cannot be budgeted because there
   * is supposedly no free space. But in most cases there is some free space:

   *   o budgeting is pessimistic, so it always budgets more than it is actually

   *     needed, so shrinking the liability is one way to make free space - the
   *     cached data will take less space then it was budgeted for;
   *   o GC may turn some dark space into free space (budgeting treats dark space
   *     as not available);
   *   o commit may free some LEB, i.e., turn freeable LEBs into free LEBs.
   *
   * So this function tries to do the above. Returns %-EAGAIN if some free space
   * was presumably made and the caller has to re-try budgeting the operation.
   * Returns %-ENOSPC if it couldn't do more free space, and other negative error
   * codes on failures.
   */

  static int make_free_space(struct ubifs_info *c)

  {

  	int err, retries = 0;
  	long long liab1, liab2;

  	do {
  		liab1 = get_liability(c);
  		/*
  		 * We probably have some dirty pages or inodes (liability), try
  		 * to write them back.
  		 */
  		dbg_budg("liability %lld, run write-back", liab1);
  		shrink_liability(c, NR_TO_WRITE);

  		liab2 = get_liability(c);
  		if (liab2 < liab1)
  			return -EAGAIN;

  		dbg_budg("new liability %lld (not shrunk)", liab2);

  		/* Liability did not shrink again, try GC */
  		dbg_budg("Run GC");

  		err = run_gc(c);
  		if (!err)
  			return -EAGAIN;

  		if (err != -EAGAIN && err != -ENOSPC)
  			/* Some real error happened */

  			return err;

  		dbg_budg("Run commit (retries %d)", retries);

  		err = ubifs_run_commit(c);
  		if (err)
  			return err;

  	} while (retries++ < MAX_MKSPC_RETRIES);

  	return -ENOSPC;
  }
  
  /**

   * ubifs_calc_min_idx_lebs - calculate amount of LEBs for the index.

   * @c: UBIFS file-system description object
   *

   * This function calculates and returns the number of LEBs which should be kept
   * for index usage.

   */
  int ubifs_calc_min_idx_lebs(struct ubifs_info *c)
  {

  	int idx_lebs;

  	long long idx_size;

  	idx_size = c->bi.old_idx_sz + c->bi.idx_growth + c->bi.uncommitted_idx;

  	/* And make sure we have thrice the index size of space reserved */

  	idx_size += idx_size << 1;

  	/*
  	 * We do not maintain 'old_idx_size' as 'old_idx_lebs'/'old_idx_bytes'
  	 * pair, nor similarly the two variables for the new index size, so we
  	 * have to do this costly 64-bit division on fast-path.
  	 */

  	idx_lebs = div_u64(idx_size + c->idx_leb_size - 1, c->idx_leb_size);

  	/*
  	 * The index head is not available for the in-the-gaps method, so add an
  	 * extra LEB to compensate.
  	 */

  	idx_lebs += 1;
  	if (idx_lebs < MIN_INDEX_LEBS)
  		idx_lebs = MIN_INDEX_LEBS;
  	return idx_lebs;

  }
  
  /**
   * ubifs_calc_available - calculate available FS space.
   * @c: UBIFS file-system description object
   * @min_idx_lebs: minimum number of LEBs reserved for the index
   *
   * This function calculates and returns amount of FS space available for use.
   */
  long long ubifs_calc_available(const struct ubifs_info *c, int min_idx_lebs)
  {
  	int subtract_lebs;
  	long long available;

  	available = c->main_bytes - c->lst.total_used;
  
  	/*
  	 * Now 'available' contains theoretically available flash space
  	 * assuming there is no index, so we have to subtract the space which
  	 * is reserved for the index.
  	 */
  	subtract_lebs = min_idx_lebs;
  
  	/* Take into account that GC reserves one LEB for its own needs */
  	subtract_lebs += 1;
  
  	/*
  	 * The GC journal head LEB is not really accessible. And since
  	 * different write types go to different heads, we may count only on
  	 * one head's space.
  	 */
  	subtract_lebs += c->jhead_cnt - 1;
  
  	/* We also reserve one LEB for deletions, which bypass budgeting */
  	subtract_lebs += 1;
  
  	available -= (long long)subtract_lebs * c->leb_size;
  
  	/* Subtract the dead space which is not available for use */
  	available -= c->lst.total_dead;
  
  	/*
  	 * Subtract dark space, which might or might not be usable - it depends
  	 * on the data which we have on the media and which will be written. If
  	 * this is a lot of uncompressed or not-compressible data, the dark
  	 * space cannot be used.
  	 */
  	available -= c->lst.total_dark;
  
  	/*
  	 * However, there is more dark space. The index may be bigger than
  	 * @min_idx_lebs. Those extra LEBs are assumed to be available, but
  	 * their dark space is not included in total_dark, so it is subtracted
  	 * here.
  	 */
  	if (c->lst.idx_lebs > min_idx_lebs) {
  		subtract_lebs = c->lst.idx_lebs - min_idx_lebs;
  		available -= subtract_lebs * c->dark_wm;
  	}
  
  	/* The calculations are rough and may end up with a negative number */
  	return available > 0 ? available : 0;
  }
  
  /**
   * can_use_rp - check whether the user is allowed to use reserved pool.
   * @c: UBIFS file-system description object
   *
   * UBIFS has so-called "reserved pool" which is flash space reserved
   * for the superuser and for uses whose UID/GID is recorded in UBIFS superblock.
   * This function checks whether current user is allowed to use reserved pool.
   * Returns %1  current user is allowed to use reserved pool and %0 otherwise.
   */
  static int can_use_rp(struct ubifs_info *c)
  {

  	if (current_fsuid() == c->rp_uid || capable(CAP_SYS_RESOURCE) ||

  	    (c->rp_gid != 0 && in_group_p(c->rp_gid)))
  		return 1;
  	return 0;
  }
  
  /**
   * do_budget_space - reserve flash space for index and data growth.
   * @c: UBIFS file-system description object
   *

   * This function makes sure UBIFS has enough free LEBs for index growth and
   * data.

   *

   * When budgeting index space, UBIFS reserves thrice as many LEBs as the index

   * would take if it was consolidated and written to the flash. This guarantees
   * that the "in-the-gaps" commit method always succeeds and UBIFS will always
   * be able to commit dirty index. So this function basically adds amount of

   * budgeted index space to the size of the current index, multiplies this by 3,

   * and makes sure this does not exceed the amount of free LEBs.

   *

   * Notes about @c->bi.min_idx_lebs and @c->lst.idx_lebs variables:

   * o @c->lst.idx_lebs is the number of LEBs the index currently uses. It might
   *    be large, because UBIFS does not do any index consolidation as long as
   *    there is free space. IOW, the index may take a lot of LEBs, but the LEBs
   *    will contain a lot of dirt.

   * o @c->bi.min_idx_lebs is the number of LEBS the index presumably takes. IOW,
   *    the index may be consolidated to take up to @c->bi.min_idx_lebs LEBs.

   *
   * This function returns zero in case of success, and %-ENOSPC in case of
   * failure.
   */
  static int do_budget_space(struct ubifs_info *c)
  {
  	long long outstanding, available;
  	int lebs, rsvd_idx_lebs, min_idx_lebs;
  
  	/* First budget index space */
  	min_idx_lebs = ubifs_calc_min_idx_lebs(c);
  
  	/* Now 'min_idx_lebs' contains number of LEBs to reserve */
  	if (min_idx_lebs > c->lst.idx_lebs)
  		rsvd_idx_lebs = min_idx_lebs - c->lst.idx_lebs;
  	else
  		rsvd_idx_lebs = 0;
  
  	/*
  	 * The number of LEBs that are available to be used by the index is:
  	 *
  	 *    @c->lst.empty_lebs + @c->freeable_cnt + @c->idx_gc_cnt -
  	 *    @c->lst.taken_empty_lebs
  	 *

  	 * @c->lst.empty_lebs are available because they are empty.
  	 * @c->freeable_cnt are available because they contain only free and
  	 * dirty space, @c->idx_gc_cnt are available because they are index
  	 * LEBs that have been garbage collected and are awaiting the commit
  	 * before they can be used. And the in-the-gaps method will grab these
  	 * if it needs them. @c->lst.taken_empty_lebs are empty LEBs that have
  	 * already been allocated for some purpose.

  	 *

  	 * Note, @c->idx_gc_cnt is included to both @c->lst.empty_lebs (because
  	 * these LEBs are empty) and to @c->lst.taken_empty_lebs (because they
  	 * are taken until after the commit).
  	 *
  	 * Note, @c->lst.taken_empty_lebs may temporarily be higher by one
  	 * because of the way we serialize LEB allocations and budgeting. See a
  	 * comment in 'ubifs_find_free_space()'.

  	 */
  	lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt -
  	       c->lst.taken_empty_lebs;
  	if (unlikely(rsvd_idx_lebs > lebs)) {
  		dbg_budg("out of indexing space: min_idx_lebs %d (old %d), "

  			 "rsvd_idx_lebs %d", min_idx_lebs, c->bi.min_idx_lebs,

  			 rsvd_idx_lebs);
  		return -ENOSPC;
  	}
  
  	available = ubifs_calc_available(c, min_idx_lebs);

  	outstanding = c->bi.data_growth + c->bi.dd_growth;

  
  	if (unlikely(available < outstanding)) {
  		dbg_budg("out of data space: available %lld, outstanding %lld",
  			 available, outstanding);
  		return -ENOSPC;
  	}
  
  	if (available - outstanding <= c->rp_size && !can_use_rp(c))
  		return -ENOSPC;

  	c->bi.min_idx_lebs = min_idx_lebs;

  	return 0;
  }
  
  /**
   * calc_idx_growth - calculate approximate index growth from budgeting request.
   * @c: UBIFS file-system description object
   * @req: budgeting request
   *
   * For now we assume each new node adds one znode. But this is rather poor
   * approximation, though.
   */
  static int calc_idx_growth(const struct ubifs_info *c,
  			   const struct ubifs_budget_req *req)
  {
  	int znodes;
  
  	znodes = req->new_ino + (req->new_page << UBIFS_BLOCKS_PER_PAGE_SHIFT) +
  		 req->new_dent;
  	return znodes * c->max_idx_node_sz;
  }
  
  /**
   * calc_data_growth - calculate approximate amount of new data from budgeting
   * request.
   * @c: UBIFS file-system description object
   * @req: budgeting request
   */
  static int calc_data_growth(const struct ubifs_info *c,
  			    const struct ubifs_budget_req *req)
  {
  	int data_growth;

  	data_growth = req->new_ino  ? c->bi.inode_budget : 0;

  	if (req->new_page)

  		data_growth += c->bi.page_budget;

  	if (req->new_dent)

  		data_growth += c->bi.dent_budget;

  	data_growth += req->new_ino_d;
  	return data_growth;
  }
  
  /**
   * calc_dd_growth - calculate approximate amount of data which makes other data
   * dirty from budgeting request.
   * @c: UBIFS file-system description object
   * @req: budgeting request
   */
  static int calc_dd_growth(const struct ubifs_info *c,
  			  const struct ubifs_budget_req *req)
  {
  	int dd_growth;

  	dd_growth = req->dirtied_page ? c->bi.page_budget : 0;

  
  	if (req->dirtied_ino)

  		dd_growth += c->bi.inode_budget << (req->dirtied_ino - 1);

  	if (req->mod_dent)

  		dd_growth += c->bi.dent_budget;

  	dd_growth += req->dirtied_ino_d;
  	return dd_growth;
  }
  
  /**
   * ubifs_budget_space - ensure there is enough space to complete an operation.
   * @c: UBIFS file-system description object
   * @req: budget request
   *
   * This function allocates budget for an operation. It uses pessimistic
   * approximation of how much flash space the operation needs. The goal of this
   * function is to make sure UBIFS always has flash space to flush all dirty
   * pages, dirty inodes, and dirty znodes (liability). This function may force
   * commit, garbage-collection or write-back. Returns zero in case of success,
   * %-ENOSPC if there is no free space and other negative error codes in case of
   * failures.
   */
  int ubifs_budget_space(struct ubifs_info *c, struct ubifs_budget_req *req)
  {
  	int uninitialized_var(cmt_retries), uninitialized_var(wb_retries);

  	int err, idx_growth, data_growth, dd_growth, retried = 0;

  	ubifs_assert(req->new_page <= 1);
  	ubifs_assert(req->dirtied_page <= 1);
  	ubifs_assert(req->new_dent <= 1);
  	ubifs_assert(req->mod_dent <= 1);
  	ubifs_assert(req->new_ino <= 1);
  	ubifs_assert(req->new_ino_d <= UBIFS_MAX_INO_DATA);

  	ubifs_assert(req->dirtied_ino <= 4);
  	ubifs_assert(req->dirtied_ino_d <= UBIFS_MAX_INO_DATA * 4);

  	ubifs_assert(!(req->new_ino_d & 7));
  	ubifs_assert(!(req->dirtied_ino_d & 7));

  
  	data_growth = calc_data_growth(c, req);
  	dd_growth = calc_dd_growth(c, req);
  	if (!data_growth && !dd_growth)
  		return 0;
  	idx_growth = calc_idx_growth(c, req);

  
  again:
  	spin_lock(&c->space_lock);

  	ubifs_assert(c->bi.idx_growth >= 0);
  	ubifs_assert(c->bi.data_growth >= 0);
  	ubifs_assert(c->bi.dd_growth >= 0);

  	if (unlikely(c->bi.nospace) && (c->bi.nospace_rp || !can_use_rp(c))) {

  		dbg_budg("no space");
  		spin_unlock(&c->space_lock);
  		return -ENOSPC;
  	}

  	c->bi.idx_growth += idx_growth;
  	c->bi.data_growth += data_growth;
  	c->bi.dd_growth += dd_growth;

  
  	err = do_budget_space(c);
  	if (likely(!err)) {
  		req->idx_growth = idx_growth;
  		req->data_growth = data_growth;
  		req->dd_growth = dd_growth;
  		spin_unlock(&c->space_lock);
  		return 0;
  	}
  
  	/* Restore the old values */

  	c->bi.idx_growth -= idx_growth;
  	c->bi.data_growth -= data_growth;
  	c->bi.dd_growth -= dd_growth;

  	spin_unlock(&c->space_lock);
  
  	if (req->fast) {
  		dbg_budg("no space for fast budgeting");
  		return err;
  	}

  	err = make_free_space(c);
  	cond_resched();

  	if (err == -EAGAIN) {
  		dbg_budg("try again");

  		goto again;
  	} else if (err == -ENOSPC) {

  		if (!retried) {
  			retried = 1;
  			dbg_budg("-ENOSPC, but anyway try once again");
  			goto again;
  		}

  		dbg_budg("FS is full, -ENOSPC");

  		c->bi.nospace = 1;

  		if (can_use_rp(c) || c->rp_size == 0)

  			c->bi.nospace_rp = 1;

  		smp_wmb();
  	} else
  		ubifs_err("cannot budget space, error %d", err);
  	return err;
  }
  
  /**
   * ubifs_release_budget - release budgeted free space.
   * @c: UBIFS file-system description object
   * @req: budget request
   *
   * This function releases the space budgeted by 'ubifs_budget_space()'. Note,
   * since the index changes (which were budgeted for in @req->idx_growth) will
   * only be written to the media on commit, this function moves the index budget

   * from @c->bi.idx_growth to @c->bi.uncommitted_idx. The latter will be zeroed
   * by the commit operation.

   */
  void ubifs_release_budget(struct ubifs_info *c, struct ubifs_budget_req *req)
  {

  	ubifs_assert(req->new_page <= 1);
  	ubifs_assert(req->dirtied_page <= 1);
  	ubifs_assert(req->new_dent <= 1);
  	ubifs_assert(req->mod_dent <= 1);
  	ubifs_assert(req->new_ino <= 1);
  	ubifs_assert(req->new_ino_d <= UBIFS_MAX_INO_DATA);

  	ubifs_assert(req->dirtied_ino <= 4);
  	ubifs_assert(req->dirtied_ino_d <= UBIFS_MAX_INO_DATA * 4);

  	ubifs_assert(!(req->new_ino_d & 7));
  	ubifs_assert(!(req->dirtied_ino_d & 7));

  	if (!req->recalculate) {
  		ubifs_assert(req->idx_growth >= 0);
  		ubifs_assert(req->data_growth >= 0);
  		ubifs_assert(req->dd_growth >= 0);
  	}
  
  	if (req->recalculate) {
  		req->data_growth = calc_data_growth(c, req);
  		req->dd_growth = calc_dd_growth(c, req);
  		req->idx_growth = calc_idx_growth(c, req);
  	}
  
  	if (!req->data_growth && !req->dd_growth)
  		return;

  	c->bi.nospace = c->bi.nospace_rp = 0;

  	smp_wmb();
  
  	spin_lock(&c->space_lock);

  	c->bi.idx_growth -= req->idx_growth;
  	c->bi.uncommitted_idx += req->idx_growth;
  	c->bi.data_growth -= req->data_growth;
  	c->bi.dd_growth -= req->dd_growth;
  	c->bi.min_idx_lebs = ubifs_calc_min_idx_lebs(c);
  
  	ubifs_assert(c->bi.idx_growth >= 0);
  	ubifs_assert(c->bi.data_growth >= 0);
  	ubifs_assert(c->bi.dd_growth >= 0);
  	ubifs_assert(c->bi.min_idx_lebs < c->main_lebs);
  	ubifs_assert(!(c->bi.idx_growth & 7));
  	ubifs_assert(!(c->bi.data_growth & 7));
  	ubifs_assert(!(c->bi.dd_growth & 7));

  	spin_unlock(&c->space_lock);
  }
  
  /**
   * ubifs_convert_page_budget - convert budget of a new page.
   * @c: UBIFS file-system description object
   *
   * This function converts budget which was allocated for a new page of data to

   * the budget of changing an existing page of data. The latter is smaller than

   * the former, so this function only does simple re-calculation and does not
   * involve any write-back.
   */
  void ubifs_convert_page_budget(struct ubifs_info *c)
  {
  	spin_lock(&c->space_lock);
  	/* Release the index growth reservation */

  	c->bi.idx_growth -= c->max_idx_node_sz << UBIFS_BLOCKS_PER_PAGE_SHIFT;

  	/* Release the data growth reservation */

  	c->bi.data_growth -= c->bi.page_budget;

  	/* Increase the dirty data growth reservation instead */

  	c->bi.dd_growth += c->bi.page_budget;

  	/* And re-calculate the indexing space reservation */

  	c->bi.min_idx_lebs = ubifs_calc_min_idx_lebs(c);

  	spin_unlock(&c->space_lock);
  }
  
  /**
   * ubifs_release_dirty_inode_budget - release dirty inode budget.
   * @c: UBIFS file-system description object
   * @ui: UBIFS inode to release the budget for
   *
   * This function releases budget corresponding to a dirty inode. It is usually
   * called when after the inode has been written to the media and marked as

   * clean. It also causes the "no space" flags to be cleared.

   */
  void ubifs_release_dirty_inode_budget(struct ubifs_info *c,
  				      struct ubifs_inode *ui)
  {

  	struct ubifs_budget_req req;

  	memset(&req, 0, sizeof(struct ubifs_budget_req));

  	/* The "no space" flags will be cleared because dd_growth is > 0 */

  	req.dd_growth = c->bi.inode_budget + ALIGN(ui->data_len, 8);

  	ubifs_release_budget(c, &req);
  }
  
  /**

   * ubifs_reported_space - calculate reported free space.
   * @c: the UBIFS file-system description object
   * @free: amount of free space
   *
   * This function calculates amount of free space which will be reported to
   * user-space. User-space application tend to expect that if the file-system
   * (e.g., via the 'statfs()' call) reports that it has N bytes available, they
   * are able to write a file of size N. UBIFS attaches node headers to each data

   * node and it has to write indexing nodes as well. This introduces additional
   * overhead, and UBIFS has to report slightly less free space to meet the above
   * expectations.

   *
   * This function assumes free space is made up of uncompressed data nodes and
   * full index nodes (one per data node, tripled because we always allow enough
   * space to write the index thrice).
   *
   * Note, the calculation is pessimistic, which means that most of the time
   * UBIFS reports less space than it actually has.
   */

  long long ubifs_reported_space(const struct ubifs_info *c, long long free)

  {

  	int divisor, factor, f;

  
  	/*
  	 * Reported space size is @free * X, where X is UBIFS block size
  	 * divided by UBIFS block size + all overhead one data block
  	 * introduces. The overhead is the node header + indexing overhead.
  	 *

  	 * Indexing overhead calculations are based on the following formula:
  	 * I = N/(f - 1) + 1, where I - number of indexing nodes, N - number
  	 * of data nodes, f - fanout. Because effective UBIFS fanout is twice
  	 * as less than maximum fanout, we assume that each data node

  	 * introduces 3 * @c->max_idx_node_sz / (@c->fanout/2 - 1) bytes.

  	 * Note, the multiplier 3 is because UBIFS reserves thrice as more space

  	 * for the index.
  	 */

  	f = c->fanout > 3 ? c->fanout >> 1 : 2;

  	factor = UBIFS_BLOCK_SIZE;
  	divisor = UBIFS_MAX_DATA_NODE_SZ;

  	divisor += (c->max_idx_node_sz * 3) / (f - 1);

  	free *= factor;

  	return div_u64(free, divisor);

  }
  
  /**

   * ubifs_get_free_space_nolock - return amount of free space.

   * @c: UBIFS file-system description object
   *

   * This function calculates amount of free space to report to user-space.
   *
   * Because UBIFS may introduce substantial overhead (the index, node headers,

   * alignment, wastage at the end of LEBs, etc), it cannot report real amount of
   * free flash space it has (well, because not all dirty space is reclaimable,
   * UBIFS does not actually know the real amount). If UBIFS did so, it would
   * bread user expectations about what free space is. Users seem to accustomed
   * to assume that if the file-system reports N bytes of free space, they would
   * be able to fit a file of N bytes to the FS. This almost works for

   * traditional file-systems, because they have way less overhead than UBIFS.
   * So, to keep users happy, UBIFS tries to take the overhead into account.

   */

  long long ubifs_get_free_space_nolock(struct ubifs_info *c)

  {

  	int rsvd_idx_lebs, lebs;

  	long long available, outstanding, free;

  	ubifs_assert(c->bi.min_idx_lebs == ubifs_calc_min_idx_lebs(c));
  	outstanding = c->bi.data_growth + c->bi.dd_growth;
  	available = ubifs_calc_available(c, c->bi.min_idx_lebs);

  
  	/*
  	 * When reporting free space to user-space, UBIFS guarantees that it is
  	 * possible to write a file of free space size. This means that for
  	 * empty LEBs we may use more precise calculations than
  	 * 'ubifs_calc_available()' is using. Namely, we know that in empty
  	 * LEBs we would waste only @c->leb_overhead bytes, not @c->dark_wm.
  	 * Thus, amend the available space.
  	 *
  	 * Note, the calculations below are similar to what we have in
  	 * 'do_budget_space()', so refer there for comments.
  	 */

  	if (c->bi.min_idx_lebs > c->lst.idx_lebs)
  		rsvd_idx_lebs = c->bi.min_idx_lebs - c->lst.idx_lebs;

  	else
  		rsvd_idx_lebs = 0;
  	lebs = c->lst.empty_lebs + c->freeable_cnt + c->idx_gc_cnt -
  	       c->lst.taken_empty_lebs;
  	lebs -= rsvd_idx_lebs;
  	available += lebs * (c->dark_wm - c->leb_overhead);

  
  	if (available > outstanding)
  		free = ubifs_reported_space(c, available - outstanding);
  	else
  		free = 0;
  	return free;
  }

  
  /**
   * ubifs_get_free_space - return amount of free space.
   * @c: UBIFS file-system description object
   *

   * This function calculates and returns amount of free space to report to

   * user-space.
   */
  long long ubifs_get_free_space(struct ubifs_info *c)
  {
  	long long free;
  
  	spin_lock(&c->space_lock);
  	free = ubifs_get_free_space_nolock(c);
  	spin_unlock(&c->space_lock);
  
  	return free;
  }