LXR uboot/fs/ubifs/budget.c

   1/*
   2 * This file is part of UBIFS.
   3 *
   4 * Copyright (C) 2006-2008 Nokia Corporation.
   5 *
   6 * This program is free software; you can redistribute it and/or modify it
   7 * under the terms of the GNU General Public License version 2 as published by
   8 * the Free Software Foundation.
   9 *
  10 * This program is distributed in the hope that it will be useful, but WITHOUT
  11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  13 * more details.
  14 *
  15 * You should have received a copy of the GNU General Public License along with
  16 * this program; if not, write to the Free Software Foundation, Inc., 51
  17 * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
  18 *
  19 * Authors: Adrian Hunter
  20 *          Artem Bityutskiy (Битюцкий Артём)
  21 */
  22
  23/*
  24 * This file implements the budgeting sub-system which is responsible for UBIFS
  25 * space management.
  26 *
  27 * Factors such as compression, wasted space at the ends of LEBs, space in other
  28 * journal heads, the effect of updates on the index, and so on, make it
  29 * impossible to accurately predict the amount of space needed. Consequently
  30 * approximations are used.
  31 */
  32
  33#include "ubifs.h"
  34#include <linux/math64.h>
  35
  36/**
  37 * ubifs_calc_min_idx_lebs - calculate amount of eraseblocks for the index.
  38 * @c: UBIFS file-system description object
  39 *
  40 * This function calculates and returns the number of eraseblocks which should
  41 * be kept for index usage.
  42 */
  43int ubifs_calc_min_idx_lebs(struct ubifs_info *c)
  44{
  45        int idx_lebs, eff_leb_size = c->leb_size - c->max_idx_node_sz;
  46        long long idx_size;
  47
  48        idx_size = c->old_idx_sz + c->budg_idx_growth + c->budg_uncommitted_idx;
  49
  50        /* And make sure we have thrice the index size of space reserved */
  51        idx_size = idx_size + (idx_size << 1);
  52
  53        /*
  54         * We do not maintain 'old_idx_size' as 'old_idx_lebs'/'old_idx_bytes'
  55         * pair, nor similarly the two variables for the new index size, so we
  56         * have to do this costly 64-bit division on fast-path.
  57         */
  58        idx_size += eff_leb_size - 1;
  59        idx_lebs = div_u64(idx_size, eff_leb_size);
  60        /*
  61         * The index head is not available for the in-the-gaps method, so add an
  62         * extra LEB to compensate.
  63         */
  64        idx_lebs += 1;
  65        if (idx_lebs < MIN_INDEX_LEBS)
  66                idx_lebs = MIN_INDEX_LEBS;
  67        return idx_lebs;
  68}
  69
  70/**
  71 * ubifs_reported_space - calculate reported free space.
  72 * @c: the UBIFS file-system description object
  73 * @free: amount of free space
  74 *
  75 * This function calculates amount of free space which will be reported to
  76 * user-space. User-space application tend to expect that if the file-system
  77 * (e.g., via the 'statfs()' call) reports that it has N bytes available, they
  78 * are able to write a file of size N. UBIFS attaches node headers to each data
  79 * node and it has to write indexing nodes as well. This introduces additional
  80 * overhead, and UBIFS has to report slightly less free space to meet the above
  81 * expectations.
  82 *
  83 * This function assumes free space is made up of uncompressed data nodes and
  84 * full index nodes (one per data node, tripled because we always allow enough
  85 * space to write the index thrice).
  86 *
  87 * Note, the calculation is pessimistic, which means that most of the time
  88 * UBIFS reports less space than it actually has.
  89 */
  90long long ubifs_reported_space(const struct ubifs_info *c, long long free)
  91{
  92        int divisor, factor, f;
  93
  94        /*
  95         * Reported space size is @free * X, where X is UBIFS block size
  96         * divided by UBIFS block size + all overhead one data block
  97         * introduces. The overhead is the node header + indexing overhead.
  98         *
  99         * Indexing overhead calculations are based on the following formula:
 100         * I = N/(f - 1) + 1, where I - number of indexing nodes, N - number
 101         * of data nodes, f - fanout. Because effective UBIFS fanout is twice
 102         * as less than maximum fanout, we assume that each data node
 103         * introduces 3 * @c->max_idx_node_sz / (@c->fanout/2 - 1) bytes.
 104         * Note, the multiplier 3 is because UBIFS reserves thrice as more space
 105         * for the index.
 106         */
 107        f = c->fanout > 3 ? c->fanout >> 1 : 2;
 108        factor = UBIFS_BLOCK_SIZE;
 109        divisor = UBIFS_MAX_DATA_NODE_SZ;
 110        divisor += (c->max_idx_node_sz * 3) / (f - 1);
 111        free *= factor;
 112        return div_u64(free, divisor);
 113}
 114