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114 lines
4.1 KiB
C
114 lines
4.1 KiB
C
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/*
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* This file is part of UBIFS.
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*
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* Copyright (C) 2006-2008 Nokia Corporation.
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*
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* This program is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 as published by
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* the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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* more details.
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*
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* You should have received a copy of the GNU General Public License along with
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* this program; if not, write to the Free Software Foundation, Inc., 51
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* Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*
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* Authors: Adrian Hunter
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* Artem Bityutskiy (Битюцкий Артём)
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*/
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/*
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* This file implements the budgeting sub-system which is responsible for UBIFS
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* space management.
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*
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* Factors such as compression, wasted space at the ends of LEBs, space in other
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* journal heads, the effect of updates on the index, and so on, make it
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* impossible to accurately predict the amount of space needed. Consequently
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* approximations are used.
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*/
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#include "ubifs.h"
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#include <linux/math64.h>
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/**
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* ubifs_calc_min_idx_lebs - calculate amount of eraseblocks for the index.
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* @c: UBIFS file-system description object
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*
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* This function calculates and returns the number of eraseblocks which should
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* be kept for index usage.
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*/
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int ubifs_calc_min_idx_lebs(struct ubifs_info *c)
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{
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int idx_lebs, eff_leb_size = c->leb_size - c->max_idx_node_sz;
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long long idx_size;
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idx_size = c->old_idx_sz + c->budg_idx_growth + c->budg_uncommitted_idx;
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/* And make sure we have thrice the index size of space reserved */
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idx_size = idx_size + (idx_size << 1);
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/*
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* We do not maintain 'old_idx_size' as 'old_idx_lebs'/'old_idx_bytes'
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* pair, nor similarly the two variables for the new index size, so we
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* have to do this costly 64-bit division on fast-path.
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*/
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idx_size += eff_leb_size - 1;
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idx_lebs = div_u64(idx_size, eff_leb_size);
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/*
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* The index head is not available for the in-the-gaps method, so add an
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* extra LEB to compensate.
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*/
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idx_lebs += 1;
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if (idx_lebs < MIN_INDEX_LEBS)
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idx_lebs = MIN_INDEX_LEBS;
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return idx_lebs;
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}
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/**
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* ubifs_reported_space - calculate reported free space.
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* @c: the UBIFS file-system description object
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* @free: amount of free space
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*
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* This function calculates amount of free space which will be reported to
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* user-space. User-space application tend to expect that if the file-system
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* (e.g., via the 'statfs()' call) reports that it has N bytes available, they
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* are able to write a file of size N. UBIFS attaches node headers to each data
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* node and it has to write indexing nodes as well. This introduces additional
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* overhead, and UBIFS has to report slightly less free space to meet the above
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* expectations.
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*
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* This function assumes free space is made up of uncompressed data nodes and
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* full index nodes (one per data node, tripled because we always allow enough
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* space to write the index thrice).
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*
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* Note, the calculation is pessimistic, which means that most of the time
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* UBIFS reports less space than it actually has.
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*/
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long long ubifs_reported_space(const struct ubifs_info *c, long long free)
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{
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int divisor, factor, f;
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/*
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* Reported space size is @free * X, where X is UBIFS block size
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* divided by UBIFS block size + all overhead one data block
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* introduces. The overhead is the node header + indexing overhead.
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*
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* Indexing overhead calculations are based on the following formula:
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* I = N/(f - 1) + 1, where I - number of indexing nodes, N - number
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* of data nodes, f - fanout. Because effective UBIFS fanout is twice
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* as less than maximum fanout, we assume that each data node
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* introduces 3 * @c->max_idx_node_sz / (@c->fanout/2 - 1) bytes.
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* Note, the multiplier 3 is because UBIFS reserves thrice as more space
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* for the index.
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*/
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f = c->fanout > 3 ? c->fanout >> 1 : 2;
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factor = UBIFS_BLOCK_SIZE;
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divisor = UBIFS_MAX_DATA_NODE_SZ;
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divisor += (c->max_idx_node_sz * 3) / (f - 1);
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free *= factor;
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return div_u64(free, divisor);
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}
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