* 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.
* ubifs_calc_min_idx_lebs - calculate amount of eraseblocks for the index.
* @c: UBIFS file-system description object
* This function calculates and returns the number of eraseblocks which should
* be kept for index usage.
int ubifs_calc_min_idx_lebs(struct ubifs_info *c)
int idx_lebs, eff_leb_size = c->leb_size - c->max_idx_node_sz;
long long idx_size;
idx_size = c->old_idx_sz + c->budg_idx_growth + c->budg_uncommitted_idx;
/* And make sure we have thrice the index size of space reserved */
idx_size = 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_size += eff_leb_size - 1;
idx_lebs = div_u64(idx_size, eff_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;
* 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
* 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);