/* | |

* 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/math64.h> | |

/** | |

* 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; | |

return idx_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 | |

* 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); | |

} |