xref: /openbmc/u-boot/fs/ubifs/budget.c (revision a89c33db)
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  */
43 int 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  */
90 long 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