1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * bitext.c: kernel little helper (of bit shuffling variety).
4 *
5 * Copyright (C) 2002 Pete Zaitcev <zaitcev@yahoo.com>
6 *
7 * The algorithm to search a zero bit string is geared towards its application.
8 * We expect a couple of fixed sizes of requests, so a rotating counter, reset
9 * by align size, should provide fast enough search while maintaining low
10 * fragmentation.
11 */
12
13 #include <linux/string.h>
14 #include <linux/bitmap.h>
15
16 #include <asm/bitext.h>
17
18 /**
19 * bit_map_string_get - find and set a bit string in bit map.
20 * @t: the bit map.
21 * @len: requested string length
22 * @align: requested alignment
23 *
24 * Returns offset in the map or -1 if out of space.
25 *
26 * Not safe to call from an interrupt (uses spin_lock).
27 */
28 int bit_map_string_get(struct bit_map *t, int len, int align)
29 {
30 int offset, count; /* siamese twins */
31 int off_new;
32 int align1;
33 int i, color;
34
35 if (t->num_colors) {
36 /* align is overloaded to be the page color */
37 color = align;
38 align = t->num_colors;
39 } else {
40 color = 0;
41 if (align == 0)
42 align = 1;
43 }
44 align1 = align - 1;
45 if ((align & align1) != 0)
46 BUG();
47 if (align < 0 || align >= t->size)
48 BUG();
49 if (len <= 0 || len > t->size)
50 BUG();
51 color &= align1;
52
53 spin_lock(&t->lock);
54 if (len < t->last_size)
55 offset = t->first_free;
56 else
57 offset = t->last_off & ~align1;
58 count = 0;
59 for (;;) {
60 off_new = find_next_zero_bit(t->map, t->size, offset);
61 off_new = ((off_new + align1) & ~align1) + color;
62 count += off_new - offset;
63 offset = off_new;
64 if (offset >= t->size)
65 offset = 0;
66 if (count + len > t->size) {
67 spin_unlock(&t->lock);
68 /* P3 */ printk(KERN_ERR
69 "bitmap out: size %d used %d off %d len %d align %d count %d\n",
70 t->size, t->used, offset, len, align, count);
71 return -1;
72 }
73
74 if (offset + len > t->size) {
75 count += t->size - offset;
76 offset = 0;
77 continue;
78 }
79
80 i = 0;
81 while (test_bit(offset + i, t->map) == 0) {
82 i++;
83 if (i == len) {
84 bitmap_set(t->map, offset, len);
85 if (offset == t->first_free)
86 t->first_free = find_next_zero_bit
87 (t->map, t->size,
88 t->first_free + len);
89 if ((t->last_off = offset + len) >= t->size)
90 t->last_off = 0;
91 t->used += len;
92 t->last_size = len;
93 spin_unlock(&t->lock);
94 return offset;
95 }
96 }
97 count += i + 1;
98 if ((offset += i + 1) >= t->size)
99 offset = 0;
100 }
101 }
102
103 void bit_map_clear(struct bit_map *t, int offset, int len)
104 {
105 int i;
106
107 if (t->used < len)
108 BUG(); /* Much too late to do any good, but alas... */
109 spin_lock(&t->lock);
110 for (i = 0; i < len; i++) {
111 if (test_bit(offset + i, t->map) == 0)
112 BUG();
113 __clear_bit(offset + i, t->map);
114 }
115 if (offset < t->first_free)
116 t->first_free = offset;
117 t->used -= len;
118 spin_unlock(&t->lock);
119 }
120
121 void bit_map_init(struct bit_map *t, unsigned long *map, int size)
122 {
123 bitmap_zero(map, size);
124 memset(t, 0, sizeof *t);
125 spin_lock_init(&t->lock);
126 t->map = map;
127 t->size = size;
128 }
129
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