1 /*
2 * linux/fs/hfs/bitmap.c
3 *
4 * Copyright (C) 1996-1997 Paul H. Hargrove
5 * (C) 2003 Ardis Technologies <roman@ardistech.com>
6 * This file may be distributed under the terms of the GNU General Public License.
7 *
8 * Based on GPLed code Copyright (C) 1995 Michael Dreher
9 *
10 * This file contains the code to modify the volume bitmap:
11 * search/set/clear bits.
12 */
13
14 #include "hfs_fs.h"
15
16 /*
17 * hfs_find_zero_bit()
18 *
19 * Description:
20 * Given a block of memory, its length in bits, and a starting bit number,
21 * determine the number of the first zero bits (in left-to-right ordering)
22 * in that range.
23 *
24 * Returns >= 'size' if no zero bits are found in the range.
25 *
26 * Accesses memory in 32-bit aligned chunks of 32-bits and thus
27 * may read beyond the 'size'th bit.
28 */
29 static u32 hfs_find_set_zero_bits(__be32 *bitmap, u32 size, u32 offset, u32 *max)
30 {
31 __be32 *curr, *end;
32 u32 mask, start, len, n;
33 __be32 val;
34 int i;
35
36 len = *max;
37 if (!len)
38 return size;
39
40 curr = bitmap + (offset / 32);
41 end = bitmap + ((size + 31) / 32);
42
43 /* scan the first partial u32 for zero bits */
44 val = *curr;
45 if (~val) {
46 n = be32_to_cpu(val);
47 i = offset % 32;
48 mask = (1U << 31) >> i;
49 for (; i < 32; mask >>= 1, i++) {
50 if (!(n & mask))
51 goto found;
52 }
53 }
54
55 /* scan complete u32s for the first zero bit */
56 while (++curr < end) {
57 val = *curr;
58 if (~val) {
59 n = be32_to_cpu(val);
60 mask = 1 << 31;
61 for (i = 0; i < 32; mask >>= 1, i++) {
62 if (!(n & mask))
63 goto found;
64 }
65 }
66 }
67 return size;
68
69 found:
70 start = (curr - bitmap) * 32 + i;
71 if (start >= size)
72 return start;
73 /* do any partial u32 at the start */
74 len = min(size - start, len);
75 while (1) {
76 n |= mask;
77 if (++i >= 32)
78 break;
79 mask >>= 1;
80 if (!--len || n & mask)
81 goto done;
82 }
83 if (!--len)
84 goto done;
85 *curr++ = cpu_to_be32(n);
86 /* do full u32s */
87 while (1) {
88 n = be32_to_cpu(*curr);
89 if (len < 32)
90 break;
91 if (n) {
92 len = 32;
93 break;
94 }
95 *curr++ = cpu_to_be32(0xffffffff);
96 len -= 32;
97 }
98 /* do any partial u32 at end */
99 mask = 1U << 31;
100 for (i = 0; i < len; i++) {
101 if (n & mask)
102 break;
103 n |= mask;
104 mask >>= 1;
105 }
106 done:
107 *curr = cpu_to_be32(n);
108 *max = (curr - bitmap) * 32 + i - start;
109 return start;
110 }
111
112 /*
113 * hfs_vbm_search_free()
114 *
115 * Description:
116 * Search for 'num_bits' consecutive cleared bits in the bitmap blocks of
117 * the hfs MDB. 'mdb' had better be locked or the returned range
118 * may be no longer free, when this functions returns!
119 * XXX Currently the search starts from bit 0, but it should start with
120 * the bit number stored in 's_alloc_ptr' of the MDB.
121 * Input Variable(s):
122 * struct hfs_mdb *mdb: Pointer to the hfs MDB
123 * u16 *num_bits: Pointer to the number of cleared bits
124 * to search for
125 * Output Variable(s):
126 * u16 *num_bits: The number of consecutive clear bits of the
127 * returned range. If the bitmap is fragmented, this will be less than
128 * requested and it will be zero, when the disk is full.
129 * Returns:
130 * The number of the first bit of the range of cleared bits which has been
131 * found. When 'num_bits' is zero, this is invalid!
132 * Preconditions:
133 * 'mdb' points to a "valid" (struct hfs_mdb).
134 * 'num_bits' points to a variable of type (u16), which contains
135 * the number of cleared bits to find.
136 * Postconditions:
137 * 'num_bits' is set to the length of the found sequence.
138 */
139 u32 hfs_vbm_search_free(struct super_block *sb, u32 goal, u32 *num_bits)
140 {
141 void *bitmap;
142 u32 pos;
143
144 /* make sure we have actual work to perform */
145 if (!*num_bits)
146 return 0;
147
148 mutex_lock(&HFS_SB(sb)->bitmap_lock);
149 bitmap = HFS_SB(sb)->bitmap;
150
151 pos = hfs_find_set_zero_bits(bitmap, HFS_SB(sb)->fs_ablocks, goal, num_bits);
152 if (pos >= HFS_SB(sb)->fs_ablocks) {
153 if (goal)
154 pos = hfs_find_set_zero_bits(bitmap, goal, 0, num_bits);
155 if (pos >= HFS_SB(sb)->fs_ablocks) {
156 *num_bits = pos = 0;
157 goto out;
158 }
159 }
160
161 hfs_dbg(BITMAP, "alloc_bits: %u,%u\n", pos, *num_bits);
162 HFS_SB(sb)->free_ablocks -= *num_bits;
163 hfs_bitmap_dirty(sb);
164 out:
165 mutex_unlock(&HFS_SB(sb)->bitmap_lock);
166 return pos;
167 }
168
169
170 /*
171 * hfs_clear_vbm_bits()
172 *
173 * Description:
174 * Clear the requested bits in the volume bitmap of the hfs filesystem
175 * Input Variable(s):
176 * struct hfs_mdb *mdb: Pointer to the hfs MDB
177 * u16 start: The offset of the first bit
178 * u16 count: The number of bits
179 * Output Variable(s):
180 * None
181 * Returns:
182 * 0: no error
183 * -1: One of the bits was already clear. This is a strange
184 * error and when it happens, the filesystem must be repaired!
185 * -2: One or more of the bits are out of range of the bitmap.
186 * Preconditions:
187 * 'mdb' points to a "valid" (struct hfs_mdb).
188 * Postconditions:
189 * Starting with bit number 'start', 'count' bits in the volume bitmap
190 * are cleared. The affected bitmap blocks are marked "dirty", the free
191 * block count of the MDB is updated and the MDB is marked dirty.
192 */
193 int hfs_clear_vbm_bits(struct super_block *sb, u16 start, u16 count)
194 {
195 __be32 *curr;
196 u32 mask;
197 int i, len;
198
199 /* is there any actual work to be done? */
200 if (!count)
201 return 0;
202
203 hfs_dbg(BITMAP, "clear_bits: %u,%u\n", start, count);
204 /* are all of the bits in range? */
205 if ((start + count) > HFS_SB(sb)->fs_ablocks)
206 return -2;
207
208 mutex_lock(&HFS_SB(sb)->bitmap_lock);
209 /* bitmap is always on a 32-bit boundary */
210 curr = HFS_SB(sb)->bitmap + (start / 32);
211 len = count;
212
213 /* do any partial u32 at the start */
214 i = start % 32;
215 if (i) {
216 int j = 32 - i;
217 mask = 0xffffffffU << j;
218 if (j > count) {
219 mask |= 0xffffffffU >> (i + count);
220 *curr &= cpu_to_be32(mask);
221 goto out;
222 }
223 *curr++ &= cpu_to_be32(mask);
224 count -= j;
225 }
226
227 /* do full u32s */
228 while (count >= 32) {
229 *curr++ = 0;
230 count -= 32;
231 }
232 /* do any partial u32 at end */
233 if (count) {
234 mask = 0xffffffffU >> count;
235 *curr &= cpu_to_be32(mask);
236 }
237 out:
238 HFS_SB(sb)->free_ablocks += len;
239 mutex_unlock(&HFS_SB(sb)->bitmap_lock);
240 hfs_bitmap_dirty(sb);
241
242 return 0;
243 }
244
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