summaryrefslogtreecommitdiff
path: root/fs/hfs/bitmap.c
blob: c6e97366e8ac3f362d0f08d63d0234d837e14103 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
/*
 *  linux/fs/hfs/bitmap.c
 *
 * Copyright (C) 1996-1997  Paul H. Hargrove
 * (C) 2003 Ardis Technologies <roman@ardistech.com>
 * This file may be distributed under the terms of the GNU General Public License.
 *
 * Based on GPLed code Copyright (C) 1995  Michael Dreher
 *
 * This file contains the code to modify the volume bitmap:
 * search/set/clear bits.
 */

#include "hfs_fs.h"

/*
 * hfs_find_zero_bit()
 *
 * Description:
 *  Given a block of memory, its length in bits, and a starting bit number,
 *  determine the number of the first zero bits (in left-to-right ordering)
 *  in that range.
 *
 *  Returns >= 'size' if no zero bits are found in the range.
 *
 *  Accesses memory in 32-bit aligned chunks of 32-bits and thus
 *  may read beyond the 'size'th bit.
 */
static u32 hfs_find_set_zero_bits(__be32 *bitmap, u32 size, u32 offset, u32 *max)
{
	__be32 *curr, *end;
	u32 mask, start, len, n;
	__be32 val;
	int i;

	len = *max;
	if (!len)
		return size;

	curr = bitmap + (offset / 32);
	end = bitmap + ((size + 31) / 32);

	/* scan the first partial u32 for zero bits */
	val = *curr;
	if (~val) {
		n = be32_to_cpu(val);
		i = offset % 32;
		mask = (1U << 31) >> i;
		for (; i < 32; mask >>= 1, i++) {
			if (!(n & mask))
				goto found;
		}
	}

	/* scan complete u32s for the first zero bit */
	while (++curr < end) {
		val = *curr;
		if (~val) {
			n = be32_to_cpu(val);
			mask = 1 << 31;
			for (i = 0; i < 32; mask >>= 1, i++) {
				if (!(n & mask))
					goto found;
			}
		}
	}
	return size;

found:
	start = (curr - bitmap) * 32 + i;
	if (start >= size)
		return start;
	/* do any partial u32 at the start */
	len = min(size - start, len);
	while (1) {
		n |= mask;
		if (++i >= 32)
			break;
		mask >>= 1;
		if (!--len || n & mask)
			goto done;
	}
	if (!--len)
		goto done;
	*curr++ = cpu_to_be32(n);
	/* do full u32s */
	while (1) {
		n = be32_to_cpu(*curr);
		if (len < 32)
			break;
		if (n) {
			len = 32;
			break;
		}
		*curr++ = cpu_to_be32(0xffffffff);
		len -= 32;
	}
	/* do any partial u32 at end */
	mask = 1U << 31;
	for (i = 0; i < len; i++) {
		if (n & mask)
			break;
		n |= mask;
		mask >>= 1;
	}
done:
	*curr = cpu_to_be32(n);
	*max = (curr - bitmap) * 32 + i - start;
	return start;
}

/*
 * hfs_vbm_search_free()
 *
 * Description:
 *   Search for 'num_bits' consecutive cleared bits in the bitmap blocks of
 *   the hfs MDB. 'mdb' had better be locked or the returned range
 *   may be no longer free, when this functions returns!
 *   XXX Currently the search starts from bit 0, but it should start with
 *   the bit number stored in 's_alloc_ptr' of the MDB.
 * Input Variable(s):
 *   struct hfs_mdb *mdb: Pointer to the hfs MDB
 *   u16 *num_bits: Pointer to the number of cleared bits
 *     to search for
 * Output Variable(s):
 *   u16 *num_bits: The number of consecutive clear bits of the
 *     returned range. If the bitmap is fragmented, this will be less than
 *     requested and it will be zero, when the disk is full.
 * Returns:
 *   The number of the first bit of the range of cleared bits which has been
 *   found. When 'num_bits' is zero, this is invalid!
 * Preconditions:
 *   'mdb' points to a "valid" (struct hfs_mdb).
 *   'num_bits' points to a variable of type (u16), which contains
 *	the number of cleared bits to find.
 * Postconditions:
 *   'num_bits' is set to the length of the found sequence.
 */
u32 hfs_vbm_search_free(struct super_block *sb, u32 goal, u32 *num_bits)
{
	void *bitmap;
	u32 pos;

	/* make sure we have actual work to perform */
	if (!*num_bits)
		return 0;

	mutex_lock(&HFS_SB(sb)->bitmap_lock);
	bitmap = HFS_SB(sb)->bitmap;

	pos = hfs_find_set_zero_bits(bitmap, HFS_SB(sb)->fs_ablocks, goal, num_bits);
	if (pos >= HFS_SB(sb)->fs_ablocks) {
		if (goal)
			pos = hfs_find_set_zero_bits(bitmap, goal, 0, num_bits);
		if (pos >= HFS_SB(sb)->fs_ablocks) {
			*num_bits = pos = 0;
			goto out;
		}
	}

	dprint(DBG_BITMAP, "alloc_bits: %u,%u\n", pos, *num_bits);
	HFS_SB(sb)->free_ablocks -= *num_bits;
	hfs_bitmap_dirty(sb);
out:
	mutex_unlock(&HFS_SB(sb)->bitmap_lock);
	return pos;
}


/*
 * hfs_clear_vbm_bits()
 *
 * Description:
 *   Clear the requested bits in the volume bitmap of the hfs filesystem
 * Input Variable(s):
 *   struct hfs_mdb *mdb: Pointer to the hfs MDB
 *   u16 start: The offset of the first bit
 *   u16 count: The number of bits
 * Output Variable(s):
 *   None
 * Returns:
 *    0: no error
 *   -1: One of the bits was already clear.  This is a strange
 *	 error and when it happens, the filesystem must be repaired!
 *   -2: One or more of the bits are out of range of the bitmap.
 * Preconditions:
 *   'mdb' points to a "valid" (struct hfs_mdb).
 * Postconditions:
 *   Starting with bit number 'start', 'count' bits in the volume bitmap
 *   are cleared. The affected bitmap blocks are marked "dirty", the free
 *   block count of the MDB is updated and the MDB is marked dirty.
 */
int hfs_clear_vbm_bits(struct super_block *sb, u16 start, u16 count)
{
	__be32 *curr;
	u32 mask;
	int i, len;

	/* is there any actual work to be done? */
	if (!count)
		return 0;

	dprint(DBG_BITMAP, "clear_bits: %u,%u\n", start, count);
	/* are all of the bits in range? */
	if ((start + count) > HFS_SB(sb)->fs_ablocks)
		return -2;

	mutex_lock(&HFS_SB(sb)->bitmap_lock);
	/* bitmap is always on a 32-bit boundary */
	curr = HFS_SB(sb)->bitmap + (start / 32);
	len = count;

	/* do any partial u32 at the start */
	i = start % 32;
	if (i) {
		int j = 32 - i;
		mask = 0xffffffffU << j;
		if (j > count) {
			mask |= 0xffffffffU >> (i + count);
			*curr &= cpu_to_be32(mask);
			goto out;
		}
		*curr++ &= cpu_to_be32(mask);
		count -= j;
	}

	/* do full u32s */
	while (count >= 32) {
		*curr++ = 0;
		count -= 32;
	}
	/* do any partial u32 at end */
	if (count) {
		mask = 0xffffffffU >> count;
		*curr &= cpu_to_be32(mask);
	}
out:
	HFS_SB(sb)->free_ablocks += len;
	mutex_unlock(&HFS_SB(sb)->bitmap_lock);
	hfs_bitmap_dirty(sb);

	return 0;
}