2 * linux/fs/hfs/bitmap.c
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.
8 * Based on GPLed code Copyright (C) 1995 Michael Dreher
10 * This file contains the code to modify the volume bitmap:
11 * search/set/clear bits.
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)
24 * Returns >= 'size' if no zero bits are found in the range.
26 * Accesses memory in 32-bit aligned chunks of 32-bits and thus
27 * may read beyond the 'size'th bit.
29 static u32 hfs_find_set_zero_bits(__be32 *bitmap, u32 size, u32 offset, u32 *max)
32 u32 mask, start, len, n;
40 curr = bitmap + (offset / 32);
41 end = bitmap + ((size + 31) / 32);
43 /* scan the first partial u32 for zero bits */
48 mask = (1U << 31) >> i;
49 for (; i < 32; mask >>= 1, i++) {
55 /* scan complete u32s for the first zero bit */
56 while (++curr < end) {
61 for (i = 0; i < 32; mask >>= 1, i++) {
70 start = (curr - bitmap) * 32 + i;
73 /* do any partial u32 at the start */
74 len = min(size - start, len);
80 if (!--len || n & mask)
85 *curr++ = cpu_to_be32(n);
88 n = be32_to_cpu(*curr);
95 *curr++ = cpu_to_be32(0xffffffff);
98 /* do any partial u32 at end */
100 for (i = 0; i < len; i++) {
107 *curr = cpu_to_be32(n);
108 *max = (curr - bitmap) * 32 + i - start;
113 * hfs_vbm_search_free()
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.
122 * struct hfs_mdb *mdb: Pointer to the hfs MDB
123 * u16 *num_bits: Pointer to the number of cleared bits
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.
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!
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.
137 * 'num_bits' is set to the length of the found sequence.
139 u32 hfs_vbm_search_free(struct super_block *sb, u32 goal, u32 *num_bits)
144 /* make sure we have actual work to perform */
148 mutex_lock(&HFS_SB(sb)->bitmap_lock);
149 bitmap = HFS_SB(sb)->bitmap;
151 pos = hfs_find_set_zero_bits(bitmap, HFS_SB(sb)->fs_ablocks, goal, num_bits);
152 if (pos >= HFS_SB(sb)->fs_ablocks) {
154 pos = hfs_find_set_zero_bits(bitmap, goal, 0, num_bits);
155 if (pos >= HFS_SB(sb)->fs_ablocks) {
161 dprint(DBG_BITMAP, "alloc_bits: %u,%u\n", pos, *num_bits);
162 HFS_SB(sb)->free_ablocks -= *num_bits;
163 hfs_bitmap_dirty(sb);
165 mutex_unlock(&HFS_SB(sb)->bitmap_lock);
171 * hfs_clear_vbm_bits()
174 * Clear the requested bits in the volume bitmap of the hfs filesystem
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):
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.
187 * 'mdb' points to a "valid" (struct hfs_mdb).
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.
193 int hfs_clear_vbm_bits(struct super_block *sb, u16 start, u16 count)
199 /* is there any actual work to be done? */
203 dprint(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)
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);
213 /* do any partial u32 at the start */
217 mask = 0xffffffffU << j;
219 mask |= 0xffffffffU >> (i + count);
220 *curr &= cpu_to_be32(mask);
223 *curr++ &= cpu_to_be32(mask);
228 while (count >= 32) {
232 /* do any partial u32 at end */
234 mask = 0xffffffffU >> count;
235 *curr &= cpu_to_be32(mask);
238 HFS_SB(sb)->free_ablocks += len;
239 mutex_unlock(&HFS_SB(sb)->bitmap_lock);
240 hfs_bitmap_dirty(sb);