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 */
29static 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
69found:
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	}
106done:
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 */
139u32 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);
164out:
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 */
193int 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	}
237out:
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