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Diffstat (limited to 'fs/hfs/bitmap.c')
-rw-r--r-- | fs/hfs/bitmap.c | 243 |
1 files changed, 243 insertions, 0 deletions
diff --git a/fs/hfs/bitmap.c b/fs/hfs/bitmap.c new file mode 100644 index 00000000..c6e97366 --- /dev/null +++ b/fs/hfs/bitmap.c @@ -0,0 +1,243 @@ +/* + * 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; +} |