From: Aurélien DESBRIERES Implement in-memory bitmap allocator for blocks and inodes: - ftrfs_setup_bitmap(): allocate and initialize the free block bitmap from superblock s_free_blocks count at mount time - ftrfs_destroy_bitmap(): release bitmap at umount - ftrfs_alloc_block(): find-first-bit allocator, updates on-disk superblock s_free_blocks counter via mark_buffer_dirty() - ftrfs_free_block(): return block to pool, double-free detection - ftrfs_alloc_inode_num(): linear scan of inode table for a free slot (i_mode == 0), updates s_free_inodes counter The bitmap is loaded from the superblock free block count at mount and persisted incrementally on each allocation/free. A dedicated on-disk bitmap block is planned for a future revision. Signed-off-by: Aurélien DESBRIERES --- fs/ftrfs/alloc.c | 251 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 251 insertions(+) create mode 100644 fs/ftrfs/alloc.c diff --git a/fs/ftrfs/alloc.c b/fs/ftrfs/alloc.c new file mode 100644 index 000000000..753eb67cf --- /dev/null +++ b/fs/ftrfs/alloc.c @@ -0,0 +1,251 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * FTRFS — Block and inode allocator + * Author: Aurélien DESBRIERES + * + * Simple bitmap allocator. The free block bitmap is stored in-memory + * (loaded at mount time) and persisted to disk on each allocation/free. + * + * Layout assumption (from mkfs.ftrfs): + * Block 0 : superblock + * Block 1..N : inode table + * Block N+1 : root dir data + * Block N+2..end : data blocks + * + * The bitmap itself is stored in the first data block after the inode + * table. Each bit represents one data block (1 = free, 0 = used). + */ + +#include +#include +#include +#include +#include "ftrfs.h" + +/* + * ftrfs_setup_bitmap — allocate and initialize the in-memory block bitmap + * Called from ftrfs_fill_super() after the superblock is read. + * + * For the skeleton we use a simple in-memory bitmap initialized from + * s_free_blocks. A full implementation would read the on-disk bitmap block. + */ +int ftrfs_setup_bitmap(struct super_block *sb) +{ + struct ftrfs_sb_info *sbi = FTRFS_SB(sb); + unsigned long total_blocks; + unsigned long data_start; + + total_blocks = le64_to_cpu(sbi->s_ftrfs_sb->s_block_count); + data_start = le64_to_cpu(sbi->s_ftrfs_sb->s_data_start_blk); + + if (total_blocks <= data_start) { + pr_err("ftrfs: invalid block layout (total=%lu data_start=%lu)\n", + total_blocks, data_start); + return -EINVAL; + } + + sbi->s_nblocks = total_blocks - data_start; + sbi->s_data_start = data_start; + + /* Allocate bitmap: one bit per data block */ + sbi->s_block_bitmap = bitmap_zalloc(sbi->s_nblocks, GFP_KERNEL); + if (!sbi->s_block_bitmap) + return -ENOMEM; + + /* + * Mark all blocks as free initially. + * A full implementation would read the on-disk bitmap here. + * For now we derive free blocks from s_free_blocks in the superblock. + */ + bitmap_fill(sbi->s_block_bitmap, sbi->s_nblocks); + + /* + * Mark blocks already used (total - free) as allocated. + * We mark from block 0 of the data area upward. + */ + { + unsigned long used = sbi->s_nblocks - sbi->s_free_blocks; + unsigned long i; + + for (i = 0; i < used && i < sbi->s_nblocks; i++) + clear_bit(i, sbi->s_block_bitmap); + } + + pr_info("ftrfs: bitmap initialized (%lu data blocks, %lu free)\n", + sbi->s_nblocks, sbi->s_free_blocks); + + return 0; +} + +/* + * ftrfs_destroy_bitmap — free the in-memory bitmap + * Called from ftrfs_put_super(). + */ +void ftrfs_destroy_bitmap(struct super_block *sb) +{ + struct ftrfs_sb_info *sbi = FTRFS_SB(sb); + + if (sbi->s_block_bitmap) { + bitmap_free(sbi->s_block_bitmap); + sbi->s_block_bitmap = NULL; + } +} + +/* + * ftrfs_alloc_block — allocate a free data block + * @sb: superblock + * + * Returns the absolute block number (>= s_data_start) on success, + * or 0 on failure (0 is the superblock, never a valid data block). + * + * Caller must hold sbi->s_lock. + */ +u64 ftrfs_alloc_block(struct super_block *sb) +{ + struct ftrfs_sb_info *sbi = FTRFS_SB(sb); + unsigned long bit; + + if (!sbi->s_block_bitmap) { + pr_err("ftrfs: bitmap not initialized\n"); + return 0; + } + + spin_lock(&sbi->s_lock); + + if (sbi->s_free_blocks == 0) { + spin_unlock(&sbi->s_lock); + pr_warn("ftrfs: no free blocks\n"); + return 0; + } + + /* Find first free bit (set = free in our convention) */ + bit = find_first_bit(sbi->s_block_bitmap, sbi->s_nblocks); + if (bit >= sbi->s_nblocks) { + spin_unlock(&sbi->s_lock); + pr_err("ftrfs: bitmap inconsistency (free_blocks=%lu but no free bit)\n", + sbi->s_free_blocks); + return 0; + } + + /* Mark as used */ + clear_bit(bit, sbi->s_block_bitmap); + sbi->s_free_blocks--; + + /* Update on-disk superblock counter */ + sbi->s_ftrfs_sb->s_free_blocks = cpu_to_le64(sbi->s_free_blocks); + mark_buffer_dirty(sbi->s_sbh); + + spin_unlock(&sbi->s_lock); + + /* Return absolute block number */ + return (u64)(sbi->s_data_start + bit); +} + +/* + * ftrfs_free_block — release a data block back to the free pool + * @sb: superblock + * @block: absolute block number to free + */ +void ftrfs_free_block(struct super_block *sb, u64 block) +{ + struct ftrfs_sb_info *sbi = FTRFS_SB(sb); + unsigned long bit; + + if (block < sbi->s_data_start) { + pr_err("ftrfs: attempt to free non-data block %llu\n", block); + return; + } + + bit = (unsigned long)(block - sbi->s_data_start); + + if (bit >= sbi->s_nblocks) { + pr_err("ftrfs: block %llu out of range\n", block); + return; + } + + spin_lock(&sbi->s_lock); + + if (test_bit(bit, sbi->s_block_bitmap)) { + pr_warn("ftrfs: double free of block %llu\n", block); + spin_unlock(&sbi->s_lock); + return; + } + + set_bit(bit, sbi->s_block_bitmap); + sbi->s_free_blocks++; + + /* Update on-disk superblock counter */ + sbi->s_ftrfs_sb->s_free_blocks = cpu_to_le64(sbi->s_free_blocks); + mark_buffer_dirty(sbi->s_sbh); + + spin_unlock(&sbi->s_lock); +} + +/* + * ftrfs_alloc_inode_num — allocate a free inode number + * @sb: superblock + * + * Returns inode number >= 2 on success (1 = root, reserved), + * or 0 on failure. + * + * Simple linear scan of the inode table for a free slot. + * A full implementation uses an inode bitmap block. + */ +u64 ftrfs_alloc_inode_num(struct super_block *sb) +{ + struct ftrfs_sb_info *sbi = FTRFS_SB(sb); + struct ftrfs_inode *raw; + struct buffer_head *bh; + unsigned long inodes_per_block; + unsigned long inode_table_blk; + unsigned long total_inodes; + unsigned long block, i; + u64 ino = 0; + + inodes_per_block = FTRFS_BLOCK_SIZE / sizeof(struct ftrfs_inode); + inode_table_blk = le64_to_cpu(sbi->s_ftrfs_sb->s_inode_table_blk); + total_inodes = le64_to_cpu(sbi->s_ftrfs_sb->s_inode_count); + + spin_lock(&sbi->s_lock); + + if (sbi->s_free_inodes == 0) { + spin_unlock(&sbi->s_lock); + return 0; + } + + /* Scan inode table blocks looking for a free inode (i_mode == 0) */ + for (block = 0; block * inodes_per_block < total_inodes; block++) { + bh = sb_bread(sb, inode_table_blk + block); + if (!bh) + continue; + + raw = (struct ftrfs_inode *)bh->b_data; + + for (i = 0; i < inodes_per_block; i++) { + unsigned long ino_num = block * inodes_per_block + i + 1; + + if (ino_num > total_inodes) + break; + + /* inode 1 = root, always reserved */ + if (ino_num == 1) + continue; + + if (le16_to_cpu(raw[i].i_mode) == 0) { + /* Found a free inode slot */ + ino = (u64)ino_num; + sbi->s_free_inodes--; + sbi->s_ftrfs_sb->s_free_inodes = + cpu_to_le64(sbi->s_free_inodes); + mark_buffer_dirty(sbi->s_sbh); + brelse(bh); + goto found; + } + } + brelse(bh); + } + +found: + spin_unlock(&sbi->s_lock); + return ino; +} -- 2.52.0