From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C918035028D; Mon, 13 Apr 2026 15:21:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776093662; cv=none; b=YtWZcZiW5hXxMDF7gs9CXM/QqbqSey6THwVmX1dQ6+jWahg5M00EzoBFZic3o0lThZyI79SC4wum9eZcxrd6SAHpGKHqH+aVqgLHgXhQEowU5M1z/MJrSrZMTrhAmiimWoMEIL3hVW3tUYenh8s3RZ6fVUrqYniWkLLocjP7Ui0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776093662; c=relaxed/simple; bh=cbIErmOBF2C7H+EIBxKKAjVwgufrayq2sLUjY/7AzyA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rzmsAfV1La2GEzyiMfGszG3YCMfsnH0Rj/I+OnO4rETro4mKMc7mvTFB1X3C2quj7qWxjv4nUZS4Ilf/AeaWRWbXCZ522MO4OvH0bI07IKeB8LmiL0JrMmuwbXJFnua8nIOofiA29dLzaGOLpwAR+XWER2brrksX8C6N+yTWQWE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CfSFz2E/; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="CfSFz2E/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6B90CC2BCAF; Mon, 13 Apr 2026 15:21:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776093662; bh=cbIErmOBF2C7H+EIBxKKAjVwgufrayq2sLUjY/7AzyA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=CfSFz2E/pWwkWd50PjnKyiw2ePqqh/TZfnVWHlkPuSAWGR4a3m/POrSiLzLmuOIjo vVgEH0ciuGuW0j5TJLcowAQV4yZIsFJgzguJVFP1rWcR7CcLwLCA26DMo9LuOdC4gX 1O1tYuYQ6nF9vbRvoTPKRbFOLB78OX/KnDNzctnC0EW7lLXQXxKX9ESk3epk8ndebq NP1eT8VpUdM3WqeVoGe8PFiFVtkI0UhVRNTao3sRkiRPIpS69HWREvNjls1tkEpF7t vuBeZ1YoaGkUg+KY/pD8uI1X36BYiQURYMNSWgJv9uU1EbILgoRz5dijYyOUKJa/qB ihXsL+x/QoWYA== Date: Mon, 13 Apr 2026 08:21:01 -0700 From: "Darrick J. Wong" To: Aurelien DESBRIERES Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org Subject: Re: [RFC PATCH 06/10] ftrfs: add block and inode allocator Message-ID: <20260413152101.GX6202@frogsfrogsfrogs> References: <20260413142357.515792-1-aurelien@hackers.camp> <20260413142357.515792-7-aurelien@hackers.camp> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260413142357.515792-7-aurelien@hackers.camp> On Mon, Apr 13, 2026 at 04:23:52PM +0200, Aurelien DESBRIERES wrote: > 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); No journalling? Or even COW metadata? How is this fault tolerant?? --D > + > + 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 > >