linux-ext4 - Re: [PATCH e2fsprogs] libext2fs: fix orphan file size

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Message-ID: <20251112183609.GN196358@frogsfrogsfrogs>
Date: Wed, 12 Nov 2025 10:36:09 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: libaokun@...weicloud.com
Cc: linux-ext4@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca,
	jack@...e.cz, yangerkun@...wei.com, libaokun1@...wei.com
Subject: Re: [PATCH e2fsprogs] libext2fs: fix orphan file size > kernel limit
 with large blocksize

On Wed, Nov 12, 2025 at 08:21:57PM +0800, libaokun@...weicloud.com wrote:
> From: Baokun Li <libaokun1@...wei.com>
> 
> Kernel commit 0a6ce20c1564 ("ext4: verify orphan file size is not too big")
> limits the maximum supported orphan file size to 8 << 20.
> 
> However, in e2fsprogs, the orphan file size is set to 32–512 filesystem
> blocks when creating a filesystem.
> 
> With 64k block size, formatting an ext4 fs >32G gives an orphan file bigger
> than the kernel allows, so mount prints an error and fails:
> 
>     EXT4-fs (vdb): orphan file too big: 8650752
>     EXT4-fs (vdb): mount failed
> 
> Therefore, synchronize the kernel change to e2fsprogs to avoid creating
> orphan files larger than the kernel limit.
> 
> Signed-off-by: Baokun Li <libaokun1@...wei.com>
> ---
>  lib/ext2fs/ext2fs.h |  2 ++
>  lib/ext2fs/orphan.c | 12 +++++++-----
>  2 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/lib/ext2fs/ext2fs.h b/lib/ext2fs/ext2fs.h
> index bb2170b7..d9df007c 100644
> --- a/lib/ext2fs/ext2fs.h
> +++ b/lib/ext2fs/ext2fs.h
> @@ -1819,6 +1819,8 @@ errcode_t ext2fs_set_data_io(ext2_filsys fs, io_channel new_io);
>  errcode_t ext2fs_rewrite_to_io(ext2_filsys fs, io_channel new_io);
>  
>  /* orphan.c */
> +#define EXT4_MAX_ORPHAN_FILE_SIZE	8 << 20
> +#define EXT4_DEFAULT_ORPHAN_FILE_SIZE	2 << 20

These #defines ought to have parentheses guarding the expression for
good hygiene.  Also, if this is an artifact of the ondisk format, then
shouldn't it be in ext2_fs.h?  and fs/ext4/ext4.h?

>  extern errcode_t ext2fs_create_orphan_file(ext2_filsys fs, blk_t num_blocks);
>  extern errcode_t ext2fs_truncate_orphan_file(ext2_filsys fs);
>  extern e2_blkcnt_t ext2fs_default_orphan_file_blocks(ext2_filsys fs);
> diff --git a/lib/ext2fs/orphan.c b/lib/ext2fs/orphan.c
> index 14ac3569..40b1c5c7 100644
> --- a/lib/ext2fs/orphan.c
> +++ b/lib/ext2fs/orphan.c
> @@ -164,6 +164,8 @@ errcode_t ext2fs_create_orphan_file(ext2_filsys fs, blk_t num_blocks)
>  	memset(zerobuf, 0, fs->blocksize);
>  	ob_tail = ext2fs_orphan_block_tail(fs, buf);
>  	ob_tail->ob_magic = ext2fs_cpu_to_le32(EXT4_ORPHAN_BLOCK_MAGIC);
> +	if (num_blocks * fs->blocksize > EXT4_MAX_ORPHAN_FILE_SIZE)
> +		num_blocks = EXT4_MAX_ORPHAN_FILE_SIZE / fs->blocksize;
>  	oi.num_blocks = num_blocks;
>  	oi.alloc_blocks = 0;
>  	oi.last_blk = 0;
> @@ -216,18 +218,18 @@ out:
>  
>  /*
>   * Find reasonable size for orphan file. We choose orphan file size to be
> - * between 32 and 512 filesystem blocks and not more than 1/4096 of the
> - * filesystem unless it is really small.
> + * between 32 filesystem blocks and EXT4_DEFAULT_ORPHAN_FILE_SIZE, and not
> + * more than 1/fs->blocksize of the filesystem unless it is really small.
>   */
>  e2_blkcnt_t ext2fs_default_orphan_file_blocks(ext2_filsys fs)
>  {
>  	__u64 num_blocks = ext2fs_blocks_count(fs->super);
> -	e2_blkcnt_t blks = 512;
> +	e2_blkcnt_t blks = EXT4_DEFAULT_ORPHAN_FILE_SIZE / fs->blocksize;
>  
>  	if (num_blocks < 128 * 1024)
>  		blks = 32;
> -	else if (num_blocks < 2 * 1024 * 1024)
> -		blks = num_blocks / 4096;
> +	else if (num_blocks < EXT4_DEFAULT_ORPHAN_FILE_SIZE)
> +		blks = num_blocks / fs->blocksize;

If the number of blocks in the filesystem is less than the default
orphan file size in bytes?  I don't understand that logic, particularly
because EXT4_DEFAULT_ORPHAN_FILE_SIZE == 2<<20 == 2097152 == 2 * 1024 *
1024.

--D

>  	return (blks + EXT2FS_CLUSTER_MASK(fs)) & ~EXT2FS_CLUSTER_MASK(fs);
>  }
>  
> -- 
> 2.46.1
> 
>