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

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Message-ID: <gqpzieqatnjndg64ui3rwaxzaq4bym34hydf6qnevrbk5jk73n@in4zjfln4ahs>
Date: Wed, 12 Nov 2025 20:55:17 +0100
From: Jan Kara <jack@...e.cz>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: libaokun@...weicloud.com, 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 12-11-25 10:36:09, Darrick J. Wong wrote:
> 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>
...
> >  /*
> >   * 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.

Yeah, these were just more or less ad hoc constants picked by me to make
sure orphan file doesn't consume too much space and they are unrelated to
the constant I've picked in the kernel limiting orphan file size. And I
agree making sure blks isn't larger than EXT4_DEFAULT_ORPHAN_FILE_SIZE
makes sense but otherwise I don't think we need to change anything here.

								Honza

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR