Re: [PATCH V9 15/19] xfs: Directory's data fork extent counter can never overflow

["Darrick J. Wong" <djwong@kernel.org>]

On Thu, Apr 07, 2022 at 11:13:11AM +1000, Dave Chinner wrote:
> On Wed, Apr 06, 2022 at 11:48:59AM +0530, Chandan Babu R wrote:
> > The maximum file size that can be represented by the data fork extent counter
> > in the worst case occurs when all extents are 1 block in length and each block
> > is 1KB in size.
> > 
> > With XFS_MAX_EXTCNT_DATA_FORK_SMALL representing maximum extent count and with
> > 1KB sized blocks, a file can reach upto,
> > (2^31) * 1KB = 2TB
> > 
> > This is much larger than the theoretical maximum size of a directory
> > i.e. XFS_DIR2_SPACE_SIZE * 3 = ~96GB.
> > 
> > Since a directory's inode can never overflow its data fork extent counter,
> > this commit removes all the overflow checks associated with
> > it. xfs_dinode_verify() now performs a rough check to verify if a diretory's
> > data fork is larger than 96GB.
> > 
> > Signed-off-by: Chandan Babu R <chandan.babu@oracle.com>
> 
> Mostly OK, just a simple cleanup needed.
> 
> > diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
> > index ee8d4eb7d048..54b106ae77e1 100644
> > --- a/fs/xfs/libxfs/xfs_inode_buf.c
> > +++ b/fs/xfs/libxfs/xfs_inode_buf.c
> > @@ -491,6 +491,15 @@ xfs_dinode_verify(
> >  	if (mode && nextents + naextents > nblocks)
> >  		return __this_address;
> >  
> > +	if (S_ISDIR(mode)) {
> > +		uint64_t	max_dfork_nexts;
> > +
> > +		max_dfork_nexts = (XFS_DIR2_MAX_SPACES * XFS_DIR2_SPACE_SIZE) >>
> > +					mp->m_sb.sb_blocklog;
> > +		if (nextents > max_dfork_nexts)
> > +			return __this_address;
> > +	}
> 
> max_dfork_nexts for a directory is a constant that should be
> calculated at mount time via xfs_da_mount() and stored in the
> mp->m_dir_geo structure. Then this code simple becomes:
> 
> 	if (S_ISDIR(mode) && nextents > mp->m_dir_geo->max_extents)
> 		return __this_address;

I have the same comment as Dave, FWIW. :)

--D

> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com