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

Dave Chinner
2022-04-07T01:20:05Z

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;

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com