Re: [PATCH V4 09/10] xfs: Check for extent overflow when swapping extents

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Sep 18, 2020 at 03:17:58PM +0530, Chandan Babu R wrote:
> Removing an initial range of source/donor file's extent and adding a new
> extent (from donor/source file) in its place will cause extent count to
> increase by 1.
> 
> Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
> ---
>  fs/xfs/libxfs/xfs_bmap.c       | 18 +++++++++---------
>  fs/xfs/libxfs/xfs_bmap.h       |  1 +
>  fs/xfs/libxfs/xfs_inode_fork.h |  7 +++++++
>  fs/xfs/xfs_bmap_util.c         | 17 +++++++++++++++++
>  4 files changed, 34 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 51c2d2690f05..9c665e379dfc 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -6104,15 +6104,6 @@ xfs_bmap_split_extent(
>  	return error;
>  }
>  
> -/* Deferred mapping is only for real extents in the data fork. */
> -static bool
> -xfs_bmap_is_update_needed(
> -	struct xfs_bmbt_irec	*bmap)
> -{
> -	return  bmap->br_startblock != HOLESTARTBLOCK &&
> -		bmap->br_startblock != DELAYSTARTBLOCK;
> -}
> -
>  /* Record a bmap intent. */
>  static int
>  __xfs_bmap_add(
> @@ -6144,6 +6135,15 @@ __xfs_bmap_add(
>  	return 0;
>  }
>  
> +/* Deferred mapping is only for real extents in the data fork. */
> +bool
> +xfs_bmap_is_update_needed(
> +	struct xfs_bmbt_irec	*bmap)
> +{
> +	return  bmap->br_startblock != HOLESTARTBLOCK &&
> +		bmap->br_startblock != DELAYSTARTBLOCK;
> +}

I think the predicate you want below is xfs_bmap_is_real_extent().

(I think that mostly because I'm going to kill this predicate entirely
in a patch for the next cycle, because it is redundant and
_is_real_extent is a better name.)

--D

> +
>  /* Map an extent into a file. */
>  void
>  xfs_bmap_map_extent(
> diff --git a/fs/xfs/libxfs/xfs_bmap.h b/fs/xfs/libxfs/xfs_bmap.h
> index e1bd484e5548..60fbe184d5f4 100644
> --- a/fs/xfs/libxfs/xfs_bmap.h
> +++ b/fs/xfs/libxfs/xfs_bmap.h
> @@ -263,6 +263,7 @@ struct xfs_bmap_intent {
>  	struct xfs_bmbt_irec			bi_bmap;
>  };
>  
> +bool	xfs_bmap_is_update_needed(struct xfs_bmbt_irec *bmap);
>  int	xfs_bmap_finish_one(struct xfs_trans *tp, struct xfs_inode *ip,
>  		enum xfs_bmap_intent_type type, int whichfork,
>  		xfs_fileoff_t startoff, xfs_fsblock_t startblock,
> diff --git a/fs/xfs/libxfs/xfs_inode_fork.h b/fs/xfs/libxfs/xfs_inode_fork.h
> index ded3c1b56c94..837c01595439 100644
> --- a/fs/xfs/libxfs/xfs_inode_fork.h
> +++ b/fs/xfs/libxfs/xfs_inode_fork.h
> @@ -102,6 +102,13 @@ struct xfs_ifork {
>  #define XFS_IEXT_REFLINK_REMAP_CNT(smap_real, dmap_written) \
>  	(((smap_real) ? 1 : 0) + ((dmap_written) ? 1 : 0))
>  
> +/*
> + * Removing an initial range of source/donor file's extent and adding a new
> + * extent (from donor/source file) in its place will cause extent count to
> + * increase by 1.
> + */
> +#define XFS_IEXT_SWAP_RMAP_CNT		(1)
> +
>  /*
>   * Fork handling.
>   */
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index 0776abd0103c..542f990247c4 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -28,6 +28,7 @@
>  #include "xfs_icache.h"
>  #include "xfs_iomap.h"
>  #include "xfs_reflink.h"
> +#include "xfs_bmap.h"
>  
>  /* Kernel only BMAP related definitions and functions */
>  
> @@ -1407,6 +1408,22 @@ xfs_swap_extent_rmap(
>  					irec.br_blockcount);
>  			trace_xfs_swap_extent_rmap_remap_piece(tip, &uirec);
>  
> +			if (xfs_bmap_is_update_needed(&uirec)) {
> +				error = xfs_iext_count_may_overflow(ip,
> +						XFS_DATA_FORK,
> +						XFS_IEXT_SWAP_RMAP_CNT);
> +				if (error)
> +					goto out;
> +			}
> +
> +			if (xfs_bmap_is_update_needed(&irec)) {
> +				error = xfs_iext_count_may_overflow(tip,
> +						XFS_DATA_FORK,
> +						XFS_IEXT_SWAP_RMAP_CNT);
> +				if (error)
> +					goto out;
> +			}
> +
>  			/* Remove the mapping from the donor file. */
>  			xfs_bmap_unmap_extent(tp, tip, &uirec);
>  
> -- 
> 2.28.0
>