Re: [PATCH 10/21] xfs: calculate the log reservation for logging data checksum buffers

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

On Thu, Sep 24, 2026 at 11:59:42AM +0200, Christoph Hellwig wrote:
> The data checksum is logged in its own transaction, and only logs
> transactions buffers.  While the maximum size of a checksummed data write
> is the same as that of a single checksum buffer, the Zone Append based
> zoned write path can't guarantee alignment, so it might be spread over
> up to three buffers.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/libxfs/xfs_trans_resv.c | 21 +++++++++++++++++++++
>  fs/xfs/libxfs/xfs_trans_resv.h |  4 ++++
>  2 files changed, 25 insertions(+)
> 
> diff --git a/fs/xfs/libxfs/xfs_trans_resv.c b/fs/xfs/libxfs/xfs_trans_resv.c
> index 5382ece51812..8854253afba0 100644
> --- a/fs/xfs/libxfs/xfs_trans_resv.c
> +++ b/fs/xfs/libxfs/xfs_trans_resv.c
> @@ -11,6 +11,7 @@
>  #include "xfs_log_format.h"
>  #include "xfs_trans_resv.h"
>  #include "xfs_mount.h"
> +#include "xfs_rtcsumfile.h"
>  #include "xfs_da_format.h"
>  #include "xfs_da_btree.h"
>  #include "xfs_inode.h"
> @@ -1233,6 +1234,22 @@ xfs_calc_qm_dqalloc_reservation_minlogsize(
>  	return xfs_calc_qm_dqalloc_reservation(mp, true);
>  }
>  
> +/*
> + * Log data checksums for a write.
> + *
> + * Must cover a checksum for each FSB of data written, and the checksums can
> + * span the FSB-sized checksum buffers at both ends.
> + */
> +unsigned int
> +xfs_calc_csum_reservation(
> +	struct xfs_mount	*mp,
> +	unsigned int		csum_len)
> +{
> +	return xfs_calc_buf_res(
> +			howmany(csum_len, xfs_rtcsum_payload_size(mp)) + 1,
> +			mp->m_rtcsum_bsize);
> +}
> +
>  /*
>   * Syncing the incore super block changes to disk.
>   *     the super block to reflect the changes: sector size
> @@ -1354,6 +1371,10 @@ xfs_trans_resv_calc(
>  
>  	xfs_calc_namespace_reservations(mp, resp);
>  
> +	resp->tr_csum.tr_logres =
> +		xfs_calc_csum_reservation(mp, XFS_RTCSUM_MAX_WRITE);
> +	resp->tr_csum.tr_logcount = XFS_DEFAULT_LOG_COUNT;

Going back to a question I had in "xfs: prepare
xfs_rtfile_initialize_blocks for larger than FSB blocks", should we be
using tr_csum for the transaction to write out new checksum file block
contents?

Patch itself looks ok though,
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> +
>  	/*
>  	 * The following transactions are logged in logical format with
>  	 * a default log count.
> diff --git a/fs/xfs/libxfs/xfs_trans_resv.h b/fs/xfs/libxfs/xfs_trans_resv.h
> index 1804e821f382..127db4da31c1 100644
> --- a/fs/xfs/libxfs/xfs_trans_resv.h
> +++ b/fs/xfs/libxfs/xfs_trans_resv.h
> @@ -49,6 +49,7 @@ struct xfs_trans_resv {
>  	struct xfs_trans_res	tr_sb;		/* modify superblock */
>  	struct xfs_trans_res	tr_fsyncts;	/* update timestamps on fsync */
>  	struct xfs_trans_res	tr_atomic_ioend; /* untorn write completion */
> +	struct xfs_trans_res	tr_csum;	/* data checksums in metafile */
>  };
>  
>  /* shorthand way of accessing reservation structure */
> @@ -122,6 +123,9 @@ unsigned int xfs_calc_itruncate_reservation_minlogsize(struct xfs_mount *mp);
>  unsigned int xfs_calc_write_reservation_minlogsize(struct xfs_mount *mp);
>  unsigned int xfs_calc_qm_dqalloc_reservation_minlogsize(struct xfs_mount *mp);
>  
> +unsigned int xfs_calc_csum_reservation(struct xfs_mount *mp,
> +		unsigned int csum_len);
> +
>  xfs_extlen_t xfs_calc_max_atomic_write_fsblocks(struct xfs_mount *mp);
>  xfs_extlen_t xfs_calc_atomic_write_log_geometry(struct xfs_mount *mp,
>  		xfs_extlen_t blockcount, unsigned int *new_logres);
> -- 
> 2.53.0
> 
>