Re: [RFC 2/3] xfs: Refactoring the nagcount and delta calculation

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

On Thu, Jul 17, 2025 at 04:00:44PM +0530, Nirjhar Roy (IBM) wrote:
> Introduce xfs_growfs_get_delta() to calculate the nagcount
> and delta blocks and refactor the code from xfs_growfs_data_private().
> No functional changes.
> 
> Signed-off-by: Nirjhar Roy (IBM) <nirjhar.roy.lists@gmail.com>
> ---
>  fs/xfs/libxfs/xfs_ag.c | 25 +++++++++++++++++++++++++
>  fs/xfs/libxfs/xfs_ag.h |  3 +++
>  fs/xfs/xfs_fsops.c     | 17 ++---------------
>  3 files changed, 30 insertions(+), 15 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> index e6ba914f6d06..dcaf5683028e 100644
> --- a/fs/xfs/libxfs/xfs_ag.c
> +++ b/fs/xfs/libxfs/xfs_ag.c
> @@ -872,6 +872,31 @@ xfs_ag_shrink_space(
>  	return err2;
>  }
>  
> +void
> +xfs_growfs_get_delta(struct xfs_mount *mp, xfs_rfsblock_t nb,

/me suggests xfs_growfs_compute_deltas() but otherwise this hoist looks
fine to me;

Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> +	int64_t *deltap, xfs_agnumber_t *nagcountp)
> +{
> +	xfs_rfsblock_t nb_div, nb_mod;
> +	int64_t delta;
> +	xfs_agnumber_t nagcount;
> +
> +	nb_div = nb;
> +	nb_mod = do_div(nb_div, mp->m_sb.sb_agblocks);
> +	if (nb_mod && nb_mod >= XFS_MIN_AG_BLOCKS)
> +		nb_div++;
> +	else if (nb_mod)
> +		nb = nb_div * mp->m_sb.sb_agblocks;
> +
> +	if (nb_div > XFS_MAX_AGNUMBER + 1) {
> +		nb_div = XFS_MAX_AGNUMBER + 1;
> +		nb = nb_div * mp->m_sb.sb_agblocks;
> +	}
> +	nagcount = nb_div;
> +	delta = nb - mp->m_sb.sb_dblocks;
> +	*deltap = delta;
> +	*nagcountp = nagcount;
> +}
> +
>  /*
>   * Extent the AG indicated by the @id by the length passed in
>   */
> diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
> index 1f24cfa27321..190af11f6941 100644
> --- a/fs/xfs/libxfs/xfs_ag.h
> +++ b/fs/xfs/libxfs/xfs_ag.h
> @@ -331,6 +331,9 @@ struct aghdr_init_data {
>  int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
>  int xfs_ag_shrink_space(struct xfs_perag *pag, struct xfs_trans **tpp,
>  			xfs_extlen_t delta);
> +void
> +xfs_growfs_get_delta(struct xfs_mount *mp, xfs_rfsblock_t nb,
> +	int64_t *deltap, xfs_agnumber_t *nagcountp);
>  int xfs_ag_extend_space(struct xfs_perag *pag, struct xfs_trans *tp,
>  			xfs_extlen_t len);
>  int xfs_ag_get_geometry(struct xfs_perag *pag, struct xfs_ag_geometry *ageo);
> diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
> index 0ada73569394..91da9f733659 100644
> --- a/fs/xfs/xfs_fsops.c
> +++ b/fs/xfs/xfs_fsops.c
> @@ -92,18 +92,17 @@ xfs_growfs_data_private(
>  	struct xfs_growfs_data	*in)		/* growfs data input struct */
>  {
>  	xfs_agnumber_t		oagcount = mp->m_sb.sb_agcount;
> +	xfs_rfsblock_t nb = in->newblocks;
>  	struct xfs_buf		*bp;
>  	int			error;
>  	xfs_agnumber_t		nagcount;
>  	xfs_agnumber_t		nagimax = 0;
> -	xfs_rfsblock_t		nb, nb_div, nb_mod;
>  	int64_t			delta;
>  	bool			lastag_extended = false;
>  	struct xfs_trans	*tp;
>  	struct aghdr_init_data	id = {};
>  	struct xfs_perag	*last_pag;
>  
> -	nb = in->newblocks;
>  	error = xfs_sb_validate_fsb_count(&mp->m_sb, nb);
>  	if (error)
>  		return error;
> @@ -122,20 +121,8 @@ xfs_growfs_data_private(
>  			mp->m_sb.sb_rextsize);
>  	if (error)
>  		return error;
> +	xfs_growfs_get_delta(mp, nb, &delta, &nagcount);
>  
> -	nb_div = nb;
> -	nb_mod = do_div(nb_div, mp->m_sb.sb_agblocks);
> -	if (nb_mod && nb_mod >= XFS_MIN_AG_BLOCKS)
> -		nb_div++;
> -	else if (nb_mod)
> -		nb = nb_div * mp->m_sb.sb_agblocks;
> -
> -	if (nb_div > XFS_MAX_AGNUMBER + 1) {
> -		nb_div = XFS_MAX_AGNUMBER + 1;
> -		nb = nb_div * mp->m_sb.sb_agblocks;
> -	}
> -	nagcount = nb_div;
> -	delta = nb - mp->m_sb.sb_dblocks;
>  	/*
>  	 * Reject filesystems with a single AG because they are not
>  	 * supported, and reject a shrink operation that would cause a
> -- 
> 2.43.5
> 
>