Re: [PATCH 8/9] xfs: remove l_iclog_heads

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

On Mon, Oct 13, 2025 at 11:42:12AM +0900, Christoph Hellwig wrote:
> l_iclog_heads is only used in one place and can be trivially derived
> from l_iclog_hsize by a single shift operation.  Remove it, and switch
> the initialization of l_iclog_hsize to use struct_size so that it is
> directly derived from the on-disk format definition.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/xfs_log.c      | 11 ++++++-----
>  fs/xfs/xfs_log_priv.h |  1 -
>  2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index 8b3b79699596..47a8e74c8c5c 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -1279,11 +1279,12 @@ xlog_get_iclog_buffer_size(
>  	log->l_iclog_size = mp->m_logbsize;
>  
>  	/*
> -	 * # headers = size / 32k - one header holds cycles from 32k of data.
> +	 * Combined size of the log record headers.  The first 32k cycles
> +	 * are stored directly in the xlog_rec_header, the rest in the
> +	 * variable number of xlog_rec_ext_headers at its end.
>  	 */
> -	log->l_iclog_heads =
> -		DIV_ROUND_UP(mp->m_logbsize, XLOG_HEADER_CYCLE_SIZE);
> -	log->l_iclog_hsize = log->l_iclog_heads << BBSHIFT;
> +	log->l_iclog_hsize = struct_size(log->l_iclog->ic_header, h_ext,
> +		DIV_ROUND_UP(mp->m_logbsize, XLOG_HEADER_CYCLE_SIZE) - 1);

Hrm.  offsetof(xlog_rec_header::h_ext) == 512 and
sizeof(xlog_rec_ext_header) == 512, so I think this computation still
yields the same results.

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

--D

>  }
>  
>  void
> @@ -1526,7 +1527,7 @@ xlog_pack_data(
>  		dp += BBSIZE;
>  	}
>  
> -	for (i = 0; i < log->l_iclog_heads - 1; i++)
> +	for (i = 0; i < (log->l_iclog_hsize >> BBSHIFT) - 1; i++)
>  		rhead->h_ext[i].xh_cycle = cycle_lsn;
>  }
>  
> diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
> index ac98ac71152d..17733ba7f251 100644
> --- a/fs/xfs/xfs_log_priv.h
> +++ b/fs/xfs/xfs_log_priv.h
> @@ -406,7 +406,6 @@ struct xlog {
>  	struct list_head	*l_buf_cancel_table;
>  	struct list_head	r_dfops;	/* recovered log intent items */
>  	int			l_iclog_hsize;  /* size of iclog header */
> -	int			l_iclog_heads;  /* # of iclog header sectors */
>  	uint			l_sectBBsize;   /* sector size in BBs (2^n) */
>  	int			l_iclog_size;	/* size of log in bytes */
>  	int			l_iclog_bufs;	/* number of iclog buffers */
> -- 
> 2.47.3
> 
>