Re: [PATCH v2 2/2] xfs: clean up calculation of LR header blocks

[Brian Foster <bfoster@redhat.com>]

On Fri, Sep 04, 2020 at 04:25:16PM +0800, Gao Xiang wrote:
> Let's use DIV_ROUND_UP() to calculate log record header
> blocks as what did in xlog_get_iclog_buffer_size() and
> wrap up common helpers for log recovery.
> 
> Signed-off-by: Gao Xiang <hsiangkao@redhat.com>
> ---
> v1: https://lore.kernel.org/r/20200902140923.24392-1-hsiangkao@redhat.com
> 
> changes since v1:
>  - add another helper xlog_logrec_hblks() for the cases with
>    xfs_sb_version_haslogv2(), and use xlog_logrecv2_hblks()
>    for the case of xlog_do_recovery_pass() since it has more
>    complex logic other than just calculate hblks...
> 
>  fs/xfs/xfs_log.c         |  4 +--
>  fs/xfs/xfs_log_recover.c | 53 ++++++++++++++++------------------------
>  2 files changed, 22 insertions(+), 35 deletions(-)
> 
...
> diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> index 28d952794bfa..c6163065f6e0 100644
> --- a/fs/xfs/xfs_log_recover.c
> +++ b/fs/xfs/xfs_log_recover.c
> @@ -397,6 +397,23 @@ xlog_find_verify_cycle(
>  	return error;
>  }
>  
> +static inline int xlog_logrecv2_hblks(struct xlog_rec_header *rh)
> +{
> +	int	h_size = be32_to_cpu(rh->h_size);
> +
> +	if ((be32_to_cpu(rh->h_version) & XLOG_VERSION_2) &&
> +	    h_size > XLOG_HEADER_CYCLE_SIZE)
> +		return DIV_ROUND_UP(h_size, XLOG_HEADER_CYCLE_SIZE);
> +	return 1;
> +}
> +
> +static inline int xlog_logrec_hblks(struct xlog *log, xlog_rec_header_t *rh)
> +{
> +	if (!xfs_sb_version_haslogv2(&log->l_mp->m_sb))
> +		return 1;
> +	return xlog_logrecv2_hblks(rh);
> +}
> +

h_version is assigned based on xfs_sb_version_haslogv2() in the first
place so I'm not sure I see the need for multiple helpers like this, at
least with the current code. I can't really speak to why some code
checks the feature bit and/or the record header version and not the
other way around, but perhaps there's some historical reason I'm not
aware of. Regardless, is there ever a case where
xfs_sb_version_haslogv2() == true and h_version != 2? That strikes me as
more of a corruption scenario than anything..

Brian

>  /*
>   * Potentially backup over partial log record write.
>   *
> @@ -489,15 +506,7 @@ xlog_find_verify_log_record(
>  	 * reset last_blk.  Only when last_blk points in the middle of a log
>  	 * record do we update last_blk.
>  	 */
> -	if (xfs_sb_version_haslogv2(&log->l_mp->m_sb)) {
> -		uint	h_size = be32_to_cpu(head->h_size);
> -
> -		xhdrs = h_size / XLOG_HEADER_CYCLE_SIZE;
> -		if (h_size % XLOG_HEADER_CYCLE_SIZE)
> -			xhdrs++;
> -	} else {
> -		xhdrs = 1;
> -	}
> +	xhdrs = xlog_logrec_hblks(log, head);
>  
>  	if (*last_blk - i + extra_bblks !=
>  	    BTOBB(be32_to_cpu(head->h_len)) + xhdrs)
> @@ -1184,22 +1193,7 @@ xlog_check_unmount_rec(
>  	 * below. We won't want to clear the unmount record if there is one, so
>  	 * we pass the lsn of the unmount record rather than the block after it.
>  	 */
> -	if (xfs_sb_version_haslogv2(&log->l_mp->m_sb)) {
> -		int	h_size = be32_to_cpu(rhead->h_size);
> -		int	h_version = be32_to_cpu(rhead->h_version);
> -
> -		if ((h_version & XLOG_VERSION_2) &&
> -		    (h_size > XLOG_HEADER_CYCLE_SIZE)) {
> -			hblks = h_size / XLOG_HEADER_CYCLE_SIZE;
> -			if (h_size % XLOG_HEADER_CYCLE_SIZE)
> -				hblks++;
> -		} else {
> -			hblks = 1;
> -		}
> -	} else {
> -		hblks = 1;
> -	}
> -
> +	hblks = xlog_logrec_hblks(log, rhead);
>  	after_umount_blk = xlog_wrap_logbno(log,
>  			rhead_blk + hblks + BTOBB(be32_to_cpu(rhead->h_len)));
>  
> @@ -3024,15 +3018,10 @@ xlog_do_recovery_pass(
>  		if (error)
>  			goto bread_err1;
>  
> -		if ((be32_to_cpu(rhead->h_version) & XLOG_VERSION_2) &&
> -		    (h_size > XLOG_HEADER_CYCLE_SIZE)) {
> -			hblks = h_size / XLOG_HEADER_CYCLE_SIZE;
> -			if (h_size % XLOG_HEADER_CYCLE_SIZE)
> -				hblks++;
> +		hblks = xlog_logrecv2_hblks(rhead);
> +		if (hblks != 1) {
>  			kmem_free(hbp);
>  			hbp = xlog_alloc_buffer(log, hblks);
> -		} else {
> -			hblks = 1;
>  		}
>  	} else {
>  		ASSERT(log->l_sectBBsize == 1);
> -- 
> 2.18.1
>