Re: [PATCH 6/4] mkfs: round log size down if rounding log start up causes overflow

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

On Fri, Apr 15, 2022 at 04:57:58PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> If rounding the log start up to the next stripe unit would cause the log
> to overrun the end of the AG, round the log size down by a stripe unit.
> We already ensured that logblocks was small enough to fit inside the AG,
> so the minor adjustment should suffice.

Self NAK, Eric pointed out more ways this can fail.  New patch coming
soon.

--D

> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> ---
>  mkfs/xfs_mkfs.c |   12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
> index b932acaa..cfa38f17 100644
> --- a/mkfs/xfs_mkfs.c
> +++ b/mkfs/xfs_mkfs.c
> @@ -3219,9 +3219,19 @@ align_internal_log(
>  	int			max_logblocks)
>  {
>  	/* round up log start if necessary */
> -	if ((cfg->logstart % sunit) != 0)
> +	if ((cfg->logstart % sunit) != 0) {
>  		cfg->logstart = ((cfg->logstart + (sunit - 1)) / sunit) * sunit;
>  
> +		/*
> +		 * If rounding up logstart to a stripe boundary moves the end
> +		 * of the log past the end of the AG, reduce logblocks to get
> +		 * it back under EOAG.
> +		 */
> +		if (!libxfs_verify_fsbext(mp, cfg->logstart, cfg->logblocks) &&
> +		    cfg->logblocks > sunit)
> +			cfg->logblocks -= sunit;
> +	}
> +
>  	/* If our log start overlaps the next AG's metadata, fail. */
>  	if (!libxfs_verify_fsbno(mp, cfg->logstart)) {
>  		fprintf(stderr,