Re: [PATCH V2] mkfs.xfs: fix ASSERT on too-small device with stripe geometry

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Mon, Sep 14, 2020 at 02:00:52PM -0500, Eric Sandeen wrote:
> When a too-small device is created with stripe geometry, we hit an
> assert in align_ag_geometry():
> 
> # truncate --size=10444800 testfile
> # mkfs.xfs -dsu=65536,sw=1 testfile 
> mkfs.xfs: xfs_mkfs.c:2834: align_ag_geometry: Assertion `cfg->agcount != 0' failed.
> 
> This is because align_ag_geometry() finds that the size of the last
> (only) AG is too small, and attempts to trim it off.  Obviously 0
> AGs is invalid, and we hit the ASSERT.
> 
> Fix this by skipping the last-ag-trim if there is only one AG, and
> add a new test to validate_ag_geometry() which offers a very specific,
> clear warning if the device (in dblocks) is smaller than the minimum
> allowed AG size.
> 
> Reported-by: Zdenek Kabelac <zkabelac@redhat.com>
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>

Seems fine to me,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
> 
> V2: remove stray printf, sorry
> 
> diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
> index a687f385..2139aedb 100644
> --- a/mkfs/xfs_mkfs.c
> +++ b/mkfs/xfs_mkfs.c
> @@ -1038,6 +1038,15 @@ validate_ag_geometry(
>  	uint64_t	agsize,
>  	uint64_t	agcount)
>  {
> +	/* Is this device simply too small? */
> +	if (dblocks < XFS_AG_MIN_BLOCKS(blocklog)) {
> +		fprintf(stderr,
> +	_("device (%lld blocks) too small, need at least %lld blocks\n"),
> +			(long long)dblocks,
> +			(long long)XFS_AG_MIN_BLOCKS(blocklog));
> +		usage();
> +	}
> +
>  	if (agsize < XFS_AG_MIN_BLOCKS(blocklog)) {
>  		fprintf(stderr,
>  	_("agsize (%lld blocks) too small, need at least %lld blocks\n"),
> @@ -2827,11 +2836,11 @@ validate:
>  	 * and drop the blocks.
>  	 */
>  	if (cfg->dblocks % cfg->agsize != 0 &&
> +	     cfg->agcount > 1 &&
>  	     (cfg->dblocks % cfg->agsize < XFS_AG_MIN_BLOCKS(cfg->blocklog))) {
>  		ASSERT(!cli_opt_set(&dopts, D_AGCOUNT));
>  		cfg->dblocks = (xfs_rfsblock_t)((cfg->agcount - 1) * cfg->agsize);
>  		cfg->agcount--;
> -		ASSERT(cfg->agcount != 0);
>  	}
>  
>  	validate_ag_geometry(cfg->blocklog, cfg->dblocks,
> 
>