Re: [PATCH 1/2] mkfs: fix assertion failure on empty data file

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

On Sun, Apr 05, 2026 at 12:36:39AM +0800, Zorro Lang wrote:
> mkfs.xfs triggers an assertion failure, when it trys to make a xfs
> on an empty file:
>   # echo > emptyfile
>   # mkfs.xfs emptyfile
>   mkfs.xfs: xfs_mkfs.c:3852: validate_datadev: Assertion `cfg->dblocks' failed.
>   Aborted                    (core dumped) mkfs.xfs emptyfile
> 
> This shouldn't be an assertion, but a warning.
> 
> Signed-off-by: Zorro Lang <zlang@kernel.org>
> ---
>  mkfs/xfs_mkfs.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
> index 527a662f..9a93330f 100644
> --- a/mkfs/xfs_mkfs.c
> +++ b/mkfs/xfs_mkfs.c
> @@ -3848,8 +3848,13 @@ validate_datadev(
>  		if (!xi->data.isfile) {
>  			fprintf(stderr, _("can't get size of data subvolume\n"));
>  			usage();
> +		} else {
> +			if (!cli->dsize) {
> +				fprintf(stderr,
> +_("Warning: Empty file needs a data subvolume size by -d size=<value> option\n"));

I'm not sure why "Warning" is appropriate here -- this error is fatal to
the program, and most fatal mkfs error messages don't have a prefix.

Other than that, the logic is sound that we need a softer landing for
this scenario.

--D

> +				usage();
> +			}
>  		}
> -		ASSERT(cfg->dblocks);
>  	} else if (cfg->dblocks) {
>  		/* check the size fits into the underlying device */
>  		if (cfg->dblocks > DTOBT(xi->data.size, cfg->blocklog)) {
> -- 
> 2.52.0
> 
>