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

[Zorro Lang <zorro.lang@gmail.com>]

On Mon, Apr 06, 2026 at 08:26:28AM -0700, Darrick J. Wong wrote:
> 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.

Oh, you're right, the mkfs.xfs command failing here is a total failure, not
just a warning.

How about:
_(Bad empty file, needs a data subvolume size by -d size=<value> option)

or any other you feel good.

Thanks,
Zorro

> 
> 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
> > 
> > 
>