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

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

On Mon, Apr 13, 2026 at 03:52:59AM +0800, Zorro Lang wrote:
> 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.

"Please specify desired data subvolume file size by -d size=<value> option\n" ?

--D

> 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
> > > 
> > > 
> > 
>