Re: [PATCH 1/2] xfs: validate that zoned RT devices are zone aligned

[Christoph Hellwig <hch@lst.de>]

On Mon, Dec 15, 2025 at 11:15:06AM -0800, Darrick J. Wong wrote:
> > +	if (xfs_sb_is_v5(sbp) &&
> > +	    (sbp->sb_features_incompat & XFS_SB_FEAT_INCOMPAT_ZONED)) {
> > +		uint32_t		mod;
> > +
> > +		/*
> > +		 * Zoned RT devices must be aligned to the rtgroup size, because
> > +		 * garbage collection can't deal with rump RT groups.
> 
> I've decided that I'm ok with imposing this new restriction after the
> fact, but only because actual zoned hardware will never expose a runt
> group, so the only way you could end up with one now is if you formatted
> with zoned=1 without a hardware-zoned storage device.
> 
> Could this comment be expanded to say that explicitly?

That comment would not actually be true.  The hardware specs do allow
for runt zones.  No shipping hardware that I know of does that, and
mkfs protects against it, but the statement would be at best misleading
if not outright wrong.  The real reason why this is fine is because
mkfs rounds the capacity down to the zone size.