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

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

On Tue, Dec 16, 2025 at 06:10:02AM +0100, Christoph Hellwig wrote:
> 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.

Bah.  That figures. :(

> 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.

"...garbage collection won't deal with rump RT groups because the size
increase isn't worth the corner case complexity.", then? :D

--D