Re: [PATCH 6/6] xfs: adjust datadev sector count to reflect internal rt volumes

[Christoph Hellwig <hch@infradead.org>]

On Wed, Aug 12, 2026 at 10:25:25PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> A media scan of a filesystem containing an internal rt volume produced
> an error in xfs_scrub phase 6 complaining about a truncated realtime
> device.  The rt device wasn't truncated, but the media scan code thought
> we were trying to start a scan past the end of m_rtdev_targp.  That in
> turn is an alias for m_ddev_targp, but in xfs_configure_buftarg we set
> nr_sectors to the size of the data section.  Oops.

Can you share your reproducer for this?

> 
> On these filesystems, the internal rt section comes immediately after
> the data section.  We need to set the sector count for the data device
> buftarg to the size of both sections.  Without this, media scans don't
> work and media failure notifications from the kernel will be discarded
> silently.
> 
> We also need to fix the superblock buffer recovery code to do the same.

I still think messing with the kernel buftarg nr_sectors is wrong for
this.  The kernel view of the buftarg should be correct and just include
the part of the device that matters.  So I think the right fix in the
kernel is changing xfs_verify_media to add the internal RT device offset
before sending the bios.   We might need additional userland fixes,
but from a quick look I think it should be fine (famous last words)