Re: [PATCH v4 13/13] block: flag zoned disks with GENHD_FL_NO_PART

[Christoph Hellwig <hch@lst.de>]

On Fri, Aug 14, 2026 at 03:32:01PM +0900, Damien Le Moal wrote:
> Zoned block devices do not support partitions. However, the partition
> table is nevertheless still inspected, and any partition found ignored
> with a warning in add_partition(). While this is generally not a problem,
> and in fact beneficial to the user as it indicates an invalid use of a
> zoned block device, scanning for a partition table on the device may
> result in issuing read operations to offline zones (e.g. after a disk head
> is depopulated for disks that support head management operations).
> 
> Since partitions are ignored anyway, completely disable partition scanning
> for zoned gendisks by setting the flag GENHD_FL_NO_PART in __add_disk().
> The existing check in add_partition() is left as-is to ensure that we
> still get a warning if for whatever reason, despite GENHD_FL_NO_PART, we
> still endup trying to add partitions.
> 
> Flagging zoned disks with GENHD_FL_NO_PART also has the benefit to expose
> through sysfs the ext_range attribute with the value of 1 instead of the
> default DISK_MAX_PARTS, thus correctly advertizing the fact that zoned
> disks do not support partitions.
> 
> Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
> Reviewed-by: Bart Van Assche <bvanassche@acm.org>
> Reviewed-by: Hannes Reinecke <hare@kernel.org>

This really should get a Fixes for my original patch that skipped
partitions and go to -stable (and into 7.3 even if Jens won't take
the whole series) as it causes totally pointless I/O.  I also suspect
the partition scanning and blkid interaction might be related to some
of the weirdo xfstests failure I see where blkid doesn't detect
xfs file systems in synthetic devices.

Reviewed-by: Christoph Hellwig <hch@lst.de>