dm: add non power of 2 zoned target
Only power of 2(po2) zoned devices were supported in linux but now non
power of 2(npo2) zoned device support has been added to the block layer.
Filesystems such as F2FS and btrfs have support for zoned devices with
po2 zone size assumption. Before adding native support for npo2 zoned
devices, it was suggested to create a dm target for npo2 zoned device to
appear as po2 device so that file systems can initially work without any
explicit changes by using this target.
The design of this target is very simple: introduce gaps between the zone
capacity and the po2 zone size of the underlying device. All IOs will be
remapped from target to the actual device location. For devices that use
zone append, the bi_sector is remapped from device to target's layout.
The read IOs that fall in the "emulated" gap area will return 0 and all
the other IOs in that area will result in an error. If an read IO span
across the zone capacity boundary, then the IOs are split between the
boundary. All other IO operations that span across a zone capacity
boundary will result in an error.
The target can be easily updated as follows:
dmsetup create <label> --table '0 <size_sects> zoned-npo2 /dev/nvme<id>'
Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
[rebased onto next-20220707 and ajust commit log]
Suggested-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Suggested-by: Damien Le Moal <damien.lemoal@wdc.com>
Suggested-by: Hannes Reinecke <hare@suse.de>
Reported-by: kernel test robot <lkp@intel.com>
4 files changed
