On Fri, Dec 13, 2019 at 01:08:47PM +0900, Naohiro Aota wrote: > This series adds zoned block device support to btrfs. > > Changes: > - Changed -EINVAL to -EOPNOTSUPP to reject incompatible features > within HMZONED mode (David) > - Use bitmap helpers (Johannes) > - Fix calculation of a string length > - Code cleanup > > Userland series is unchaged with the last version: > https://lore.kernel.org/linux-btrfs/20191204082513.857320-1-naohiro.aota@xxxxxxx/T/ > > * Patch series description > > A zoned block device consists of a number of zones. Zones are either > conventional and accepting random writes or sequential and requiring > that writes be issued in LBA order from each zone write pointer > position. This patch series ensures that the sequential write > constraint of sequential zones is respected while fundamentally not > changing BtrFS block and I/O management for block stored in > conventional zones. One more high-level comment: let's please call it 'zone' mode, without the 'host managed' part. That term is not relevant for a filesystem. The zone allocator, or zone append-only allocator or similar describe what happens on the filesystem layer. The constraint posed by device is to never overwrite in place, that's fine for COW design and that's what should be kept in mind while adding the limitations (no nocow/raid56/...) or exceptions into the code. In some cases it's not possible to fold the zoned support into existing helpers but we should do that wherever we can. While reading the code the number of if (HMZONED) felt too intrusive. This needs to be adjusted, but I think it's mostly cosmetic or basic refactoring, not changing the core of the implementation. So in particular: remove 'hm' everywhere, filename, identifiers. For short I'd call it 'zone' mode but full description would be something like 'zone aware append-only allocation mode'. I'll do another review pass to point out what I think can be refactored but I hope that with the above gives enough hint.
