On 2020/06/26 18:11, hch@xxxxxx wrote: > On Fri, Jun 26, 2020 at 01:14:30AM +0000, Damien Le Moal wrote: >> As long as you keep ZNS namespace report itself as being "host-managed" like >> ZBC/ZAC disks, we need the consistency and common interface. If you break that, >> the meaning of the zoned model queue attribute disappears and an application or >> in-kernel user cannot rely on this model anymore to know how the drive will behave. > > We just need a way to expose to applications that new feature are > supported. Just like we did with zone capacity support. That is why > we added the feature flags to uapi zone structure. > >> Think of a file system, or any other in-kernel user. If they have to change >> their code based on the device type (NVMe vs SCSI), then the zoned block device >> interface is broken. Right now, that is not the case, everything works equally >> well on ZNS and SCSI, modulo the need by a user for conventional zones that ZNS >> do not define. But that is still consistent with the host-managed model since >> conventional zones are optional. > > That is why we have the feature flag. That user should not know the > underlying transport or spec. But it can reliably discover "this thing > support zone capacity" or "this thing supports offline zones" or even > nasty thing like "this zone can time out when open" which are much > harder to deal with. > >> For this particular patch, there is currently no in-kernel user, and it is not >> clear how this will be useful to applications. At least please clarify this. And > > The main user is the ioctl. And if you think about how offline zones are > (suppose to) be used driving this from management tools in userspace > actually totally make sense. Unlike for example open/close all which > just don't make sense as primitives to start with. OK. Adding a new BLKZONEOFFLINE ioctl is easy though and fits into the current zone management plumbing well, I think. So the patch can be significantly simplified (no need for the new zone management op function with flags). > -- Damien Le Moal Western Digital Research
