Re: [PATCH V4 2/9] nvmet: add ZNS support for bdev-ns

[Christoph Hellwig <hch@lst.de>]

On Fri, Dec 04, 2020 at 03:13:40AM +0000, Chaitanya Kulkarni wrote:
> >> +	if (!bdev_is_zoned(nvmet_bdev(req)))
> >> +		return NVME_SC_SUCCESS;
> >> +
> >> +	return nvmet_copy_ns_identifier(req, NVME_NIDT_CSI, NVME_NIDT_CSI_LEN,
> >> +					&nvme_cis_zns, off);
> >> +}
> > This looks weird.  We can want to support the command set identifier in
> > general, so this should go into common code, and just look up the command
> > set identifier in the nvmet_ns structure.
> 
> ZNS is the only user for this, so I've added to the zns code. I'll move to
> 
> admin-cmd.

CSI is a generic feature, ZNS is just the first thing that requires it.

> > This will change the limit when a new namespaces is added.  I think we need
> > to just pick the value of the first namespaces and refuse adding a new
> > one if the limit is lower to not completely break hosts.
> 
> But that will force users to add ns with highest zasl first no matter what.
> 
> Isn't there should be a way to update the host with async event
> 
> so that host can refresh the ctrl->zasl when ns addition async notification
> 
> is generated ?

I'd rather not go too dynamic and change capabilities down dynamically.
I think that will cause all kinds of fun problems with I/Os already
queue up in the block layer while the limit changes.