[SPDK] NVMf namespace masking 2nd

[Jonas Pfefferle <pepperjo at japf.ch>]

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Hi all,

I updated the NVMf namespace masking PR:
https://review.spdk.io/gerrit/c/spdk/spdk/+/7821

Changes to RFC:
- Address concerns of overhead of checking on IO path.
   If a namepsace is active is only checked where needed and
   validity checks for NSID is only done once.
- Allow to hot and cold attach/detach
- It is no longer possible to call the new RPCs without
   hostNQN. The auto attach bevahior cannot be changed
   after add_ns. We might add an additional RPC for this
   later.
- identify ns now correctly response with zeros for
   inactive namespace
- Address concurrency concerns: attaching/detaching
   now pauses the subsystem for changes
- ns change log is updated on attach/detach
- tests

I would be happy to get some feeedback.

Thanks,
Jonas

  On Sat, 08 May 2021 15:37:09 +0200
  "Jonas Pfefferle" <pepperjo(a)japf.ch> wrote:
> Hi all,
> 
> I would be happy to get some feedback on my NVMf target namespace 
>masking implementation using attach/detach:
> https://review.spdk.io/gerrit/c/spdk/spdk/+/7821
> 
> The patch introduces namespace masking for NVMe-over-fabrics
> targets by allowing to (dynamically) attach and detach
> controllers to/from namespaces, cf. NVMe spec 1.4 - section 6.1.4.
> Since SPDK only supports the dynamic controller model a new
> controller is allocated on every fabric connect command.
> This allows to attach/detach controllers of a specific
> host NQN to/from a namespace. A host can only perform
> operations to an active namespace. Inactive namespaces can
> be listed (not supported by SPDK) but no additional
> information can be retrieved:
> "Unless otherwise noted, specifying an inactive NSID in a
> command that uses the Namespace Identifier (NSID) field shall
> cause the controller to abort the command with status
> Invalid Field in Command" - NVMe spec 1.4 - section 6.1.5
> Note that this patch does not implement the NVMe namespace
> attachment command but allows to attach/detach via RPCs only.
> To preserve current behavior all controllers are auto attached.
> To not not auto attach controllers the nvmf_subsystem_add_ns
> shall be called with "--no-auto-attach". We introduce two new
> RPC calls:
> - nvmf_ns_attach_ctrlr <subsysNQN> <NSID> [--host <hostNQN>]
> - nvmf_ns_detach_ctrlr <subsysNQN> <NSID> [--host <hostNQN>]
> If no host NQN is specified all controllers
> (new and currently connected) will attach/detach to/from the
> namespace specified.
> The list in spdk_nvmf_ns is used to keep track of hostNQNs
> which controllers should be attached on connect.
> The active_ns array in spdk_nvmf_ctrlr is used for fast lookup
> to check whether a NSID is active/inactive on command execution.
> 
> Thanks,
> Jonas
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