Re: [RFC PATCH V2 00/11] hw/block/nvme: support multi-path for ctrl/ns

[Minwoo Im <minwoo.im.dev@gmail.com>]

On 21-01-18 22:14:45, Klaus Jensen wrote:
> On Jan 17 23:53, Minwoo Im wrote:
> > Hello,
> > 
> > This patch series introduces NVMe subsystem device to support multi-path
> > I/O in NVMe device model.  Two use-cases are supported along with this
> > patch: Multi-controller, Namespace Sharing.
> > 
> > V1 RFC has been discussed with Klaus and Keith, I really appreciate them
> > for this patch series to have proper direction [1].
> > 
> > This patch series contains few start-up refactoring pathces from the
> > first to fifth patches to make nvme-ns device not to rely on the nvme
> > controller always.  Because nvme-ns shall be able to be mapped to the
> > subsystem level, not a single controller level so that it should provide
> > generic initialization code: nvme_ns_setup() with NvmeCtrl.  To do that,
> > the first five patches are to remove the NvmeCtrl * instance argument
> > from the nvme_ns_setup().  I'd be happy if they are picked!
> > 
> > For controller and namespace devices, 'subsys' property has been
> > introduced to map them to a subsystem.  If multi-controller needed, we
> > can specify 'subsys' to controllers the same.
> > 
> > For namespace deivice, if 'subsys' is not given just like it was, it
> > will have to be provided with 'bus' parameter to specify a nvme
> > controller device to attach, it means, they are mutual-exlusive.  To
> > share a namespace between or among controllers, then nvme-ns should have
> > 'subsys' property to a single nvme subsystem instance.  To make a
> > namespace private one, then we need to specify 'bus' property rather
> > than the 'subsys'.
> > 
> > Of course, this series does not require any updates for the run command
> > for the previos users.
> > 
> > Plase refer the following example with nvme-cli output:
> > 
> > QEMU Run:
> >   -device nvme-subsys,id=subsys0 \
> >   -device nvme,serial=foo,id=nvme0,subsys=subsys0 \
> >   -device nvme,serial=bar,id=nvme1,subsys=subsys0 \
> >   -device nvme,serial=baz,id=nvme2,subsys=subsys0 \
> >   -device nvme-ns,id=ns1,drive=drv10,nsid=1,subsys=subsys0 \
> >   -device nvme-ns,id=ns2,drive=drv11,nsid=2,bus=nvme2 \
> >   \
> >   -device nvme,serial=qux,id=nvme3 \
> >   -device nvme-ns,id=ns3,drive=drv12,nsid=3,bus=nvme3
> > 
> > nvme-cli:
> >   root@vm:~/work# nvme list -v
> >   NVM Express Subsystems
> > 
> >   Subsystem        Subsystem-NQN                                                                                    Controllers
> >   ---------------- ------------------------------------------------------------------------------------------------ ----------------
> >   nvme-subsys1     nqn.2019-08.org.qemu:subsys0                                                                     nvme0, nvme1, nvme2
> >   nvme-subsys3     nqn.2019-08.org.qemu:qux                                                                         nvme3
> > 
> >   NVM Express Controllers
> > 
> >   Device   SN                   MN                                       FR       TxPort Address        Subsystem    Namespaces
> >   -------- -------------------- ---------------------------------------- -------- ------ -------------- ------------ ----------------
> >   nvme0    foo                  QEMU NVMe Ctrl                           1.0      pcie   0000:00:06.0   nvme-subsys1 nvme1n1
> >   nvme1    bar                  QEMU NVMe Ctrl                           1.0      pcie   0000:00:07.0   nvme-subsys1 nvme1n1
> >   nvme2    baz                  QEMU NVMe Ctrl                           1.0      pcie   0000:00:08.0   nvme-subsys1 nvme1n1, nvme1n2
> >   nvme3    qux                  QEMU NVMe Ctrl                           1.0      pcie   0000:00:09.0   nvme-subsys3
> > 
> >   NVM Express Namespaces
> > 
> >   Device       NSID     Usage                      Format           Controllers
> >   ------------ -------- -------------------------- ---------------- ----------------
> >   nvme1n1      1        134.22  MB / 134.22  MB    512   B +  0 B   nvme0, nvme1, nvme2
> >   nvme1n2      2        268.44  MB / 268.44  MB    512   B +  0 B   nvme2
> >   nvme3n1      3        268.44  MB / 268.44  MB    512   B +  0 B   nvme3
> > 
> > Summary:
> >   - Refactored nvme-ns device not to rely on controller during the
> >     setup.  [1/11 - 5/11]
> >   - Introduced a nvme-subsys device model. [6/11]
> >   - Create subsystem NQN based on subsystem. [7/11]
> >   - Introduced multi-controller model. [8/11 - 9/11]
> >   - Updated namespace sharing scheme to be based on nvme-subsys
> >     hierarchy. [10/11 - 11/11]
> > 
> > Since RFC V1:
> >   - Updated namespace sharing scheme to be based on nvme-subsys
> >     hierarchy.
> > 
> 
> Great stuff Minwoo. Thanks!
> 
> I'll pick up [01-05/11] directly since they are pretty trivial.

Thanks! will prepare the next series based on there.

> The subsystem model looks pretty much like it should, I don't have a lot
> of comments.
> 
> One thing that I considered, is if we should reverse the "registration"
> and think about it as namespace attachment. The spec is about
> controllers attaching to namespaces, not the other way around.
> Basically, let the namespaces be configured first and register on the
> subsystem (accumulating in a "namespaces" array), then have the
> controllers register with the subsystem and attach to all "non-detached"
> namespaces. This allows detached namespaces to "linger" in the subsystem
> to be attached later on. If there are any private namespaces (like ns2
> in your example above), it will be defined after the controller with the
> bus=ctrlX parameter like normal.

Revisited spec. again.  5.19 says "The Namespace Attachment command is
used to attach and detach controllers from a namespace.".  and 5.20 says
"Host software uses the Namespace Attachment command to attach or detach
a namespace to or from a controller. The create operation does not attach
the namespace to a controller."

	-device nvme-subsys,id=subsys0
	-device nvme-ns,id=ns1,drive=<drv>,nsid=1,subsys=subsys0
	-device nvme,id=nvme0,serial=foo,subsys=subsys0

In this case, the 'nvme0' controller will have no namespace at the
initial time of the boot-up.  'nvme0' can be attached to the namespace
'ns1' with namespace attach command.  'nvme-ns' device is same as the
'create-ns' operation in a NVMe subsystem.  This makes sense as spec
5.19 says "from a namespace".

	-device nvme,id=nvme1,serial=bar,subsys=subsys0b
	-device nvme-ns,id=ns2,drive=<drv>,nsid=1,bus=nvme1

This case if for private namespace directly attached to controller.
This makes sense as spec 5.20 says "to or from a controller".

All looks fine to me, but one thing I an wondering is that how can we
attach a controller to shared namespace(s) at the initial time?