Re: [PATCH v7 08/14] nvmet-core: allow one host per passthru-ctrl

[Max Gurtovoy]

On 8/15/2019 7:06 PM, Logan Gunthorpe wrote:
> On 2019-08-15 6:36 a.m., Max Gurtovoy wrote:
> > On 8/2/2019 2:45 AM, Logan Gunthorpe wrote:
> > > This patch rejects any new connection to the passthru-ctrl if this
> > > controller is already connected to a different host. At the time of
> > > allocating the controller we check if the subsys associated with
> > > the passthru ctrl is already connected to a host and reject it
> > > if the hostnqn differs.
> > This is a big limitation.
> >
> > Are we plan to enable many front-end ctrl's to connect to the single
> > back-end ctrl in the future ?
> Honestly, I don't know that it's really necessary, but the limitation
> was requested by Sagi the first time this patch-set was submitted[1]
> citing unspecified user troubles. If there's consensus to remove the
> restriction I certainly can.
>
> Logan
>
> [1] http://lists.infradead.org/pipermail/linux-nvme/2018-April/016588.html

I don't understand why we don't limit a regular ctrl to single access 
and we do it for the PT ctrl.

I guess the block layer helps to sync between multiple access in 
parallel but we can do it as well.

Also, let's say you limit the access to this subsystem to 1 user, the 
bdev is still accessibly for local user and also you can create a 
different subsystem that will use this device (PT and non-PT ctrl).

Sagi,

can you explain the trouble you meant and how this limitation solve it ?