[PATCH 2/3] nvmet: prevent creating ctrl with no namespace

[Sagi Grimberg]

>  From Spec :-
> 
> If the controller supports Asymmetric Namespace Access Reporting, then
> MNAN shall be set to a non-zero value that is less than or equal
> to the NN value.
> 
> In current implementation if subsys has 0 namespaces then we report
> wrong MNAN value for the controller if we allow controller creation.
> 
> Prevent new controller creation if the subsys associated with the new
> controller has no namespaces.

This is a perfectly valid thing to do, preventing this is not the
solution here.

Why not just set both nn and mnan to NVMET_MAX_NAMESPACES and be done
with it?

> 
> Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni at wdc.com>
> ---
>   drivers/nvme/target/core.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c
> index 146909486b8f..26d93ac9bd2e 100644
> --- a/drivers/nvme/target/core.c
> +++ b/drivers/nvme/target/core.c
> @@ -1325,6 +1325,15 @@ u16 nvmet_alloc_ctrl(const char *subsysnqn, const char *hostnqn,
>   		goto out;
>   	}
>   
> +	mutex_lock(&subsys->lock);
> +	if (!subsys->max_nsid) {
> +		mutex_unlock(&subsys->lock);
> +		pr_err("invalid mnan value for the ana enabled controller\n");
> +		status = NVME_SC_INTERNAL;
> +		goto out_put_subsystem;
> +	}
> +	mutex_unlock(&subsys->lock);
> +
>   	down_read(&nvmet_config_sem);
>   	if (!nvmet_host_allowed(subsys, hostnqn)) {
>   		pr_info("connect by host %s for subsystem %s not allowed\n",
>