linux-kernel - Re: [PATCH v2] driver/nvme/host: Support duplicated nsid for the private ns

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Date:   Tue, 15 Mar 2022 09:40:35 +0100
From:   "hch@....de" <hch@....de>
To:     Sagi Grimberg <sagi@...mberg.me>
Cc:     "hch@....de" <hch@....de>, Sungup Moon <sungup.moon@...sung.com>,
        "kbusch@...nel.org" <kbusch@...nel.org>,
        "axboe@...com" <axboe@...com>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] driver/nvme/host: Support duplicated nsid for the
 private ns

On Tue, Mar 15, 2022 at 10:18:30AM +0200, Sagi Grimberg wrote:
>> +static struct nvme_ns_head *nvme_find_ns_head(struct nvme_ctrl *ctrl,
>>   		unsigned nsid)
>>   {
>> +	struct nvme_subsystem *subsys = ctrl->subsys;
>>   	struct nvme_ns_head *h;
>>     	lockdep_assert_held(&subsys->lock);
>
> IMO it is a bit strange that we now don't pass in the subsystem but
> require that the subsys->lock is taken...

We do things like that in various places, mostly because information
needed that is subsystem-wide hangs of the nvme_ctrl structure, in
this case the various feature bitmaps.  We could move them to the
subsystem structure, which would be the right thing to do but a fair
amout of churn for little savings.

>> +++ b/drivers/nvme/host/multipath.c
>> @@ -504,10 +504,11 @@ int nvme_mpath_alloc_disk(struct nvme_ctrl *ctrl, struct nvme_ns_head *head)
>>     	/*
>>   	 * Add a multipath node if the subsystems supports multiple controllers.
>> -	 * We also do this for private namespaces as the namespace sharing data could
>> -	 * change after a rescan.
>> +	 * We also do this for private namespaces as the namespace sharing flag
>> +	 * could change after a rescan.
>
> What happens in this case? we now have non-unique shared namespaces?

The non-uniqueue NSIDs can only happen for private namespaces.