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

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Date:   Mon, 14 Mar 2022 08:08:08 +0100
From:   "hch@....de" <hch@....de>
To:     Sungup Moon <sungup.moon@...sung.com>
Cc:     "kbusch@...nel.org" <kbusch@...nel.org>,
        "axboe@...com" <axboe@...com>, "hch@....de" <hch@....de>,
        "sagi@...mberg.me" <sagi@...mberg.me>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] driver/nvme/host: Support duplicated nsid for the
 private

On Mon, Mar 14, 2022 at 04:05:05PM +0900, Sungup Moon wrote:
> When the multi-controller, managed by a special admin command, has private
> namespace with same nsid, current linux driver raise "Duplicate unshared
> namespace" error. But, NVMe Specification defines the NSID usage like this:
> 
> If Namespace Management, ANA Reporting, or NVM Sets are supported, the
> NSIDs shall be unique within the NVM subsystem. If the Namespace
> Management, ANA Reporting, and NVM Sets are not supported, then NSIDs:
> a) for shared namespace shall be unique; and
> b) for private namespace are not required to be unique.
> (reference: 6.1.6 NSID and Namespace Usage; NVM Express 1.4c spec)
> 
> So, if a multi-controller, which is not managed by Namespace Management
> function, creates some private namespaces without ANA and NVM Sets, the
> duplicated NSID should be allowed because that is not a NVMe specification
> violation.
> 
> But, current nvme driver checks only namespace is shared or not, so I
> propose following patch:
> 1. nvme_ctrl has unique_nsid field to identify that controller should
>    assign unique nsid.
> 2. nvme_init_ns_head function creates new nvme_ns_head instance not only
>    head is null but controller's unique_nsid is false (no flagged
>    attribute) and namespace is not shared.
> 3. for creating bdev device file, nvme_mpath_set_disk_name will return
>    false when unique_nsid is false and namespace is not shared.
> 4. also, nvme_mpath_alloc_disk alto return 0 with same manner.

>From a very quick glance this looks good.  But please make sure you don't
spill over 80 charactes per line.  Also I think instead of adding the
unique_nsid field a little helper that checks the relevant flags might
be a lіttle nicer.  It is not checked in a fast path anywere and the
checks are pretty trivial.