linux-kernel - Re: [PATCH] nvme-core: Fix subsystem instance mismatches

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Message-ID: <20190904060558.GA10849@lst.de>
Date:   Wed, 4 Sep 2019 08:05:58 +0200
From:   Christoph Hellwig <hch@....de>
To:     Keith Busch <kbusch@...nel.org>
Cc:     Logan Gunthorpe <logang@...tatee.com>,
        Keith Busch <keith.busch@...el.com>,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>, Jens Axboe <axboe@...com>,
        Hannes Reinecke <hare@...e.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH] nvme-core: Fix subsystem instance mismatches

On Tue, Sep 03, 2019 at 10:46:20AM -0600, Keith Busch wrote:
> Could we possibly make /dev/nvmeX be a subsystem handle without causing
> trouble for anyone? This would essentially be the same thing as today
> for non-CMIC controllers with a device-per-controller and only affects
> the CMIC ones.

A per-subsyste character device doesn't make sense, as a lot of admin
command require a specific controller.

If this really is an isue for people we'll just need to refcount the
handle allocation.  That is:

 - nvme_init_ctrl allocates a new nvme_instance or so object, which
   does the ida_simple_get.
 - we allocate a new subsystem that reuses the handle and grabs
   a reference in nvme_init_subsystem, then if we find an existing
   subsystem we drop that reference again.
 - last free of a ctrl or subsystem also drops a reference, with
   the final free releasing the ida