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From: Keith Busch <kbusch@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Keith Busch <keith.busch@intel.com>,
	Hannes Reinecke <hare@suse.com>, Sagi Grimberg <sagi@grimberg.me>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
	Jens Axboe <axboe@fb.com>, Logan Gunthorpe <logang@deltatee.com>
Subject: Re: [PATCH] nvme-core: Fix subsystem instance mismatches
Date: Wed, 4 Sep 2019 08:44:27 -0600	[thread overview]
Message-ID: <20190904144426.GB21302@localhost.localdomain> (raw)
In-Reply-To: <20190904060558.GA10849@lst.de>

On Wed, Sep 04, 2019 at 08:05:58AM +0200, Christoph Hellwig wrote:
> 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.

Yeah, I was hoping to provide something special for CMIC controllers
so you can do path specific admin, but that looks sure to break user
space.

> 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

Let me step through an example:

  Ctrl A gets instance 0.

  Its subsystem gets the same instance, and takes ref count on it:
  all namespaces in this subsystem will use '0'.

  Ctrl B gets instance 1, and it's in the same subsystem as Ctrl A so
  no new subsytem is allocated.

  Ctrl A is disconnected, dropping its ref on instance 0, but the
  subsystem still has its refcount, making it unavailable.

  Ctrl A is reconnected, and allocates instance 2 because 0 is still in
  use.

Now all the namespaces in this subsystem are prefixed with nvme0, but no
controller exists with the same prefix. We still have inevitable naming
mismatch, right?

_______________________________________________
Linux-nvme mailing list
Linux-nvme@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-nvme

WARNING: multiple messages have this Message-ID (diff)
From: Keith Busch <kbusch@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@fb.com>, Hannes Reinecke <hare@suse.com>,
	Sagi Grimberg <sagi@grimberg.me>,
	"Martin K . Petersen" <martin.petersen@oracle.com>,
	linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
	Keith Busch <keith.busch@intel.com>,
	Logan Gunthorpe <logang@deltatee.com>
Subject: Re: [PATCH] nvme-core: Fix subsystem instance mismatches
Date: Wed, 4 Sep 2019 08:44:27 -0600	[thread overview]
Message-ID: <20190904144426.GB21302@localhost.localdomain> (raw)
In-Reply-To: <20190904060558.GA10849@lst.de>

On Wed, Sep 04, 2019 at 08:05:58AM +0200, Christoph Hellwig wrote:
> 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.

Yeah, I was hoping to provide something special for CMIC controllers
so you can do path specific admin, but that looks sure to break user
space.

> 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

Let me step through an example:

  Ctrl A gets instance 0.

  Its subsystem gets the same instance, and takes ref count on it:
  all namespaces in this subsystem will use '0'.

  Ctrl B gets instance 1, and it's in the same subsystem as Ctrl A so
  no new subsytem is allocated.

  Ctrl A is disconnected, dropping its ref on instance 0, but the
  subsystem still has its refcount, making it unavailable.

  Ctrl A is reconnected, and allocates instance 2 because 0 is still in
  use.

Now all the namespaces in this subsystem are prefixed with nvme0, but no
controller exists with the same prefix. We still have inevitable naming
mismatch, right?

  reply	other threads:[~2019-09-04 14:46 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-31  0:01 [PATCH] nvme-core: Fix subsystem instance mismatches Logan Gunthorpe
2019-08-31  0:01 ` Logan Gunthorpe
2019-08-31 15:29 ` Keith Busch
2019-08-31 15:29   ` Keith Busch
2019-09-03 16:08   ` Logan Gunthorpe
2019-09-03 16:08     ` Logan Gunthorpe
2019-09-03 16:46     ` Keith Busch
2019-09-03 16:46       ` Keith Busch
2019-09-03 18:13       ` Logan Gunthorpe
2019-09-03 18:13         ` Logan Gunthorpe
2019-09-04  6:05       ` Christoph Hellwig
2019-09-04  6:05         ` Christoph Hellwig
2019-09-04 14:44         ` Keith Busch [this message]
2019-09-04 14:44           ` Keith Busch
2019-09-04 15:42           ` Christoph Hellwig
2019-09-04 15:42             ` Christoph Hellwig
2019-09-04 15:54             ` Keith Busch
2019-09-04 15:54               ` Keith Busch
2019-09-04 16:02               ` Christoph Hellwig
2019-09-04 16:02                 ` Christoph Hellwig
2019-09-04 16:07               ` Logan Gunthorpe
2019-09-04 16:07                 ` Logan Gunthorpe
2019-09-04 16:35                 ` Keith Busch
2019-09-04 16:35                   ` Keith Busch
2019-09-04 17:01                   ` Logan Gunthorpe
2019-09-04 17:01                     ` Logan Gunthorpe
2019-09-04 17:14                     ` Keith Busch
2019-09-04 17:14                       ` Keith Busch
2019-09-04 17:29                       ` Logan Gunthorpe
2019-09-04 17:29                         ` Logan Gunthorpe

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