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?
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next prev parent reply other threads:[~2019-09-04 14:46 UTC|newest]
Thread overview: 15+ 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 15:29 ` Keith Busch
2019-09-03 16:08 ` Logan Gunthorpe
2019-09-03 16:46 ` Keith Busch
2019-09-03 18:13 ` Logan Gunthorpe
2019-09-04 6:05 ` Christoph Hellwig
2019-09-04 14:44 ` Keith Busch [this message]
2019-09-04 15:42 ` Christoph Hellwig
2019-09-04 15:54 ` Keith Busch
2019-09-04 16:02 ` Christoph Hellwig
2019-09-04 16:07 ` Logan Gunthorpe
2019-09-04 16:35 ` Keith Busch
2019-09-04 17:01 ` Logan Gunthorpe
2019-09-04 17:14 ` Keith Busch
2019-09-04 17:29 ` Logan Gunthorpe
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