linux-kernel - Re: [PATCH] NVMe: Add a character device for each nvme device

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Date:	Fri, 27 Jul 2012 16:30:51 -0400
From:	Matthew Wilcox <willy@...ux.intel.com>
To:	Greg KH <greg@...ah.com>
Cc:	Keith Busch <keith.busch@...el.com>,
	linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] NVMe: Add a character device for each nvme device

On Fri, Jul 27, 2012 at 12:21:00PM -0700, Greg KH wrote:
> > > Also, why are you creating your own class?  Can't this just be a misc
> > > device?  And if you want to create your own class, please don't, use a
> > > bus, as that is what is really happening here, right?  We are trying to
> > > move away from using 'struct class' wherever possible (one of these days
> > > we'll just remove it...)
> > 
> > What we're trying to achieve here is to create one character device
> > per NVMe controller that gets plugged in.  Each NVMe controller is-a
> > PCI function.  The reason we're trying to do this is so that we can send
> > commands to the NVMe controller, even when there is no storage present
> > (eg a drive is shipped from the factory with no configured storage).
> > 
> > So we have no particular desire to create a new struct class, or struct
> > bus.  If we can create a misc device per PCIe function that's bound to our
> > driver, that's great!  Can you recommend a driver that does this already?
> 
> I don't think there is one, but it shouldn't be that hard to just create
> a 'struct misdevice' for each one of the devices you want to create,
> would it?
> 
> But, as you really are a "specific type", a bus_type might be overkill,
> so the original use of device_create() should be fine.  Just be sure to
> fix the parent pointer issue, and you should be fine, right?

Works for me.  I don't think we're going to have any software that
depends on it being a class or a bus, so it's easy to change later.
All we really care about is /dev/nvmeN being created.
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