linux-kernel - Re: [Scst-devel] [PATCH 8/19]: SCST SYSFS interface implementation

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Date:	Fri, 19 Nov 2010 13:16:49 -0800
From:	Greg KH <greg@...ah.com>
To:	Vladislav Bolkhovitin <vvvvvst@...il.com>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Richard Williams <richard@...chsoft.com>,
	Bart Van Assche <bvanassche@....org>,
	Boaz Harrosh <bharrosh@...asas.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Mike Christie <michaelc@...wisc.edu>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	scst-devel <scst-devel@...ts.sourceforge.net>,
	Hannes Reinecke <hare@...e.de>, Andy Yan <ayan@...vell.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vu Pham <vuhuong@...lanox.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Joel Becker <joel.becker@...cle.com>
Subject: Re: [Scst-devel] [PATCH 8/19]: SCST SYSFS interface implementation

On Fri, Nov 19, 2010 at 11:50:43PM +0300, Vladislav Bolkhovitin wrote:
> Dmitry Torokhov, on 11/19/2010 11:22 PM wrote:
> >> None of the SCST objects are Linux devices. None of them has entries in
> >> /dev, none of them needs to send any events to udev and none of them
> >> sends or receives data from DMA, hence has any DMA parameters or
> >> restrictions. So, how can them fit into the driver/bus/device model you
> >> are enforcing?
> > 
> > Note that the entities in /sys/devices/... tree and not necessarily
> > physical devices bit rather interface abstractionss. Consider, for
> > example, /sys/class/input/*. None of the "devices" there talk directly
> > to hardware, do DMA or other things. Some of them don't even talk to
> > usrespace directly but rather through additional interfaces (evdev.
> > mousedev, ect). Still they are represented there and even have suspend
> > and resume methods (because even for logical devices it makes sense to
> > save and restore some state).

This is correct.

> SCST devices are not even logical devices. As I wrote, "devices" word is
> misleading. SCST devices are converse of what Linux means under this
> word. SCST devices are like NFS exports: a place where those events
> generated and those requests received.

No, that's fine.

> Think of SCST device as if it sits on the opposite side of the PCI bus
> of the corresponding SCSI device Linux sees in /sys/class and /sys/bus.

Again, that's fine, look at usb gadgets, it's the same thing.

> So, if we need Linux devices for SCST devices, we create them using
> scst_local driver. And then, of course, all them have their place in
> /sys/class/ and /sys/bus.

No, just /sys/bus/ which will cause them to become part of the big
device tree in /sys/devices/

Again, use this interface, it is what it is there for, to not use it is
just wrong.

good luck,

greg k-h
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