linux-kernel - RE: [PATCH 0/2] staging: comedi: per-file read/write subdevice choice

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Date:	Tue, 4 Nov 2014 18:44:52 +0000
From:	Hartley Sweeten <HartleyS@...ionengravers.com>
To:	Ian Abbott <abbotti@....co.uk>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 0/2] staging: comedi: per-file read/write subdevice
 choice

On Tuesday, November 04, 2014 11:09 AM, Ian Abbott wrote:
> This series of patches adds a couple of ioctl codes to the Comedi core
> to allow the current "read" and "write" subdevice to be changed after
> opening the comedi device.  The current read and write subdevice
> information is stored in file private data allocated for the lifetime of
> the file object, so the notion of current "read" and "write" subdevice
> is local to the file object and does not alter anything in the main
> control structure for the comedi device.  An extra level of indirection
> is now required to access the main control structure.
>
> I've tested the multiple "read" subdevice case using a modified version
> of the "comedi_test" module (modifying it to clone the existing AI
> subdevice), and a modified version of the "comedi_test" application
> (part of the "comedilib" installation) modified to use the new ioctls.
> There isn't any support in comedilib itself yet.
>
> 1) staging: comedi: prepare support for per-file read and write
>    subdevices
> 2) staging: comedi: add ioctls to set per-file read and write subdevice
>
>  drivers/staging/comedi/comedi.h          |   2 +
>  drivers/staging/comedi/comedi_compat32.c |   2 +
>  drivers/staging/comedi/comedi_fops.c     | 217 +++++++++++++++++++++++++++----
>  3 files changed, 196 insertions(+), 25 deletions(-)

Ian,

If I understand this correctly, the user can now open the "comediX"
device which will give then access to the default dev->read_subdev
and dev->write_subdev. They can then use the new ioctls to change
the read/write subdevice and use them without having the open the
"comediX_subdY" devices.

If this is correct it seems like a good idea.

Reviewed-by: H Hartley Sweeten <hsweeten@...ionengravers.com>

Also, does this mean we can get rid of comedi_alloc_subdevice_minor()
and the "comediX_sudbY" stuff?

Regards,
Hartley

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