linux-kernel - Re: [PATCH v7] scsi: ufs: add ioctl interface for query request

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Date:	Thu, 10 Mar 2016 08:24:29 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	ygardi@...eaurora.org
Cc:	james.bottomley@...senpartnership.com,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, santoshsy@...il.com,
	linux-scsi-owner@...r.kernel.org,
	Dolev Raviv <draviv@...eaurora.org>,
	Gilad Broner <gbroner@...eaurora.org>,
	Vinayak Holikatti <vinholikatti@...il.com>,
	"James E.J. Bottomley" <jbottomley@...n.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Michael Neuling <mikey@...ling.org>,
	"Matthew R. Ochs" <mrochs@...ux.vnet.ibm.com>,
	Wen Xiong <wenxiong@...ux.vnet.ibm.com>,
	Subhash Jadavani <subhashj@...eaurora.org>,
	"open list:ABI/API" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v7] scsi: ufs: add ioctl interface for query request

On Thu, Mar 10, 2016 at 03:52:54PM -0000, ygardi@...eaurora.org wrote:
> > On Wed, Mar 09, 2016 at 08:52:59PM -0000, ygardi@...eaurora.org wrote:
> >> > On Wed, Mar 09, 2016 at 07:09:49PM -0000, ygardi@...eaurora.org wrote:
> >> >> > On Wed, Mar 09, 2016 at 04:11:33PM +0200, Yaniv Gardi wrote:
> >> >> >> This patch exposes the ioctl interface for UFS driver via SCSI
> >> device
> >> >> >> ioctl interface. As of now UFS driver would provide the ioctl for
> >> >> query
> >> >> >> interface to connected UFS device.
> >> >> >>
> >> >> >> Reviewed-by: Subhash Jadavani <subhashj@...eaurora.org>
> >> >> >> Signed-off-by: Dolev Raviv <draviv@...eaurora.org>
> >> >> >> Signed-off-by: Gilad Broner <gbroner@...eaurora.org>
> >> >> >> Signed-off-by: Yaniv Gardi <ygardi@...eaurora.org>
> >> >> >
> >> >> > What tool is going to use this ioctl?  Why does userspcae want to
> >> do
> >> >> > something "special" with UFS devices?  Shouldn't they just be
> >> treated
> >> >> > like any other normal block device?
> >> >> >
> >> >>
> >> >> Any userspace application can be a tool.
> >> >> We already implemented and used a user space application, that sent
> >> >> queries to the UFS devices in order to get information and
> >> descriptors.
> >> >
> >> > But do you want to do with that information?  Why does userspace care?
> >> >
> >>
> >> i don't really understand the subtext of your question -
> >> as ANY ioctl cb, we decided to implement the ioctl callback of this scsi
> >> device in order to get information like UNIT DESC, DEVICE DESC, FLAGs,
> >> ATTRIBUTES.
> >> When dealing with UFS devices, one should be able to read the
> >> characteristics of the device. why ? well, why not ?
> >
> > Why aren't those characteristics just exported as sysfs attributes under
> > control by the UFS controller driver?  Why do you need/want an ioctl for
> > this?
> >
> 
> Hi greg k-h,
> 
> in our code, we used the IOCTL during runtime, in order to determine some
> information about the RPMB well known lun.
> with the rpmb lun ID we could then go to /dev/sgX and issue
> UFS_IOCTL_QUERY to this lun and get the data -
> reading the QUERY_DESC_IDN_GEOMETRY descriptor and reading the
> QUERY_DESC_IDN_UNIT descriptor.
> 
> this was crucial to the work we do in RPMB.

What is RPMB?

And again, why not just use sysfs attributes on your host controller
device?  Why does this have to be a custom ioctl?

greg k-h