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

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Message-ID: <20160309224716.GA30523@kroah.com>
Date:	Wed, 9 Mar 2016 14:47:16 -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 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?

> during development of this driver, it was useful in many cases to be able
> to communicate with the device, by simple IOCTL command, rather than
> implementing ad-hock.

Do other storage busses have these types of "custom" ioctls for their
bus-type alone?  For simple attributes like this, shouldn't you be using
sysfs instead so that it is much easier for userspace tools to get
access to them?

thanks,

greg k-h