linux-kernel - Re: New IOCTLs

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Message-ID: <20080918091107.GE20061@hawkmoon.kerlabs.com>
Date:	Thu, 18 Sep 2008 11:11:07 +0200
From:	Louis Rilling <Louis.Rilling@...labs.com>
To:	Singaravelan Nallasellan <singaravelann@...il.com>
Cc:	Chris Snook <csnook@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: New IOCTLs

On Thu, Sep 18, 2008 at 09:53:51AM +0530, Singaravelan Nallasellan wrote:
> Thank you for your response.
> 
> The driver needs to assign an id for each open and create a sysfs
> entry based on that id and expose some properties.
> 
> For example, if the driver assigns an id 2, the sysfs entry will be as below:
> /sys/class/xxx/<drivername>/2/version
> 
> When the driver close is invoked, it will have to remove the entry.
> 
> The issue here is that the application needs:
> 1. To know the id it should use to access properties after the open.
> 2. To have exclusive access to the sysfs entries. No other application
> should and open the entry and use it. There is a chance the the other
> application could open the entries before this application opens it.
> 
> The driver allows multiple opens and assigns any random id.
> 
> I appreciate your suggestion on alternate ways to implement the functionality.

What about using configfs? A user could create an id using mkdir in the driver's
configfs subsystem, and this would make the driver create the matching sysfs
entry.

# mkdir /sys/kernel/config/<driver_subsys>/2
-> reserve id 2 for the caller, and create /sys/class/xxx/<drivername>/2

You could even put whatever configuration items inside configfs instead of
sysfs.

Louis

> 
> 
> On Thu, Sep 18, 2008 at 1:42 AM, Chris Snook <csnook@...hat.com> wrote:
> > Singaravelan Nallasellan wrote:
> >>
> >> I need to send device control messages to the driver. I am planning to
> >> use the IOCTLs. But I came to know that Linux community does not
> >> accept any new IOCTLs anymore.
> >> Can somebody provide the reason behind the decision? Are there any
> >> better approach to implement the device control interface other than
> >> sysfs interface. I have some issues in using the sysfs interface.
> >> Thanks in advance.
> >
> > IOCTLs are discouraged, but not strictly forbidden.  Is there something
> > about sysfs that would make it an unsuitable interface, or are you just
> > having trouble finding good documentation on using it?
> >
> > -- Chris
> >
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-- 
Dr Louis Rilling			Kerlabs
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