Need help in understanding sysfs

[Vaibhav Jain]

On Wed, Aug 10, 2011 at 3:12 PM, Greg KH <greg at kroah.com> wrote:

> On Wed, Aug 10, 2011 at 02:43:31PM -0700, Vaibhav Jain wrote:
> > Sorry for the vague question. I would clarify. There are two things I
> need :
> >
> > 1-  I need to know how information is organized in the sysfs and
>  understand
> > the concepts of kobjects , attributes etc.
>
> Please read the in-kernel documentation for kobjects and sysfs which
> will explain this.  If not, please let us know what is lacking.
>
> The sysfs documentation in the kernel is a bit old, but the basics
> remain the same.  The kobject documentation is quite up to date, and
> should be very useful.
>
> But, it turns out you really don't want to mess with a kobject directly
> because:
>
> > 2.- I need to understand how to create a file entry in the sysfs.
> > Particulary i need to create an entry inside the
> > directory /sys/devices/system/cpu/ .
>
> No you don't :)
>
> > I will be required to write some driver in the future which will
> > accept inputs from this file but I am not very clear about that right
> > now. So I was thinking of just trying to create an entry for now.
>
> You really don't want to create a new file there unless you really know
> what you are doing, and get a whole lot of buy-in by some of the core
> kernel developers.
>
> The sysdev code is a mess, and currently being worked on, and hopefully
> adding files to /sys/devices/system/ will be easier than it currently is
> in the future.  Until then, I'd strongly suggest staying away from
> /sys/devices/system unless you coordinate it with the sysfs and driver
> core subsystem kernel maintainer.
>
> What type of file are you wanting to add?  What do you want it to do?
>
> And most importantly, why not just look at the code that adds those
> files to sysfs for how to do it yourself?
>
> thanks,
>
> greg k-h
>


 Hi Greg,

Thanks for ther reply!
But I really need to create an entry in /sys/devices/system.
I am working on a project on extending the cpu hotplug
(/sys/devices/system/cpu) .
I went through the books LDD and LKD and got some understanding of sysfs but
they are
lacking samples. I thought of looking into the code that adds the entries
inside   /sys/devices/system/cpu   but I am unable to find it.
Could you please suggest how should I go about finding the code ?  I
searched for it in google but did not hit anything significant.

Thanks
Vaibhav Jain
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