Need help in understanding sysfs

Need help in understanding sysfs

[Vaibhav Jain]

Hi,
I need to undestand sysfs and make changes to it.
Please provide me with some good references.

Thanks
Vaibhav Jain
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20110810/402cff66/attachment.html 

Need help in understanding sysfs

[Greg KH]

On Wed, Aug 10, 2011 at 12:09:25PM -0700, Vaibhav Jain wrote:
> Hi,
> I need to undestand sysfs and make changes to it.

What specifically do you need to understand, and what do you want to
change?

sysfs is a very vast subject, and vague, we need specifics.

greg k-h

Need help in understanding sysfs

[Vaibhav Jain]

Hi,

I need to understand actually how sysfs works and what is the hierarchy of
the sysfs directory structure.
Specifically I need to know how to add entries in sysfs and how to make them
work.

Thanks
Vaibhav Jain



On Wed, Aug 10, 2011 at 12:18 PM, Greg KH <greg@kroah.com> wrote:

> On Wed, Aug 10, 2011 at 12:09:25PM -0700, Vaibhav Jain wrote:
> > Hi,
> > I need to undestand sysfs and make changes to it.
>
> What specifically do you need to understand, and what do you want to
> change?
>
> sysfs is a very vast subject, and vague, we need specifics.
>
> greg k-h
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20110810/27463d30/attachment.html 

Need help in understanding sysfs

[Greg KH]

A: No.
Q: Should I include quotations after my reply?

http://daringfireball.net/2007/07/on_top

On Wed, Aug 10, 2011 at 12:31:13PM -0700, Vaibhav Jain wrote:
> Hi,
> ?
> I need to understand actually how sysfs works and what is the hierarchy of the
> sysfs directory structure.

Again, that is very vague.

Do you want to know how the internal dentry store is working to create
the virtual filesystem, and how the namespace code handles things
properly when you are walking the tree from userspace?

Or do you just care enough as a driver developer who wants to add a new
file for their driver or device?

Those are two vastly different things, and there's stuff in the middle
as well.

> Specifically I need to know how to add entries in sysfs and how to make them
> work.

For what type of device?

And, as always, what is lacking in the existing documentation that comes
with the kernel that has you confused?

thanks,

greg k-h

Need help in understanding sysfs

[Jeff Haran]

From: kernelnewbies-bounces@kernelnewbies.org
[mailto:kernelnewbies-bounces at kernelnewbies.org] On Behalf Of Vaibhav
Jain
Sent: Wednesday, August 10, 2011 12:09 PM
To: kernelnewbies at kernelnewbies.org
Subject: Need help in understanding sysfs

 

Hi,

I need to undestand sysfs and make changes to it.

Please provide me with some good references.

 

Thanks

Vaibhav Jain

 

First thing to try would be your favorite search engine. If you do a
search for "lwn <topic>" you'll often be taken to a LWN article that is
on topic though perhaps a bit dated. For instance, a search for "lwn
sysfs" takes you to here:

 

http://lwn.net/Articles/54651/

 

Probably a good place to start. Linux is mostly good code, but the
documentation that comes with the kernel sources mostly sucks, so the
web is your friend in this regard.

 


-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20110810/0d5c3698/attachment.html 

Need help in understanding sysfs

[Vaibhav Jain]

On Wed, Aug 10, 2011 at 2:14 PM, Jeff Haran <jharan@bytemobile.com> wrote:

>    *From:* kernelnewbies-bounces at kernelnewbies.org [mailto:
> kernelnewbies-bounces at kernelnewbies.org] *On Behalf Of *Vaibhav Jain
> *Sent:* Wednesday, August 10, 2011 12:09 PM
> *To:* kernelnewbies at kernelnewbies.org
> *Subject:* Need help in understanding sysfs****
>
> ** **
>
> Hi,****
>
> I need to undestand sysfs and make changes to it.****
>
> Please provide me with some good references.****
>
>  ****
>
> Thanks****
>
> Vaibhav Jain****
>
>  ****
>
> First thing to try would be your favorite search engine. If you do a search
> for ?lwn <topic>? you?ll often be taken to a LWN article that is on topic
> though perhaps a bit dated. For instance, a search for ?lwn sysfs? takes you
> to here:****
>
> ** **
>
> http://lwn.net/Articles/54651/****
>
> ** **
>
> Probably a good place to start. Linux is mostly good code, but the
> documentation that comes with the kernel sources mostly sucks, so the web is
> your friend in this regard.****
>
> ** **
>


 Hi,

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.

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/ . 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.

I tried searching the web but there are not many articles that explain the
above two in detail unlike procfs for which there are a lot of articles with
samples.
The ones I found were not very interesting to read.

Thanks
Vaibhav Jain
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20110810/964a1b4c/attachment-0001.html 

Need help in understanding sysfs

[Anuz Pratap Singh Tomar]

On Wed, Aug 10, 2011 at 10:43 PM, Vaibhav Jain <vjoss197@gmail.com> wrote:

>
>
> On Wed, Aug 10, 2011 at 2:14 PM, Jeff Haran <jharan@bytemobile.com> wrote:
>
>>    *From:* kernelnewbies-bounces at kernelnewbies.org [mailto:
>> kernelnewbies-bounces at kernelnewbies.org] *On Behalf Of *Vaibhav Jain
>> *Sent:* Wednesday, August 10, 2011 12:09 PM
>> *To:* kernelnewbies at kernelnewbies.org
>> *Subject:* Need help in understanding sysfs****
>>
>> ** **
>>
>> Hi,****
>>
>> I need to undestand sysfs and make changes to it.****
>>
>> Please provide me with some good references.****
>>
>>  ****
>>
>> Thanks****
>>
>> Vaibhav Jain****
>>
>>  ****
>>
>> First thing to try would be your favorite search engine. If you do a
>> search for ?lwn <topic>? you?ll often be taken to a LWN article that is on
>> topic though perhaps a bit dated. For instance, a search for ?lwn sysfs?
>> takes you to here:****
>>
>> ** **
>>
>> http://lwn.net/Articles/54651/****
>>
>> ** **
>>
>> Probably a good place to start. Linux is mostly good code, but the
>> documentation that comes with the kernel sources mostly sucks, so the web is
>> your friend in this regard.****
>>
>> ** **
>>
>
>
>  Hi,
>
> 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.
>
> 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/ . 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.
>
> I tried searching the web but there are not many articles that explain the
> above two in detail unlike procfs for which there are a lot of articles with
> samples.
> The ones I found were not very interesting to read.
>
> Thanks
> Vaibhav Jain
>
>
>
>
Have you used google?
The third link in the google is a classic paper by patrick Mochel, it pretty
much covers all the basics.

There is a lot of information on sysfs in Robert love's LKD and
There is an entire chapter on sysfs in LDD, which tells all the details
about creating entry and other basics.



>
>
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20110810/5b26b8e0/attachment.html 

Need help in understanding sysfs

[Greg KH]

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

Need help in understanding sysfs

[Vaibhav Jain]

On Wed, Aug 10, 2011 at 3:12 PM, Greg KH <greg@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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20110812/6a08342e/attachment.html 

Need help in understanding sysfs

[Greg KH]

On Fri, Aug 12, 2011 at 02:25:55PM -0700, Vaibhav Jain wrote:
> Thanks for ther reply!
> But I really need to create an entry in /sys/devices/system.

Why?

> I am working on a project on extending the cpu hotplug
> (/sys/devices/system/cpu) .

What specifically are you doing here?  Are you working with the existing
CPU hotplug developers in the kernel?  If not, why not?

> 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.

Where did you look?

> Could you please suggest how should I go about finding the code ?

vim drivers/base/cpu.c

> I searched for it in google but did not hit anything significant.

I suggest you look into using grep or ack or cgvg or ctags or something
more relevant for doing source code searches.

But again, be _VERY_ careful about adding files to that location without
getting buy-in from the developers working in this area, as lots of
people seem to be writing code here and most of it is being rejected by
the maintainers due to it not doing things properly.  See the recent
conversations on the linux-kernel mailing list about moving cpus to
"offline" mode for a good example of this.

good luck,

greg k-h