/dev/fw major not constant (embedded mdev devtmpfs ieee1394)

/dev/fw major not constant (embedded mdev devtmpfs ieee1394)

[Paul Chavent]

Hi.

I'am working on an embedded gnu/linux system that allow to capture an ieee1394 stream.

The system is compound of a kernel, a basic initrd (libc,libgcc,busybox,libdc1394,...) and my app.

I use the new firewire stack.

As my system is very minimalist, i tought to create the nodes in /dev at the moment of building my initrd.

But when i needed to modify my kernel configuration, it has changed the major number of /dev/fw*.

It's not really important for the definitive system (it will be freeze), but i wonder how to solve this issue for my future works ?

I don't need hotplug, i just need to fill /dev at startup (coldplug). The target is an embedded device, so it should be easy to build/configure/install, and lightweight.

For those reasons i don't want to use udev.

I tried mdev (i run mdev -s in my startup script) from busybox. The problem is that mdev only look in /sys/class for filling /dev (i have notified their mailing list http://lists.busybox.net/pipermail/busybox/2010-January/071384.html).

The linux ieee1394 wiki people give me some idea (http://marc.info/?t=126390679500003&r=1&w=2) :
  - maintain a local patch for making the major constant
  - use devtmpfs

I prefer to try devtmpfs, but i would like to have your opinion on how would you do for me ?

Thank for your reading.

Paul.

Re: /dev/fw major not constant (embedded mdev devtmpfs ieee1394)

[Greg KH]

On Thu, Jan 21, 2010 at 09:56:10PM +0100, Paul Chavent wrote:
> Hi.
> 
> I'am working on an embedded gnu/linux system that allow to capture an ieee1394 stream.
> 
> The system is compound of a kernel, a basic initrd (libc,libgcc,busybox,libdc1394,...) and my app.
> 
> I use the new firewire stack.
> 
> As my system is very minimalist, i tought to create the nodes in /dev at the moment of building my initrd.
> 
> But when i needed to modify my kernel configuration, it has changed the major number of /dev/fw*.
> 
> It's not really important for the definitive system (it will be
> freeze), but i wonder how to solve this issue for my future works ?
> 
> I don't need hotplug, i just need to fill /dev at startup (coldplug).
> The target is an embedded device, so it should be easy to
> build/configure/install, and lightweight.
> 
> For those reasons i don't want to use udev.

Why, is udev somehow not "lightweight"?

> I tried mdev (i run mdev -s in my startup script) from busybox. The
> problem is that mdev only look in /sys/class for filling /dev (i have
> notified their mailing list
> http://lists.busybox.net/pipermail/busybox/2010-January/071384.html).
> 
> The linux ieee1394 wiki people give me some idea (http://marc.info/?t=126390679500003&r=1&w=2) :
>   - maintain a local patch for making the major constant
>   - use devtmpfs
> 
> I prefer to try devtmpfs, but i would like to have your opinion on how
> would you do for me ?

I would recommend using devtmpfs, this is exactly why it was created,
and is how lots of others are using it.  Why not try it out?

thanks,

greg k-h

Re: /dev/fw major not constant (embedded mdev devtmpfs ieee1394)

[Mike Frysinger]

On Thu, Jan 21, 2010 at 15:57, Greg KH wrote:
> On Thu, Jan 21, 2010 at 09:56:10PM +0100, Paul Chavent wrote:
>> I'am working on an embedded gnu/linux system that allow to capture an ieee1394 stream.
>>
>> The system is compound of a kernel, a basic initrd (libc,libgcc,busybox,libdc1394,...) and my app.
>>
>> I use the new firewire stack.
>>
>> As my system is very minimalist, i tought to create the nodes in /dev at the moment of building my initrd.
>>
>> But when i needed to modify my kernel configuration, it has changed the major number of /dev/fw*.
>>
>> It's not really important for the definitive system (it will be
>> freeze), but i wonder how to solve this issue for my future works ?
>>
>> I don't need hotplug, i just need to fill /dev at startup (coldplug).
>> The target is an embedded device, so it should be easy to
>> build/configure/install, and lightweight.
>>
>> For those reasons i don't want to use udev.
>
> Why, is udev somehow not "lightweight"?

in comparison, it is absolutely not
-mike

------------------------------------------------------------------------------
Throughout its 18-year history, RSA Conference consistently attracts the
world's best and brightest in the field, creating opportunities for Conference
attendees to learn about information security's most important issues through
interactions with peers, luminaries and emerging and established companies.
http://p.sf.net/sfu/rsaconf-dev2dev

Re: /dev/fw major not constant (embedded mdev devtmpfs ieee1394)

[Greg KH]

On Thu, Jan 21, 2010 at 04:21:26PM -0500, Mike Frysinger wrote:
> On Thu, Jan 21, 2010 at 15:57, Greg KH wrote:
> > On Thu, Jan 21, 2010 at 09:56:10PM +0100, Paul Chavent wrote:
> >> I'am working on an embedded gnu/linux system that allow to capture an ieee1394 stream.
> >>
> >> The system is compound of a kernel, a basic initrd (libc,libgcc,busybox,libdc1394,...) and my app.
> >>
> >> I use the new firewire stack.
> >>
> >> As my system is very minimalist, i tought to create the nodes in /dev at the moment of building my initrd.
> >>
> >> But when i needed to modify my kernel configuration, it has changed the major number of /dev/fw*.
> >>
> >> It's not really important for the definitive system (it will be
> >> freeze), but i wonder how to solve this issue for my future works ?
> >>
> >> I don't need hotplug, i just need to fill /dev at startup (coldplug).
> >> The target is an embedded device, so it should be easy to
> >> build/configure/install, and lightweight.
> >>
> >> For those reasons i don't want to use udev.
> >
> > Why, is udev somehow not "lightweight"?
> 
> in comparison, it is absolutely not

Heh, in comparison to devtmpfs, yes, good point :)

thanks,

greg k-h

Re: /dev/fw major not constant (embedded mdev devtmpfs ieee1394)

[Grant Likely]

On Thu, Jan 21, 2010 at 1:56 PM, Paul Chavent <paul.chavent@fnac.net> wrote:
> Hi.
>
> I'am working on an embedded gnu/linux system that allow to capture an
> ieee1394 stream.
[...]
> But when i needed to modify my kernel configuration, it has changed the
> major number of /dev/fw*.
[...]
> The linux ieee1394 wiki people give me some idea
> (http://marc.info/?t=126390679500003&r=1&w=2) :
>  - maintain a local patch for making the major constant
>  - use devtmpfs
>
> I prefer to try devtmpfs, but i would like to have your opinion on how would
> you do for me ?

devtmpfs is probably your best bet as that is what it is designed for.
 You can also run a trivial script at boot to read /proc/devices and
create the device nodes as described in chapter 3, page 47 of LDD3:

http://lwn.net/images/pdf/LDD3/ch03.pdf

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.