question about raw(1)

question about raw(1)

[Ruediger Meier]

Hi,

I'm just curious, would this always work?: 

  modprobe raw
  raw /dev/raw/raw1 /dev/xyz

or should you wait for /dev/raw/rawctl after modprobe (udevadm settle or 
sleep)?

cu,
Rudi

Re: question about raw(1)

[Dale R. Worley]

Ruediger Meier <sweet_f_a@gmx.de> writes:
> I'm just curious, would this always work?: 
>
>   modprobe raw
>   raw /dev/raw/raw1 /dev/xyz
>
> or should you wait for /dev/raw/rawctl after modprobe (udevadm settle or 
> sleep)?

Interesting -- the modprobe manual page doesn't state explicitly whether
or not the module initialization actions will be completed before
modprobe returns.

Dale

Re: question about raw(1)

[Karel Zak]

On Tue, Jul 05, 2016 at 02:32:24PM -0400, Dale R. Worley wrote:
> Ruediger Meier <sweet_f_a@gmx.de> writes:
> > I'm just curious, would this always work?: 
> >
> >   modprobe raw
> >   raw /dev/raw/raw1 /dev/xyz
> >
> > or should you wait for /dev/raw/rawctl after modprobe (udevadm settle or 
> > sleep)?

This is generic problem and I don't think for utils like raw(8) is
there any elegant way how to wait for rawctl node. 

IMHO the right solution is write robust scripts and expect "bad things" 
from your OS :-)

> Interesting -- the modprobe manual page doesn't state explicitly whether
> or not the module initialization actions will be completed before
> modprobe returns.

Well, module initialization may also trigger uevent and the rest is
userspace (udev) business. In this case things are completely out of
kernel+modprobe control, so "module initialization done" is irrelevant
information.

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: question about raw(1)

[Ruediger Meier]

On Thursday 07 July 2016, Karel Zak wrote:
> On Tue, Jul 05, 2016 at 02:32:24PM -0400, Dale R. Worley wrote:
> > Ruediger Meier <sweet_f_a@gmx.de> writes:
> > > I'm just curious, would this always work?:
> > >
> > >   modprobe raw
> > >   raw /dev/raw/raw1 /dev/xyz
> > >
> > > or should you wait for /dev/raw/rawctl after modprobe (udevadm
> > > settle or sleep)?
>
> This is generic problem and I don't think for utils like raw(8) is
> there any elegant way how to wait for rawctl node.
>
> IMHO the right solution is write robust scripts and expect "bad
> things" from your OS :-)

Yep, this was not a bug report. Just want to know how to write the 
script right.

It's about this openSUSE init script pull request
https://build.opensuse.org/request/show/405725

He removed the existing "sleep 2" after modprobe but I guess somebody 
had added that sleep for a good reason in past. Of course sleep is 
ugly, maybe "udevadm settle" would work too!? I simply don't know if 
udev or sleep would have any affect here at all. When testing locally 
the thing always works without any sleep. But this may not mean 
anything (as I've learned from ul test suite issues).

> > Interesting -- the modprobe manual page doesn't state explicitly
> > whether or not the module initialization actions will be completed
> > before modprobe returns.
>
> Well, module initialization may also trigger uevent and the rest is
> userspace (udev) business. In this case things are completely out of
> kernel+modprobe control, so "module initialization done" is
> irrelevant information.
>
>     Karel

Re: question about raw(1)

[Bernhard Voelker]

On 07/08/2016 01:01 AM, Ruediger Meier wrote:
> It's about this openSUSE init script pull request
> https://build.opensuse.org/request/show/405725
> 
> He removed the existing "sleep 2" after modprobe but I guess somebody 
> had added that sleep for a good reason in past. Of course sleep is 
> ugly, maybe "udevadm settle" would work too!? I simply don't know if 
> udev or sleep would have any affect here at all. When testing locally 
> the thing always works without any sleep. But this may not mean 
> anything (as I've learned from ul test suite issues).

maybe use timeout(1) instead of waiting the full 2 seconds?

  timeout 2 sh -c 'while [ ! -e /dev/raw/$rawdev ]; do sleep .1; done'

Still pretty ugly, but performs better. ;-)

Have a nice day,
Berny