Udev, hal and loading of modules

Udev, hal and loading of modules

[Erik Andrén]

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Hello.

I've recently developed an addon for hal enabling backlight on dell
machines to be controlled via dbus/hal. The catch right now is that the
"dcdbas" linux kernel module needs to be loaded for the addon to work.

My question is if there is a way for hal to suggest to udev what modules
to load? Or are there better alternatives, such as udev probing the
smbios (via dmidecode) and load the module that way?

Thanks in advance
Erik Andrén
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Re: Udev, hal and loading of modules

[Kay Sievers]

On 2/6/07, Erik Andrén <erik.andren@gmail.com> wrote:
> I've recently developed an addon for hal enabling backlight on dell
> machines to be controlled via dbus/hal. The catch right now is that the
> "dcdbas" linux kernel module needs to be loaded for the addon to work.
>
> My question is if there is a way for hal to suggest to udev what modules
> to load? Or are there better alternatives, such as udev probing the
> smbios (via dmidecode) and load the module that way?

Udev loads only modules, which are suggested by a MODALIAS value
supplied by the kernel. There is no generic infrastructure in udev to
load any module depending on other properties. Unfortunately, there is
no solution today; it's up to the distro tools to add an entry to some
file to load such modules unconditionally.

Kay
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Re: Udev, hal and loading of modules

[David Zeuthen]

On Tue, 2007-02-06 at 22:45 +0100, Kay Sievers wrote:
> On 2/6/07, Erik Andrén <erik.andren@gmail.com> wrote:
> > I've recently developed an addon for hal enabling backlight on dell
> > machines to be controlled via dbus/hal. The catch right now is that the
> > "dcdbas" linux kernel module needs to be loaded for the addon to work.
> >
> > My question is if there is a way for hal to suggest to udev what modules
> > to load? Or are there better alternatives, such as udev probing the
> > smbios (via dmidecode) and load the module that way?
> 
> Udev loads only modules, which are suggested by a MODALIAS value
> supplied by the kernel. There is no generic infrastructure in udev to
> load any module depending on other properties. 

Supposedly 

 - the kernel could export some node in sysfs describing the system
   (akin to HAL's computer root object); for smbios it would contain
   some DMI data; for other machine types it would contain something
   else (e.g. EFI)

 - modules like dcdbas could suggest a MODALIAS value and we could
   match this on the system node

 - udev would load the driver on matches

How about that?

> Unfortunately, there is
> no solution today; it's up to the distro tools to add an entry to some
> file to load such modules unconditionally.

This sucks and therefore we should change it.

     David




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Re: Udev, hal and loading of modules

[Kay Sievers]

On Tue, 2007-02-06 at 21:38 -0500, David Zeuthen wrote:
> On Tue, 2007-02-06 at 22:45 +0100, Kay Sievers wrote:
> > On 2/6/07, Erik Andrén <erik.andren@gmail.com> wrote:
> > > I've recently developed an addon for hal enabling backlight on dell
> > > machines to be controlled via dbus/hal. The catch right now is that the
> > > "dcdbas" linux kernel module needs to be loaded for the addon to work.
> > >
> > > My question is if there is a way for hal to suggest to udev what modules
> > > to load? Or are there better alternatives, such as udev probing the
> > > smbios (via dmidecode) and load the module that way?

On which property would we match? That it's a Dell Laptop? Or a specific
model?

> > Udev loads only modules, which are suggested by a MODALIAS value
> > supplied by the kernel. There is no generic infrastructure in udev to
> > load any module depending on other properties. 
> 
> Supposedly 
> 
>  - the kernel could export some node in sysfs describing the system
>    (akin to HAL's computer root object); for smbios it would contain
>    some DMI data; for other machine types it would contain something
>    else (e.g. EFI)
> 
>  - modules like dcdbas could suggest a MODALIAS value and we could
>    match this on the system node
> 
>  - udev would load the driver on matches
> 
> How about that?

Maybe, if the values in smbios can be used as a wildcard, to match a
modalias contained in the module.
But there once was a try to export smbios properties in /proc, but that
never made it somewhere, because userspace could handle it just fine by
reading /dev/mem ...

> > Unfortunately, there is
> > no solution today; it's up to the distro tools to add an entry to some
> > file to load such modules unconditionally.
> 
> This sucks and therefore we should change it.

We probably just want a static list, that is composed by some program
that reads smbios values and stores the needed modulelist on disk, to
load modules unconditionally?

I wouldn't mind, to put such a list in /etc/udev/<whatever> and load all
these modules with the udev init-script at every bootup.

Thanks,
Kay



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