I knew how to do this once...

I knew how to do this once...

[clemens]

How do you set up a rule, so that a module gets loaded
whenever (or rather the first time) a file gets accessed.

In this case it is /dev/ttyS0

Also, If I need to load two modules, in a specific order,
does referencing one in a rule cause the other to be loaded,
or do I have to do some magic in the modprobe rules.
-- 
                                        Reg.Clemens
                                        reg@dwf.com




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Re: I knew how to do this once...

[Greg KH]

On Wed, Feb 15, 2006 at 10:30:29PM -0700, clemens@dwf.com wrote:
> How do you set up a rule, so that a module gets loaded
> whenever (or rather the first time) a file gets accessed.
> 
> In this case it is /dev/ttyS0

Do you have CONFIG_KMOD enabled in your kernel?  You also need to have
the /dev/ttyS0 (or whatever) device node created already when you do
this.  udev will not automatically load the module if you try to open a
device node that isn't present (see the udev FAQ for why.)

> Also, If I need to load two modules, in a specific order,
> does referencing one in a rule cause the other to be loaded,
> or do I have to do some magic in the modprobe rules.

Is one module dependant on the other one?  If so, modprobe will handle
it automatically.  Otherwise, just put it in the file that your distro
uses to load modules at boot time, in the order you want it to be
loaded.

Hope this helps,

greg k-h


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Re: I knew how to do this once...

[Reg Clemens]

OK, sorry to bother you again, but perhaps you can fill me in on this.
> 
> Is one module dependant on the other one?  If so, modprobe will handle
> it automatically.  Otherwise, just put it in the file that your distro
> uses to load modules at boot time, in the order you want it to be
> loaded.
>
OK, excuse me if this seems like a dumb question, but I am not familiar
with whats included in a kernel module.  If I have the source is there
some line to look for that tells the kernel that this guy is dependant on 
another module?  Or vice versa?

Ditto, is there something there that tells the kernel that this 
should be loaded when /dev/ttyS0 is touched?  From what you say
Ill assume so, but what is it so I can check to see if its there
or not.

I understand how to do this using modprobe rules at boot time,
its just getting it to work auto-magically that I am questioning.
 
-- 
                                        Reg.Clemens
                                        reg@dwf.com



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Re: I knew how to do this once...

[Greg KH]

On Fri, Feb 17, 2006 at 12:47:38PM -0700, Reg Clemens wrote:
> OK, sorry to bother you again, but perhaps you can fill me in on this.
> > 
> > Is one module dependant on the other one?  If so, modprobe will handle
> > it automatically.  Otherwise, just put it in the file that your distro
> > uses to load modules at boot time, in the order you want it to be
> > loaded.
> >
> OK, excuse me if this seems like a dumb question, but I am not familiar
> with whats included in a kernel module.  If I have the source is there
> some line to look for that tells the kernel that this guy is dependant on 
> another module?  Or vice versa?

modprobe -n -v module_name
will show you what modules will be loaded in what order so that any
dependancies in "module_name" are handled properly.

> Ditto, is there something there that tells the kernel that this 
> should be loaded when /dev/ttyS0 is touched?  From what you say
> Ill assume so, but what is it so I can check to see if its there
> or not.

Yes, look for the MODULE_ALIAS_CHARDEV_MAJOR() macro.

But please realize, that's the "old style" way of loading modules, and
is not recommended.  It's because the major:minor does not describe a
driver properly anymore, with the different types of serial, usb, and
other drivers.

Hope this helps,

greg k-h


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