How does Linux handle wireless card drivers?

A few questions about how Linux handles wireless drivers:

I understand that in Linux most device drivers are already
compiled into the kernel, others can be inserted later as
kernel modules. What is the situation with regard to
wireless card drivers? Which ones come already compiled
into the kernel, e.g. the current v.2.6.15? What about
prism2, prism54, madwifi, wlan-ng, etc.? How can I find
out? And how do I find that out for the kernel I'm
currently running, v.2.6.11?

Are all the wireless drivers any distro provides beyondA
what comes already compiled into the kernel to be found
in /lib/modules/2.6.xx/kernel/drivers/net/wireless, as
xxxx.ko files?

And how are the wireless drivers loaded on bootup? Is it
correct to assume that during hardware recognition the OS
first identifies the hardware, then looks whether an
appropriate driver is in the above directory, then runs
insmod for it and finally brings up the interface? And
where does the lookup table reside that presumably matches
wireless adapter pciid's and usbid's with drivers in the
above directory? I'm running Debian 3.1.

Robert

On 2006-03-21, Robert Glueck <(E-Mail Removed)> wrote:
>
> I understand that in Linux most device drivers are already
> compiled into the kernel, others can be inserted later as
> kernel modules. What is the situation with regard to
> wireless card drivers? Which ones come already compiled
> into the kernel, e.g. the current v.2.6.15? What about
> prism2, prism54, madwifi, wlan-ng, etc.? How can I find
> out? And how do I find that out for the kernel I'm
> currently running, v.2.6.11?

In backwards order, you can zless /proc/config.gz or less /proc/config,
if your kernel supports that feature. For each driver, some are
included in the kernel source, some not; you'd need to look at the
config (the easiest way for me is to make menuconfig in the kernel
source tree). Which specific drivers are in the kernel vs. compiled as
modules is an option you select in make menuconfig, so the person
compiling the kernel can do what they want. IME, most network device
drivers are generally compiled as modules. Drivers that are not in the
source tree are more frequently compiled as kernel modules.

> Are all the wireless drivers any distro provides beyondA
> what comes already compiled into the kernel to be found
> in /lib/modules/2.6.xx/kernel/drivers/net/wireless, as
> xxxx.ko files?

Probably yes, unless the distro maintainer chose to compile a module
into the kernel directly. Again, zless /proc/config.gz or less
/proc/config to find out.

> And how are the wireless drivers loaded on bootup? Is it
> correct to assume that during hardware recognition the OS
> first identifies the hardware, then looks whether an
> appropriate driver is in the above directory, then runs
> insmod for it and finally brings up the interface? And
> where does the lookup table reside that presumably matches
> wireless adapter pciid's and usbid's with drivers in the
> above directory? I'm running Debian 3.1.

I'll give you a tentative yes here, with the caveats that a) I don't
know hotplug, udev, and friends very well, and b) I don't run Debian.
Strictly speaking, it would be hotplug, not any hardware recognition
tool (like kudzu?), that would find the right kernel module to load.
(And it probably runs modprobe, not insmod.) hotplug would then call a
helper script to bring up the interface.

If you don't use hotplug, then typically you load the appropriate
modules in a boot script.

--keith

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Robert Glueck <(E-Mail Removed)> writes:

>A few questions about how Linux handles wireless drivers:

>I understand that in Linux most device drivers are already

No. Only critical drivers (eg ext2, or other filesystem stuff since it is
needed to read the modules from the disk)

>compiled into the kernel, others can be inserted later as
>kernel modules. What is the situation with regard to

Most of them.

>wireless card drivers? Which ones come already compiled

Modules

>into the kernel, e.g. the current v.2.6.15? What about

None.

>prism2, prism54, madwifi, wlan-ng, etc.? How can I find
>out? And how do I find that out for the kernel I'm
>currently running, v.2.6.11?

None.


>Are all the wireless drivers any distro provides beyondA
>what comes already compiled into the kernel to be found
>in /lib/modules/2.6.xx/kernel/drivers/net/wireless, as
>xxxx.ko files?

No. It depends. depmod tell s the system where the modules are. (It
searches /lib/modules/<kernel number>/)



>And how are the wireless drivers loaded on bootup? Is it

modules.

>correct to assume that during hardware recognition the OS
>first identifies the hardware, then looks whether an
>appropriate driver is in the above directory, then runs
>insmod for it and finally brings up the interface? And

No. The installation scripts will try to recognize the hardware and set up
the system to load the correct module.

>where does the lookup table reside that presumably matches
>wireless adapter pciid's and usbid's with drivers in the
>above directory? I'm running Debian 3.1.

No idea. It depends on the distribution and I do not know Debian.


>Robert