Kernel modules (dynamic, static, none)

[PKraszewski]

Hello!
I'm looking for a definitive answer on:
* what's the difference between device DEVICE, nodevice DEVICE and no line at all in kernelconfig.
* where do some defaults I didn't set come from? I didn't use any include in kernel config, yet modules not specified or explicitly nodevice are still built...
* what's going on in here (vanilla, unaltered, up-to-date FreeBSD 13):

> uname -a
FreeBSD node-01 13.0-RELEASE-p4 FreeBSD 13.0-RELEASE-p4 #0: Tue Aug 24 07:33:27 UTC 2021     root@amd64-builder.daemonology.net:/usr/obj/usr/src/amd64.amd64/sys/GENERIC  amd64

> kldload aesni
kldload: can't load aesni: module already loaded or in kernel

> ls -al /boot/kernel/aesni*
-r-xr-xr-x  2 root  wheel  67712 Apr  9 08:36 /boot/kernel/aesni.ko

> kldstat | grep aesni | wc -l
0

So... Is aesni statically linked into kernel? If yes, then why there's aesni.ko? What part of kernelconfig decides, if a module is statically linked into kernel or built as .ko?

My ultimate goal is to have a fully statically linked kernel with only the modules that are necessary for the device. For a very specific embedded machine, that must have zero unused parts.

 

[SirDice]

what's the difference between device DEVICE, nodevice DEVICE and no line at all in kernelconfig.

device DEVICE adds that device statically in the kernel, nodevice DEVICE is useful if you start by including the GENERIC config and want to remove something from it. No line at all just means that device is only built as a module.

where do some defaults I didn't set come from? I didn't use any include in kernel config, yet modules not specified or explicitly nodevice are still built...

There's sys/<arch>/conf/ that includes devices/configuration specific to that architecture. There's also sys/conf/ that has the configuration that is common to all architectures.

what's going on in here (vanilla, unaltered, up-to-date FreeBSD 13)

With 13.0-RELEASE aesni(4) is statically built into the kernel. On previous versions it wasn't statically included in the kernel and had to be loaded as a module if you wanted to use it.

It's included with the GENERIC kernel on 13.0-RELEASE:

GENERIC « conf « amd64 « sys - src - FreeBSD source tree

cgit.freebsd.org

Compare with the GENERIC kernel from 12.2-RELEASE for example:

GENERIC « conf « amd64 « sys - src - FreeBSD source tree

cgit.freebsd.org

If yes, then why there's aesni.ko?

Every module is always built, even the ones you statically include in the kernel config.

     LOCAL_MODULES        A list of external kernel modules that should be
                          built and installed as part of the buildkernel and
                          installkernel process.  Defaults to the list of sub-
                          directories of LOCAL_MODULES_DIR.

     LOCAL_MODULES_DIR    The directory in which to search for the kernel
                          modules specified by LOCAL_MODULES.  Each kernel
                          module should consist of a directory containing a
                          makefile.  Defaults to ${LOCALBASE}/sys/modules.

See build(7).

 

[PKraszewski]

OK, so device DEV'ing what I need and not copying effectively unnecessary .ko files to target is my way?

 

[zirias@]

You can also avoid to build any modules at all with NO_MODULES=yes in /etc/src.conf (that's documented in make.conf(5) and will work there as well of course, but should still be put in src.conf(5) cause it only affects /usr/src)