[RFC] shipping kernels with default modules?

David Schultz das at FreeBSD.ORG
Sat Jun 11 17:29:03 UTC 2011

On Sat, Jun 11, 2011, Adrian Chadd wrote:
> Hi guys,
> Has there been any further thought as of late about shipping kernels
> with modules only by default, rather than monolithic kernels?
> I tried this experiment a couple years ago and besides a little
> trickery with ACPI module loading, it worked out fine.
> Is there any reason we aren't doing this at the moment? Eg by having a
> default loader modules list populated from the kernel config file?

I've been doing this for years, and it has come in quite handy.
For instance, when my if_msk gets wedged, the only way to fix it
short of rebooting seems to be reloading the driver.

One issue, however, is that the boot loader is horrendously slow
at loading modules.  (Either that or my BIOS has a braindead int 13h
handler.)  Most of these modules aren't actually needed until much
later in the boot process, so a mechanism to load non-essential
modules after the file systems are mounted might provide a good

OS X has an interesting solution, intended to preserve the
flexibility of dynamic modules, while minimizing boot time.
It provides a kextcache utility, which packages the kernel
and all of the needed modules into a single binary for better
locality on disk.  Unlike recompiling the kernel, running
kextcache is fast, and the system runs it automatically when
hardware or driver changes necessitate it.

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