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[20070618] Kernel-tuning without recompiling
NetBSD's i386 GENERIC kernel has ACPI enabled nowadays. Given that there's more than enough (i386ish) hardware out there that plainly doesn't work with ACPI, it's sort of inconvenient to have the default kernel not work. Possible workarounds for this situation are offering a kernel that has ACPI disabled (like the GENERIC_NOACPI kernel that I've added just in time for NetBSD 4.0), or using userconf to disable ACPI[1]. The drawback is that you either need a special kernel, or that it's not permanent.

A possible solution is available in OpenBSD's config(8) command: By running "config -e /kernel", userconf commands can be "saved" into the kernel binary, preventing the need to re-run userconf on every boot.

Jared McNeill has proposed another approach for NetBSD now: Instead of modifying the kernel binary, have the bootloader read a list of (userconf) commands, and have the kernel execute them automatically.

Instead of introducing yet another config file format, Jared has opted for (re)using the proplib API functions to load the config file from disk and pass it on to the kernel. Those crying "YEEK, XML!" now can rest assured: there's a policy in NetBSD that XML is not used for config files that the user needs to edit, and the idea is to use userconf as usual, then dump the settings to the config file and use that on the next boot, see Jared's second patch for the most recent code version.

With this scheme, there's a common file where boot-time information can be stored, and the eventual idea is not only to have all ports' bootloaders read that file, but also store further information into the file to make settings other than those available via userconf today: Jared's ideas include storing bootloader settings (timeout, serial console speed, ...) and kernel tuneables like PCI_*_FIXUPs in there. I guess we can stay tuned to see what will happen on this front!


[1] What is userconf? Make sure you have "options USERCONF" in your kernel, then interrupt the bootloader and type "boot -c". You can then type "disable acpi" to, well, disable ACPI. It works for other drivers as well, but it won't be persistant and has to be done on every boot.

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