On Jan 19, 6:48am, p...@whooppee.com (Paul Goyette) wrote: -- Subject: Re: Fixed modular kernel path and different kernels | | Well, yes, that's what I said above regarding modules "pushed from the | boot loader." :-) | | It seems to me that we have a similar restriction on where the boot | loader locates the /boot.cfg file. It currently comes from boot | device, regardless of what device will eventually become your root | device. (Indeed, if I am not mistaken, the /boot.cfg file is located | on the _initial_ boot device that was selected by the BIOS, and not | the device specified in any 'boot xxx' command.) | | Prompting for a module location at boot-loader time means you need to | specify the path using BIOS devices (hd0, hd1, etc.), and then after | autoconfigure is done you need to translate BIOS specification into a | real path, which may or may not be possible (BIOS device might not be | mounted yet, and might not even be listed in /etc/fstab). | | | So, consider the following scenario: | | 1. boot from BIOS device cd0 with 'boot -a' | 2. when asked, tell it to load modules from hd1a:/my_modules/ since | that is where your test modules lie | 3. the cd9660 file system module is pushed from file | hd1a:/my_modules/cd9660/cd9660.kmod | 4. the kernel continues with autoconfig() | 5. now it prompts for a root device, and you answer "wd0" | | I assume that you would want subsequent module loads to come from the | test modules on wd1a:/my_modules/ Unfortunately, we don't know where | (or even if) wd1a will be mounted, so we cannnot translate the "hd1a:" | device specification to a file system path. Even if we did know where | "wda1" would be mounted, we might attempt to load modules before the | mount occurs. | | As I see it, we can either | | a) Implement the proposed patch which tells the kernel where to find | module which are loaded after the kernel is running, and accept | the restriction that any modules "pushed" from the boot loader come | from the default location, in /stand/$ARCH/$VERSION/modules/ | | or | | b) Provide a prompt, within the boot-loader itself, on where to find | modules being "pushed", in addition to the prompt I proposed which | tells the kernel where to find modules loaded after the kernel is | running | | or | | c) Leave things as they are, and not provide any option to specify | the module path during boot. (Note also that the sysctl variable | kern.module.path is Read-Only, so you cannot even change the | location manually; changing the sysctl variable to Read-Write | could be a security concern...) | | | My preference is (a), as it addresses _most_ situations. | | | FWIW, the restriction also applies to MD disk images (such as the | miniroot module); these are pushed as modules...
I just think it is enough to override one component in the path via a boot command; like VERSION=x.y.z.new and then both the boot loader and the kernel can just do what they normally do. It is less general, but gives enough flexibility for testing. christos
