On Wed, Oct 09, 2024 at 05:56:54PM +0200, Christian Weisgerber wrote:
> Thomas:
>
> > - the 2nd stage bootloader in the softraid volume, the man page says
> > "in the storage area oft he softraid volume".
>
> The start of /usr/src/sys/dev/softraidvar.h holds a number of defines
> that relate this. It might be worth looking into the installboot(8)
> source how this is actually used.
>
> > If I wanted to check the integrity of the bootloaders against what is in
> > /usr/mdec, how would I go about it?
>
> Figure out the relevant offsets and extract the corresponding sectors
> with dd(1) from the raw disk device.
>
> At least that's how I would approach this.
>
> --
> Christian "naddy" Weisgerber [email protected]
>
In the the 2nd stage bootloader gets stored in a kind special way: a
rudimentary filesystem image consisting of
- no superblock,
- 1 file (the actual 2nd stage boostrap code) of a few data blocks and
- 1 block containing a single inode is constructed.
The inode blocklist points to the data blocks. This image is stored in
a special area next to the softraid meta-data.
For BIOS boot the 1st stage bootloader is patched to contain the right
filesystem parameters to find the inode. The BIOS 1st stage is a very
small assembly program, it has no room to do any real filesystem
operations, like scanning for a superblock or interpreting a
superblock.
The code constructing the filesystem image can be found in
/usr/src/usr.sbin/installboot/i386_softraid.c (also used for amd64).
I am still very fond of the idea and my implementation of this
mechanism.
A side note: the 1st stage bootloader code can be found in
/usr/src/sys/arch/amd64/stand/biosboot/biosboot.S
-Otto
