On Jan 2, 2007, at 3:06 PM, David Laight wrote:

> The MBR extended partition is a linked list, not a tree, and is  
> (IMHO as
> well) treated if it were just a method of splitting a large chunk of
> disk into pieces.

Well, it's a tree in the sense that each partition itself can have  
nested partitions, so you can think of the top-level MBR the  
"trunk" (with 4 leaves/branches), and the first MBR sector as being  
the "root".  That is, unless I fundamentally misunderstand how it  
works :-)

> However I think you need to worry about restricting write access to
> ranges of disk blocks, and not to partitions (maybe unless the secure
> level has been raised).  In particular:
>
> 1) You need to be able to read and write boot information from  
> 'partitions'
>    that have mounted filesystems, and (probably) be directly  
> accesing the
>    relevant offsets from the 'entire disk' device.
>    (This means that a ufs mount must release the first 8k...)

This might be done using an ioctl designed for this purpose, as well,  
that the file systems participate in.

> 2) You needs to be able to dump directly into disk space occupied by  
> the
>    'swap' partition of a raid volume.

And this is a problem how?

> You also don't want to be able to move the base sector of a mounted  
> filesystem!
> (I've managed that one!) Nor be able (easily) to write to the disk  
> area
> underlying a mounted filesystem.

And this is a problem how?

-- thorpej