[RFC] Remove requirement of alignment to track from MBR scheme

[Andrey V. Elsukov]

On 23.05.2011 13:55, Andrey V. Elsukov wrote:
> Since after r221788 many people report about lost of access to their
> MBR partitions, i prepared new patch:
> 	
> 	http://people.freebsd.org/~ae/mbr_geometry.diff
> 
> It removes from GEOM_PART_MBR constraints to alignment to track.
> Now it is possible to create MBR partitions with exactly specified
> start offset and size, and they will not be recalculated by kernel.
> 
> Also the patch adds new option "-g" to the gpart(8) utility. This
> option can be specified for "add" and "resize" subcommands.
> gpart(8) uses information about provider's "geometry" and does
> partition alignment how it did before for MBR.
> 
> With these changes we give to users the choice how align their
> partitions and also we still able to use some "broken" partition
> tables.

For a summary:
1. I left the code of auto-align untouched, MBR still aligns new
partitions. It seems for the consensus it is better keep it for 9.0-RELEASE.
The "-g" option seems useless until this behavior will not be changed,
so i did not add it.

2. The probe routine now does not truncate available disk space
to the track boundary. Also new partition tables will not do that.

3. For the MBR scheme was added new checking and if partition starts
from within the first track, its space will not be reserved as before.

It seems these changes should resolve most of false positives for
the integrity checks.

-- 
WBR, Andrey V. Elsukov

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